String Theory is Losing the Public Debate

By Sean Carroll | March 31, 2007 3:20 pm

I have a long-percolating post that I hope to finish soon (when everything else is finished!) on “Why String Theory Must Be Right.” Not because it actually must be right, of course; it’s an hypothesis that will ultimately have to be tested against data. But there are very good reasons to think that something like string theory is going to be part of the ultimate understanding of quantum gravity, and it would be nice if more people knew what those reasons were.

Of course, it would be even nicer if those reasons were explained (to interested non-physicists as well as other physicists who are not specialists) by string theorists themselves. Unfortunately, they’re not. Most string theorists (not all, obviously; there are laudable exceptions) seem to not deem it worth their time to make much of an effort to explain why this theory with no empirical support whatsoever is nevertheless so promising. (Which it is.) Meanwhile, people who think that string theory has hit a dead end and should admit defeat — who are a tiny minority of those who are well-informed about the subject — are getting their message out with devastating effectiveness.

The latest manifestation of this trend is this video dialogue on Bloggingheads.tv, featuring science writers John Horgan and George Johnson. (Via Not Even Wrong.) Horgan is explicitly anti-string theory, while Johnson is more willing to admit that it might be worthwhile, and he’s not really qualified to pass judgment. But you’ll hear things like “string theory is just not a serious enterprise,” and see it compared to pseudoscience, postmodernism, and theology. (Pick the boogeyman of your choice!)

One of their pieces of evidence for the decline of string theory is a recent public debate between Brian Greene and Lawrence Krauss about the status of string theory. They seemed to take the very existence of such a debate as evidence that string theory isn’t really science any more — as if serious scientific subjects were never to be debated in public. Peter Woit agrees that “things are not looking good for a physical theory when there start being public debates on the subject”; indeed, I’m just about ready to give up on evolution for just that reason.

In their rush to find evidence for the conclusion they want to reach, everyone seems to be ignoring the fact that having public debates is actually a good thing, whatever the state of health of a particular field might be. The existence of a public debate isn’t evidence that a field is in trouble; it’s evidence that there is an unresolved scientific question about which many people are interested, which is wonderful. Science writers, of all people, should understand this. It’s not our job as researchers to hide away from the rest of the world until we’re absolutely sure that we’ve figured it all out, and only then share what we’ve learned; science is a process, and it needn’t be an especially esoteric one. There’s nothing illegitimate or unsavory about allowing the hoi-polloi the occasional glimpse at how the sausage is made.

What is illegitimate is when the view thereby provided is highly distorted. I’ve long supported the rights of stringy skeptics to get their arguments out to a wide audience, even if I don’t agree with them myself. The correct response on the part of those of us who appreciate the promise of string theory is to come back with our (vastly superior, of course) counter-arguments. The free market of ideas, I’m sure you’ve heard it all before.

Come on, string theorists! Make some effort to explain to everyone why this set of lofty speculations is as promising as you know it to be. It won’t hurt too much, really.

Update: Just to clarify the background of the above-mentioned debate. The original idea did not come from Brian or Lawrence; it was organized (they’ve told me) by the Smithsonian to generate interest and excitement for the adventure of particle physics, especially in the DC area, and they agreed to participate to help achieve this laudable purpose. The fact, as mentioned on Bloggingheads, that the participants were joking and enjoying themselves is evidence that they are friends who respect each other and understand that they are ultimately on the same side; not evidence that string theory itself is a joke.

It would be a shame if leading scientists were discouraged from participating in such events out of fear that discussing controversies in public gave people the wrong impression about the health of their field.

CATEGORIZED UNDER: Science, Science and the Media
  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    Sean,

    My comment about debates did explicitly refer to “physical theories”, and I think it’s true that it’s highly unusual for abstract theories about physics to become the topic of this kind of public debate (by the way, on the whole I think such debates are a good thing, modulo obvious problems with dealing with technical issues in this kind of forum). Johnson did try and come up with an example of such a debate from earlier periods in physics (he thought maybe there had been some about relativity). I’m quite curious to know if anyone can point to such an example.

    Horgan enjoys being extreme and provocative, so some of his over-the-top comments weren’t surprising and one would be justified in not taking them completely seriously, but I do find it striking that string theorists are losing people like George Johnson, who traditionally have been quite sympathetic to what they are doing. I think one important reason is the way they have reacted to the challenge posed by my book and Smolin’s. Johnson makes it pretty clear that he was strongly struck (and not positively), by the way people at the KITP behaved in the discussion he held on the topic there.

    I’ve also been kind of amazed by what a terrible job string theorists are doing of responding to criticism. The most sensible ones are pretty much keeping quiet, letting the response (at least on the web and in blogs) be dominated by some of their colleagues with less than good judgement, especially ones who think that ad hominem attacks are an appropriate response to criticism of a scientific theory.

  • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

    Peter, if you look closely you’ll see that I actually linked to such an example in my post. (Today, the question of whether nebulae are galaxies or just gas clouds doesn’t seem that abstract, but in the 1920’s it was.) That’s just the most famous one; I don’t think examples are that hard to come by. The Bohr-Einstein debates about quantum mechanics weren’t carried out in front of public audiences, but they easily could have been, and it might have been a good thing.

    I agree with you that the most sensible string theorists are (pretty much) keeping quiet — this post was in part an attempt to tweak them into speaking up!

  • Aaron Bergman

    You know, I promised myself I’d give up Lee Smolin for Lent (when is that, anyways?), and now you try to pull me back in.

    So, I’ll just suffice with self-promotion and refer back to my review of Peter’s book where I try to do just what you say.

    On the other hand, I think is is part of a natural media cycle of promotion and backlash. Once people are through proving their iconoclasm bona fides, I tend to think things will even out to a reasonably sober equilibrium.

  • Rob

    I am not a scientist, (I don’t speak math, so that kills any scientific aspirations), but love reading and learning about what’s going on in different scientific fields. I guess you could say I’m the audience that consumes scientific dialog “for dummies”.

    I could never write a paper on string theory or quantum-loop gravity, but I can certainly discuss the benefits of funding programs of discovery. So to read a statement such as “things are not looking good for a physical theory when there start being public debates on the subject”, stuns me. Did these words actually come from a scientific mind? Does discussion of scientific theory constitute valid data that the theory is flawed? Or is public discussion viewed as evidence that the subject matter is too accessible to the minds of little people, and therefore not worthy of attention by great minds?

    I doubt such an (ego-driven?) attitude will get real legs…at least I would hope not. The backlash from the public for such thinking would likely be similarly childish; “If you’re are unwilling to discuss it, we’re unwilling to fund it.”

    As for me, I think these are heady times for scientific observers. It seems to me that we, (by which I mean you science types), have really begun to learn how to learn. That may seem offensive, but when I read about all the various data points supporting global warming and consider that “connecting the dots” has really only come together in earnest over the past ten years, you can see my pov.

    In fact, it is only by taking scientific dialog out of the lab and making it available to a broader audience that allows the “dots” to be connected. My understanding is that cosmic microwave background radiation was discovered (when it was) because a guy who knew the scientists at both Princeton and Bell Labs learned what each were working on and introduced them, thereby literally connecting the “dots”.

    So I support your view that public discussion of scientific developments is a good thing. And not just because I am personally interested. Rather, I feel such dialog will bring closer the day that a room full of politicians can publicly laugh Intelligent Design right back under the rock from which it crawled. But until the public can discern between science and philosophy, (ok, string theory isn’t helping there YET), politicians will play ball with both crowds. And they make the appropriations decisions so discuss, discuss, discuss!

  • Moshe

    Sorry Sean, but I came with time to precisely the opposite conclusion. At least as far as the public blogosphere is concerned, I have no evidence of anyone ever changing their minds, or even changing any of the details of their arguments. More generally, this is a highly technical subject, inevitably any public debate will come down to who is the nice guy and who sounds more reasonable. Personally, if I had any intention of engaging in marketing I would want to get paid more for it…

    Luckily, as you note, among quantum gravity experts there is a near consensus on the merits of this approach, this ought to be the important thing. Of course, technical debates among experts are going on all the time, let’s just say they have a slightly different flavor than the public debates.

    (not to say that string theory should not be explained to the public, and to our colleagues, but debate and explanation are two separate issues).

  • http://stevens.edu/csw John Horgan

    Sean, thanks for your thoughtful post on my conversation with George Johnson. Just let me clarify my view of the debate between Greene and Krauss over strings. Contrary to what you imply, I don’t think a scientific theory loses credibility just because it’s debated publicly. It was the jokey tone of the Krauss-Greene debate–at least as described in one online report–that struck me as yet more evidence that strings are in big trouble. Neither Krauss nor Greene seemed to be even attempting to be serious about strings. They were just posturing, performing, for fun. In other words, they seem to tacitly agree with my description of string theory in The End of Science as “ironic science,” which is more akin to philosophy or even literature than real science and should not be taken literally. Sean, jump off the sinking ship while you still can!

  • Aaron Bergman

    God forbid scientists should have a sense of humor.

  • http://quantumfieldtheory.org nc

    “Johnson did try and come up with an example of such a debate from earlier periods in physics (he thought maybe there had been some about relativity).” – Peter Woit

    Einstein debated general relativity on 25 September 1920 with his Nobel Laureate Philipp Lenard:

    “On September 25, the day of the debate on relativity, Born and Einstein walked out of the train station to face a changed scene: guards armed with fixed bayonets. Not trusting the scientists’ sangfroid, the government prepared for trouble, unnecessarily, as it turned out.

    “In Bathhouse 8, five to six hundred eager listeners “squeezed together on seats, stood along the walls, filled the balcony … .” First came hours of invited papers, until session chair Max Planck finally opened the floor to discussion. Lenard spoke first. When Einstein followed, Planck was forced to silence heckling, perhaps orchestrated. Lenard and Einstein rebutted each other’s comments, as others in the audience asked questions and offered opinions, including Born. Then Planck, who had maintained a more dignified proceeding than many had considered possible, observed that relativity theory still had not made it possible to extend the time for the meeting and ended the discussion.

    “Einstein was disappointed in his performance. “I will … not allow myself to get excited again, as in Nauheim,” he wrote Born. “It is quite inconceivable to me how I could have lost my sense of humour to such an extent through being in bad company.” Born knew that Einstein suffered under the attacks and worried that he might leave Germany. This was all the more reason for the Borns to react strongly to the swirl of publicity that surrounded Einstein and, in their opinion, made him more vulnerable to attack – publicity that the Borns and other friends such as Max Wertheimer attributed to Einstein’s good nature and Elsa’s enjoyment of the attention.”

    http://www.maxborn.net/index.php?page=excerpts

    Relativity was an ad hoc explanation for existing physical concepts such as the FitzGerald-Lorentz transformation (including length contraction, time dilation, and mass increase after 1897 when J.J. Thomson showed that the mass of a charge is inversely proportional to its radius), so it’s not a good analogy to string theory. Relativity was a working theory, addressing data, straight off. String theory isn’t even a model of anything already known to exist.

    A better anology to string theory is the debates concerning the Bohr-Heisenberg Copenhagen, particularly during the 1927 and 1930 Solvay Congresses, which led to the EPR paradox published in the Physics Review (1935), “Is the quantum description of physical reality complete?” In turn, this first led to Bell’s inequality and then to Aspect’s tests in 1982, so although interpretational difficulties still abound the foundations of quantum mechanics, at least the subject isn’t hyped up so much now as ending with Copenhagen. There was eventually interesting physics generated from the arguments: it wasn’t a waste of time.

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    Rob,

    “Did these words actually come from a scientific mind?”

    Yes, these words did come from a scientific mind, mine. Do you really think it’s necessary to make insulting comments like this to make your argument? The point I was making (as were Horgan and Johnson) is not that there is anything wrong with these debates, just that they are an unusual phenomenon in this particular science and thus indicate something unusual is going on. Sean has helpfully pointed to another example, from astrophysics, but it’s one from nearly a century ago. I don’t think it is in any way unreasonable to suggest that the existence of these debates suggests that something unusual is going on in this subject.

    One thing that struck me in reading the transcript of the recent Smolin/Duff debate were Chris Isham’s remarks that quantum gravity is not like other subfields of physics because theoretical claims can’t at all be confronted with experiment, and scientific disagreements adjudicated through this means. This has a lot to do with the unusual current situation. Nobody was holding public debates in the early seventies about the Weinberg-Salam model and whether there were weak neutral currents. They were making models that made distinct predictions about this and evaluating them as the data came in. Maybe they should have been having public debates, and that would have been fine, but the debates would have had a different nature, with everyone looking to experimental results to sustain their points.

    Again, I don’t think there’s anything at all “wrong” with these debates, actually I think their existence is great. I’m a big fan of the free marketplace of ideas, whenever it’s a free marketplace…

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  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    John and Aaron,

    One of the things that most struck me about some of the KITP on-line videos of talks on the Landscape is the amount of nervous laughter involved. People seemed to be very much aware of the kind of ludicrous nature of some of the arguments being presented. Nothing wrong with a sense of humor, but this seemed to me something different. There’s a difference between making jokes about one’s ideas and the ideas being a joke.

  • http://tsm2.blogspot.com wolfgang

    I think Jacques Distler did a very good job, explaining the Motivation(s) for string theory in this blog post.

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    I’m noticing that everyone here is being careful to describe the debate about string theory as a debate about its merits as a theory of quantum gravity. As someone who has always been most concerned with its merits as a supposed theory that explains things we can actually hope to observe (e.g. particle physics), I’m just wondering: is the debate on that point over?

  • http://tsm2.blogspot.com wolfgang

    Sean,

    > The Bohr-Einstein debates

    Actually, I find comparisons of the recent debate about string theory and the Bohr-Einstein debate (and other historical debates) very painful.
    The contrast between the high level of discourse in the past and the low level now, often quickly degenerating into name-calling, is perhaps a major reason why string theory might be ‘loosing the public debate’.
    Bohr did not call Einstein a ‘crackpot’, but tried to convince him…

  • http://quantumfieldtheory.org nc

    Wolfgang, many string theorists can’t respond directly to criticisms because M-theory originator Ed Witten has stated in a letter to Nature that responding to criticisms may add fuel to controversies:

    ‘The critics feel passionately that they are right, and that their viewpoints have been unfairly neglected by the establishment. … They bring into the public arena technical claims that few can properly evaluate. … Responding to this kind of criticism can be very difficult. It is hard to answer unfair charges of élitism without sounding élitist to non-experts. A direct response may just add fuel to controversies.’ – Dr Edward Witten, M-theory originator, Nature, Vol 444, 16 November 2006.

    For those who aren’t aware of Dr Witten’s view:

    ‘String theory has the remarkable property of predicting gravity.’ – Dr Edward Witten, M-theory originator, Physics Today, April 1996.

    Wonder why he won’t respond directly to criticisms?

  • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

    Moshe, it’s a shame you feel that way. I was talking, of course, about “explanation” more than “debate,” and in a broader context than just the blogosphere. But I think that too many sensible people read some pointless name-calling on blogs, and conclude that it’s a waste of time to talk to non-specialists in general. Which is a mistake.

    And I should say specifically that the “it’s a technical subject” argument is missing the point in an important way. Of course, non-experts (whether they are non-scientists or other physicists) aren’t going to be adjudicate the role of polymer representations of non-seperable Hilbert spaces, or the difficulty of stabilizing moduli in a controlled large-volume approximation. But they certainly can understand the basic reasons why an approach might be promising even in the absence of direct experimental support. It’s worth making an effort to make those reasons clear. (Which I know that you, as one of the good guys, appreciate.)

  • Ellipsis

    It might be nice if the academic system allowed young folks to just spend 7 years in their attic — a la Andrew Wiles & Fermat’s Last Theorem — to actually work out an actual mathematically-consistent alternative to string theory… But this is fundamentally not possible with the present system (due to publication, tenure, and career pressures), thus all we get is a Soviet-style single (and untestable) choice in the matter of a quantum mechanical theory of gravity. (I don’t think many people would consider quantum loop gravity to be an alternative, at least at this point.)

    Dimension is actually an operator that acts on a state.
    Minkowski space is its vacuum expectation. Complete those two sentences… :)

    What happens if one were to promote dimension to an operator? Many people have wondered about that — note that one would need to establish its commutation relations, for one thing — but no one has been able to do the resulting mathematics. So maybe that line _might_ even end up resulting in an alternative to string theory — but no one has been able to take the plunge, mostly because of academic pressures.

    I think that’s unfortunate.

  • Aaron Bergman

    Peter — I was responding to the fact that Mr. Horgan seems to think of it as an indictment of a theory that people are willing and able to debate it in good humor.

    As for the landscape, you know as well as I do that the debate about the landscape within the string theory community has been at least as vehement as that without, if not nearly as public.

    As for the other, no attempt at a theory of quantum gravity has been able to produce a falsifiable prediction. There are various things that might be confirmatory, however. As is well-known, there are effective field theory arguments that make it extremely difficult to directly observe quantum gravitational effects. Nonetheless, there are conjectural restrictions on the sort of effective field theories that might arise out of string theory. If these could be more firmly established, they would constitute falsifiable predictions and/or retrodictions.

  • tomasiello

    It seems to me that Horgan’s attack is really on theoretical high-energy physics, not on string theory. His arguments are against the whole idea of unifying quantum mechanics and relativity. The idea is that physics has gotten as far as it possibly can, and that from now on it is bound to be theology. Johnson’s praises a “pragmatic” approach of… just giving up. Why do we need a single, unified theory anyway?

    That’s the saddest thing about today’s “public debate”: the people who brought string theory to the court of public opinion don’t realize that what they are sinking is their ship too. If tomorrow LQG were to become the new darling of high energy physicists, people like Horgan would be bashing it just like today they are doing with string theory, on precisely the same grounds.

    I don’t suppose I will be the one who will convince these critics that they’re being short-sighted. I’ll just add that it is rarely mentioned that string theory has _already_ led to very nice progress in mathematics. Oh yea, but maybe not even geometry is a “serious enterprise”.

  • Josh

    Peter, about your comment #13: I find it hard to understand how you can totally separate debating string theory’s promise in understanding quantum gravity from a larger debate of it’s viability. I agree that string theory seems unlikely to tell us anything about electroweak scale particle physics(except perhaps through gauge/gravitational duality as applied to QCD). But it isn’t really fair to claim that it is thus dead in water. String theory excited many theorists by providing a quantum gravity candidate and, in the end, exploring that regime will be what determines if it sinks or swims. Admittedly, that doesn’t appear like it will happen soon. But does the fact that one doesn’t know when one can test an idea make the idea unscientific?

  • Josh

    I see my previous comment strayed a bit from what you were saying, Peter. I can’t speak for every string theorist(many will disagree with me probably), but I don’t think there’s much chance of string theory saying much about “particle physics”. I use the quotes since what is usually meant by that term is electroweak scale collider physics, where QCD is weakly coupled. But I do think string theory may provide insight into hadron physics, strongly coupled QCD etc. through dual gravitational models. This would be very different from string theory as the “theory of everything” since such a thing would be an effective model which may only apply in a certain regime.

  • Eric Mayes

    As a string phenomenologists, I find the comments by the anti-string people that string theory cannot be tested to be somewhat insulting and completely wrong. We can now competely derive the MSSM from string theory, including the quark, tau lepton, and neutrino mass matrices and mixings (see our paper on Monday), so these people should sit down and be quiet.

  • Michael

    I would like to see a semi-popular debate on the issues. The landscape, extra dimensions, branes/strings/particles, Maldacena conjecture would all be covered. With most pop physics books, the assumption is that the reader is a complete idiot. Yet there are plenty of pop math books that include a “lite” version of various concepts and equations. Books like Superstrings (edited by Davies) were a step in the right direction.

    The ad hominem attacks are degrading the signal to noise ratio, but they do have a point. String theory is a technical field, thus it’s fair to question the credentials of the critics.

    Easy to read papers like “A Laymen’s Guide to M-theory” (hep-th/9805177) are good idea too.

  • http://CapitalistImperialistPig.blogspot.com CapitalistImperialistPig

    Eric,

    Your paper sounds very exciting. How about a hint. What is the mass of the Higgs and the what particle is the LSP?

  • Ellipsis

    Eric: “derive” (i.e. “predict”) … or “construct”.
    An important logical distinction…

    If it’s really the former, then what is the value of delta (the Dirac CP phase)?

    If you can actually predict that, and you are proven to be correct, then clearly you will have a Nobel prize waiting for you.

  • Josh

    Eric,

    Intriguing stuff but I still think there is a bit of an issue. Given the vast variety of string constructions, I don’t doubt that there is one that contains the MSSM at low energies with all of the couplings consistent with current measurements. But one expects that there will actually be many such string models which look roughly the same at low energy(since renormalization group isn’t actually a group and so isn’t uniquely invertible). Now, any given model which is consistent with SM will give unique predictions for higher energy physics. But let’s say you have one and it’s gets proven wrong by future experiments. “No big deal,” you say and move onto a slightly different model so string theory still lives. This is the feature that many people object to. That string theory won’t be falsified by the falsification of some model and doesn’t seem to give any unique predictions. The converse also seems to be true. If your model stands up to scrutiny in the next round of experiments, I’m not sure this gives much in the way of evidence for string theory, just for some effective field theory like the MSSM. To get real direct evidence for string theory, I think you probably need some data from the Planck scale, where string theory is qualitatively different from quantum field theory.

    On the other hand, I think there are many channels of indirect evidence for string theory. Experimentally, finding low-energy SUSY at LHC will give a big boost of confidence that we’re on track with this set of ideas. Theoretically, things like black hole microstate counting, including higher derivative stringy corrections give (me, at least) confidence that the string program is on to something.

    I don’t mean to deride your work, I think the sort of model-building you describe is important. But it seems to me mostly a “proof of concept”, like most, if not all, work in string theory.

  • http://theeternaluniverse.blogspot.com Joseph Smidt

    Two things: First, I think Sean is right when he says often those manifestly opposed to string theory are those “who are a tiny minority of those who are well-informed about the subject.” It seems most anti-string theory people I meet have never taken formal courses on the matter. They form their opinions based off the opinions of others.

    I don’t think it would be fair for me to judge until I have taken some formal courses so as I can judge for myself. (Only a couple of years more! :) ) Then I will be in a better position to have a credible opinion.

    Second: It seems the more I study high energy theory the more you have to evoke whatever works. You say “well, we get this infinity so we will just do this, and, oh look we get the right answer.” It seems sometimes we just play the game of finding the math that works best. If it turns out you have to call on higher dimensions and unseen fields and so forth to get the math to work out maybe that should be okay.

    But again, I am no expert yet so I’m just throwing stuff out there. I am just grateful to be going into a high energy area and exploring these effects on the Universe. Keep the debate live and well.

  • Thomas Larsson

    Like Aaron, I’ll just suffice with self-promotion and refer back to my no-go theorem for string theory.

    For a presumably well-informed opinion about string theory, consider what the founder of the string theory group at Rutgers write in subsection 1.6 of hep-th/0204131.

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  • Haelfix

    The only blog thats even attempted to pose the question scientifically is Professor Distlers excellent series on motivation for quantum gravity (sorry dont have the link handy).

    The simple arguments contained therein are more or less the prime reason people take it seriously. Namely quantum field theory doesn’t leave us many options for a consistent logical framework, and it seems the only way out leads straight smack into string theory (whether you are looking for it or not).

    If string theory is wrong it nearly (but not quite) implies a massive inconsistency in the fundamental theorems of either special relativity, general relativity or quantum mechanics, and the possibiliities for an escape shrinks to an almost intractable level.

    Naturally theorists took the easy way out of that problem and assumed thats not the case, rather than tackling the much harder problem of making sense of the inconsistency given that we know those three key aspects of the physical world make good sense in just about every experiment ever conducted.

  • http://quantumfieldtheory.org nc

    “If string theory is wrong it nearly (but not quite) implies a massive inconsistency in the fundamental theorems of either special relativity, general relativity or quantum mechanics, and the possibiliities for an escape shrinks to an almost intractable level.” -Haelfix.

    Jacques Distler’s defence of string theory ends with the following comment about LQG:

    “Urs is right that LQG isn’t, strictly, a discretized model, though the use of the spin-network basis does introduce a fundamental length scale into the theory. It’s, more properly, a continuum theory, quantized in a Hamiltonian framework (albeit, a very, very unconventional one). The words I wrote above were geared to a Lagrangian formalism. It’s not hard to adapt them to a Hamiltonian one.” – Dr Distler’s Musings blog

    LQG isn’t complete, so this sort of dismissal is unhelpful. LQG is far more economic than string theory. It introduces questions about special relativity on the quantum scale, hence “doubly special relativity”. Because there is a fundamental grain size in LQG, the Lorentz contraction can’t make that smaller due to motion, so the grain size is a fixed size irrespective of motion. This limits the scale of application of special relativity.

    Maybe you think string theory is right because there are no alternatives and string is consistent with special relativity, etc? M-theory is claimed to be a self-consistent theory of quantum gravity. However, self-consistency in a totally speculative framework isn’t so stringent: what counts is consistency with facts.

    The immense number of speculative, uncheckable assumptions involved in string theory: gravitons, 6/7 extra dimensions, supersymmetric partners for all observable particles, Planck scale unification, branes, etc., make it clear that it is not consistent with what is known. Ockham’s razor tells you that LQG is closer to reality. The path integral in LQG is the sum of all interaction graphs in the Penrose spin network. The result of this gives Einstein’s field equation. It’s not really a continuum, because each interaction graph is a quantum interaction. So Dr Distler is being misleading.

  • mclaren

    Much as I admire the fine physicists who collaborate to produce this blog, it seems to me that Sean unjustifiably and unfairly caricatures Peter Woit’s position when he flippantly claims:

    “Peter Woit agrees that `things are not looking good for a physical theory when there start being public debates on the subject'; indeed, I’m just about ready to give up on evolution for just that reason.”

    To put it bluntly, this verges on deliberate deception because Woit’s statement is taken so far out of context. What Peter Woit is clearly saying is that that “Things are not looking good for a physical theory when there start being public debates on the subject between recognized credentialed scientists about whether the theory even qualifies as either scientific or a theory.

    As you can see, this completely blows Sean’s grossly distortive quip that “indeed, I’m just about ready to give up on evolution for just that reason” out of the water.

    There is NO debate among serious credentialed scientists about whether the theory of evolution qualifies as either scientific or a theory. None. Zero. Zilch. Nada. Zip. Diddly.

    What we get in regards to the theory of evoluiton is a bunch of phoney staged pseudo-controversies in which people with no qualifications and no credentials and no expertise in biology, people without degrees in biology, people without PhDs in biology, people who have never published any papers on evolution in recognized peer-reviewed professional academic journals, stand up and make long-debunked claims which the biologists who have published countless articles in peer-reviewed professional academic journals then shoot down in a few seconds. The biologists typically respond to these kinds of canards by remarking, “This is the fallacy of the second law of thermodynamics, which reflects a misunderstanding of the definition of a closed system and was original raised in [year X] and was definitively rebutted in [year Y].”

    This is the same kind of pseudo-controversy you get when a flying saucer cultist stands up and makes wild claims, and skeptics debunk them by pointing to Project Blue Book and citing case after case after case where previous claims for the existence of flying saucers turned out to be hoaxes or lenticular clouds or lens caustics in cheap cameras.

    Let’s be clear. That’s not a “debate.” It’s one kook spouting gibberish, and a scientist debunking it.

    That’s no debate. An actual debate occurs when person X stands up and provide facts and logic to support his claim, and then person Y rebuts those facts and logic and provides facts and logic for hi/r own contrary assertion.

    String theorists have no facts to support their assertion that string theory is science. They don’t have a single experimental result to support their contention that string theory is either scientific or a theory.

    Consequently, all string theory “debates” (so-called) twixt serious scientists thus far have taken the following form: skeptical scientist A points out that a theory isn’t scientific and isn’t a theory if it can’t make any testable predictions and if no testable predictions have been adduced to support it. Credulous scientist B, a string theory supporter, indulges in hand-waving and blows a lot of smoke up everyone’s hoo-ha to disguise the fact that s/he cannot provide even one (1) testable predictions from string theory, and cannot provide even one (1) piece of experimental data published in the peer-reviewed professional physics literature to support the assertion that string theory is either scientific or a theory.

    You tell me. Is that a debate?

    No, that’s one scientist demanding that the so-called “theory” make predicitons and that experimental physicists provide evidence to back those predictions up. Then another guy waves his hands in the air and tries to distract attention from the hard cold provable fact that there are no testable predictions and there is no hard scientific evidence for string theory. None whatsoever.

    To see how badly distorted and how fundamentally deceptive Sean’s false analogy with evolution is, let’s compare evolution with string theory:

    If any scientist like Woit or Smolin demands hard experimental evidence for string theory, the string theorists provide nothing but hand-waving.

    By contrast, if any scientist _were_ to demand that evolutionists provide testable predictions (no reputable scientist does, because evolution is so well-established and backed up by so much evidence the very question would be foolish), the evolutionists could deluge ‘em with testable predictions. Let’s just run through 10 testable evolutionary predictions off the top of my head — first, evolution would predict that vaccines would gradually become ineffective as viruses and bacteria mutate over time. We have tested this prediction and it has proven irrefutably true. Second, evolution predicts that mammalian males will be generally larger than females because of selective pressure for males to battle other males over mates. Once again, this prediction has been extensively tested and has proven true. Third, evolution predicts that we’ll get the ratios Gregor Mendel found in his plant breeding experiments. This prediction has been tested and has proven true. Fourth, evolution predicts intermediate stages in the fossil records. While a few gaps exist, we have so many examples (such as Archaeopteryx) that this prediction has also proven true. Fifth, evolution predicts that developed characteristics cannot be inherited — i.e., Lamarckism isn’t correct and the children of people who exercise and build up their muscles are not born with larger muscles. This prediction has been tested and has been found true. Sixth, evolution predicts that because of the problems caused by inbreeding in humans, selective pressures will tend to favor the differentially greater reproduction of individuals with an innate aversion to incest. This prediction has been tested and has been found to be true in interesting studies which show that unrelated children raised together are not sexually attracted to one another, while related children raised apart can and sometimes do become sexually attracted to one another. Seventh, evolution predicts a common ancestor for all current forms of life. This prediction has been tested with DNA sequencing, most spectacularly with mitochondrial RNA sequencing, and has been proven true. Eighth, evolution predicts vestigial organs (Dollo’s Law). Once again this prediction has been tested and found true. Ninth, evolution predicts anatomical and molecular parahomology. This has been tested and found true by both paeloanatomists and by molecular biologists. Tenth, evolution predicts statistical support for phylogenies. The stats have been run on many different cases, and in each case cladistic analysis supports virtually completely and almost perfectly the known phylogeny.

    To hammer this point home and demonstrate the thoroughly slipshod and inexcusably sophistical nature of Sean’s faulty analogy twixt string theory and evolution, there exist literally hundreds of websites which pile up mountains of evidence from the peer-reviewed scientific literature to support evolution as a scientific theory. Sites like

    http://www.talkorigins.org/faqs/comdesc/
    http://www.bartleby.com/65/ev/evolutio.html
    http://www.txtwriter.com/backgrounders/Evolution/EVcontents.html
    http://www.gate.net/~rwms/EvoEvidence.html
    http://www.talkorigins.org/faqs/evolution-research.html
    http://books.nap.edu/html/creationism/evidence.html
    http://evolution.berkeley.edu/evolibrary/article/0_0_0/lines_01
    http://www.evolutionpages.com/

    Googling for the phrase “evidence for evolution” produces 1,130,000 pages containing that phrase. You could literally spend the rest of your life reading the gigantic mountain of evidence that has been published supporting predictions made by the theory of evolution, and you would still not reach the end of it.

    Now let us compare with string theory.

    Name me one peer-reviewed scientific journal, Sean, which has published a single experimental result predicted by string theory.

    Name me one.

    Just one.

    You can’t. Because string theory makes no testable predictions.

    Okay, Sean. Now show me the 1,300,000 websites contains peer-reviewed published evidence for string theory.

    Show ‘em to me, Sean. I want to see all those websites. Let me see ‘em.

    Whoops! There aren’t any.

    Not ANY.

    On the one hand, the theory of evolution, with more than a million pages citing peer-reviewed scientific literature chock full of evidence directly supporting it…

    …And on the other hand, string theory — with not a single web page citing a single peer-reviewed piece of scientific literature directly supporting it.

    Are they comparable?

    You tell me, folks. Is Sean’s analogy valid, or is he being deliberately and flagrantly deceptive?

    To compare the theory of evolution, which is supported by a vast Himalayan mountain range of evidence that vasts up so high that if you printed it all out, it would reach to the moon and well beyond, with the idle unsupported speculations of string theory which have not yet made a single testable prediction after 30+ years and for which not a single scrap of peer-reviewed published experimental evidence exists…it’s insulting.

    Sean, there is little doubt that you are a lot smarter than I am. You’re almost certainly a lot smarter than 99% of the human race. But don’t piss on my leg, Sean, and tell me it’s raining.

    I know the difference between a scientific theory for which a colossal pile of peer-reviewed experimental physical evidence exists, and a set of idle speculations which have never succeeded in making even a single testable prediction and for which not one single peer-reviewed journal article can be found adducing experimental evidence in support of those idle speculations.

    Don’t insult my intelligence, Sean, by even _trying_ to compare string theory with the theory of evolution. Just as there is NO debate among ANY members of the serious scientific community about whether Darwin’s theory of macorevolution constitutes a scientific and testable and thoroughly-supported theory, there is NO debate among ANY members of the serious scientific community that there current exists not a single currently testable prediction made by string theory.

    Even string theorists admit that they have no testable predictions. Lubos et al. resort to claiming that string theory’s prediction will become testable someday…or they resort to claiming that if we run enough stats on the cosmic background we might someday find circumstantial evidence which ambiguous relates to the landscape hypothesis. In short, even the string theorists themselves can only provide a vague hope that someday, somewhere, over the rainbow, enough stats or sufficiently novel tech might (somewhere, over the rainbow) provide some kind of ambiguous circumstantial evidence in favor of some part of string theory.

    Guess what?

    That’s not hard evidence. That’s a wish and a pipe dream. “Somewhere, over the rainbow.” Let’s give every string theorist the benefit of the doubt. Let’s assume they’re right. Someday, maybe we’ll get some kind of vague circumstantial evidence for some parts of string theory.

    We don’t have it now.

    Right now, we have nothing. And science isn’t about what somebody might find someday, somewhere over the rainbow. Science is about what we can find evidence for right here, right now. If we can’t find hard evidence for it, Occam’s Razor says throw it out. Hypotheses non fingo. Dump it. Junk it. Don’t need it. Phlogiston? Press the eject button. Luminiferous ether? Outa here. Vital animistic fluids? History. Theory of humours? Toast.

    I’m sorry to say it, but even the deceptive and profoundly sophistical effort to _try_ to compare the massively-well-grounded theory of evolution (for which enormous amounts of scientific evidence exist) with a flimsy tissue of speculations and numerology like string theory is insulting. It’s an insult to my intelligence and it’s an insult to the intelligence of every thinking person reading this blog.

    Look, I have nothing against string theory. Maybe it’s right. Maybe it isn’t. I don’t know. No one does. What string theory ISN’T right now is testable. Hand-waving about the landscape just makes the problem worse because as Woit and Smolin and any number of other folks with common sense point out, the landscape predicts everything you could ever possibly observe. Just plug in the fudge factors (AKA “parameters”) and voila! There you go. The universe we see around us.

    That’s not a testable prediction. A theory that predicts everything you could possibly observe, as Woit and Smolin et al. have pointed out, actually predicts nothing.

    To put it bluntly, the landscape is no different from the con job that phoney psychics sometimes try to pull on the Amazing Randi when they claim that their conjuring tricks no longer work because Randi’s skepticism interferes with the alleged delicate psychic energies involved in parapsychology. Catch-22 — as long as Randi is around being skeptical, the alleged parapsychological phenomena never seem to occur. Likewise, as long as we plug in the proper fudge factors into our landscape, we always get the universe we observe..but, unfortunately, since we can’t observe other universes, we can’t ever test the landscape hypothesis. What a wonderful Catch-22! As with the phoney psychic, the null hypothesis can never be tested.

    Let’s turn Sean’s flippant and egregiously false analogy around. If Sean can practice the most outrageous kind of sophistry, so can we.

    For Sean to compare the theory of evolution with string theory is like a ufologist claiming that astral projection disproves Einstein’s theory of general relativity because people who project themselves astrally travel faster than the speed of light.

    That’s not a serious argument. Consequently Sean is not engaging in a genuine debate, he’s playing word games.

    People who want to engage in a serious debate about string theory are going to have to bring more than deceptive and contemptibly casuistical verbal calesthenics to the table. They are going to have to bring testable predictions made by string theory, and experimental results published in the peer-reviewed physical literature to back up those testable string theory predictions.

    Ball’s in your court, Sean. Let’s have ‘em. Right now, on the table. Experimental results backing up testable predictions made by string theory. Show them to us right here, right now. Journal name, author(s), issue number, page numbers.

  • http://www.math.columbia.edu/~woit/blog Peter Woit

    Josh,

    The problem with string theory as a way to unify particle physics is not just at the electroweak breaking scale. It doesn’t predict anything at any scale up to the GUT scale, and only vague predictions even above that.

    Eric,

    Is your comment an April Fool’s joke? Honestly, I can’t tell. Seems to be hard to tell when string theorists are joking…

  • Levi

    I suspect the Eric Mayes remark is in reference to a follow up paper to hep-th 0612087, but I could be wrong.

  • http://countiblis.blogspot.com Count Iblis

    It would be nice if a skeptic (e.g. Woit), a neutral person and a strong advocate write a big article together, similar to this article about the number of dimensionful constants

  • Gina

    John Horgan said: “Sean, jump off the sinking ship while you still can! ”

    I don’t get it. John Horgan does not claim that the ship is sinking but rather that the whole ocean (of science) is drying.

    (Is the Horgan’s suggestion for scientists is to go work on wall-street? :) )

  • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

    Eric Mayes (22): You might have forgotten that Cosmic Variance is on Central time, so you’re post appeared a few minutes before it was officially April 1.

    mclaren (32): If you brush up on your reading comprehension, you’ll notice that I never compared the evidence for evolution with the evidence for string theory, about which you rant at such length. So your intelligence is somewhat self-insulting.

  • http://tsm2.blogspot.com wolfgang

    Eric,

    if hep-th/0703280 is the paper you refer to, then it seems that there is a little bit of work left (perhaps as homework assignment for the reader).
    E.g. on p.4 we learn that the electron mass comes out 6.5 times larger than it should be and the muon is 40% lighter.
    But it seems that another paper is coming, which will fix this.

    By the way, I thought that Volker Braun et al. already derived the MSSM from heterotic string theory some time ago, so there seems to be more than one way to do this.

  • http://golem.ph.utexas.edu/~distler/blog/ Jacques Distler

    Josh wrote

    Given the vast variety of string constructions, I don’t doubt that there is one that contains the MSSM at low energies with all of the couplings consistent with current measurements. But one expects that there will actually be many such string models which look roughly the same at low energy(since renormalization group isn’t actually a group and so isn’t uniquely invertible).

    So far (Eric’s paper, which I haven’t read, aside), there aren’t any. Finding one would be significant progress.

    Now, it’s true that, if you find one, you may be able to find others.

    In orientifold flux compactifications, the visible gauge and its matter content are localized on some brane(s) at some singularity of the CY. Varying the fluxes elsewhere on the CY wll change the cosmological constant. But the properties of the SM couplings will relatively insensitive to changes made elsewhere on the CY.

    It is far from clear that you will be able to “tune all of the knobs” (corresponding to the 100+ couplings of the MSSM) independently. I rather doubt that you will. Every knob that “can’t be tuned independently” is a prediction, and there’s no more reason to believe that number is zero than there is to believe that all 100+ parameters are uniquely determined.

    But the real point is that I (and everyone else who opines on this question) is, at this point, simply speculating. We just don’t know, and expressing our personal prejudices on how this will work out is not a scientific argument.

    “No big deal,” you say and move onto a slightly different model so string theory still lives.

    If only it were that easy …

    The converse also seems to be true. If your model stands up to scrutiny in the next round of experiments, I’m not sure this gives much in the way of evidence for string theory, just for some effective field theory like the MSSM.

    If you discovered proton decay tomorrow, would that give evidence for GUTs? After all, proton decay (and any other particle physics effect you could ever hope to measure) is completely adequately described by an effective field theory.

    It seems to me that, if you find a microscopic explanation for certain relations between couplings in the low energy effective theory (in the case of GUTs, for instance, sin^2 of the Weinberg angle), you don’t say “Oh, that’s not evidence for anything about short-distance physics. All we’re doing is learning about properties of some effective field theory.

  • http://CapitalistImperialistPig.blogspot.com CapitalistImperialistPig

    Sean,

    You contemptuously dis mcclaren’s reading ability, but somehow managed to miss his central points – that you willfully distorted Peter Woit’s statement, and that the status of evolution and string theory are hardly comparable. You are the one who made this comparison, so it’s disingenuous of you to blame it on mcclaren. Moreover, you made the comparison on the basis of a distortion of Peter Woit’s statement.

  • Josh

    Jacques,

    I agree that the sort of model-building that Eric brought up is important and I said so explicitly. It would indeed be progress to find a model with exactly the SM in it at low energy, with all couplings and phases right. And maybe it would give evidence for string theory if such a model made a very surprising prediction for some slightly higher energy phenomena which is then verified at LHC; especially if this prediction is very natural in a string/brane setup up but not expected from field theory reasoning. Nature may surprise us and maybe it won’t.

    You are right that we are speculating here, but I don’t see that as bad or necessarily unscientific as long as we recognize what we’re engaged in.

    You have a good point in your analogy with proton decay and EFT. My only real point regarding EFT was that what we would really like to see is evidence of physics which can’t be captured by quantum field theory but is found in string theory. I could be wrong, but it seems like this would require near Planck scale experiments.

    Peter,

    I was just using the electroweak scale as an example since this is basically the region we are probing currently. I agree that there doesn’t seem to be specific, unique predictions at even much higher energies. My point was just that the motivation for string theory is really anchored in its candidacy as a theory of quantum gravity, and so I don’t expect it will be properly tested until we can test that regime somehow. If we also learn about particle physics that would be icing on the cake, but string theory’s fortunes do not rise and fall based on its implications for particle physics. Just my view though.

  • http://evolutionarydesign.blogspot.com/ island

    Gina asked:
    Is the Horgan’s suggestion for scientists is to go work on wall-street?

    If they ever get the LHC working and furter findings of nothing particularly interesting are further confirmed, then there will be a very long line of PhDs at ‘the Wallstreet employment office’, becauses stubborn pride will pretty much kill the whole field before it can be rebuilt from WAY BACK when they first started *believing* that ad hoc and theoretically flawed assumptions are proven facts… ;)

    “The End of Particle Theory” JoAnne Hewett sets the Date

    Horganism and John Baez

  • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

    Except, CIP, that I did not distort anybody’s statement; the bit about “debates among credentialed scientists” was an interpolation on mclaren’s part, not part of what Peter or John originally said. If either of them would like to clarify, they are welcome to do so; it wouldn’t change the truth-value of what they are saying, but it would render the evolution example inapplicable.

    I never compared the status of evolution and string theory, because that would be silly; the cases are not remotely comparable. What I did was to point out that the existence of public debates about a subject says nothing whatsoever about the status of that subject among people who are familiar with the details; evolution is the most obvious example.

    The truth is, there is a long and honorable history of public debates about legitimate scientific questions between respectable scientists, and I think that’s a good thing.

  • Gordon

    Sean: You are going to get into the same very tedious loops that frustrated
    Clifford on Asymptotia. One very trivial and peripheral comment of yours mentioning evolution generates a “War and Peace” length irrelevant rant.
    The Horgan/Johnson dialogue is almost content-free. And, from what I have seen, arguing with Peter is like trying to hold quicksilver.

  • Rob

    Peter,

    As you are aware, I did misunderstand (4) your position from what was presented. Having now caught up with the comments, (39 as I write), I see that I am not unique in that.

    It appears to me that there are actually multiple issues at play here which make miscommunication inevitable. On one level is the issue of whether string theory is is right or not, and on another level is the issue of whether string theory is even a scientific theory, since it cannot yet be tested. I interpret your statement:

    The point I was making (as were Horgan and Johnson) is not that there is anything wrong with these debates, just that they are an unusual phenomenon in this particular science and thus indicate something unusual is going on.

    …as reference to the position mclaren takes in (32):

    science isn’t about what somebody might find someday, somewhere over the rainbow. Science is about what we can find evidence for right here, right now. If we can’t find hard evidence for it, Occam’s Razor says throw it out.

    It seems inevitable that the grow of our scientific foundation will lead to theories that exceed the testable reach of current instrumentation. I don’t view that as a bad thing, though I understand it may be decidedly uncomfortable to see the clear line between science and philosophy tested on both sides, (e.g. string theory as scientific philosophy and ID as philosophy pitched as science).

    But there appears to be a third aspect of this discussion which elevates the tension for both issues mentioned at the top, (string theory’s veracity and whether or not it is even a scientific theory). That issue is how the scientific profession identifies winners.

    In business and political blogs the participants often claim to want people who are willing to think creatively and take risks. But “risk” inherently means there are more losers than winners, so the question becomes “what happens to risk takers who lose?”

    In poker losing the pot will get you invited back. In the science profession, if you bet the pot and lose, your career is typically taken out back and shot.

    So public debate of unproven theory is risky, and dangerous to ones career. But is that good for science (and scientists)? Wouldn’t we all be better off by encouraging debate, and the attendant creative thinking, while reducing risk to the participant’s career?

  • http://CapitalistImperialistPig.blogspot.com CapitalistImperialistPig

    Sean,

    Ouch! Mea culpa. My apologies.

    I looked, and you are right. I trusted mcclaren’s version of the quote and it’s not what Peter has up and it’s not what Horgan & Johnson said.

    Never mind.

    I will shut up now.

  • http://golem.ph.utexas.edu/~distler/blog/ Jacques Distler

    Josh wrote:

    You are right that we are speculating here, but I don’t see that as bad or necessarily unscientific as long as we recognize what we’re engaged in.

    Absolutely!

    As long as we’re clear about what’s speculation, and what’s established, this is a very useful conversation to have. The problem arises when people (not you) put forward their speculations and personal prejudices as established facts.

    what we would really like to see is evidence of physics which can’t be captured by quantum field theory but is found in string theory. I could be wrong, but it seems like this would require near Planck scale experiments.

    Unless we get extremely lucky (large extra dimensions), some effective field theory description is likely to be valid up to very high energies. So, yes, direct observation of non-field-theoretic (“stringy”) behaviour is rather too much to hope for. There are people thinking hard about indirect manifestations of non-field-theoretic behaviour — in cosmology, for instance — so, even there, it is possible that we may get by without a Planckian accelerator.

  • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

    CIP, no problem.

  • Rob

    though I understand it may be decidedly uncomfortable to see the clear line between science and philosophy tested on both sides, (e.g. string theory as scientific philosophy and ID as philosophy pitched as science).

    “Pushed” (on both sides) would have been a better choice of word than “tested”…particularly in a science forum :)

  • TimG

    Would it be accurate to say that the arguments in favor of string theory all boil down to the following?

    (A) It has passed various consistency checks that could potentially have doomed it

    (B) Every other proposed theory of quantum gravity suffers from more serious (arguably fatal) problems

    That’s how it seems from this (non-high energy) physics student’s perspective. Based on (B) I can understand why a person studying quantum gravity would choose string theory over an alternative. What I don’t understand is why string theorists seem so convinced that the theory is correct. Should we be very surprised if string theory turns out to be both self-consistent and wrong? Or if the correct theory happens to be one we’ve never thought of?

    I guess what I’m asking is: Why do string theorists seem so certain that this is the only possible answer? (Or am I overestimating their sense of certainty based on message board rhetoric?)

  • http://evolutionarydesign.blogspot.com/ island

    Oh good grief, if Paul Davies and John Wheeler are correct, then evolutionary theory is missing a key piece to the purposefully structured puzzle that only creationists and semi-religious foundations, like the templeton organization, support, so don’t pretend that Lynn Marguilis doesn’t call extremists among her own peers, “neodarwinian bullies” because she thinks that the Dawkins mentality isn’t equally over the antifanatical top!

    Doncha just love how they only see the other side’s dogma?

  • Ellipsis

    Just to bait the readers here — nobody has answered my question: what does one end up with if one promotes dimension to an operator? There are good reasons to think that dimension may be more than just a constant — for example: as energy density increases, the gravitational manifold couples to itself more and more strongly — one could think of this as a “cloud of virtual gravitons” around a point mass, for example — and those virtual gravitons themselves perturb the manifold (no longer a manifold) further (as they are energetic), resulting in more “virtual gravitons”, etc, etc, effectively resulting in a fractal pattern type distortion of the “manifold” in regions of very high energy density. This “fractal” distortion thus changes the Hausdorff dimension in a local region around a point mass.

    So one might thing that dimension is in fact an operator related in some way to Hamiltonian density.

    What happens if this is done?

  • http://www.physicsofsuperheroes.com Jim Kakalios

    To quote James Thurber: Fools rush in where angels fear to tread – but many fools are alive, while all the angels are dead.

    So, let me risk being a fool and pose the following question: What’s the physics motivation for String Theory?

    I’m serious – what is the physics that is driving this train?

    At the start of the 20th century, physicists made theoretical proposals that were at least as unconventional and counter-intuitive as anything in String Theory. A key difference is that physicists were trying to explain experimental observations for which classical physics could not account, which drove the development of quantum mechanics.

    What is the experimental observation that is motivating String Theory, that can not be explained with conventional physics? By the way, I personally am in the Feynmann camp. That is – while I think it would be cool if quantum mechanics and gravity could be reconciled into a single theory – until such a theory is developed, that accounts for the observed world, I’m agnostic on whether or not such a theory even exists.

    My reference to Feynmann refers to an interview he gave, wherein he was asked about the latest trends in HEP Theory, that seemed to use mathematical elegance as a guide. He allowed that while in the past, physical theories that turned out to be correct were indeed mathematically beautiful, there is no reason to suppose that this would continue, and that it was perfectly possible (in his opinion) that peeling matter down to the next layer might reveal something mathematically complex, lacking all elegance. For what does Nature care whether we find the equations pretty or not?

    Now – here’s where my ignorance may have led me int a trap. Is it that, from our understanding of the Big Bang and the evolution of the universe, that at some point in the distant past – for the merest fraction of a second, gravity and QM MUST have been the same? Is that the motivation? (I’m not trying to be snarky – I don’t know). [My own research field is in Experimental Condensed Matter – developing materials for solar cells and doing some collaborating with a Neuroscientist – where we may have found something relevant for understanding of Parkinson’s].

    If that is the only physical motivation (that at some point in the early universe gravity and QM must have been joined), then this seems to be thin soup.

    Sean, you mention String Theory as being promising. And I agree, it is. But when we hire a promising assistant professor, we give him or her seven years to pay off on their potential. At some point the plug gets pulled. What would you agree to be a fair timeline for String Theory? Eventually I imagine the field will vote with their feet, and researchers will move on.

    Some of my colleagues are concerned about blowback. There was a great deal of attention when high temperature superconductivity was discovered, but its now 20 years and the trains still do not levitate. Some early promises have had to be abandoned. String Theory has been presented to a considerable subset of the non-physics professor community. I think many do not recognize the provisional nature of the theory. If it all turns out to be a false approach (of which there have been many in physics, and it is after all how we get to correct theories, crawling over the corpses of incorrect ones) will there be a backlash with the public?

    Well, I have to go pick up my son. I think I’ve embarassed myself enough with this post.

  • http://www.physicsofsuperheroes.com Jim Kakalios

    And I see that while I was writing, Tim G two posts above gets at my point in 1/4 the space, and better.

  • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

    There are many very good reasons to believe that string theory has something to do with quantum gravity in the real world. That’s why so many smart people are devoting their professional lives to working on it. It’s much better behaved at short distances than conventional field theories; it has proven fruitful in shedding insight on longstanding problems (such as a microscopic understanding of black-hole entropy); and by dualities it is part and parcel of our understanding of field theory itself. More details will have to wait for the post foreshadowed above — or until more string theorists decide to try harder to explain themselves.

  • Ellipsis

    Jim:

    That’s a good question. One experimental observable that I think any quantum gravity theory should probably explain would be the value of the cosmological constant (or the properties of dark energy).

    None have done so yet. (Model constructions .. not predictions! … aside).

    Another example is so ubiquitous people often just forget that it is an experimental observable. That is the fact that, at least macroscopically, our universe has 3+1 dimensions. I think any quantum gravity theory should explain _why_, at macroscopic scales, Minkowski space is the appropriate metric (again, not as a possible construction/”compactification”, but an actual prediction).

  • Aaron Bergman

    Hi Jim.

    The problem with quantum mechanics and gravity is not that they’re separate; it’s that they are incompatible. You need to turn quantum mechanical matter into classical gravitation and nobody knows how to do that. Now, maybe the problem is just too hard to solve without experiments to guide us, but the problem is there, and it has to have a solution.

  • http://www.physicsofsuperheroes.com Jim Kakalios

    Ellipses:

    You raise two excellent observables. Now, I’m not, by any stretch, an expert on String Theory. Is this what the theorists are trying to explain? I thought that rather than account for our 3 + 1 dimensions, we are to take seriously the existence of higher dimensions, which are hiding in very small or very large length scales.

    [The geek in me loves the notion that the exctra dimensions may be vary large. I call that the Good Omens Hypothesis – in Neil Gaimen and Terry Pratchets book of the same name, they explain why psychics were unable to detect the “aura” around the son of the Devil – they couldn’t see it for the same reason that you can’t see England when you’re standing in Hyde Park]

    Sean:

    You said: “There are many very good reasons to believe that string theory has something to do with quantum gravity in the real world.”

    I don’t doubt it. but what are the real world arguments for quantum gravity? What physical phenomena have we observed that must include both? No one has observed Hawking Radiation, or anything like it, have they?

  • Aaron Bergman

    Why do string theorists seem so certain that this is the only possible answer? (Or am I overestimating their sense of certainty based on message board rhetoric?)

    I know next to no one in the field who believes that string theory is the only possible answer. I do know lots of people who believe that it must be some element of the right answer, however.

  • http://quantumfieldtheory.org nc

    “… it [string] has proven fruitful in shedding insight on longstanding problems (such as a microscopic understanding of black-hole entropy); and by dualities …” – Sean Carroll

    If I can quote a contrary argument:

    “The claim to explain black-hole entropy is (as noted in chapter 9) exaggerated, because the string theory results work only for special and aytpical black holes.”

    – Lee Smolin, The Trouble with Physics, US ed., p. 277. (In chapter 9, Smolin explains that Andrew Strominger and Cumrun Vafa showed that extremal black holes, i.e., black holes with about maximum possible electric/magnetic charge while remaining stable, have identical thermodynamics to extremal stringy branes.)

    Regarding Maldacena’s duality between string theory and gauge theory:

    “Even if it is true, the duality conjecture can be useful only if one side of the duality can be defined precisely. So far, it has been possible to define the relevant version of string theory only in special cases.”

    – Lee Smolin, The Trouble with Physics, US ed., p. 143.

  • http://www.physicsofsuperheroes.com Jim Kakalios

    Aaron:

    Thank you. I see. Sorry for being dense.

    This reminds me of a conversation I had over ten years ago, with Sir Sam Edwards. He argued that since we were unable to reconcile Quantum Mechanics with General Relativity – that we should toss out General Relativity. After all – the list of experimental confirmations for GR is MUCH shorter than for QM. My teenagers could live without GR, but not without their cell phones, laptops, DVD’s iPods, CD players – none of which are possible without the transistor and/or the laser, neither of which could be invented without QM.

    So perhaps there’s a theory of Gravity that can do what GR can, plus be quantized – just as GR could do what Newton could, plus some extra bits. Is this the physical motivation for String Theory? That it intends to replace GR with a new, quantizable theory of gravity? But there are many other alternative models for quantum gravity. I know that some are concerned that these other appraoches are being starved for oxygen , due to all the love garnered by String Theory. Which again raises the timeline question.

    Thanks again.

  • Eric Mayes

    The paper that I referred to is indeed hep-th/0703280 (Chen, Li, Mayes, Nanopoulos) which will be available on the archive tonight. We describe a three-generation model in which the gauge couplings are unified and for which we can calculate all of the Yukawa mass matrices and mixings, as well as the low-energy phenomenology. This is the first model that we are aware of that has all of these properties. It is true that the muon and electron masses are a little off. However, it should be kept in mind that these states are very light and subject to quantum corrections.

    Eric

  • http://quantumfieldtheory.org nc

    (sorry for the typo: aytpical should be atypical)

  • Ellipsis

    You raise two excellent observables. Now, I’m not, by any stretch, an expert on String Theory. Is this what the theorists are trying to explain? I thought that rather than account for our 3 + 1 dimensions, we are to take seriously the existence of higher dimensions, which are hiding in very small or very large length scales.

    Yes — in trying to reconcile GR with QM, string theorists (not me, by any means — I’m an experimental particle & astroparticle physicist — if you must know, junior faculty at a major research university) posit an 11-D space, which then is “compactified” at macroscopic length scales. Why one precisely ends up with Minkowski space, though, has _never_ been given a good explanation, to my knowledge.

    ———–

    As an aside, no one has ever answered my question (comment #52). Anyone want to bite?

    ———–

    Anxiously awaiting Mayes’ hep-th/0703280 to see if it explains the universe. I’m sitting down.

  • http://quasar9.blogspot.com/ Quasar9

    “Seventh, evolution predicts a common ancestor for all current forms of life. This prediction has been tested with DNA sequencing, most spectacularly with mitochondrial RNA sequencing, and has been proven true.”

    Always knew ‘everything’ was related,
    Everything is related, and everyone too.
    So which came first the chicken or the egg?

    “Like all quanta, the photon has both wave and particle properties, exhibiting wave—particle duality.”

    So which came first the ‘particle’ or the ‘wave’?

  • http://tsm2.blogspot.com wolfgang

    > Anxiously awaiting Mayes’ hep-th/0703280 to see if it explains the universe.

    You can read it here.

  • anon.

    Arxiv bug making papers available early? Hmm.

    So, Eric Mayes, since this apparently is not an April Fool’s joke: does your model have a cosmological moduli problem?

  • Eric Mayes

    If by cosmological moduli problem you mean the problem of moduli stablization, it has already been shown that all moduli can be stabilized in the model by turning on fluxes (Chen, Li, Nanopoulos ’06). If you’re referring to the the problem of obtaining a cosmological constant, then that is a story we’ll have more on later which will likely involve noncritical string theory.

  • Ellipsis

    Eric,

    I don’t want to be too harsh on your paper, because I think models like these have some value, but I’d like you to explain:

    1) Why did you choose: epsilon^{D1} = 0.061 and kappa^{(1)} = 39.6i. To match the data, right? _That’s not a prediction, my friend_. That is a post-diction to match what experimentalists have already told you.

    2) Same for v^1_u, v^2_u, v^3_u, etc. etc. etc.

    3) Where are the CP phases in either the CKM or PMNS matrices? The latter would be especially nice to know because it would be a _prediction_ (you haven’t forgotten what that means, have you?)

  • Mike

    I have my physics diploma from 10 years ago. Now I earn my money with software and physics is kind of a hobby. So at least I have no personal stake in the subject.
    My 50 cent are, that string theory is loosing the public debate, because Woit and especially Smolin have the better arguments. To me it looks just that simple. You can say I am too dumb because I am not able to follow the complicated mathematics of string theory (still struggeling with ordinary field theory) (@Sean: I was however able to follow your three hours introduction to general relativity, which is available online, very nice). But so far I have not read a reply to Smolin’s book from a string theorist that really convinced me. The ideas presented by Lee (Loop quantum gravity, deformed special relativity) just seem more exciting and really falsifiable.

  • Michael

    “Ockham’s razor tells you that LQG is closer to reality.”

    Ockham’s razor is a load of crap. The “aether” was seemingly simple and straightforward, yet it was wrong. a^4 + b^4 + c^4 = d^4 was long thought to have no integer solutions. That was wrong too. Goethe (or somebody) said that once you scratch the surface of something “simple”, you find it’s complex and deep.

  • anon.

    Eric, sorry — what I actually meant to ask was, do you have a moduli-induced gravitino problem? (Moduli decaying to the gravitino, which is long-lived, and can screw up BBN etc…)

  • http://mingus.as.arizona.edu/~bjw/ Ben

    Sean,

    The proposed title “Why String Theory Must Be Right” falls into the rhetorical trap-hole that both string theorists and their detractors have collaborated in digging. I know you don’t actually believe that it is necessarily right and therefore experimental verification is merely a filigree on its mathematical edifice, but that is the impression such a title gives.

    In my limited understanding a more accurate, but less catchy title would be “Why String Theory Must Be Useful [in constructing a theory of quantum gravity, whatever that theory turns out to be in the long run].” Sometimes, a theory that is useful is even more worthwhile than one that might in the long run be right. I didn’t watch any of the Horgan/Johnson exchange because I’m not interested in the rhetoric surrounding this subject. One thing that string theorists have not always succeeded in getting across is that (so far as I know) constructing a mathematically consistent and elegant theory that reduces to our current low-energy understanding of the universe is difficult. So working out such a theory would be a major mathematical-physics success even if it made no new experimental predictions.

    Part of the problem is that string theory is legitimately difficult to explain, and the culture of superiority that has existed among high-energy theorists (We are the most fundamental, etc) has meant that they haven’t always bothered to try. This has alienated even many fellow scientists, let alone the public. (I am not a theorist, but I did go to physics grad school at Rutgers, so I am quite familiar with this phenomenon.) I’ve seen Ed Witten give a brilliant talk in which he made us feel for half an hour like we sort of understood string theory. An hour later, I realized I still didn’t understand it at all. But, he was talking to the audience, rather than engaging in triumphalist rhetoric. I do think one reason string theory is getting this flak is that people, including PhD physicists, are threatened by things they don’t understand, especially when the proponents are overbearing.

  • http://www.math.columbia.edu/~woit/blog Peter Woit

    Sean,

    Don’t you think there’s something funny going on here when you and others assume that a string phenomenology paper is an April Fool’s joke, but its authors don’t seem to think so?

    “[string theory is] much better behaved at short distances than conventional field theories”

    This is really a misleading statement. Yang-Mills theories, the ones that are the main component of the Standard Model, are precisely formulated even outside of perturbation theory, and asymptotically free. Their short distance behavior is arguably better than that of string theory, where one doesn’t have a non-perturbative definition. Perhaps you were just referring to “conventional” qfts of quantum gravity, but if so you should make that clear. And even there, the recent evidence about finiteness of N=8 supergravity may make this statement incorrect.

  • http://www.math.columbia.edu/~woit/blog Peter Woit

    Rob,

    I’ve never claimed there is anything wrong with working on speculative ideas that can’t be immediately tested. That’s a misinterpretation of things I have written. I actually spend as much of my time as I can manage working on such speculative ideas.

    You’re right that the crucial question is how such work gets evaluated. It’s not true that working on something speculative that isn’t successful will destroy one’s career. Lots of people doing this have tenure. The people participating in these public debates all have tenure, and aren’t going to lose their jobs if they lose the debate (my situation is somewhat special: I don’t have tenure, but do have a pretty secure permanent position). The problem is mainly for junior people, where the reward structure is such that getting another job and getting tenure requires that they either work on certain widely accepted speculative ideas, or, if they decide to do something else, are both lucky and brilliant enough to make a big breakthrough. This reward structure would make sense if these widely accepted speculative ideas seemed to be working out, it’s counter-productive when there’s strong evidence that they are not working out as hoped.

  • Eric Mayes

    Anon: We do not claim that this is THE model or that we are ‘predicting’ the masses of the elementary particles. The point of the model is that string theory CAN correctly describe our universe, and can do so in a elegant, geometrical way. I don’t know of any other theoretical framework which can make this claim or even come close.

  • Ellipsis

    Eric,

    Did you, or did you not, say that you

    “competely derive the MSSM from string theory, including the quark, tau lepton, and neutrino mass matrices and mixings”

    Now you say that, actually, those masses and mixings are in fact just pasted in from experimental results right out of the PDG.

    I think that’s actually more than disingenuous. I think it helps contribute to the low reputation that “string theory” enjoys today.

  • Eric Mayes

    Ellipses,
    The Yukawa couplings depend crucially on the details of the model and are not just put in by hand. The mass hierachies between the three generations arise naturally.

  • http://tsm2.blogspot.com wolfgang

    Eric,

    I agree with you and I think your work is very interesting and valuable.

    But in your first comment you wrote “We can now completely derive the MSSM from string theory” and to be honest, it seems to me that this would somewhat overstate what you have achieved so far.

  • http://thechocolatefish.blogspot.com/ Yvette

    As a physics undergraduate, I have to agree with Mike in post #70. While I may not understand the math behind the debate, the way I see it it’s more about the scientific justification and motivation behind string theory and if those justifications are a reflection of the actual merit. This idea is a rather simple one to grasp and understand, and when most laypersons apply their knowledge of the scientific method to string theory they don’t see the point of the argument for it. We’ve spent an awful lot of time telling everyone about the merits of experimental evidence in science and the like, so what’s the motivation?

    Plus there are adverse effects to this as well- I run public observing nights with our university telescopes, and one of the comments I often get is “science isn’t really about proving anything or about evidence- just look at string theory!” At this point I howl and cry a little but have a hard time explaining to some why this “doesn’t count,” and it’s frustrating.

    (By the way, if someone more knowledgable on the subject than me has a good way to answer the “just look at string theory!” comment, please let me know. It would be much appreciated.)

  • anon.

    Eric, you address your comment to “anon.”, but I gather you are replying to someone else? I understand what your paper claims and what it does not claim, and I never meant to suggest I thought you were claiming to have ‘the’ model. Your use of the word “derive” earlier was a bit strong, but anyone who looks at the paper should understand what you really mean.

    The reason I ask about the moduli-induced gravitino problem, though, is that in model-building it is not enough to have soft terms that reproduce the SM and get the right dark-matter abundance (though that’s certainly a good start!). One also has to worry about various astrophysical tests, inflation, reheating, BBN, etc…. So I wonder if you or your collaborators have thought these things through.

    At any rate, it seems like an interesting direction and I hope to read more details in the future….

  • Eric Mayes

    Wolfgang,
    The model is the MSSM in respect to the fact that it has the following properties:
    1. Three generations of quarks and leptons.
    2. Gauge coupling unification is realized.
    3. Realisitic mass hierachies between the different generations are realized.
    4. Realistic SUSY spectrum.

    Show me one other example where you can find all of these properties!

  • Eric Mayes

    Anon:
    Sorry, I meant to address the earlier message to Elipses. All of your points are very interesting and the answer is yes, we have thought about them and are presently working on them.

  • former string theorist

    Hello, Sean and everybody. This post is a wonderful addition to the public debate, which I think is valuable. The blogosphere is indeed very repetitious in the absence of fresh news but there is much to be learned by watching it and in the absence of anything better it’s the most recent significant development in human communication. Watching it interact with string theory is fascinating indeed.

    But Sean’s principal point is correct; string theorists are losing the public debate because they don’t think it’s worth their time to explain their point of view to others. That would involve explaining at least some string theory, because it is a difficult and technical subject, and requires not just patience but also talent to understand. It will therefore always be a subject which only a privileged minority will be able to understand. The people who don’t become experts in string theory will just have to learn to live with the fact that they aren’t qualified to judge how likely it is to be true because they can’t perceive how richly it interweaves the areas of physics which have already been confirmed by experiment, but not yet unified into a single theory.

    That is what I was told before I decided to become a string theorist. I was the brightest in my undergraduate institution and had never had trouble understanding anything mathematical or technical, and from there I went to a Major American University which was one of the centers of string theory, where people talked in hushed whispers in the corridors about how great a genius such-and-such a person was (who I had never heard of). After a while I had heard all the rumors and knew about how so-and-so had done such-and-such by the age of nine (in a certain person’s case it was that he had set c=hbar=G=1 (sometimes belief looks like understanding, you know)).

    Meanwhile I studied Green, Schwartz and Witten and Polchinsky and interacted with the string theorists who were supposed to be geniuses and found that I needed to brush up on some mathematics (although the mathematics department from which I had come had given me an undergraduate education second to none). I did so. I learned my Calabi-Yau’s, and my Yang-Mills; I geometrically quantized this and harmonically formed that. But I couldn’t understand why everybody about me was behaving in such a bizarre way when it came to REPUTATIONS. Why was I being asked to respect these people’s intelligences so much? They had not earned it. Their request was illegitimate (yes, I probably have Asperger’s, and so do a lot of these people). No. Earn it first. Do something intelligent.

    I did not actually say this, of course (I’m high-functioning). I engaged diplomacy and patience. When I asked them questions about technical matters, they told me I was probably too stupid to understand. The mathematics was fine; nothing difficult really, except that the language they used was rather flowery, and occasionally turned into some kind of hand-on-heart saluting the beauty of string theory and the universe, like the way that American children are trained to behave when they ritualistically worship their flag every day. This kind of behavior always irritated me. The stupid savages were using peer pressure to enforce conformity. All of this “We have to be reverent in front of this holy thing” crap is illegitimate. Against the law of my understanding.

    And these people didn’t seem at all to be able to answer any of my questions about string theory. What does it mean for a mathematical structure to be “true”? How can you claim to have explained everything when you have said nothing about quantum mechanics, which is quite clearly the thing most in need of explanation? The connection to experiment was not what I was concerned about at all (at the time, I disrespected experiment). I wanted to see if these people had their LOGIC correct.

    I was told that, if you want to make progress, you have to abandon the hope of understanding every tiny little bit. You have to build a conjecture here on top of an opinion there. We don’t have to worry ourselves about it; there are very clever people in string theory and the consensus of many geniuses is that this or that thing is true. Occasionally people had told me things like that throughout my life, and I had always thought to myself “Oh, you’re one of those subhumans with no respect for his own intelligence, who is led around like a slave by other minds because you yield to others the ability to think for yourself.” Was I supposed to think that about EVERY string theorist? The mathematicians had never told me that; neither had the physicists, except when they quoted the mathematicians.

    It seemed that the physicists and mathematicians were working within a structure where they knew they had to earn my respect, and they did so. The string theorists did not seem to understand this; they expected my respect (for their intelligence and the idea that they knew what they were doing) as though they were entitled to it without proving anything to me, and they insulted me if I asked for any proof, despite the fact that my mathematical skills and intelligence could clearly equal theirs.

    I have to say that I think it is very unwise to demand of somebody that they should feel despicable compared to you. Yet that is the one message that the string theorists constantly produced: Feel despicable compared to us because of our Big Brains and our Big Theory, which is too complicated for Stupid You to understand.

    So in the end they lost me, and I think I was very fair to give some number of years of my life to hear what they had to say.

    Now of course here I am not saying that I think string theory is false. Rather, the two-dimensional conformal field theory which they are studying is a part of pure mathematics, and therefore the assertions they make about it are true. But the string theorists as a community have some problems, and a great many of them place too high a value on this reputation for being a genius, and they have become disdainful of others, and this is leading to their downfall.

  • kostya

    Eric,
    Is it possible to have m_{3/2}~O(TeV) in Type IIA with fluxes???
    I thought that the flux superpotential in Type IIA can’t be tuned to be small, unlike in the Type IIB case.
    Since m_{3/2}~e^(K/2)*|W_{flux}| and W_{flux} is is of order one in Planck units, the gravitino mass should be of GUT scale, unless the compactification volume is exponentially large (a la Conlon & Quevedo constructionin in Type IIB).

    Kostya

  • TimG

    Aaron Bergman wrote:
    “I know next to no one in the field who believes that string theory is the only possible answer. I do know lots of people who believe that it must be some element of the right answer, however.”

    OK, but that still leaves the *why* unanswered. To reiterate my comment from above, the fact that competing theories may have worse problems explains why people work on string theory, but not why they believe it’s right. Most of the pro-string arguments seem to be that it passes consistency checks, although each of these come with their own caveats:

    – anomalies cancel in 10 dimensions (and perhaps we live in a 10-dimensional world)

    – the different versions of string theory seem to be limiting cases of a single theory (but we don’t know what it is)

    – black hole entropy has the right form for “extremal black holes” (and maybe this will prove true for other black holes)

    etc.

    These things are good signs, but how do we know an incorrect theory couldn’t pass these checks? It seems like we’d need to know every *possible* theory of quantum gravity to make that assessment.

    Then again, I suppose you could say the same about empirically tested theories: How do we know an incorrect theory couldn’t have predicted such-and-such experimental result? But the history of science seems to show that at least provisionally trusting your theory when it passes experimental tests is an OK thing to do. Whereas I don’t have a clue whether trusting a theory based on “anomaly cancellation” or what have you is a good idea.

    Despite all of the above, I’m really not at all anti-string theory. I freely admit that I don’t know enough about string theory to form an educated opinion pro or con. But I’d love to see an explanation (intelligible to non-high energy physicists) of why so many people are convinced it’s right — something that goes beyond the laundry list of string theory achievements, to address the underlying question how much weight these achievements should carry as evidence in the theory’s favor.

  • Eric Mayes

    Hi Kostya,
    We haven’t turned on any fluxes in doing the phenomenological analysis we present in the paper.

  • kostya

    Hi Eric,
    But how do you then stabilize the moduli?
    Are you just assuming that the moduli are somehow stabilized and pick some values? Do you know of any mechanism other than the fluxes to fix the complex structure moduli in Type IIA?

    Kostya

  • Eric Mayes

    Hi Kostya,
    The moduli can be stablized with fluxes, which in this case do not contribute to the Ramond-Ramond tadpoles (see Chen, Li, and Nanopoulos ’06). However, the phenomenological analysis becomes very complicated if we include fluxes, so for the present analysis we turn them off. You are correct that the fluxes should be taken into account, and we plan to do this in later work.

  • kostya

    Hi Eric,
    I was not concerned about the tadpoles, this should not be a problem.
    My concern was the order one (in 4D Plack units) flux superpotential
    W_{flux}~sum_i{q_iU_i} which results in the gravitino mass being of order GUT scale since m_{3/2}=e^{K/2}|W_{flux}| and the only suppression is from the inverse volume^{3/2}. Presumably, since you claim to have the standard gauge coupling unification at ~10^16 GeV, the volume can’t be exponentially large to give you the TeV scale superpartners.
    Hence, if you say that the complex structure moduli can be stabilized by fluxes you automatically get a huge m_{3/2} in this case. So, unless someone comes up with a new way to fix the CC moduli in Type IIA, getting low scale superpartners from Type IIA is problematic.
    You say that you turn off the fluxes but in this case you can’t claim that the moduli are stabilized can you?

    Kostya

  • http://eskesthai.blogspot.com/2007/03/its-penquin.html Plato

    Sean:The existence of a public debate isn’t evidence that a field is in trouble; it’s evidence that there is an unresolved scientific question about which many people are interested, which is wonderful. Science writers, of all people, should understand this.

    You leave lots of information which to discern what is going on. I don’t think anyone is being fooled here. The public either. It’s been explained time and time again and the recurrent conversations attest to this.

    I call it the “Pink Elephant.” We get this wonderful view of people holding different parts of the elephant, and they are the product of research in terms of quantum gravity models.

    Why Pink elephant?

    Well Susskinds provides for a thought experiment, and information given from entanglement from inside the blackhole? Now this elephant takes on all kinds of attributes, maybe as Babar looking through a window? Or, it being, just a plain Dumbo elephant. :)

    So “string theory” is about the Pink elephant?

  • http://countiblis.blogspot.com Count Iblis

    Yvette’s and Mike’s comment also suggests that string theory is losing the debate precisely because it is too much debated in public. When science is discussed in the popular literature, newspapers etc. then it usually become hyped too much and that then backfires.

    My personal opinion is that string theory is not the solution because it is not really new physics. It is the same old known physics (quantum mechanics) applied to new postulated degrees of freedom. A good analogy would be if 19-th centrury physics were applying ordinary Classical Mechanics to imagined degrees of freedom to find a theory of everything that would explain the unsolved problems they were dealing with.

    Except for ‘t Hooft’s deterministic models, no new physical theories have been proposed since the invention of quantum mechanics and general relativity.

  • Ijon Tichy

    Sean wrote:
    Peter Woit agrees that “things are not looking good for a physical theory when there start being public debates on the subject”; indeed, I’m just about ready to give up on evolution for just that reason.

    Firstly, there are no public debates on evolution. There are pseudo-debates caused by religious nuts, but no real debates. Your sarcastic analogy (I assume you were being sarcastic) would work if there really was an actual debate going on about whether or not evolution was a scientific theory. But there isn’t.

    Secondly, Peter Woit may agree with John Horgan and George Johnson that “things are not looking good for a physical theory when there start being public debates on the subject” but in the link you provided (i.e. the blog article) he did not actually say that he agreed with them. So you must have misread that.

  • Moshe

    Thanks Sean, I am more or less in agreement with you, except for matters of packaging. Strangely enough there is a large number of people (including professional physicists, some of them even blog…) who are very interested in forming and expressing strong opinions on the merits of string theory (and theorists), but show no interest whatsoever in the physics. I personally have no problem with losing the debate among that crowd.

    However, there are some very beautiful aspects of string theory that may appeal to non experts, would be a shame to keep them to ourselves, only one has to think carefully on how to talk about the subject. I have no good ideas, but at the very least it seems to me that framing the discussion in terms of motivation or justification (e.g. explaining why the approach seems promising) is counter-productive, it invites the kind of uninformed commentary we are all too familiar with. Perhaps one can simply describe all kinds of things we find kind of neat, or even pretty, other people might enjoy those as well, and we can leave the debates and judgments to those who enjoy them.

  • http://eskesthai.blogspot.com/2006/10/history-of-star-shine-to-now.html Plato

    Quantum Tunnelling and the Landscape?

    For a quantum particle moving against a potential energy “hill”, the wave function describing the particle can extend to the other side of the hill. This wave represents the probability of finding the particle in a certain location, meaning that the particle has the possibility of being detected on the other side of the hill. This behavior is called tunnelling; it is as if the particle has ‘dug’ through the potential hill.

    For layman “the question about the String Landscape” may still exist?

  • George R

    I’m an interested layman, which is why I read this blog. It is my feeling that when the general public reads the popular literature in physics, they do not expect to come away ‘understanding’ what string theory is really all about. Frankly, it is such a complex subject I suspect there are only a very few people in the world who understand it. I think what captivates the public interest, is the idea of what appears to be very esoteric thought, being applied in a quest for an understanding of our universe, the world around us. For me this type of thinking is beautiful, it represents a pinnacle in mans ability to formulate abstract concepts, concepts which may or may not describe the physical world, but which already have succeeded in extending our understanding of the mathematical world.

    Count Iblis said, When science is discussed in the popular literature, newspapers etc. then it usually become hyped too much and that then backfires.

    I would respectfully disagree. As far as the public is concerned, I believe it is a good thing for us to see the debate, to see the mechanism of disagreement, the quibbling among scientists, that it follows a complex process not unlike other areas of human endeavor. Ultimately, string theory will be a valid solution, a partial solution or no solution at all. For the interested public it won’t matter because the current research will eventually lead to some further evolution of our understanding of the universe, and it is the process as well as the progress of knowledge which is interesting.

    I can’t wait until they fix that little part that broke on the LHC and plug it back in :-)

  • Rob

    Yvette quoted members of the public saying:

    “science isn’t really about proving anything or about evidence- just look at string theory!”

    …and requested suggested replies.

    I would tell them that science is exactly about proving things and evidence, which is why many scientists do not consider string theory true science…because it can’t yet be tested with experiments or prove it’s validity with predictions.

    I would also tell them that to take the current debate over string theory and use it to draw conclusions that discount all scientific advances suggests they don’t believe in the existence of the telescope they just looked through, and that they should throw away their cell phone and walk home, because neither could exist without the advances of science.

    But then, I’m not long on tact.

  • Ellipsis

    Personally, although a quantum theory of gravity that can predict the value of something that hasn’t been measured yet, and might be within this century, would be lovely, all I’d really like is to get a response to my comment #52.

  • Michael

    Rob said: “I would also tell them that to take the current debate over string theory and use it to draw conclusions that discount all scientific advances …”

    There was a time when people would drop dead at age 30. In many developed nations, the life expectancy is beyond 70. It wouldn’t surprise me if the life span (for all nations) was up to 100 years, by 2100 or 2200. Science is extending / enriching lives, so that we have the time and energy to debate how many angels on the head of a pin.

  • Eric Mayes

    Hi Ellipsis,
    In regards to your comment #52, this is basically what string theory does. For example, in the bosonic string there are 26 bosonic fields which ‘live’ on the string worldsheet which are interpreted as dimensions. These bosonic fields are needed to cancel the conformal anomaly, however one can trade bosonic degrees of freedom for fermionic degress of freedom (two fermions for each boson) and reduce the number of required dimensions. This is why the superstring requires 10 dimensions instead of the 26 for the bosonic string.

  • Ellipsis

    Eric,

    If dimension were an operator, then why would it necessarily take integer eigenvalues? There should be a physical reason for that, right? Let me know if I’m wrong, but I don’t think string theory provides an answer (at least at present).

  • WC

    The basic idea of String theory, that of replacing a particle by a string, seems too simple to be true.
    One of the commentators above is correct in saying that there is nothing really new in String theory (except the above idea). There is no awe one feels on learning it (unlike GR and QM). This of course, is nothing against the theory. It may be that we have already discovered all the mind-bending ideas that nature has to offer.

    Obviously, its most serious failure is that it predicts nothing at this point. It also does not connect in a satisfactory way with Quantum Field theory.

    The fact that it is consistent, in not really a big point in its favor, because all the consistency is really coming from the two dimensional conformal field theory of the worldsheet.

    Its biggest success till today seems to be that one of the string states is a massless spin two particle. Sean mentions black hole entropy and field dualities above, but I personally have’nt looked into them.

    However, since String theory is not a finished product, hope is not dead. There are still enough loose ends in it, that people can work on. Having done so much work, I don’t think researchers will be ready to give up until they have followed every lead to its bitter end. Or insightful turn, that leads to predictions, and maybe even awe (Are’nt we all in physics for the thrills?).

    The string army, may be losing the battle, but its resources are not exhausted yet.

  • Eric Mayes

    Ellipsis,
    Every bosonic degree of freedom corresponds to one dimension. If you like, you can look at the spin as being the eigenvalue, so that in some sense fermionic degrees of freedom give us half-dimensions.

  • Ellipsis

    Need to grade problem sets, so I’m going to have to leave this productive discussion — it’s been fun…

  • Thomas Larsson

    Rather, the two-dimensional conformal field theory which they are studying is a part of pure mathematics, and therefore the assertions they make about it are true.

    Former string theorist, if you anytime get bored with being stuck in 2D, maybe you are interested in some post-stringy mathematics. A nice thing is that this is pretty much virgin territory, which hasn’t been beaten to death by Witten & Co for the past 25 years.

  • a

    Eric Mayes:

    In your comment 22 you announced that after your complete derivation of neutrino masses and mixings anti-string people should sit down and be quiet. In your paper I find: “Moreover, the suitable neutrino masses and mixings can be generated via the seesaw mechanism by choosing suitable Majorana mass matrix for the right-handed neutrinos”. Is this a 1 Aprile joke or hironic science?

    In the conclusions you write: “We have calculated the supersymmetry breaking soft terms, and obtained the low energy supersymmetric particle spectrum within the reach of the LHC”. Maybe “We have fixed by hand m_3/2 = 1100 GeV and other 26 free parameters such that sparticles are within the reach of LHC” is a more precise summary of what you did? (Unless kostya is right and you will have to increase m_3/2 by 16 orders of magnitude).

    What is really depressing is not that you have many free parameters, but that you do not even try to see if, despite the many free parameters, your construction gives some acceptable prediction.

  • http://quantumfieldtheory.org nc

    “… You’re right that the crucial question is how such work gets evaluated. It’s not true that working on something speculative that isn’t successful will destroy one’s career. Lots of people doing this have tenure. The people participating in these public debates all have tenure, and aren’t going to lose their jobs if they lose the debate (my situation is somewhat special: I don’t have tenure, but do have a pretty secure permanent position). The problem is mainly for junior people, where the reward structure is such that getting another job and getting tenure requires that they either work on certain widely accepted speculative ideas, or, if they decide to do something else, are both lucky and brilliant enough to make a big breakthrough. …” – Peter Woit

    There’s a contradiction in Lee Smolin’s sociological arguments about this in The Trouble with Physics. In the text, he writes on p. 309 (US ed.):

    “The prime example is Einstein, who … was slow in argument, easily confused; others were much better at mathematics. Einstein himself is said to have remarked, ‘It’s not that I’m so smark. It’s just that I stay with problems longer.’ Niels Bohr was an even more extreme case. … there is not a single calculation in his research notebooks, which were all verbal argument and pictures.”

    He adds that de Broglie’s 1924 PhD thesis on particle-wave duality was only saved from being failed by the examiners when Einstein stepped in with praise. (Einstein himself published 4 major papers, including his future PhD thesis, as papers before his PhD was accepted.) However, Smolin in endnote 9 on p. 370 writes of his defence of free-thinkers:

    “I have here to again emphasize that I am talking only about people with a good training all the way through to a PhD. This is not a discussion about quacks …”

    So you have to get a PhD, and today (unlike the case in Einstein’s time) that isn’t just a case of submittting a thesis on what you are interested in, but of being conformist and doing what you are told in some mainstream area.

    The contradiction is, Smolin’s prime case studies, Einstein and de Broglie, didn’t have PhD’s when they published their first papers with crucial new ideas, yet Smolin implies that such people are ignorant quacks in his endnote…

  • http://thechocolatefish.blogspot.com/ Yvette

    Rob in #97- thanks for the reply! I like it and admit I’m a touch tactless myself, so I may use it. People only take college students as seriously as they want to, anyway. ;)

  • Seth

    My concern is that some proponents of string theory, who have worked to popularize it, have misrepresented string theory as nearly finished and/or already known to be correct, rather than simply as promising. I see the new counterarguments, and their effectiveness, as a backlash against these overstated claims.

  • http://thecrossedpond.com adam

    Either I forgot to submit my post on (I think) Saturday, or else it was deleted for making mention of a Certain String Theorist at Harvard.

    Anyhow, the point I was trying to make (and apologies if someone else has made the same point in the subsequent 100ish posts) is that a fair amount of money that goes into research comes from the taxpaying public. Additionally, many research institutions are tax-exempt. The public, therefore, has an entirely legitimate interest in what’s happening with that money and if there is a debate as to the worth of a particular area of research (and I think that there really is; many of the other physicists that I’ve spoken to aren’t at all enthused with string theory either) then string theorists do have to make their case, both to their fellow physicists and to the general public. It’ll work best if it’s not done with a “you’re just too stupid to understand” sort of sneer, too (I don’t think that most string theorists are guilty of that but it’s not something I’ve been devotedly studying). If researchers don’t like that, well, stop taking the public dime.

    Of course, it would be possible to agree with the string theorists that there is great promise in string theory and still want, say, to cut funding for research in string theory down to 20% of whatever the current level is. Money is finite and subject to competition, after all.

  • MP-S

    Just a remark somewhat aside of the issue. It is a bit strange that people choose to focus some much effort in a single-minded pursuit of theoretical physics problems which are so remote and so far from the experimental/observational world. It is not that is wrong to do it – either following the mainstream, or following a more original set of hypotheses -, but that it is strange that they do not choose to also work in problems from areas of physics where the confrontation with the experimental phenomena is possible. After all, working in string theory should create a lot of frustration due to the lack of experimental input, and it would be natural to diversify the research.

    The great heroes of the early 20th worked on a wide range of subjects. Am I wrong to have the impression that this is not the case nowadays?

  • http://backreaction.blogspot.com/ B

    The great heroes of the early 20th worked on a wide range of subjects. Am I wrong to have the impression that this is not the case nowadays?

    Yes, you are wrong. String theory does not equal theoretical physics. In fact, open an arbitrary physics magazine, like e.g. Physics Today and you’ll notice that we are talking about a sub-field of a sub-field which just currently happens to be subject of open-heart surgery in the public domain. Even by reading nothing else than CV you will notice that the range of subjects is wider than a single-minded pursuit of theoretical physics problems which are so remote and so far from the experimental/observational world.

    Best,

    B.

  • http://eskesthai.blogspot.com/2007/04/blackhole-horizon-as-hill.html Plato

    If one cannot see “the mechanism being used” then of course it won’t make sense.

    String Theory Landscape

    Quantum Effect, however allow a manifold to change state abruptly at some point-to tunnel through the intervening ridge to a nearby lower valley.

    Some maybe happy with the propagation of the species :) but one would have to draw their attention to the geometrical basis of these two differing views on the landscape brought forward?

    I am invoking “Boltzmann’s brain” here. :) While it may ensue from “first principles” I am still referring to quantum gravity in both regards.

    If this is not done, then the debate will continue, “in the land of babble” and “Pink Elephants.” Us lay people are not happy about this.

  • George Musser

    Here at Scientific American, I can say that the perception that string theory has lost the debate has definitely been filtering into our staff discussions, and I bet the same is true at other magazines, too. That said, I have seen the theory go through too many ups and downs (real and perceived) to get too excited about the current trough.

    I long for a debate where we roll up our sleeves and solve problems rather than snipe. For instance, I think we can find common ground on the fact that the system of science funding in this country is broken; the grant process devours too much productive time and discourages out-of-the-box thinking of the sort Peter thinks is neglected. Let’s work that problem rather than turn on one another.

    George

  • MP-S

    B, I am affraid I didn’t state my point/question clearly. I know that theoretical physics is much, much more than string theory. My question is: do string theorists work on other areas of physics closer to experimentation – just like as many other famous theor. physicists of the past have worked in more than one sub-field of physics. If not, why?

  • http://backreaction.blogspot.com/ B

    Hi MP-S,

    My question is: do string theorists work on other areas of physics closer to experimentation – just like as many other famous theor. physicists of the past have worked in more than one sub-field of physics. If not, why?

    Because theoretical physics today has gotten significantly more involved, there are many areas that require a rather long phase of learning, and to work at the front of research it has become necessary to specialize at some point. (I should add though that I don’t think it has to be as extreme as it is today, and I don’t think the present situation is good for progress, but that’s a different issue. Right now, this is just the fact. )

    I don’t know many theorists that work on other areas besides their main interest, regardless of whether they are string theorists. I know several cases where theorists have changed their research topics, but also that is an exception. I think it would be beneficiary for the whole community if all ‘areas of physics’ were kept closer together. I sometimes feel like working on the tower of Babel. Again, I don’t understand why all these problems are exercised on the example of string theory since there are many other areas that suffer from similar problems.

    Best,

    B.

  • MP-S

    Hi B.,

    “I think it would be beneficiary for the whole community if all ‘areas of physics’ were kept closer together. I sometimes feel like working on the tower of Babel.”

    Yes, I agree.

    ” Again, I don’t understand why all these problems are exercised on the example of string theory since there are many other areas that suffer from similar problems.”

    Absolutely, this applies to the other areas too. My impression is that the over-specialization may also be caused by the tenure and grant processes mentioned in some comments.

  • http://www.physicsofsuperheroes.com Jim Kakalios

    B said: “I don’t know many theorists that work on other areas besides their main interest, regardless of whether they are string theorists. ”

    Interestingly, I know many experimentalists who DO work in different areas, and its not just a case of doing Raman Spectroscopy on whofnium, whafnium, etc. and counting those as different fields. Look at the career of Sid Nagel at the University of Chicago and you’ll see a common theme (complex systems) but no one experimental technique nor material system. I myself work in amorphous semiconductors, granular media and neuroscience, and the experimental techniques are all over the map, and the shifting of gears is a challenge, I can assure you. I may not understand the mathematics of M-Branes, but I’d put Sid’s intellectual chops against anyones.

    And George Musser: I agree wholeheartedly that the real funding crisis is the ever increasing amount of the work day that the search for research support has been demanding, as more and more scientists chase relatively fewer dollars (the NSF’s budget could be doubled with what is spent in three weeks in Iraq, but that’s another topic). I’ve been doing my part to speak to the general public (nine public lectures scheduled for the first six months of this year alone). In every talk I point out how the work of a few physicists, developing Quantum Mechanics, directly led to the lifestyle we enjoy today. Moreoever, at no other point in our history have so many people been so wealthy, directly owing to their education! (That is, not owning land, serfs or mineral rights). These points seem to register with high school students and their parents. I’d like to see more of this along the lines of Yvette’s work described above.

  • Lee Smolin

    Hi Ellipsis, dimension, properly defined is an observable in several background independent approaches to quantum gravity including causal dynamical triagulations and causal sets. You can find papers on these subjects where the haussdorf or scaling dimensions are measured. Indeed, in these kinds of theories, the effective dimension matter degrees of freedom see as they propagate can depend on scale, and these can be fractional. See recent works of Ambjorn, Loll and collaborators for calculations where the dimension, as a function of scale, is an output rather than an input. Indeed, a good feature of their model is that at large scales their measurements are consistent with 3+1 dimensions, and at short distances at 1+1,

    Thanks,

    Lee

  • Eric Mayes

    Lee,
    Just want to say I have enjoyed your books. I don’t know that much about Loop Quantum Gravity, but I do think that in the end, it will probably be part of the solution and more people should probably be working to connect it with string theory.

  • Eric Mayes

    Lee,
    Any possibility that the worldsheet bosons and fermions of string theory are related to the spin networks of LQG?

  • http://predelusional.blogspot.com/ Stephen Uitti

    Getting String Theory funded to the levels that Theology is funded would probably be a good thing for String Theory.

  • Doug

    The most salient comment thus far, in my opinion, is that of the Count:

    My personal opinion is that string theory is not the solution because it is not really new physics. It is the same old known physics (quantum mechanics) applied to new postulated degrees of freedom. A good analogy would be if 19-th centrury physics were applying ordinary Classical Mechanics to imagined degrees of freedom to find a theory of everything that would explain the unsolved problems they were dealing with.

    Except for ‘t Hooft’s deterministic models, no new physical theories have been proposed since the invention of quantum mechanics and general relativity.

    The fact that it requires 6/7 extra space dimensions that are not observed, and that time seems to be emergent, implying that physics must somehow be done without time, is enough to give serious thinkers pause. Not about string theory per se, which is only the symptom of the trouble, but about our understanding of the true nature of space and time.

    We know that something very fundamental in our understanding in this regard is wrong, so Peter’s thesis that string theory is not even wrong really implies that our physical theory in general can’t be argued cogently. Of course it’s wrong and for the very same reasons that the Count points out: As many are now coming to realize, it’s an extension of a more fundamental idea that is wrong. Therefore, the broader implication is that all current physical theory is not even wrong; that is, current theories can’t be defended logically from the point of view of what is right and what is wrong, because they are all founded on the same wrong assumptions, and thus are not capable of even being evaluated in the context of right or wrong.

    All that can be said of them is that they are successful to some degree or another, but not that they are right or wrong.

  • http://www.physicsofsuperheroes.com Jim Kakalios

    Well, I don’t think it would be a good thing for ANY sub-field of physics to be funded at THAT level. But, speaking of which, from this week’s Newsweek poll:

    Nearly half (48 percent) of the public rejects the scientific theory of evolution; one-third (34 percent) of college graduates say they accept the Biblical account of creation as fact. Seventy-three percent of Evangelical Protestants say they believe that God created humans in their present form within the last 10,000 years; 39 percent of non-Evangelical Protestants and 41 percent of Catholics agree with that view.

    The 10,000 years part gets me. We didn’t pull the agoe fo the Earth out of a hat. It’s based upon radioactive isotope dating. It’s been 60+ years since the atomic bomb was developed. At this point, we understand radioactivity (at least for applications like dating the Earth or the Shroud of Turin). If you don’t believe that we understand radioactivity, then we must also not understand Quantum Mechanics. And if you don’t accept quantum mechanics, that’s fine, just please, put the cell phone down!

  • Marty Tysanner

    Sean coaxingly requested,

    Come on, string theorists! Make some effort to explain to everyone why this set of lofty speculations is as promising as you know it to be. It won’t hurt too much, really.

    It seems remarkable to me, 120+ comments later, how few people have responded in this vein. Over at Clifford’s blog there have been some angry discussions (e.g., this and this) about the merits of Lee’s and Peter’s books, and some string theorists and partisans were quite vocal in their usually unfavorable opinions about the books (often without having read either of them), jumping at the chance to trash Lee and Peter or repeat common assertions like “string theory is the only game in town.” But now, when Sean has offered an excellent opportunity in a widely read forum to make a case in favor of string theory (rather than just another opportunity to trash its opponents), it seems most proponents have little to say:

    1. Moshe (comment #5), a string theorist, seems to view Sean’s request as an invitation to continue a debate, which he is not inclined to do, apparently believing it is unproductive;

    2. Wolfgang (comment #12) pointed to a blog post by Jacques Distler that he felt did a good job of addressing Sean’s request;

    3. Sean (comment #16) asked Moshe to reconsider his inclination, arguing that it is very worthwhile to try to educate the non-experts about the primary merits of the string program, but Moshe (comment #94) later says he doesn’t mind losing a debate among those scientists who are willing to judge the string program without understanding it at a technical level;

    4. Eric Mayes (comment #22 and others later) claims to have a phenomenological construction of much of the standard model from string theory, which if true and is not too ad hoc could be a step forward;

    5. Haelfix (comment #30) refers to Distler’s blog as a good place to look for reasons why string theory should be taken seriously;

    6. Sean tries to very briefly answer his own call in comment #55.

    That seems to be about the extent of “why string theory is compelling” from string theorists and partisans! A couple of references to Jacques’ blog and Sean partly answering his own request!

    If one needed a better understanding of why string theory may be losing the public debate, this pathetic response by its proponents speaks loudly. Given that Cosmicvariance is a popular blog that is read widely by the lay public and journalists as well as scientists, it is especially hard for me to understand why the string theory community should be content to put the onus of looking for reasons why the string program is worthwhile onto the public that funds most of the effort. A reference to Jacques Distler’s blog is not a substitute for a coherent, concise argument, especially because the level of discussion at Jacques’ blog is not what the typical lay reader would find comfortable. One could easily come away from the above discussion assuming that either string theorists are spending time on it because it is “the only game in town” or that they really could care less whether anyone knows why it is worth doing as long as the dollars keep flowing.

    This is the observation of a physics grad student who doesn’t currently count himself among the string theory partisans.

  • amused

    Following up on Former string theorist’s insightful comment above:

    There is nothing new or intrinsically bad about an “elite” research subcommunity detaching from the main community and exalting in the brilliance of its members. That seems to happen quite a bit in pure mathematics, for example. Elitism in science is not a bad thing, it seems to have been beneficial for progress in the past. Also, if the elite community attracts and admits the best and the brightest then it is natural that these people should dominate the job market. But such a community really needs to earn its status on merit. The “sociological objection” that some of us have about the string theory community is that its status is way out of proportion with what has been earned on merit. That’s not to say that ST isn’t an interesting and worthwhile research topic (which I certainly consider it to be from a mathematical physics perspective, regardless of the lack of connection to nature so far). But there is no way it can reasonably claim to have earned the hegemonic position that it now occupies in formal particle theory.

    If ST had earned its position it would be demonstrated in tangible ways. For example, ST papers would be dominating the pages of PRL. Yes, I know the usual string theorists’ retort to that argument: journals are irrelevant, no one cares or attaches value to being published in a particular journal anymore, etc etc. Funny then how string theorists who profess not to care about journals seem so keen to get published in that particular journal when they have done something they consider a big deal. We have an example right here in this thread: take a look at the paper hep-th/0703280 by Eric Mayes et al discussed above — it’s clear from the format which journal they hope to publish in. That particular journal involves much extra hassle; the draconian 4 page limit is just the beginning of it. Why go to all the trouble when other journals, e.g. JHEP, are much less hassle? The schizophrenic attitude of string theorists towards journals, and PRL in particular, is really quite funny.

    If string theory is losing the public debate it’s pretty naive to think that that could be reversed simply by better explaining the motivations for ST. Journalists who write about this will surely also be taking into account the vibe they pick up from insiders within the mainstream physics community, and Sean has already noted in an earlier post the “surprising” level of distain and resentment towards ST there. Even people who are basically sympathetic to ST and fully understand its motivations are not happy with the current situation (remember JoAnne’s post?). String theorists need to stop responding by strawman arguments – pretending that the issue is whether or not string theory is a waste of time and then arguing that it isn’t. The issue is all about merit – having to earn what you get rather then claiming exemption from usual competition due to special genius status. The most important message from the growing antagonism towards ST is that string theorists need to start proving themselves meritous of their privileged status in tangible ways. Non-string physicists seem to be no longer swallowing “Ed Witten is our leader and he is smarter than everyone else” as a justification for continued string dominance. Writing out a list of motivations and nice features of ST won’t cut it either – people working on other topics can do that as well.

    As mentioned, elite research sub-communities are nothing new and sometimes form, e.g., in pure maths. But those elites are never recipients of the kind of antagonism currently directed at string theory. If anyone were to complain, the members of the elite could simply respond as follows: “Look, we play by the same rules as everyone else. There are tangible, universally accepted measures of merit in our community, and by these we have proven ourselves more meritous than the other folks. You might not be able to appreciate the greatness of the work we are doing (after all, it isn’t your topic) but you certainly know and respect the standards of the Annals of Math. and Inventiones Mathematicae, and look how many papers we have published there! A whole lot more than you and your cohorts. So shut up and sod off.” What can string theorists offer as tangible justification for ST dominance? Imagine a hypothetical job interview for hot young string theorist X: Non-string committee member A askes: “Dude, if you are as brilliant as you and other stringers think you are, how come you don’t have some papers in PRL?” To which X responds: “Oh, I could have published plenty there if I wanted to, but I just couldn’t be bothered. As long as Joe Polchinski thinks my work is great, why should I care what the editors and referees of PRL think?” To which A replies: “But then how am I supposed to compare and evaluate you against the non-string candidates?” X replies: “Come on man, if they were any good they would have been doing string theory!”.

    Yes, I know, publishing in PRL doesn’t prove that the paper is great, etc, etc. But on the other hand, it’s still the least trivial physics journal to get publish in, and if someone has done something great they should be able to get it published there. So, unless they have a better idea for how to prove themselves meritous of their special genius status and the perks that go with it, string theorists might want to consider PRL publications as a way to do it. Lets see if they can dominate the pages of PRL as much as they dominate the job market. If dimwitted outsiders like yours truly can manage to publish there it should be a piece of cake for brilliant young string theorists. In any case, I don’t think string theorists have any chance of winning the public debate until they manage to convince the bulk of non-string physicists that their exalted position is based on tangible merit rather than various sociological peculiarities.

    (Damn, I’ve got to get out of this marathon comment habit.)

  • http://eskesthai.blogspot.com/2007/04/blackhole-horizon-as-hill.html Plato

    George Musser:the grant process devours too much productive time and discourages out-of-the-box thinking of the sort Peter thinks is neglected.

    String theory is thinking outside the box, so I do not know how one could claim that we should be doing this, and then criticize such thinking? :) I’d be interested to know how your staff can come to any such conclusion as you have explained above.

    As per #125, I do not know why more string theorists have not step forward?

  • George Musser

    Plato writes:

    George Musser:the grant process devours too much productive time and discourages out-of-the-box thinking of the sort Peter thinks is neglected.

    String theory is thinking outside the box, so I do not know how one could claim that we should be doing this, and then criticize such thinking? :) I’d be interested to know how your staff can come to any such conclusion as you have explained above.

    Sorry, I don’t understand what you’re saying. When did I criticize that you are doing out-of-the-box thinking? What conclusions have my fellow-staffers or I reached? Maybe you are reading more into my little message than I said!

    It does seem, though, that insides and outsides of boxes are frame-dependent.

    George

  • Aaron Bergman

    The issue is all about merit – having to earn what you get rather then claiming exemption from usual competition due to special genius status.

    I’m very confused here. Who’s claiming to be exempt from usual competition?

    The most important message from the growing antagonism towards ST is that string theorists need to start proving themselves meritous of their privileged status in tangible ways. Non-string physicists seem to be no longer swallowing “Ed Witten is our leader and he is smarter than everyone else” as a justification for continued string dominance.

    I certainly hope no one ever states that as justification. It’s inane. I can certainly say that when I was looking at graduate schools and talking to people about various things to study, statements such as the above or the experiences of “former string theorist” above never ocurred. In fact, I remember various people patiently responding to my questions about background independence, the perturbation expansion, etc. Perhaps I was just lucky.

    I can’t say I understand this PRL fetish though. Maybe it’s just cultural. I certainly would not agree with the statement that journals are irrelevant; publication provides a valuable check on preprint culture (which reminds me that I need to replace one of my preprints with the published version.) String theorists publish in PRD, NPB, CQG, CMP, ATMP, JHEP and probably plenty of others. I bet there are even been publications in PRL. What’s the big deal?

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    George,

    Thanks for your comment, which does bring things back to what I see as the most important point, which is how to get particle theory out of its current doldrums. It seems to me that we’re stuck for several reasons, with some of them ones we can’t do anything about:

    1. Our experimental techniques are reaching fundamental technological limits: it’s harder and harder to get to higher energy.

    2. The standard model is too good: the absence of experimental anomalies that could tell us which direction to look for progress is a huge handicap.

    That said, there are aspects of the problem that in principle can be addressed, especially:

    3. A huge amount of time and effort has gone into the pursuit of a very speculative idea (string-based unification) which does not work. People who have put in this time and effort are loathe to admit failure, and to make the effort to retool and try other speculative ideas.

    The main question I see is that of figuring out how to change the incentive structure in this field to get people to try a wider variety of ideas. As long as the incentives are set so as to encourage continuing down a failed path, that’s what we’re going to get. I think it’s highly unfortunate that I, Lee and others have had to spend our time dealing with ad hominem attacks from people who want to deny that this program has failed, and claim that it continues to be the most promising way for people to spend their time. I don’t think Sean has it right: what’s needed is not more string theorists publicly making the case for string theory. Lots of people don’t want to do this because they know how weak it is. What is needed is instead some serious coming to grips with the problems Lee and I have discussed, acknowledgment that they are real and serious proposals about what to do about them.

  • David B.

    Dear Amused,

    String theorists do publish in PRL occasionally. For most string theory papers this is not possible: the length restriction is the main reason. For technical reasons, modern string theory papers require long computations of certain kinds and presenting them in a four page format is very difficult. Moreover, since in general it’s hard to compare to data, one can not very easily just write a paper about such a hypothetical comparison for a model. You also have to remember that papers published in PRL should be interesting to a broad audience.

    Regarding your other comments, string theorists do compete for grant money with other physicists that do particle physics phenomenology and sometimes gravitational physics as well. There is no preferential treatment (no string theory section of NSF, lets say). A lot of the debate is misleading exactly because people who do research in string theory are characterized as “hogging the money”, as if there would be no competition.

    The main reason I usually stay out of the “string waars” debate is because in my experience people do not want to listen to reason: they already know what their opinion is and are not willing to change it. Instead the discussion degenerates very quickly.

  • http://thecrossedpond.com adam

    If most people in, say, particle theory are string theorists (not sure if that’s true, just a hypothetical) would it not be the case that most people sitting on the funding panels are string theorists? If that were the case, there wouldn’t have to be a ‘string theory section of NSF’ for string theory to maintain a financial edge.

  • Moshe

    Marty (#125), please re-read precisely what I wrote in #94, and try not to substitute with what you think would make a better story. For example, not sure where “understand it on a technical level” came from, I don’t see it in anything I wrote here or elsewhere. I can be quite confident in that since it is contrary to my opinions.

    And to reiterate, there are a lot of discussions here and elsewhere on various topics in physics, they are pleasant and fun for everyone involved, professional and lay-people. I think that a precondition to have (one of these days) such a physics discussion on the subject of string theory, on any level of technical knowledge, is to lay the debate on its merits to rest. Everyone already made up their minds long time ago, it’s not going anywhere.

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  • Marty Tysanner

    Moshe,

    I wasn’t intentionally trying to misrepresent your point of view. I agree that after reading your comment #133 and rereading #94 I very may well have done so. What gave me the impression was where you said,

    … who are very interested in forming and expressing strong opinions on the merits of string theory (and theorists), but show no interest whatsoever in the physics. I personally have no problem with losing the debate among that crowd.

    Apparently I read more into “the physics” than what you meant. I apologize, but trust that you can at least imagine how I might have interpreted your comment that way.

    Nonetheless, I think you and others who agree with you are making a strategic mistake to act on the belief that

    I think that a precondition to have (one of these days) such a physics discussion on the subject of string theory, on any level of technical knowledge, is to lay the debate on its merits to rest. Everyone already made up their minds long time ago, it’s not going anywhere.

    The universe of people who can form opinions is not limited to those you and others have publicly sparred with, so I think it is a bit of a generalization to say that everyone has already made up their mind. I also think it is unfair to assume that everyone who has already formed an opinion is unwilling to change that opinion.

    This blog is widely read by people of different kinds of expertise. Certainly some journalists, perhaps more than we may think, use it as a resource to gain insight into the status of a major research program in theoretical physics, and then use that to inform or influence others who will never read this blog. It is hard to know how many other people of influence in science funding do the same thing. If those who find the string program most compelling are unwilling to explain why they think it is so worthwhile when offered a good forum for it, then by default the dominant impression is less favorable. I don’t see how that can work to the advantage of string theorists, especially because the prospects that string theory will have practical use are close to none; over the long term, the case for continued levels of significant funding will ultimately need to be made on more aesthetic grounds.

  • Moshe

    Marty, thanks a lot for the clarification. Let me try to respond in kind.

    So, there is no doubt that string theory, and any other research program, needs to be presented to the public, who is after all the main source of funding for the program. I think string theory has, over the years, been very successful in presenting itself to the public on different levels. Of course having an exceptional communicator such as Brian Greene does not hurt. So I really see no general problem at the level of activity on the “outreach” front. I certainly have no objections for people to keep presenting the wonderful things we keep on discovering.

    What I think has exhausted itself is the attempt to justify ourselves in this forum, and in fact right now this stands on the way of trying to have any exposition of the physics that does not immediately turn into a free for all “debate”. There is the set of people whom I referred to earlier, the ones that think that things like “string theorists are arrogant” is the ultimate argument on the subject , and I don’t think anything we can say about the physics of string theory will change their minds, so be it. There are also people like Lee and Peter, who for the most part present technical points. Those points have been thoroughly discussed many times, most recently here by no other than Joe Polchinski, so at this point we can just agree to disagree. If there are additional such points I’d be happy to discuss them in detail, but that has not happened in a little while.

    Also, one of your points is very well taken. The commentary on blogs somehow tends to exaggerate the loudest voices, and after hearing the same voices completely unchanged for a couple of years, it is heartening to discover that some people are actually listening.

  • Gavin Polhemus

    Peter,

    At present we do not have any consistent theory that contains the standard model and gravity. I’d like to have one. Do you think this is a reasonable goal? In my opinion, string theory is the closest to meeting that goal. Do you have another recommendation?

  • http://thecrossedpond.com adam

    Presumably, whether it is a reasonable goal has to be informed in part by how achieveable we believe it to be, rather than just picking the most promising. It seems that not everyone believes that it’s possible in the now, at least not in the scientific way, to wit, by making falsifiable predictions.

    I’d like an everlasting jetpack that weighs 3 pounds. Is that a reasonable goal?

  • Postmodern Bootstrap Theorist

    Jim writes: “The 10,000 years part gets me. We didn’t pull the [age of] the Earth out of a hat. It’s based upon radioactive isotope dating.”

    Agreed. There are a couple of arguments that strict Creationists use. One is that all of this fossil evidence (and cosmological evidence) was “planted” by God. (A test of faith.) Other Creationists argue that C-14 (etc) dating is flawed. As I recall, most of the Creationist experts do not have PhDs in physics.

    I see a vast range of belief between strict neo-darwinism/cosmology and the 5000 year Earth theory. Most public debates are between radicals on both sides (“minds are computers made of meat” vs timelines based on Biblical family trees).

    Evolution is a touchy issue a) because people don’t like being compared to monkeys and b) because it conflicts with some literal readings of religious texts. But the Bible has tons of symbolism, and much Buddhist text is similar, not *all* of it is meant to be taken literally. And the Bible never ever says the first few “days” were Earth days.

  • Torbjörn Larsson

    Moshe:

    I have no good ideas, but at the very least it seems to me that framing the discussion in terms of motivation or justification (e.g. explaining why the approach seems promising) is counter-productive, it invites the kind of uninformed commentary we are all too familiar with.

    This is the second comment you do here that doesn’t ring 100 % true to me. About the first, about no one changing his mind, wasn’t too clear if it was referring to experts or not. But in this comment you refer to non experts, so I feel that I can speak up.

    When I out of curiosity tried to orient myself about the front edges of theoretical physics, it was exactly the information about motivations behind string theory that was hardest to come by. It wasn’t obvious what motivated the idea to look at objects such as strings – which seems natural to ask when there is only consistency and unverified results. (Branes was much easier to grasp in comparison, IMHO they don’t look so ad hoc at first glance.)

    Compare with LQG, which presented both motivations and results up front. It takes a while to see penetrate the bluster to see that one can’t find many attempts to check for obvious things, but rather statements that it is possible or done.

    So for once Wikipedia seems to be on the level of many blog commenters and papers: “LQG is a quantization of a classical Lagrangian field theory which is equivalent to the usual Einstein-Cartan theory in that it leads to the same equations of motion describing general relativity with torsion. As such, it can be argued that LQG respects local Lorentz invariance.” ( http://en.wikipedia.org/wiki/Quantum_loop_gravity )

    Yeah, right, perhaps the quantization doesn’t change the thing we presumably want to check, so at least we can argue. (Funny that QFT’s seems to have a need to do this, though. At least what I can grasp of the descriptions with my feeble understanding here.)

    Now, perhaps I can interest the author of above in a certain bridge I happen to own…

    In conclusion, why not present the motivations to help laymen and other interested access the ideas and their results? For example, Distler’s post is quite good. One must but find it.

  • Torbjörn Larsson

    because people don’t like being compared to monkeys

    Ahh, the polyphyletic heresy! In the cladists view we *are* monkeys. :-)

  • Bootstrap Theorist

    I think I can summarize the debate. Theory is *way* ahead of experiment. The LHC will turn up some new stuff, and everyone will scramble to explain it. But I think the law of diminishing returns will hit colliders soon.

    And even if string theory fizzles out, there will be some other crazy theory in its place. Unless government comes up with a few trillion for a collider, there is going to be a lot of mathematical masturbation / speculation in the next few years.

    The solution is obvious … convince the DOD that this research can lead to new weapons.

  • amused

    Aaron,

    My “exemption from usual competition” remark was referring to the fact that over the last decade or so many young string theorists have been hired to faculty positions, often with relatively short publication records, while the same was not happening to anywhere near the same extent for young people working on other topics and whose publication records were just as good if not better in some cases. (Not me, but i know of others.) Why was this happening? Presumably because senior string theorists promoted these people as being extremely good, and string theory was considered hot at the time. Regardless of how brilliant these young string theorists might or might not have been, I hardly think the hirings can be described as based on tangible merit which was clear to all.

    Regarding the “Ed Witten” remark, it was of course an oversimplification (for the sake of brevity). But wouldn’t it be fair to say that a large part of the reasons why physics departments were willing to stock up on string theorists to the extent that they did were because Witten and other leading lights in particle theory considered it the way to go and were so excited about it? I’m not trying to say that they all followed Witten like mindless zombies, but when the leading lights of fundamental physics get so excited about something and devote themselves to working on it that’s obviously going to have a big impact on what other people think, especially those working in other fields who dont’ have the background or inclination to look into the string developments themselves.

    As for PRL, anyone who submits a paper there must have a fetish! For the simple reason that submitting there is more hassle than submittting to a regular journal (there’s the 4 page limit, and then you also have to be careful to write the paper in a certain way to pretend that it’s addressed to the “broad audience”, etc). No reason at all to put yourself through that unless you feel there is something special about publishing in that journal. (If someone just wants to publish in a broad audience journal they can avoid the hassle and use Ann.Phys.) Witten, Vafa, Strominger and many of the other leading figures of ST have published in PRL in recent years so I guess they must all have the fetish. Seriously though, have things really reached the stage where journal publications are nothing more than a check on the preprint culture? When I was a grad student in the mid ’90’s there definitely seemed to be a journal hierarchy in theoretical hep, with PRL at the top (or CMP for the mathematically inclined), followed by NPB, and then the more “lowly” ones. I remember a string theory postdoc at my institution being congradulated and praised by the faculty not so much for the work he had done but for the fact that he got it published in PRL! Having a journal hierarchy with a broad spectrum journal like PRL at the top is very valuable imo since it provides an objective measure system for determining relative meritousness of people working on different topics. The mathematicians have this and it has stood them in very good stead. Of course, it can only work if people take it seriously and unfortunately that doesn’t seem to be the case anymore in theoretical hep. But I think it would be very much in string theorists’ long-term interests to re-establish it, since then they will be able to use it to demonstrate that their own dominant position in formal particle theory is merit-based.

    David B,

    I can’t imagine string theory being that different from other topics in hep theory regarding long calculations. The usual thing in my experience when one wants to publish in PRL (or any letter journal) is to outline the key steps of the calculation and then give the full details in a subsequent longer paper. As for your remark about PRL papers having to be interesting to a broad audience, my impression is that if you can make a good enough case for the importance of the result(s) then it will get through. I’ve managed to slip some pretty technical stuff into PRL in the past, and have seen others do it as well.

    As for competition for grants, I can’t say anything about that since I’ve no experience or knowledge of it. The things I wrote were mainly concerning the merit issue in for getting jobs. It seems to me that there is indirect preferential treament happening here, not due to any “string conspiracy” but simply because of the need to have the strong support of influential senior people if you want to get anywhere. This means that you had better be working on a topic that plenty of such people have committed themselves to, which pretty much excludes anything other than strings/branes in formal particle theory. This wouldn’t be the case if we had a journal system as in the maths community since then young people could prove themselves meritous simply by publishing in the top journals.

  • http://eskesthai.blogspot.com/2007/04/blackhole-horizon-as-hill.html Plato

    String theory is thinking outside the box, so I do not know how one could claim that we should be doing this, and then criticize such thinking

    Actually George the right person picked up on it and thanked you, thinking it was a attack on them. This was not meant to be a sarcastic but a true observation before the rise of science wars.

    I think someone said conflict in physics is good from the perspective that it could bring forward further information? If someone acts as a resounding board and continually repeats the same mantra, they become it.

    So society is manifesting the mantra and reporters too? How could a research media group conclude such a thing, without having someone on that group effectively trained? I have certainly been held in “this light” and I should sent this forward?

    Now, to think the technical aspect were not being dealt with and signalling out Jacques for a reference to his site is somehow going to make me feel I am in a better position speaking about string theory is ludicrous.

    If people had followed these continued debates they would have understood that the technical issues were indeed being addressed “countless times” in other places. There was progress in those cases.

    Outreach is a good thing. People have been listening. Blogs like cosmic variance have indeed played a good part in bringing people from their fields for contributions. I am glad that some string theorists have come forward.:)

    Our views on cosmology have changed by modelled approaches? Provided for a earlier perspective on the cosmos.

  • Pingback: The Adventures of Tobasco da Gama » Good Vibrations: Revising My Opinion of String Theory()

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    Gavin,

    I don’t actually agree that string theory is the “closest” to meeting the goal of having a consistent combination of the SM and quantum gravity. It hasn’t succeeded despite decades of effort, and so the LQG people can reasonably make the case that they are just as likely to be “close”. But I don’t think the LQG/string theory question is the important one.

    Personally, I’m actually not so interested in a “consistent theory of the SM and gravity” if it is highly artificial, mathematically ugly, doesn’t explain much of anything about the world, and is completely untestable. That’s where the string theory “unification” program is going. If you want the SM, you have to stabilize moduli, make all sorts of assumptions that things will work out, then end up with a complicated set of possible points in the landscape.

    What has happened is that people have pursued the string theory unification program far enough to see that hugely complicated, ugly and artificial constructions are needed in order to get something that looks like the real world, so much so that the framework is unpredictive and untestable. Pursuing this further, in hopes of tying down the technical difficulties of completely realizing this picture, seems to me like a waste of time. It’s clear by now this is just a wrong idea about how to go about getting unification.

  • tomasiello

    Here are some things _I_ like in string theory, and why I think it’s a step in the right direction.

    – It proposes a way to quantize gravity consistent with the RG ideas (see Distler’s post linked by wolfgang #13) and *at the same time* it provides ways to produce extensions of the standard model. Yes, it does so in many ways; but at least discretely many, which is better than the “continuously many” in QFT.

    – The assumptions regarding its dynamics can be put through “thought experiments” in many cases. Two examples: 1) mirror symmetry gives a spectacular check of the string instanton series. I think this would deserve to be more widely advertised outside the field. 2) AdS/CFT. To be sure: these are only “mathematical physics” tests, and of course they don’t tell us that the theory is a correct description of nature.

    – One can sometimes reproduce topology change by an effective qft (I’m referring to the way CY transitions are reproduced by massless branes), in a way which is in my opinion quite elegant.

    (This is a personal, idiosyncratic list — I left out dualities, the potential for inflation, black holes, which have all been discussed already here.)

    I don’t understand all the complaints about its not being *currently* testable. We all have a problem: how to detect quantum gravity effects? The fact that there is today no answer to this is not ST’s fault. Replace it with another theory of QG, and the problem remains.

  • Aaron Bergman

    My “exemption from usual competition” remark was referring to the fact that over the last decade or so many young string theorists have been hired to faculty positions, often with relatively short publication records, while the same was not happening to anywhere near the same extent for young people working on other topics and whose publication records were just as good if not better in some cases.

    Excuse me? Why in these discussions do I feel like I live in a completely different universe than many of the other participants? When I tell people in other areas of physics the number of postdocs that the average string theorist goes through before getting a job, they’re often shocked. I can think of a few exceptional cases, but the vast majority of string jobs, as best I can tell, go to people on at least their second postdoc.

    Seriously though, have things really reached the stage where journal publications are nothing more than a check on the preprint culture?

    What’s wrong with that?

    I guess I can’t see what the big deal is with PRL. In fact, I seem to remember seeing some pretty ordinary papers in there, but I could be misremembering. Regardless, I find your journal argument to be rather circular. Who do you think would be refereeing the relevant papers?

  • Moshe

    Alright, here are things that brighten the day, such as tomorrow, when I teach beginning string theory course: you just start with a purely intellectual exercise, quantizing a relativistic string. You know you’d immediately run into trouble because combining Lorentz invariance and quantum mechanics is very tricky in field theory, requiring delicate structures such as gauge invariance for vector fields. So you expect complete disaster, all kinds of nonsense, but you are stubborn…

    Instead, to everyone’s surprise (try to quantize relativistic membranes if you don’t believe it), everything falls into place effortlessly- the theory cannot be tuned and modified, so it lives dangerously, every time you check something new you may prove it inconsistent, and will simply have to abandon it. Somehow, again and again it is just right. Gravity, Einstein equation, matter fields with rough similarity to the real world (gauge fields, chiral fermions), they all just come out. It is impossible I think to go through the first few steps in string theory without the feeling of awe, there is something there that is very correct and unique.

    Of course, this is just the beginning, but this feeling never fades, every time you put the framework to the test it passes it in a surprising and novel way that was not anticipated before. There was a saying when I was in grad school, the string is smarter than us, that’s probably true…

  • Eric Mayes

    To answer the original question of this debate, I believe the reason more string theorists have not joined this discussion is that it isn’t a productive use of their time. From my recent experience, I would tend to agree. These sites tend to be populated by a number of people who are more interested in interjecting their own prejudices and opinions than honest debate. How can any string theorist explain why he/she works on it while being screamed and yelled at? The thing it most closely reminds me of is right-wing talk radio. I think the fundamental problem is not any problem with string theory, but rather jealosy of the attention it attracts on the part of the critics and their determination to sully its reputation.

  • amused

    “Excuse me? Why in these discussions do I feel like I live in a completely different universe than many of the other participants? When I tell people in other areas of physics the number of postdocs that the average string theorist goes through before getting a job, they’re often shocked. I can think of a few exceptional cases, but the vast majority of string jobs, as best I can tell, go to people on at least their second postdoc.”

    My impression was that the string theorists who got jobs over the last decade (at least at the big name universities) usually did so within their first couple of postdocs. It should be easy to check this, and I will check it, but not right now. Second postdoc counts as early in my book. I’m more used to seeing people hanging on for 8+ years in various temporary non-faculty positions before landing something permanent (and that’s not counting the ones who leave the field). And just to be clear, I’m not claiming that *all* string theorists have an easy time and land jobs early on etc.

    “Seriously though, have things really reached the stage where journal publications are nothing more than a check on the preprint culture?

    What’s wrong with that?”

    If nothing I’ve said already moves you, I doubt that anything else I can say will. But one last attempt anyway: In a previous exchange in the Teacup IV post over at asymptotia, Jeff Harvey wrote: “…we are lacking in good (semi-) objective measures of what work should be supported, in main part because of the absence of data.” Would you at least agree that (semi)objective measures would be a good thing to have? If so, then isn’t it worthwhile to consider what, if anything, could be done to establish them in the present data-free environment? The mathematicians have long been operating in a data-free environment and seem to have solved their measure problem through the use of publications in high-standard journals as the measure. It works for them, why not for us? Do you have a better suggestion? Maybe you think we should just accept that there aren’t going to be any objective measures. But in the absence of objective measures, how on earth can string theorists ever hope to justify their dominant position in formal particle theory to the rest of the physics community?

    You could also try asking the mathematicians at your university why the maths community continues to maintain their journal hierarchy system instead of going over to a preprint culture with journals simply used to filter out the noise. Is it just because of habit or tradition, or do they actually think it serves some useful purpose?

    “I guess I can’t see what the big deal is with PRL. In fact, I seem to remember seeing some pretty ordinary papers in there, but I could be misremembering.”

    I never said that its standards are universally high. Ordinary papers do get in. On average though, my impression is that it is tougher to publish there than in the other physics journals we have. That could make it potentially useful as an evaluation measure, albeit a limited one. It would sure beat relying exclusively on the say so of senior influential people imo.

    “Regardless, I find your journal argument to be rather circular. Who do you think would be refereeing the relevant papers?”

    Circular or not, it works for the mathematicians so why not us? As far as I can tell, the way it works for them is that, firstly there is a strong commitment to maintaining journal standards throughout the community; secondly the editors are accomplished, widely respected mathematicians who carefully chose referees that they can trust to maintain the standards. That seems to be it.

    Finally, I’m a bit curious about how things are in your universe. Is it really all rosy and swell with all decisions clearly justifiable by objective criteria and measures that everyone can agree with except a few annoying losers? Is there anything even remotely non-positive about the whole string situation there?

  • Aaron Bergman

    Second postdoc counts as early in my book. I’m more used to seeing people hanging on for 8+ years in various temporary non-faculty positions before landing something permanent (and that’s not counting the ones who leave the field)

    Really? Then perhaps I’m more out of touch with the rest of physics than I thought I was.

    The mathematicians have long been operating in a data-free environment and seem to have solved their measure problem through the use of publications in high-standard journals as the measure. It works for them, why not for us?

    Who do you think is doing the judging in mathematics? It’s not as if the people working on hardcore analysis are getting refereed by the combinatorists. People are always judged by their peers because those are the people that best understand the work. And, it’s not as if there’s this vast free-for-all journalwise. People know what the good journals are and which aren’t. That PRL isn’t at the top of the heap hardly seems like a big deal.

    As far as I can tell, the way it works for them is that, firstly there is a strong commitment to maintaining journal standards throughout the community; secondly the editors are accomplished, widely respected mathematicians who carefully chose referees that they can trust to maintain the standards. That seems to be it.

    Is what you want to say is that the referreeing process isn’t as rigorous as that of the mathematicians? You might have a case to be made there, but I’m still not sure that’s your point.

    Regardless, perhaps you can explain to me, as someone who hasn’t published outside of string theory, just how the string theory refereeing process differs from the rest of physics.

    Is it really all rosy and swell with all decisions clearly justifiable by objective criteria and measures that everyone can agree with except a few annoying losers?

    There are no completely objective criteria in hiring in any field. Are you seriously claiming that mathematics or the rest of physics, or, hell, the rest of the entire world doesn’t have people talking to each other and asking their opinions of job candidates. Do you think, for example, that the prestige of the person writing a recommendation letter makes no difference? I find it hard to believe that hiring in other field consists of simply counting one’s PRLs and making an ‘objective’ decision. And, even if it were, how is the number of PRLs anything but a proxy for what the “accomplished” editors and referees think of the work?

    Of course I’ve never been involved in actually hiring someone, so perhaps in the rest of the world hiring really is purely objective and untainted by more base considerations that apparently overwhelm any concept of merit in string theory. But I doubt it.

  • mclaren

    Sean Carroll remarked:

    mclaren (32): If you brush up on your reading comprehension, you’ll notice that I never compared the evidence for evolution with the evidence for string theory, about which you rant at such length. So your intelligence is somewhat self-insulting.

    This exemplifies the single most important reason why string theory is losing the public debate. Treating with contempt someone who stands up for the most basic foundation of post-Enlightenment Western culture — namely, the requirement that people provide evidence for the claims they make — is a starkly anti-intellectual stance.

    That kind dismissal of skeptical critical thinking on Sean Carroll’s part embodies a medieval mindset and it’s not the way to win over a popular audience. Americans may not be well educated compared to the rest of the world (American students currently rank somewhere around 15th in the world in knowledge of science/math), but they do have a saying: “I’m from Missouri — I have to be shown.”

    Sean Carroll’s contemptuous disdain for skeptical critical thinking seems to me to form part of a larger problem we’ve been seeing throughout the world for roughly the past 25 years. Call it “The New Medievalism.”

    Friends who grew up in the heart of the American Bible Belt in the 1940s and 1950s report that evolution was taught in public schools during that period without controversy — yet today, they’re building Creation Museums full of statues of Adam and Eve riding to church on dinosaurs.
    http://www.aboyandhiscomputer.com/Greetings_from_Idiot_America.html

    In literature departments in major universities throughout America, self-delusion and untestable word games have taken the place of evidence-based scholarship. (See “Come On Back to the Raft Ag’in, Huck Honey,” by Leslie Fiedler, for a classic example: http://www.howardwill.com/Come%20Back%20to%20the%20Raft%20Again.htm)

    In music departments throughout the U.S., vacuous numerology based on pitch-class set theory has taken the place of evidence-based scholarship on music using findings from psychoacoustics and ethnomusicology and musicology.

    In music, see Milton Babbitt’s “Who Cares If You Listen?” (1958) for a classic statement of numerological superstition as the ideal of music “theory” so-called.
    http://www.palestrant.com/babbitt.html

    In art departments in major universities, students now study bathroom grafiti
    http://www.uninteresting.com/glendale%20reader/sat%20jan%2020/stall_grafiti_art_class.htm rather than engaging in evidence-based study of the history and traditions of art.

    In big business, accounting games have taken the place of product development and marketing, and the Enronization of America now substitutes for evidence-based R&D and the scientific method which at one time gave us new industries and new consumer products.
    http://www.businessweek.com/bwdaily/dnflash/jun2003/nf20030610_2399_db028.htm

    In politics and the media, propaganda and Pravda-style distortions and verbal calisthenics have taken the place of evidence-based factual reporting (see Fox News for daily examples. The most glaring recent case in point: when Scooter Libby was convicted recently, Fox News put up a graphic banner reading “Libby Found Innocent” –of one of five charges.).

    In economics, Rational Choice theory is the hot field — except that Rational Choice theory systematically predicts the opposite of what we observe in the real world. For example, rational choice theory confidently predicts (and has mathematics to prove) that Martin Luther King could never have organized southern blacks to march for voting rights int he deep south, since the utility function is so low. Economists’ strategy for dealing with this misfit twixt Rational Choice theory predictions and observed reality is, of course, to ignore observed reality. In politics, the disjunction twixt claims (“We’re winning in Iraq,” “We know where the WMDs are,” “We’ll be out of Baghdad within 6 months”) and the observed reality continues to widen, with increasingly catastrophic results.

    In education, phoney statistics and grade inflation show an illusion of continued progress throughout K-12 schools
    http://www.tcrecord.org/Content.asp?ContentId=10440
    even as ever-increasing proportions of K-12 schools graduate unable to read or write or perform basic arithmetic.
    http://www.collegejournal.com/aidadmissions/newstrends/20070226-tomsho.html

    And now in physics, the last bastion of skeptical critical thinking and the scientific method, the final refuge of rationality which finds itself under assault in all sectors of American society, what do we encounter? Sneeringly contemptuous dismissal of skeptical critical thinking and ridicule of those who demand hard evidence that a claim is true. And all in defense of a string “theory” which as far as current experimental evidence is indistinguishable from the theory of welteislehre.
    http://www.mpiwg-berlin.mpg.de/en/research/projects/DeptIII-ChristinaWessely-Welteislehre

    In his classic book Fads and Fallacies In the Name Of Science, Martin Gardner describes audiences of German scientists shouting down lecturers in geology and paleontology while chanting “Welteislehre! Welteislehre!”

    When I read that passage as a high school student, I remember thinking, “Well at least we won’t see that sort of spectacle in America.”

    I was wrong.

    What we’re seeing all across the board in Western culture, it seems, is a systemic retreat from rationality into mindless faith, numerology, and cult belief systems (Rational Choice economic theory, po-mo deconstructionism, creationism, the Rapture Index, string theory) which are either untestable or which systematically contradict or ignore observables, in favor of blind adulation of jargon and tautological assertions which have no demonstrated connection with observed reality.

    Somewhere along the line, Americans stopped asking for evidence. They stopped using skeptical critical thinking and settled back into a comfortable smug mindless haze of self-delusion. This happened somewhere between the time Bonzo the chimp’s co-star told fables about mythical welfare queens driving around in Cadillacs (which everyone accepted as factual despite overwhelming evidence to the contrary) and the time we were assured that Iraq lay awash with lakes of sarin nerve gas and mountains of nuclear warheads. Exactly why Americans stopped using their heads and stopped applying skeptical critical thinking and common sense and why they stopped asking for evidence of even the craziest claims, well…that isn’t clear. But you can see it happening all around us, everywhere we look, in economics, in politics, in art theory, in literary theory, in music theory — and now in high energy physics.

    It’s clearly evident that Sean Carroll did directly compare evolution with string theory. It’s also clearly evident that he’s now trying to deny he did. The first rule of thumb, Sean, when you’re in a hole is…stop digging. The initial claim was bad enough, but denying you ever made that claim makes things worse for you.

    Let’s also be clear on exactly why Sean Carroll made the faulty and intensely disingenuous implied comparison twixt the theory of evolution and string theory. He did it because sensible educated people know full well that the only folks who deny the theory of evolution are kooks. The implication, therefore, is that since string theory is equivalent to the theory of evolution, anyone who denies string theory must also be a kook.

    This is deliberately deceptive and it smacks of character assassination of Drs. Woit & Smolin et al. There’s no evidence at all that Woit or Smolin or Kraus or any of the other reputable published scientists who have expressed serious reservations about string theory are crackpots. On the contrary, these people are the very ones calling for hard evidence and skeptical critical thinking in regard to string theory. Every time some vague expansive claim gets made to the effect that some recent experimental result allegedly “tests” some aspect of string theory
    http://ucsdnews.ucsd.edu/newsrel/science/stringtheory07.asp
    Woit is on the spot, demanding more evidence and applying critical thinking to debunk the deceptive claims.
    http://www.math.columbia.edu/~woit/wordpress/?p=510
    If there’s one thing you won’t hear from crackpots, it’s a call for critical skeptical thinking and a demand for more peer-reviewed journal-published experimental evidence — and that’s exactly what Woit and Smolin and Kraus have been calling for, over and over and over again.

    To imply that people who demand hard evidence and urge skeptical critical thinking are kooks is beyond contemptible. That’s the very basis of science. Throw out peer-reviewed journal-published experimental results and toss out skeptical critical thinking, and you’ve got dianetics, not physics.
    http://www.wired.com/wired/archive/12.06/view.html?pg=4?tw=wn_tophead_3

    Lastly, folks, keep your eye on the ball. Don’t let Sean Carroll of anyone else distract you from the real issue here. The crucial issue is whether the string theorists have made any experimentally testable predictions, and whether there exist any peer-reviewed published experimental evidence to back up those alleged predictions. I’m still waiting for Sean Carroll to provide the journal titles, article titles, issue numbers, volume numbers and page numbers of those articles chock full of experimental evidence to support string theorists’ experimentally testable predictions.

    Since my reading comprehension is defective it’s safe to assume that I missed those citations providing experimental evidence for string “theory” from the HEP literature. Please point ‘em out to me.

  • http://quantumfieldtheory.org nc

    mclaren, the response you will get is that string theorists should be free to investigate what they want forever at taxpayers expense, hyping their ideas and stamping on alternatives using tactics similar to those used successfully by Germany from 1933-45.

    Particles might well be some kind of string or loops of field lines. I’ve no problem with the idea of string.

    What upsets me is the elitism attached to the particular mainstream prescription for trying to get a model. They have adopted a methodology which is leading to religious type behaviour. The suggestion by Dr Witten not to engage in arguments for fear of controversy is like the previous Pope’s argument that theologians should not argue science, made for exactly the same reason (negative controversy).

    The way to build theories is to collect data, come up with empirical laws based on that data, and them come up with theories to model this data. That’s what Woit and Smolin advocate. Mainstream string theory is exactly the opposite: it builds an elaborate model on a massive amount of speculation and then has trouble getting any definite falsifiable predictions.

  • amused

    Just to be clear, the 8+ years I mentioned is what I often see for people working on non-string formal particle theory topics such as nonperturbative QCD (e.g. Schwinger-Dyson equations and that kind of stuff). I don’t expect that this is a unique situation though; probably it is the lot of people who are not working on the dominant topic in any given field.

    “Who do you think is doing the judging in mathematics? It’s not as if the people working on hardcore analysis are getting refereed by the combinatorists. People are always judged by their peers because those are the people that best understand the work.”

    Sure, but for the top maths journals the referees are carefully chosen accomplished experts in the relevant field, whose first commitment is to maintaining the standards of the journal. If I understand your point rightly, you are thinking that getting a paper accepted by such a person is effectively no different from getting a strong recommendation letter from them, so what difference would it make in practice? My impression however, is that it can be a huge difference in mathematics. For example, a senior person might be willing to write a glowing letter for some youngster, but that doesn’t mean he/she would be willing to accept that person’s paper for Annals of Math. The latter takes much more than the former; it is really a quality stamp of a magnitude that no reference letter can impart.

    “And, it’s not as if there’s this vast free-for-all journalwise. People know what the good journals are and which aren’t. That PRL isn’t at the top of the heap hardly seems like a big deal.”

    That’s true, but the problem with this situation as I see it is that it really doesn’t take that much to get published even in the supposedly good journals. Routine papers making incremental advances get published side by side with great papers containing major breakthroughs. Someone from another field has no way of telling the quality and importance of a paper from the journal it gets published in. In contrast, the quality and importance of a maths paper is tightly correlated with the journal it gets published in, so people can know it to a large degree just from the journal. I really think it would be a big advantage for everyone if we could have such a system in physics. It would solve the problem of finding an objective measure and assigning credit once and for all. String theorists could use it to to prove that their dominant position is merit-based (if they can ;)), and non-stringers in formal particle theory could use it to circumvent the need to get the strong personal support of senior influential people (who are almost all doing string theory and therefore not particularly inclined to support people working on other topics). That’s provided we can agree that publications are the primary measure of merit and letters of recommendation etc are secondary (which seems to be the case in the maths community to a large extent).

    “Is what you want to say is that the referreeing process isn’t as rigorous as that of the mathematicians? You might have a case to be made there, but I’m still not sure that’s your point.”

    Yes, the rigorousness of refereeing and standards for getting published in physics journals are far below that of the top maths journals. The consequence of this that I find so objectionable is that it removes the possibility of using journal publications as an objective measure for assigning merit, and there isn’t really anything else to use in its place. The closest thing we have to this at the moment imo is PRL, but at best it’s nothing more than a pale shadow of what the mathematicians have (and what we could and should have).

    “Regardless, perhaps you can explain to me, as someone who hasn’t published outside of string theory, just how the string theory refereeing process differs from the rest of physics.”

    As far as I know there isn’t any difference (and I don’t remember suggesting that there was…) Some journals are supposed to be harder to publish in than others (e.g. PRL vs PRD) but I don’t see why string and non-string papers would be treated differently. What there is, however, in general, is resentment when people get jobs ahead of others who look on paper to be better qualified as far as publications etc goes. You can imagine that more senior postdocs working on non-string things and with lots of publications and citations would find it pretty galling to see young string theorists getting jobs ahead of them. (Btw, I’m not one of those people! – my own record is much less than great.) It’s obviously something that would fuel resentment against ST itself. But again, this would be a thing of the past if we could establish a similar journal system to the mathematicians so that there was an objective measure for merit that everyone could accept.

    “There are no completely objective criteria in hiring in any field. Are you seriously claiming that mathematics or the rest of physics, or, hell, the rest of the entire world doesn’t have people talking to each other and asking their opinions of job candidates.”

    Of course, it is impossible to make hiring decisions etc completely objective; sociological factors will always be there. E.g., I’m sure it helps a lot for getting published in a top maths journal to be working on a fashionable topic at an illustrious institution and with good connections to influential people. But still, it is in principle possible for Dr. Nobody at University of Nowhere to publish in top maths journals if he/she comes up with something good enough, and thereby forge a career. In physics (at least theoretical hep), the way things are now, that isn’t a possibility. Instead, as best I an tell, people are completely reliant on gaining the strong support of influential senior people. To gain that while working on a different topic (which is basically what a non-string formal particle theory person needs to do) is going to be a lot tougher; it would take something quite dramatic.

    “I find it hard to believe that hiring in other field consists of simply counting one’s PRLs and making an ‘objective’ decision. And, even if it were, how is the number of PRLs anything but a proxy for what the “accomplished” editors and referees think of the work?”

    Of course, the decision to hire someone is always going to involve more than just counting publications, PRL or otherwise. But PRL publications do seem to count for quite a bit in some other fields, e.g. condensed matter. There it seems to be possible for someone who isn’t blessed with good connections to influential people to outcompete via PRL publications someone who does have the former. Sure, it is nothing more than the opinions of a couple of (usually well qualified) referees, backed up by an editor, but it seems to work ok as a neutral currency for merit in CM as far as I can tell.

  • http://web.mit.edu/sahughes/www/ Scott H.

    using tactics similar to those used successfully by Germany from 1933-45

    Sean, congratulations! You’ve managed to start a thread on string theory that actually descended into the territory of Godwin’s law!. Well done.

  • onymous

    amused wrote:

    “Just to be clear, the 8+ years I mentioned is what I often see for people working on non-string formal particle theory topics such as nonperturbative QCD (e.g. Schwinger-Dyson equations and that kind of stuff).”

    I suppose it’s not terribly polite to anonymously talk about the details of people’s careers on a blog, but as far as I can tell from Spires the people who have made the largest contributions to Schwinger-Dyson approaches to QCD already had faculty positions when this work began. Also, it’s confined to a relatively small number of people and a very large fraction of it happened in one place (Tuebingen). Not knowing further details of people who went through job searches and had problems, I won’t say that your example is wrong, but I don’t see clear evidence for it…. (Of course, not all aspects of the job market are the same in Europe and the US; nearly everyone involved in that approach is in Europe.)

    If people working on such things did have problems getting jobs, I think the reason is probably more that the field is not structured to support people who want to work long-term on a fairly technical program without broadening their interests and working on other things as well.

    (There are perhaps other issues here, starting with the fact that it’s not at all obvious that it makes sense to use the SDEs nonperturbatively given the presence of Gribov copies, an issue which I think is now resolved due to work by Zwanziger.)

    “Routine papers making incremental advances get published side by side with great papers containing major breakthroughs. Someone from another field has no way of telling the quality and importance of a paper from the journal it gets published in. In contrast, the quality and importance of a maths paper is tightly correlated with the journal it gets published in, so people can know it to a large degree just from the journal.”

    I find it rather surprising that there is any field in which incremental advances are not published side by side with great papers containing major breakthroughs: there simply aren’t that many breakthroughs!

  • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

    Scott, don’t forget comparisons to Pravda, Medievalism, and Rational Choice Theory! Together with the Nazis, we’re talking the Big Four of bad things to be compared to. Also Fox News.

    Now if you’ll excuse me, I’ll be back to leading the systemic retreat from rationality.

  • Elliot

    Wasn’t there consideration for some level of “moderation” on this blog. I am wondering if this thread unfortunately exemplifies the need for that.

    Elliot

  • http://eskesthai.blogspot.com/2007/04/elixir-of-bee-community.html Plato

    #150

    I am sensitive to your plight. While I cannot speak with any authority and many know this. It is necessary to somehow show the development of string theory in some other way? :)

    Well, at least make it entertaining. Break up the rigidity for a moment, so one can enjoy “the feelings emanating” from those who have found beauty in the work.

    It is unfortunate some of those who choose to do model work of one kind or another, would suffer under such a thing whilst you pursue the interest. It is not about bravado, whilst you suffer under the tutelage and take your lashes, but more that you would excel in your continued research and development from what one find works. You challenge the person to excell in the work, not to challenge the person?

    “Change your name” to protect your innocence? Then speak away?

    I have to go back and start from the beginning “every time.” :)

  • http://eskesthai.blogspot.com/2007/04/elixir-of-bee-community.html Plato

    Elliot,

    Notice the “number comments-169″ versus the actually responses showing 160?

  • Perl

    Eric Mayes writes,

    These sites tend to be populated by a number of people who are more interested in interjecting their own prejudices and opinions than honest debate. How can any string theorist explain why he/she works on it while being screamed and yelled at? The thing it most closely reminds me of is right-wing talk radio.

    And, of course, a string theorist would never do such things, right? Screaming and yelling is a feature of right-wing particle physicists, while string theorists are polite, soft spoken freedom lovers. That is the idea?

    Have you checked a few string theory blogs recently? Frankly speaking, string theorists don’t look to me like helplessly shy people, or at least the blogging ones. Thuggery is certainly not beyond the abilities of (several of) them.

  • Aaron Bergman

    Just to be clear, the 8+ years I mentioned is what I often see for people working on non-string formal particle theory topics such as nonperturbative QCD (e.g. Schwinger-Dyson equations and that kind of stuff). I don’t expect that this is a unique situation though; probably it is the lot of people who are not working on the dominant topic in any given field.

    I know string theorists on their third and fourth postdocs, too. The job market pretty much sucks for people who aren’t doing phenomenology or cosmology.

    My impression regarding mathematics is that people often get hired (at least at the lecturer level) with no publications at all, purely on the strength of their theses. But at this point, I really don’t know what I’m talking about, so I won’t bother speculating any further.

    I tend to disagree with your contention that publishing in PRL is the only way to get noticed. I’d expect that well-informed senior people will notice good work in their specialty.

  • amused

    onymous,

    I had a couple of people in mind for the DSE example, and yes, Tubingen was a common factor for both of them although in both cases DSE was just one of a number of things they work on. They have both been in the game for a good long while (satisfying my 8+ criterion), both have very decent publication lists with lots of cites etc. One of them recently managed to get a faculty job, the other is still a postdoc. One of them is in the US, the other elsewhere. Maybe you can work out who they are from this info. But I’m starting to feel a bit bad; like you said, it isn’t so nice to be discussing this stuff in public… Having just looked them up on Spires i also realized that they aren’t such great examples for what i was claiming, since they are more hep-ph (and even nucl-th) than hep-th (although I would still think of them more as QCD theory than real phenomenology or nuclear people). But in any case, the career trajectories of these guys are pretty typical for the non-string students/postdocs I’ve been aquainted with or heard of through friends/aquaintances. I could give more examples, including ones closer to hep-th, but would prefer not to do it in public…

    “I find it rather surprising that there is any field in which incremental advances are not published side by side with great papers containing major breakthroughs: there simply aren’t that many breakthroughs! ”

    True, I should have said major advances instead. Breakthroughs is overstating it. To publish in a top maths journal the work would have to be considered a major advance. Papers with only incremental advances would only be publishable in lesser journals. (I don’t have personal experience of this but spent some time in a maths dept at one point and had it all explained by the mathematicians.)

  • po

    This is boring. Let’s talk about something else or, you know, get back to doing physics.

  • amused

    Aaron, once again I never meant to imply that all string theorists have it easy. I know there are plenty who don’t.

    “I tend to disagree with your contention that publishing in PRL is the only way to get noticed.”

    Ok, I don’t remember contending that, but whatever.

    “I’d expect that well-informed senior people will notice good work in their specialty.”

    How many such people do you imagine there are for a typical non-string formal particle theory topic? In my case there were two, and they were enemies, so getting support from both was out. I was fortunate to get supported by one of them, but you can imagine for yourself how far the support of one isolated big shot is likely to take someone.

    Let’s give this a break.

  • George Musser

    Peter, you wrote in response to my comment about funding:

    Thanks for your comment, which does bring things back to what I see as the most important point, which is how to get particle theory out of its current doldrums.

    So let’s talk about that rather than rehash your critiques of string theory. Everyone, no matter what they think about string theory, can agree that science funding is seriously messed up. The competitive grant system imposes a huge amount of overhead and distorts how science is practiced.

    So what’s a better system? To take an extreme example, what if NSF just divided its money equally among everyone? No grant applications, no reviews — just ask for money and you get some. Sure, this would produce waste, but would the waste be worse than what we have now?

    George

  • Gina

    I am eagerly waiting to Sean’s promised post titled “Why String Theory Must Be Right,” or perhaps “Very Good Reasons to Think that Something like String Theory is Going to be Part of the Ultimate Understanding of Quantum Gravity.”

    It will be great to have an account of these reasons and Sean’s overall point of view. Go for it, Sean!!

    (A little remark is that the two possible titles are somewhat different. I think, for example, that Lee Smolin would agree to the second title. Also if the second title represents Sean’s point of view, it is an interesting issue if the practices of string theory research really accommodate for the possibility of “something like string theory.” From the outside, progress in string theory looks like very pointed with some sharp turns but not much backtracking. Of course this view may represent distortion caused by the popular descriptions.)

    But while waiting o Sean’s promised post, it is a pleasure to read Moshe’s beautiful comment:

    “you just start with a purely intellectual exercise, quantizing a relativistic string. You know you’d immediately run into trouble because combining Lorentz invariance and quantum mechanics is very tricky in field theory, requiring delicate structures such as gauge invariance for vector fields. So you expect complete disaster, all kinds of nonsense, but you are stubborn…

    Instead, to everyone’s surprise (try to quantize relativistic membranes if you don’t believe it), everything falls into place effortlessly- the theory cannot be tuned and modified, so it lives dangerously, every time you check something new you may prove it inconsistent, and will simply have to abandon it. Somehow, again and again it is just right. Gravity, Einstein equation, matter fields with rough similarity to the real world (gauge fields, chiral fermions), they all just come out. It is impossible I think to go through the first few steps in string theory without the feeling of awe, there is something there that is very correct and unique. ”

    Unlike most participants, I don’t know what the future of string theory will be, but however it will turn out to be, I think Moshe’s words beautifully describe the spirit of scientific work and the sweet sensation of scientific progress.

  • former string theorist

    I think that the advantage which mathematics has is also that the most important thing to check is that the proof is correct, and every question can in the end be verified through the manipulation of symbols.This objective standard is infinitely better than any journal or system of authority based on reputations. It is essentially the same as the standard in symbolic logic.

    String theorists have had to relax this standard to allow string theory to exist, partly because assuming the truth of conjectures is more common in string theory, but also partly because string theory claims to be physics and not mathematics, and claims to be able to draw on another source of information which is denied to pure mathematicians. You hear mathematicians saying things about string theorists like: “I don’t know how they manage to produce such important mathematical results. They don’t prove the assertions they make, but many of them appear on inspection to be correct.” This has been interpreted by some as evidence that the string theorists have access to some deep truth about something.

    After my experiences with string theory, I don’t think this is the case. I believe that what is happening is that the string theorists have hit upon a more productive way of doing research in mathematics. The use of the arXiv for communication has revolutionized the way that mathematics research can be done. It is now reasonable to share ideas while they are still conjectures and while proofs are intuitively understood rather than rigorously finished. Others can help tidy up the details; the big leap forward in understanding often does not come in the form of a proof.

    Things can be presented in string theory as great breakthroughs which in mathematics would be considered just a conjecture. The mathematicians don’t get it; don’t see what the success is. The string theorists get excited about it, and major results soon follow. For a mathematician this can make string theorists seem to have magic powers; they can perceive something which the mathematicians cannot and it is bringing them success. But the mathematicians cannot do what the string theorists do, because the string theorists are not rigorous and what is mathematician supposed to do if he abandons rigor?

    This has won string theory praise and respect from some of the most recognized mathematicians, and this general thumbs-up has been interpreted by some as evidence that there is a particular thing which might or might not be true, sometimes phrased as “String theory correctly describes the universe” , which is evidently true because string theorists can do things which impress mathematicians.

    I was never able to find out exactly where string theory began and where pure mathematics ended. Evidently conformal field theory wasn’t the boundary. Does string theory start when I set the trace of the energy-momentum tensor to zero? Or is it because I study this lagrangian and not that one? How does that give me a source of information which mathematicians don’t have access to? Would it help if I said “String theory correctly describes the universe” a few times?

    Everybody following the public string theory circus will know by now that many people claim they work on string theory but that the field of string theory spreads over so many areas of mathematics and has such ill-defined boundaries that this claim is easy to make.

    I can only conclude that there is no “string conjecture” which is or isn’t correct (from a mathematician’s point of view) and that the statement that “string theory correctly describes the universe” does not provide any access to a new source of information and has no mathematical content at all. So the subject which string theorists are investigating can only be pure mathematics – they have no other source of information which mathematicians don’t have.

    The great success was the introduction of a more efficient way of researching mathematics, and the people in theoretical physics adopted it because they are concerned with the applications of mathematics rather than the proofs. Their successes were all mathematical, but it gave the appearance of being an advance in physics, and the idea that “string theory correctly describes the universe” took on a life of its own in the public imagination.

  • tyler

    Dear Po and everyone – yes, this thread has perhaps reached its end with the Godwin’s Law violation, or perhaps with this absurdly long post of mine; but I hope none of the authors of the physics-related posts feel that they wasted their time. This has been the most interesting thread anywhere on the ol’ Inter-tubes for the last couple days.

    I’m pretty much the person you are all trying to convince when it comes to “the public debate” – well, me and my congressman. When string theory first came into public view I was the first person in my social group to read about it, and for a long time my friends thought it was silly. Then they all got on the bandwagon when Greene’s books came out, around the time I was starting to think “hm, isn’t it about time this went somewhere a litlle more real…?” Now, amusingly, I find myself again on the outside, simply because I am undecided; anecdotally, among my peers, who I might describe as highly intellectual, countercultural creative professionals, string theory has become decidedly unhip, old hat, and yesterday’s news.

    However, I also have noticed that the less a given person knows about physics – even by my knuckleheaded, pop-sci rating scale – the more likely they are to hold that opinion. They heard the buzz around Smolin’s book and that was that. This isn’t to dismiss the book, which is next on my reading list, it’s the exact same social effect The Elegant Universe had when it came out, which extended far beyond people who actually read it. Again, I’m not saying Smolin’s not right, I’m saying that a lot of my peers are intellectual followers, and when I challenge them to defend this new position – taking the pro-string side as a devil’s advocate – it’s clear few of them have even the low level of understanding that I do. They’re interested, they know it’s important, but they don’t grok it well enough to have an opinion they didn’t get from someone else.

    In my arrogance, I beleive I understand the debate well enough to know that I should not hold any opinion at all. Opinions get in the way of thinking and right now this all-important field is too unsettled for that.

    I learned a lot of interesting things in this thread. Such as:

    – Physicists might start off talking about physics – and some of them try to keep the conversation there – but in the end it turns into an argument about jobs. Who’s getting them, who’s not, and who deserves what. It’s understandable, but really quite depressing. As a pro-science taxpayer I’d like to fund you all and let the physics sort itself out over the next couple decades, but it’s clear this is turning into a knife fight over tenure and professional futures.

    – people seem to think it’s meaningful to debate what other people “should” do with their academic lives. Young scientists interested in strings are going to keep doing strings no matter what; and those who find them unconvincing or uninteresting are going to find other topics and ways to pursue them, resource availablility notwithstanding, just as early string theorists did when everyone thought they were nuts. Why waste your time arguing over what your peers should or should not be doing with their lives? Get on with your own life and your own work and let the results speak for themselves.

    – Peter Woit may be very intelligent, and may be right – from the evidence here, I may be the last person on Earth without a settled opinion or axe to grind on that – but he has an arrogant and manipulative rhetorical style in which he proclaims things to be True because he has decided they are true, as if this should end debate. I despise this form of argument, as it is usually a sign of intellectual dishonesty; and so this person, regardless of his expertise, intelligence or other merits, shall be excluded from my consideration of this debate unless and until he modifies his propagandistic approach. Stop telling me what has failed and what hasn’t. It’s not for you to decide, bub, ‘k?

    – Several posters whose names have appeared here many times before are revealed as off-topic windbags whose opinions may be safely ignored from here on out. Also, mclaren’s attacks on sean, IMO, cross the line from merely off-topic/irrelevant ranting to abusive and if this were my blog I’d boot him; and nc should be banned permanently for his insane and extremely offensive Nazi reference. When was the last time a string theorist murdered someone for poltical reasons? I must have missed that. Shame on you, tiny little man.

    – this thread may have killed this blog. I hope not. It’s quite a bruising fight and Sean et. al. may not be up for posting any more invitations to such a frenzy. But this sort of thing is exactly what makes this blog worthwhile – not the beer or science v. religion posts, fun as those are.

    So keep it up, people, but leave the job & tenure related BS buried in the subtext where it belongs, please. Do your best to convince me. I don’t speak higher math but don’t think I’m stupid either (to be fair, I don’t see a lot of that these days). My current state of mind is that while string theory and its extensions, all the way up to the landscape, are worth continued effort by physicists, funding by the government and others, and learning on my part; but that’s it’s also, in parallel and not instead-of, worth learning, funding and researching the alternatives, whatever they may be.

    So, with the exception of the flamers, thanks to you all for a most interesting thread.

  • http://thecrossedpond.com adam

    Yeah, tyler, if you start banning people for making nazi comparisons, it’s going to be a lonely internerd. Ridicule is probably a more appropriate reaction.

  • po

    “Somehow, again and again it is just right. Gravity, Einstein equation, matter fields with rough similarity to the real world (gauge fields, chiral fermions), they all just come out. It is impossible I think to go through the first few steps in string theory without the feeling of awe, there is something there that is very correct and unique. ”

    Yes, wow, they all just come out. Matter fields with ROUGH similarity to the REAL world just comes out. I am so awed by how matter fields with ROUGH similarity to the REAL world just comes out. Yes, there is something very correct here.

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    tyler,

    “he has an arrogant and manipulative rhetorical style in which he proclaims things to be True because he has decided they are true, as if this should end debate.”

    My references to the “failure” of string theory refer to a specific scientific argument about exactly what has failed and what the reasons for this are. The argument is outlined at a popular level in my book, in more scientific detail in many of the several hundred postings on my blog and in some recent talks I gave, available at my web-site. If you want to have an informed opinion about the question of whether my claims about string theory’s failure are correct or not, you need to try and follow that argument. If you want to decide who is right about this based on your dislike of people’s “arrogance”, I think you’ll find plenty of it on all sides of this debate, so it’s not a criterion that will help you very much.

    As for your dislike of “the job & tenure related BS”, sorry, but that’s a crucial question here that is driving this debate, as far as the people involved are concerned. How does this academic field allocate resources going forward? The people who have devoted their professional lives to working in this area care deeply about it, on both sides of the issue, and have very serious concerns about the future of this field. This future is going to be determined largely by who gets hired into permanent jobs, and who doesn’t, and everyone in the subject is well aware of that.

    George,

    I think the grant system is less of a problem in math and theoretical physics than in other parts of science, simply because the size of the grants is smaller and they are less crucial for getting your research done. Unlike experimentalists, who need money for equipment, in this area you can work successfully without a grant. But you can’t work successfully without a job, preferably at an institution set up to provide the kind of environment necessary. The situation in this field is that there are a lot of smart people getting Ph.Ds, and a small number of permanent jobs at institutions that can support research. So, one huge issue on every one’s mind is how that particular game of musical chairs gets played. The grant issue often comes into play through the way in which grant money funds positions or encourages universities to fund them.

    If you look at history, the people who have made the big breakthroughs in this subject often do so at a relatively young age, so if you want to think about how to maximize the chances of such a breakthrough, you need to think about how to encourage young people to try and do something new and ambitious. I’ve made some suggestions on my blog and in the book (e.g. instead of many short postdocs, guarantee people support for longer terms, “birth control” to bring the number of people and the number of jobs into better balance). Unfortunately I think it may also be necessary to not just provide incentives to original ideas, but disincentives to unoriginal ones. As long as people see that the most likely path to a permanent position is to keep their head down and work on the most conventionally accepted topics, that’s why many if not most people are going to do. I’d love to see some discussion and debate of these issues.

  • David B.

    Hi everyone:

    By popular demand (and to get some issues across), I will do a rant on “Why should string theory be important for describing the real world”.

    These are my personal points of view. Some may be more technical than I would like for this audiencee. but I think that comments like the one Po made above deserve a reply. Especially since Po thinks that being sarcastic will buy him points for being “oh so clever”.

    String theory was born in the late 60’s. It’s origins date to the Venziano amplitude and the era of the dual resonance models. The amplitude was an example of a setup that seems to satisfy all of the details required for an idea (the bootstrap) that was very popular at the time.

    The Veneziano amplitude was written down before it was knnown that it related to strings.

    The properties of this model were that it predicted an infinite tower of massive particles with high spin. It had the property of Regge behavior. This behavior had been observed in the tables of strongly interacting particles.

    Thus string theory was born as a model to explain the strong interactions.

    One of the biggest problems that arose then, was that the string model predicted a particle of spin two and zero mass. That particle was the source of a lot of headaches, and people tried to work it out of the string model for year.

    When QCD showed up, it took over and very few people kept working on string
    theory.

    This particle of spin 2 and mass zero shows up in another very different place:
    gravity. Any semi-classical quantization of gravitational waves will produce such a particle.

    String theory was then reinterpreted as a theory of quantum gravity. One can even check that the gravitational interactions that are described by Einstein’s equations follow from studying string interactions according to the usual rules
    for calculating in string theory.

    This is a very non-trivial check: random theories of spin two massless particles are inconsistent, unless they reproduce Einstein’s equations.

    Afterwards it was discovered that the existence of fermions (something we see every day) required that the string worldsheet have supersymmetry. Things work a lot better in that case, and one ends up with the prediction that critical strings (read Lorentz invariant in all of the dimensions of spacetime simultaneously) required 10 dimensional supergravity.

    Morever, it was possible to show that from string theory one could also produce chiral matter and that anomalies cancelled. This is also a very non-trivial check, as otherwise the theory would be inconsistent. In 10 dimensions this requirement is a lot more stringent than in four, and is enough to determine the gauge group of interactions and reduce it to very few choices.

    This idea also ties very nicely with Grand Unification ( a popular model for physics beyond the standard model) and many people took these hints very seriously.

    More recently string theory has been able to count the degrees of freedom of certain black holes from first principles and to reproduce the Bekenstein-hawking entropy of black holes by a microscopic description.

    This is amazing for various reasons: if one reads ‘t Hooft papers on the physics of black holes, if one just counts initial configurations that lead to a black hole in a region, one usually ends up undercounting the entropy. At the same time one gets that the entropy scales with the area, and not like the volume.

    ‘t Hooft also showed in the 70’s that theories with large gauge groups (of Nx N matrices) lead naturally to a string interpretation. This is believe to be behind the mechanism of confinement in QCD.

    The modern version of that idea is embodied in the AdS/CFT correspondence.
    That is an example of such a an equivalence where one can be very precise about the field theory and the string theory.

    The surprise is that the ‘t Hooft string ends up being identified with the same fundamental string that lives in 10 dimensions and was encountered previously, and that also contains gravity.

    People have shown that in toy models of this type, one gets better agreement with observations at the RHIC experiment than by using perturbative QCD. In particular, the setups involve black holes in AdS.

    There are a lot of other reasons to be optimistic about strings: it has been a soruce of inspiration for many models of physics beyond the standard model, it has produced beatiful mathematical conjectures and ideas, etc etc.

    The biggest question is whether strings will be useful at the level of precision electroweak measurements, and to get better than qualitative agreement with the strong interactions. We don’t know that, but we are hopeful that this is possible.

    I hope everyone hass a nice day.

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    David B.,

    “The biggest question is whether strings will be useful at the level of precision electroweak measurements and to get better than qualitative agreement with the strong interactions.”

    I’m quite willing to believe that string theory may some day produce a model with better than qualitative agreement with the strong interactions. But what’s the “precision electroweak measurement” reference to? To calculating QCD effects here or to explaining beyond the standard model physics? Have you completely given up on the hope of using string theory to explain where the standard model comes from? If not, wouldn’t a better way to state the question would be “will strings ever explain anything at all about the standard model Lagrangian”?

  • Gina

    Peter Woit wrote ” … the people who have made the big breakthroughs in this subject often do so at a relatively young age, so if you want to think about how to maximize the chances of such a breakthrough, you need to think about how to encourage young people to try and do something new and ambitious. I’ve made some suggestions on my blog and in the book (e.g. instead of many short postdocs, guarantee people support for longer terms, “birth control” to bring the number of people and the number of jobs into better balance). Unfortunately I think it may also be necessary to not just provide incentives to original ideas, but disincentives to unoriginal ones. As long as people see that the most likely path to a permanent position is to keep their head down and work on the most conventionally accepted topics, that’s why many if not most people are going to do. I’d love to see some discussion and debate of these issues.

    This can be very easy, Peter: Devote on your blog a special post just to this issue (and not to string theory); explain your ideas on the matter, perhaps Lee Smolin who devoted large portions of his book to these issues will present his ideas and then open it to discussion and debate (which will not be about string theory.)

    I read carefully Smolin’s suggestions on these issues and while very very original, for most parts they are also very problematic and unconvincing. Taking originality as the ultimate parameter in scientific quality is one serious problem with your approach.

    Trying to juggle together “pure” scientific issues and these serious issues regarding sociology of science is by itself very problematic.

  • tyler

    If you want to have an informed opinion about the question of whether my claims about string theory’s failure are correct or not, you need to try and follow that argument.

    So if I have not read your book, I am not informed and do not have the right to comment? I note that here you are again telling me what I “need” to do, and have cast your own role in the debate as central. I am in fact trying to follow the larger argument, including your part in it.

    However – and it’s worth mentioning again that I’m utterly undecided on the merits of either “side” here – your particular rhetorical style is one that I frankly do not want to force myself through a whole book’s worth of. But, I will probably still give it a shot, and if I have any truly well-developed skill at all it’s the ability to keep an open mind, so I’ll try to focus on the merits of what you say rather than how you say it. Right now I’m trying to do the same thing with Susskind’s book on the landscape, in which he constantly claims that String Theory (with caps like that) is the ONLY valid approach to practically any topic worth discussing. I don’t like his style, but I’m trying to get past that to the meat of his argument.

    If you want to decide who is right about this based on your dislike of people’s “arrogance”, I think you’ll find plenty of it on all sides of this debate, so it’s not a criterion that will help you very much.

    Ah, the Straw Man. I don’t want to decide “who is right” based on arrogance, flatulence, cromulence or any other such quality. It’s not for me to say who’s right, in fact I am highly suspect of any notion of final “rightness” in as primal and complex a subject as this. I am interested in the quality of the debate.

    Intellectual arrogance abounds in this field, no doubt. I’m well aware of it, given that I read nearly every popular-level book written by a physicist. I tend to let it slide since I’m not qualified to judge between competing claims. But rhetorical arrogance is a different story, and I can’t remember I had this kind of negative reaction (outside of the political arena, or perhaps the pseudoscience wars) to what I perceived as an attempt to manipulate the debate with the purpose of moving the Overton Window in your desired direction via reframing techniques.

    When I read some of your posts I find myself deconstructing them, which is the trained mind’s defensive response to manipulative, salesman-esque language. I have to force myself to go back through and read these for content in a value-neutral state.

    And, to be fair, when I do that, you do seem to have something to add to the conversation; perhaps you even deserve to be a driving force. I would contrast your very interesting reply #175 with the tone of post #130 which drove my initial comment. My point is that your tone is not equivalent, and that, in my case anyway, it hurts your case.


    This future is going to be determined largely by who gets hired into permanent jobs, and who doesn’t, and everyone in the subject is well aware of that.

    It’s certainly true that there are resource allocation issues that are valid, and the bruising realpolitik of tenure is well known. I simply think that for the physics community to hold this particular part of the debate in public is highly unwise.

    The capitalist social-darwinian competition/survival aspect of modern science has been critiqued enough without my adding much to the hot air. Clearly the system is poorly thought out. And certainly problems arise when any one subfield becomes dominant, yes, this is an obvious problem: the research equivalent of a monoculture subsistence economy, very well, let us deplore it.

    However, from the perspective of the non-working-physicist, it’s easy to think (incorrectly, but this will be the perception) that you all are less interested in the validity of the science and more interested in shoring up your own professional situations. I do not think this is true. But it is how you will all be perceived if you continue talking about this part of it in public.

    To be quite blunt, we don’t care who gets the good job at Caltech and who gets stuck at East Podunk U for their fifth postdoc; and when the debate turns that way, people will glaze over or become wary of their tax dollars. We want to know: are you making progress? Does it mean anything to me, either technologically or, I suppose, epistemologically?

    Work calls. Peter, I will read your book, and consider what you have to say. Meanwhile, please consider what I am saying: your strident tone and potent, skillful rhetoric can work against you. In the age of the All-Spin Zone many of us have become very finely attuned to this type of language; it sets off BS detectors, in many cases unfairly, because the content of the message may be entirely valid., but the messenger becomes distrusted.

  • George Musser

    Peter, what would you think about automatic postdocs for all new physical science Ph.D.s? You get a Ph.D., the NSF gives you a five-year postdoc, no need for applications. In the NSF budget, this would actually be a fair small amount. Five years would let you dive into a topic, maybe one very different from your dissertation, and give you several years before having to turn your attention to your next career move.

    The NAS report on science competitiveness, “Rising Above the Gathering Storm”, proposed expanding the early-career grant program, but their plan would still help only a few hundred people.

    George

  • David B.

    Dear Peter:

    String theory is widely believed to be a theory of beyond the standard model physics, if anything because it includes gravity. As such, one would need a complete description of how the standard model arises, and on how to calculate the various coupling constants of the standard model itself. If that turns to be an ill-defined problem (which it can), then one should try to predict new particles that are accessible to an experimenter from the data that has been already collected.

    There are various models based on strings that get some qualitative agreement with the standard model (3 generations, non-zero Yukawa couplings, etc). The devil is in the details and the standard one should meet is to get things to a level where one can compare with precision experiments in particle physics. The best data available at the moment is in precsion electroweak data. That is why I mentioned it.

    There is a possibility that a dual string theory of just the standard model exists (without gravity in 4d). This possibility is not discussed very often. At this level, that dual description should be just as good at calculating various standard model corrections as doing loop calculations in the standard model itself. Otherwise, its just a curiosity.

    In this vein, it is believed that strings have a good chance at being able to reproduce the spectrum of just QCD in the strong coupling (confinement) regime. Again, we don’t know for certain. But it is interesting to find out.

    The point I was making above (without trying to go into the details) is that all of these are questions one can address with string theory ideas and that is why one studies string theory. Indeed, some of these questions are considered to be fundamental questions in physics. String theory gives you a toolset that is in principle able to answer them (all evidence of our understanding points in that direction). In practice, we don’t know if it will for sure. That is part of the reasons research in string theory is exciting.

  • http://thecrossedpond.com adam

    Tyler, you don’t want the debate to be held in public?

    Sure, that subsection of theorists that don’t ever take public money are welcome to form some supersecret cabal to discuss Weighty Matters. The guys that are taking public money, though, are answerable to the public. Indeed, the openness, across the board, of modern science makes a great fit with public money being provided to support it.

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    George,

    I’m a bit dubious about the “postdoc for all physical science Ph. D.s” idea, partly because it seems unrealistic that such a thing would be funded, partly because there are a significant number of people getting Ph.Ds who for whom the offer to with no effort spend the next five years of their life being badly paid to do research they’re not really cut out for would not be a good idea. Either for them or for the field.

    I do think the idea of setting a standard of making all postdocs five year or longer term is a good one, at least in the field of particle theory, given the current situation. Also, some way should be found to fund postdocs not for everyone, but for those who have impressed people around them with their intelligence and promise, even if they have little to show for themselves in terms of results because they’re trying to do something overly ambitious and haven’t managed yet to get anywhere with it.

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    David B.,

    OK, I take it that your reference to “precision electroweak physics” is to the idea of string theory describing beyond the standard model physics and that you see this as something string theory promises to give us an understanding of (since you write “String theory is widely believed to be a theory of beyond the standard model physics”).

    I really don’t understand this invocation of “precision electroweak physics”. The problem with “string phenomenology” is that no one has any idea how to make any predictions with it at all, much less precise predictions about electroweak physics. String theory can’t predict even the crudest things about the standard model, such as the number of generations.

    “all of these are questions one can address with string theory ideas and that is why one studies string theory. Indeed, some of these questions are considered to be fundamental questions in physics. String theory gives you a toolset that is in principle able to answer them (all evidence of our understanding points in that direction).”

    It seems to me that, as far as the standard model is concerned, all recent evidence points in exactly the opposite direction. The lesson of the landscape is that string theory inherently can’t address any of the questions about the standard model that we’d like answers to (except for possibly how to do certain QCD calculations).

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    tyler,

    My only point about informing yourself was that there is a serious and extended argument behind the claims about “failure” that I’m making, I’m not just saying that I think something so you should believe me. Up to you whether you want to spend your time looking into this, there are good reasons not to, most people have better ways to spend their time.

    I’m actually not trying to sell anything to the public here, if I were I’d adopt a different tone and discuss different issues, in a different way. For better or worse, this blog has a mixed audience: both scientists in this area and interested on-lookers. My interest has always been in starting what I see as an important discussion among the people in this field. The book was always aimed more at such people than at the general public, and the fact that it was published by a commercial publisher and promoted widely was not my choice (I intended it for an academic press and a smaller audience).

    Particle theory does need to have a serious debate about what to do about the problematic situation it is in. Maybe it would be better if this were somehow conducted less publicly, but the past history is that of an unwillingness to confront these problems, coupled with a seriously misleading publicity campaign aimed at the public, designed to convince them that all was well with string theory. This publicity campaign now shows signs of being derailed, and I can’t say I don’t think that is a good thing.

  • David B.

    Peter:

    Just like Einstein’s gravity predicts black holes, that does not mean that every solution of gravity has black holes in it. By the same token, some solutions of string theory have three generations, therefore string theory PREDICTS three generations in one of its solutions.

    The problem with string phenomenology is not that ” no one has any idea how to make any predictions with it at all”, but rather that the typical prediction is for new particles at about the GUT scale, well beyond what we can accomplish technologically.

    That seems to be a general omission of this whole discussion. Absent an accelerator that can probe that scale directly, one has to look at small deviations from ordinary standard model physics. This means one needs to have a setup that permits one to calculate with the same precission as in the standard model to find a new efffect.

    You’re also wrong about the landscape. It makes predictions: in principle it gives a discrete description of vacua. This means that certain values of the fundamental constants are just not allowed. This is a route to falsifying the theory.

    In practice it’s too large to explore effectively, and we don’t know how to get the numbers in sufficient detail to compare to experiment. This is a motivation to try to do better.

    There is another thing: some models based on strings seem to be able to access fundamental strings near the TeV scale. These are not ruled out experimentally yet. If we are lucky, they will be seen at LHC. Some of those models can make very precise predictions for various coupling constants of new particles to the standard model. By that standard, they are just as good as usual phenomenology models of physics beyond the standard model: not ruled out yet, and with some new particles at the TeV scale.

    There is no unique preddiction from string theory for what will happen at LHC.
    I guess that’s too bad for us, but it is not as hopeless as you portray it.

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    David B.,

    You are using “prediction” in a non-standard way. Saying that string theory PREDICTS 3 generations because it has a solution with 3 generations is kind of misleading if you don’t also tell people that it has solutions with 1, 2, 4, 5, 6…., or basically any number of generations you want. String theory doesn’t determine the number of generations at all. As far as the string theory framework is concerned, this number could be anything.

    The problem with the landscape, and with the string theory framework in general if you believe that it includes the landscape, is that the nature of the vacua is so varied and complex that, as far as anyone can tell, you can get just about anything you want. You can get virtually any number of generations, any gauge group, any fermion representations, any Yukawa couplings, etc. You also can get any energy scales you want: electroweak and supersymmetry breaking scales can be anything you choose. In brief, nothing about the Standard Model Lagrangian is explained by string theory.

    It’s not just that there isn’t a “unique” prediction about LHC physics. Other than a few very conjectural “swampland” arguments that certain very exotic things can’t happen, as far as anyone knows, string theory has solutions with essentially any possible effective field theory at LHC scales. And this is not just a problem about the LHC scale. The situation wouldn’t change even slightly if physicists were given the funds to build an accelerator as large as the orbit of the moon. There are no real predictions, not just at the LHC scale, but even at the GUT scale (and very little if anything in the way of predictions even at the Planck scale). Whether experimentalists figure out how to make accelerators a billion times higher in energy, or do precision experiments to a billion times accurately, string theory can’t say what they are going to see.

    I don’t understand why you claim that the “typical prediction” is for new particle physics at the GUT scale, but not at other scales. You can write down string models with new physics at any scale you want, as long as it’s above scales visible to the Tevatron so you avoid conflict with experiment.

    As far as anyone can tell, the Landscape is so extensive that, within experimental accuracy, you can get any values of the standard model parameters you want. There also are good arguments that, if the landscape exists, you can’t ever hope to calculate these parameters, for computational reasons. This conjectured discreteness is not a viable route to falsifiability.

    Sure, maybe when the LHC is turned on, it will turn out that the fundamental string scale is such that we haven’t seen its effects at the Tevatron, but will at 7 times higher energy. After all, the string scale could be anything. There’s just not a shred of evidence for this, it’s pure wishful thinking.

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  • David B.

    Peter:

    You’re acting as a bully: Every time someone writes something that tries to capture why we do what we are doing, trying to capture some of the excitement about the work we do, you come and try to stomp over our arguments to show why your opinion counts so much. I don’t buy that.
    You just believe that if you heckle enough, you win. Well, you don’t. I won’t asnwer any more of your questions on this thread, so don’t bother asking.

    The whole issue of the GUT scale, is that the most conservative models of string theory have the string scale close to the Planck scale.

    The universal prediction of strings (if they are sufficiently weakly coupled, and the indication from the standard model is that particle physics is weakly coupled at high scales) is an infinite (or very long) tower of states of very high spin, with approximate Regge behavior, and the Regge slope is governed by the string scale.

    The big question is if that scale is near or far. If it is near, we are in luck. If it is far, we have to content ourselves with low energy approximations. People have built many models of string physics that resembles the standard model, but does not get all the details right.

    You don’t like the landscape, well, I don’t either. That does not mean that string ideas are worthless and that we are all wasting our time. We have good reasons to do what we do. I was posting what some of those reasons are. You have all the right not like them for yourself, but some of us find them very interesting. You seem to be incapable of understanding this one point: that we do what we do because we believe that what we are doing is important, and your argumenst are not convincing for peple who have studied the subject and are working on it.

    Have a good day.

  • Lee Smolin

    Dear George,

    Thanks for persisting in raising the issue, “I long for a debate where we roll up our sleeves and solve problems rather than snipe. For instance, I think we can find common ground on the fact that the system of science funding in this country is broken; the grant process devours too much productive time and discourages out-of-the-box thinking of the sort Peter thinks is neglected.”

    This is the discussion I hoped to stimulate by writing my book. This is why the discussion of string theory takes only one of four parts, and why the last of the parts is devoted to raising this question and making some concrete suggestions to address it.

    I have lots of evidence that senior people in a wide range of fields worry about these same issues. I quoted from some of them in my book, such as a biologist who was formerly the president of the NAS, and since writing it I have heard from other senior people across the sciences who worry about these issues in their fields.

    I like your suggestion of universal 5 year postdocs, there are risks of course, but in my view greater benefits. It is very important that you emphasize that compared to the overall US science budget (or even just the NSF budget) such a program would be cheap. Other suggestions I made are equally cheap such as mimic the system of Royal Society Fellowships that can identify very independent original thinkers and jump start them into faculty positions. If we fund every recent Phd in science with the rare capacity to formulate while a postdoc a novel and ambitious research program, that also would be cheap, because such people are a small percentage of the people who do get funded.

    Certainly some of these people would find that their ideas, when explored, lead nowhere. But it is an easy bet that much progress would result in science coming from the development of ideas that are going to have trouble getting supported in the present environment because they don’t fit into any decades old research program led by senior scientists.

    Given that many prominent and experienced people agree with your and my estimation of the problem, what I want to spend time discussing is how to fix the problem by getting proposals like this implemented. As you emphasize, what is required is not that expensive, nor is it that experimental given that there are good models to study in the policies of other countries and fields. So while blog discussions are a useful starting point, and I look forward to seeing if others answer your challenge, this duscussion can only be a prelude to discussing how to get proposals concretely implemented by public and private foundations and universities.

    Thanks,

    Lee

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    David B.,

    I’m not heckling you, bullying you, or “stomping over your arguments”, or trying to “show why my opinion counts so much”. I’m making objective statements about what the problems with the “Landscape”, and thus with string theory are. If something I write is inaccurate, all you have to do is point out where the inaccuracy lies. If you don’t want to take the time to do this, don’t. But attacking me in personal terms is not an answer to the scientific issues I am raising.

    In the end, your answer to the arguments about fundamental problems with the research program you’re involved with is that you’re “excited” about what you’re doing and you think it is “important”. That’s fine, every scientist should be excited about what they are doing and think it is important, but that’s not enough. The people at the Discovery Institute are excited and think they’re doing something important. Scientists are supposed to have something more: solid answers to the question of how their work is someday going to be experimentally testable and may lead to a deeper understanding of nature. Right now, string theorists are able to give some reasonable answers to this question for part of their research program, that concerned with using string theory to understand QCD. But as far as using string theory to explain anything about the standard model Lagrangian, the landscape has made this impossible.

  • http://tyrannogenius.blogspot.com Neil B.

    Folks might want to check out my discussion of justifications for why space needs to have three large dimesnions in classical terms – no string theory etc. needed. It’s based on comparing EM interactions in model universes of different space dimensionalities. Check the blog (May 05, 2006). I know I have been remiss on keeping it up, but if I get some new comments I’ll try to put up some new posts.

  • David B.

    Peter:

    You admit that string theory might be useful for QCD. But then you turn around and say that research in string theory is useless and that we should give up, mainly because you don’t like the landscape. You say your arguments are technically accurate. The arguments I gave you are also technically accurate, so then what? String theory is not just about the landscape. It is much richer than that.

    When I wrote my piece, I said that it was my personal opinion and then you went straight for trying to argue about the landscape and had all kinds of technical objections. I felt that you were getting personal so I said so. I said that you are acting like a bully and are a heckler. I did not insult you. I was making what I believe is an objective observation on your behavior. This pattern has repeated itself many times: there are many instances of other people getting tired of your style. I’m not particularly tactful sometimes. I try to be direct. Sorry you got hurt. I get frustrated, just like the next guy.

  • http://golem.ph.utexas.edu/~distler/blog/ Jacques Distler

    You can get virtually any number of generations, any gauge group, any fermion representations, any Yukawa couplings, etc.

    I don’t see the relevance of the existence of a large number of string vacua that look nothing like the real world, particularly since the Standard Model iitself has a landscape of vacua that look nothing like the real world.

    The problem with the landscape, and with the string theory framework in general if you believe that it includes the landscape, is that the nature of the vacua is so varied and complex that, as far as anyone can tell, you can get just about anything you want

    Endless repetition does not make it true. Your “objective statements about what the problems with the ‘Landscape'” (#) are nothing more than a guess at an answer to a question that is still very much open

    Perhaps your guess is correct. Most likely, it isn’t. No one knows (though everyone seems to have a strong opinion).

    I should point you to comment 39 (and countless posts on my blog) where I argue the contrary position.

    But, in all likelihood, that would be futile. I hold no particular hope of convincing you of anything. But it would be a grave disservice to the non-expert readers (assuming there are any left) of this comment thread to allow you, unchallenged, to pass off your opinions on the subject as established facts.

  • http://www.math.columbia.edu/~woit/blog Peter Woit

    David B.,

    I don’t claim “string theory is useless”, I do try and be careful to say that it seems likely to be useful for some purposes (a dual to QCD, mirror symmetry in mathematics), just not others (understanding where the standard model comes from}. Maybe someday someone will come up with a very different form of string theory that will give insight into the standard model, but what I see now is just a massive effort to study complicated backgrounds and justify why they can’t be used to make any conventional predictions.

    I’ll take your comments about my style of argumentation into consideration. On the whole, I’d rmuch rather be convincing people than pissing them off…

    Jacques,

    Not much point in trying to convince you of the untestability of string theory, since you’re the only string theorist I know of who has recently issued a press release claiming to have a way to test string theory next year at the LHC. There is the minor fact that no one seems to believe this except you (including the referee of the paper….).

  • Gina

    George wrote: “Peter, what would you think about automatic postdocs for all new physical science Ph.D.s? You get a Ph.D., the NSF gives you a five-year postdoc, no need for applications. In the NSF budget, this would actually be a fair small amount. Five years would let you dive into a topic, maybe one very different from your dissertation, and give you several years before having to turn your attention to your next career move.”

    and Lee wrote: “I like your suggestion of universal 5 year postdocs, there are risks of course, but in my view greater benefits. It is very important that you emphasize that compared to the overall US science budget (or even just the NSF budget) such a program would be cheap. Other suggestions I made are equally cheap such as mimic the system of Royal Society Fellowships that can identify very independent original thinkers and jump start them into faculty positions.”

    Automatic five-years postdocs for all new Ph. Ds in physical sciences is problematic. For one thing, getting a postdoctoral position is an important step in the academic selection of the better Ph. D graduates towards academic positions. Delaying the time when people will know if they can get into academic life or have to quit can be bad for the researchers themselves as well as for the universities.

    Such a move will probably increase the overall number of people getting Ph. D in physical sciences. I am not sure if it is desirable and it can only magnify the problems it meant to solve. Of course, like in everything else we discuss the details are quite important.

    Similarly, Lee’s suggestion for special programs for original researchers is problematic and may give the opposite incentives regarding such researchers. (I tried to analyze in some details this specific suggestion in a comment to Asymptotia tea cup VI.)

  • http://golem.ph.utexas.edu/~distler/blog/ Jacques Distler

    Not much point in trying to convince you of the untestability of string theory … no one seems to believe this except you (including the referee of the paper….).

    Yes, your unshakable conviction that String Theory is inherently untestable is every bit as solidly grounded as your speculations about the refereeing process on that paper.

    In a way, I’m kinda glad that you immediately tried to change the subject, and didn’t even attempt to respond the scientific points raised.

    That, in its own way, is progress…

  • a

    Jacques, a few years ago a possible outcome of strings seemed

    (a) a failure (this often happens even when doing good research)
    (b) masked as a success by propaganda.

    For example, somebody might have claimed that strings have been tested because WW scattering at LHC obeys causality, or that the string landscape exists because after compactifying the Standard Model one gets a few vacua, or …

    Now (b) seems avoided.

    If you or anybody else will avoid (a) by getting real physics out of strings, it will be great. Nobody wants to prevent it.

  • Marty Tysanner

    I am really hoping comments #192, #193 and #195 do not signal the start of yet another cat-and-dog fight between apparently implacable foes…

  • Joseph Conlon

    Hi Peter,

    You say and have said several times that string theory/phenomenology is a failure because it can never say anything about low energy physics; the landscape renders this impossible. In particular, you say that `as far as anyone knows, string theory has solutions with any possible effective field theory at LHC scales.’

    If you think that, then no wonder you think string phenomenology has failed as a research program. Indeed, if that were true, it would have.

    The problem is the statement isn’t true, or rather that there is no evidence it is true. For example, consider the IIB flux landscape. Maybe if all scales in the compactification are Planck-scale you can get almost anything. I don’t know. But now put the hierarchy in, specifically low-scale supersymmetry and a TeV-scale gravitino mass. When do this, you then start getting relations among the low-energy scales. For example, the soft terms are suppressed compared to m_{3/2} by a factor ln(M_P/m_{3/2}) and moduli masses rise by the same fashion. This holds in both the ways used to study TeV-scale supersymmetry in this framework, namely the mirage mediation models where W is fine-tuned small and the large-volume models I have worked on.

    So, rather than vague musings about the swampland, here’s a concrete question: can you give a IIB flux landscape model, with a low-scale gravitino mass, such that the soft terms are suppressed by ln(M_P/m_{3/2})^2 compared to m_{3/2} and moduli masses enhanced by this factor?

    While this post has focused on the narrow issue of light gravitationally coupled particles, you can extend this to the more interesting question of soft terms: what soft terms do you get from what string construction/moduli stabilisation mechanism? Again, there isn’t any evidence to suggest that the answer to this question is simply arbitrary, and indeed this is what lots of current research is on.

    To summarise: I don’t think anyone expects to go uniquely from zero free parameters to the Standard Model. But once you start putting scales and hierarchies in the compactification, then all the evidence is that you get non-trivial relations between the low-scale `observables’. If you wish to argue the contrary, I think the burden is on you to show that this does not hold.

    All best wishes
    Joe Conlon

  • http://golem.ph.utexas.edu/~distler/blog/ Jacques Distler

    197.I am really hoping comments #192, #193 and #195 do not signal the start of yet another cat-and-dog fight between apparently implacable foes…

    That would, indeed, be tiresome (and none would find it more tiresome than I).

    But there’s an important scientific point at stake — one which cuts to the heart of Woit’s “untestability” argument. Lots of people (Clifford Johnson, most notably) have tried to challenge Peter on his blithe assertions on the subject, with little success.

    I doubt that I will succeed either.

    But, as David B discovered, one can’t discuss any of the positive reasons for studying string theory, without Peter butting in to repeat his assertion that the Landscape makes string theory untestable (and hence, not even wrong).

    The best that I, realistically, hope to achieve is that ‘interested bystanders’ (such as yourself) will realize that Peter’s assertions are, at least, questionable.

    Hopefully, that won’t require another 300-comment thread that seems to go absolutely nowhere.

  • http://www.math.columbia.edu/~woit/blog Peter Woit

    Marty,

    I’m not even trying to respond to Jacques’s repetition of his usual attacks on me for the obvious reason you mention. Anyone who wants to know my argument for why string theory is untestable can find it at
    http://www.math.columbia.edu/~woit/testable.pdf.
    Anyone who wants to know why I think it would be a mistake to try and have a serious discussion with Jacques can take a look at the result of any of my large number of attempts in the past and see where they went. Or, for entertainment, take a look at his press release claiming to show that string theory is testable at the LHC, and compare it to the preprint and published versions of the paper it is based on. Other theorists have publicly characterized this as “hilarious”.

    Joe,

    In any particular class of models, I don’t doubt that once you make certain choices you get certain constraints. I’m not claiming that these models are infinitely malleable. If you set the scales of the theory in a specific way, you’ll presumably get certain relations. But the scales could be anything: we don’t know what the supersymmetry breaking scale is. The anthropic landscape people, on some days, say that they may statistically “predict” that it will be high, not low, in which case your relations won’t hold.

    The set of compactifications string phenomenologists look at is extremely complicated, and getting more and more complicated as time goes on and people find new constructions. I’m not claiming to know what the ultimate end-point of the structure of that set would be if people spend the next millenium investigating it, following the vision that many string theorists seem to have for the future of particle physics.

    What I am claiming is that enough is now known about it that no one is able to use the string theory framework to explain why any of numbers that characterize the standard model have the values they do, or to predict what new physics will be seen at the LHC, or at any future higher energy collider. The theory really is untestable.

    This kind of untestability is precisely the conventional kind you often end up with when you pursue a wrong idea. Simple versions of the idea disagree with experiment, so you have to make things more and more complicated in order to avoid contradiction with experiment. Introducing branes and fluxes can stabilize moduli and avoid predictions of unobserved long-range forces, but the cost of avoiding these predictions you don’t want is that your framework becomes not rigid enough to make solid predictions. I just don’t think it’s a controversial statement to note that there are no such predictions from string theory about LHC physics, or that we’ve been led to this situation by having to abandon simple string theory compactifications because they disagree with experiment.

  • Thomas Dent

    For some mysterious reason my prevous comment disappeared! I’ll try again:

    Should we not already count the popular books written by ‘string people’ which, without specifically addressing the vocal critics, do attempt to give a good picture of the current state of research? For example those by Brian Greene, Lisa Randall, Lenny Susskind. I think this kind of book is a much better use of time and effort than pursuing “the intestine shock and furious close of civil butchery” which the public debate currently resembles.

    Is it worthwhile for any ‘string person’ to write a book and go on a long publicity campaign *purely* in order to provide a counterweight to Woit, Smolin, Horgan etc. There are a few factors coming in here. First, that would take several months, and few string-ers want to take such a time off from actually doing research. It seems to me the books and publicity blitzes are coming from people whose research field is rather less crowded and busy than strings, who therefore, on average, have more free time… Second, if the arguments being offered against string theory are sociological or irrelevant or highly subjective, and it seems that many (I don’t say all) of them are – judging a theory by the amount of nervous laughter? – is it worth anyone’s time and effort to go into detail rebutting them? Who on earth would read a book specifically devoted to answering or debunking everything said by Woit and Smolin?

    T

  • Thomas Dent

    PS on ‘testability': gauge theory per se is, by the same standards, untestable, since you can construct a lot of strongly-coupled nonperturbative models in gauge theory that simply can’t be calculated. (Technicolor, anyone?) Electromagnetism, electroweak theory and QCD in certain regimes have turned out to be testable because, mainly, of sheer luck: we happened to encounter them in a regime where they can both be calculated and experimentally probed.

    T

  • http://eskesthai.blogspot.com/2007/04/finiteness-in-string-theory-landscape.html Plato

    As a lay person following the debate on the issue of Finiteness in String Theory landscape was the point technically reached that I was referring too.

    David has been careful to lead us through this and as a layman I am watching the way he is describing, so I am learning, as I learnt in other debates.

    I hope Jacques that you would encourage David instead of express the futility of such an debate, I have learnt as so many others that you have to “talk past a certain point” if you can no longer get the subject moving beyond the ole rhetoric.

    So while learning the difference between the “Fitness landscape” and the “String theory landscape, I learnt the difference is the “finiteness issue in the String theory Landscape?” This then been carried to the issue of Mandelstam and the triple torus?

    So this in itself was what allowed us to say that the string theory landscape was indeed working toward the issue of Finiteness with which many have found to be a problem.

  • Hendrik

    Moshe #149 (and Gina #168), my experience of ST is quite the opposite to
    your very lyrical description of an effortlessly unfolding string theory.
    (Mine is a clunkier mathematical physics point of view.)

    “quantizing a relativistic string”:-
    First, quantization is not an algorithm, there are serious mathematical
    obstructions (cf. http://arxiv.org/abs/dg-ga/9605001 ).
    Full quantization maps generally only exist on small subalgebras of the full Poisson algebra, and if they do, they need not be unique.
    OK, but let’s say you have decided for the string what your quantum observables, their algebraic relations and gauge transformations/constraints are by some method.Then you need to realize (represent) them as operators on a suitable Hilbert space, but here you find that you need to do it on a Fock-Krein space, and so the usual spectral theory is not accessible to you. (You require the spectral theory to integrate up your generators of symmetries, evolution etc, since after all we need finite transformations in real life).

    OK, so let us say you have managed to integrate up the generators of your symmetries (and it can be done, but it is hard cf. Comm. Math. Phys. Volume 156, No. 3 (1993), 435) then you need to encode your unbounded operators into an algebra of bounded operators (C*-algebra), so you can have access to different representations, and this can be done too, at least for the open bosonic string (cf. Comm. Math. Phys. Volume 156, No. 3 (1993), 435). [You need these other representations since even mild interactions move you out of your given representation, cf. J. Math. Phys., Vol. 26, No. 6 p1280, 1985, and constraint conditions can be insoluble in your original representation, but soluble in others cf. Lett. Math. Phys. 15, 205 (1988)]

    OK, so now you need to enforce your constraints, and immediately
    you see that in your initial representation there is no solution
    except in dimension 26. However, this is a representation dependent
    phenomenon and you can avoid it by going to other representations,
    but that is not the usual way…. So, you decide perversely to accept that the
    universe is 26 dimensional and forge on. The method by which you choose
    to enforce the constraints (BRST) is known to give different results
    from the usual Dirac method (for some quantum constraints),
    and it often needs to have ad hoc additions to work (I have a PhD student
    working on the maths of quantum BRST), but you forge on.
    Next, you decide that you need fermions associated to your string, so you make it supersymmetric (despite the fact that no supersymmetry has ever been seen in nature). Mathematically this seems almost impossible, due to the obstruction theorem in Commun. Math. Phys. 159, 15-27 (1994), but only very recently someone did manage to set up mathematically a supersymmetric toy model in QFT, http://arxiv.org/abs/math-ph/0604044 so maybe if you work very hard, you can at least define an open bosonic supersymmetric string properly. But your perverse choice above (to stay in the original representation) created a problem, of what to do with the extra dimensions….

    So to me, the very start of the string enterprise seems very ad hoc with
    a lot of nonphysical components. You may say that for usual QFT we do not
    demand mathematical consistency from the start, but the point is that
    we do have it, and the initial (free) quantum fields are very easily
    defined at a mathematical level with a minimum of fuss.
    (Of course, once you add in interaction, it is a different story.)

    A larger issue than the elegance of the string, is the justification question,
    – the subject of fiery debate above. I think that ultimately, there can only be
    two justifications for a physical theory
    1) direct experimental confirmation of central predictions not obtainable by existing theory,
    2) a logically consistent extrapolation of experimentally well-established
    theory.
    Criteria of elegance, beauty etc. can only be a guidance for discovery, but
    definitely not an ultimate justification for a theory.
    ST at present is not justified in the sense of (2), and I think it is timely to ask for a justification in the sense of (1), given the large amount of effort, funds and jobs that has gone into it at a time when we have sufferred many cutbacks worldwide. Of course these points have been made and argued well in the books of Peter Woit and Lee Smolin.

  • http://tsm2.blogspot.com wolfgang

    Peter,

    > enough is now known about it that no one is able to use the string theory framework to explain why any of numbers that characterize the standard model have the values they do

    what do you think about the two papers discussed here ?

    The claim is that “F-theory with all matter coming from an isolated E8 singularity predicts three generations of fermions because of purely group-theoretical reasons!”

    Do you find such results at least interesting?

  • anon.

    “Electromagnetism, electroweak theory and QCD in certain regimes have turned out to be testable because, mainly, of sheer luck…” – Thomas Dent

    There’s no luck here: these theories were based on experimental data analysed by hard work, so they made predictions automatically by extrapolation of data. You find a model to represent data, and after development the model predicts things, which allows it to be tested. There is experimental data at each end, both in the input to the theory and in other tests of the theory.

    Light was predicted by unifying electricity and magnetism, both experimentally based sciences. The velocity of light is a combination of the electric and magnetic constants put into the theory from experiment. The prediction of neutrinos was based on experimental data for beta decay plus the experimentally based principle of conservation of energy. (Some string theorists defend themselves by pretending that the neutrino is a bit like stringy predictions because it was hard to test: but it was experimentally known that 2/3rds of the energy in beta decays was disappearing, and by conservation laws the neutrino was predicted from this experimental data.)

  • http://eskesthai.blogspot.com/2007/04/finiteness-in-string-theory-landscape.html Plato

    #205

    F-theory with all matter coming from an isolated E8 singularity predicts three generations of fermions because of purely group-theoretical reasons!

    >

    hmmm….. is “theoretics” a valid research area without experimental verification? :)

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    wolfgang,

    I haven’t read the relevant paper, and Lubos’s blog entries aren’t exactly reliable sources of information, so I don’t know exactly what that particular model achieves that others don’t. There’s a huge and ever increasing number of string theory models, keeping up with the details of all of them would be a full-time job. There are already vast numbers of string theory models that have three generations, so if getting that integer right is the main reason to pay attention to this particular model, no I don’t find it interesting. It doesn’t change at all the underlying fact that you can get any number of generations you want out of string theory.

  • amused

    Personally I think it’s best to take a `live and let live’ approach to these things. In physics we all place our bets by the topics we chose to work on, and then the onus is on each of us to show that our bets are working out by making demonstratable progress in research. If a research program is doing poorly, this will manifest itself in a lack of papers making major advances in it. Conversely, if the program is doing well, people will be able to say “Look, major advances on this topic have recently been made in papers X, Y and Z…” This is where the focus should be when discussing the merits of string theory (or any other research program). Without knowing the full details of how nature works and what surprises it might have in store for us I don’t think it makes sense to say that research program X has failed for reasons A, B and C. Instead, the argument should be: researchers on program X are no longer making major advances – cut their funding until such a time that they start making major advances again. People should of course be free to work on whatever they think is most interesting and promising, but in the knowledge that the onus is on them to make advances in their chosen topic (which will be compared against advances in other topics) and that if they don’t make sufficient progress then they will pay the price.

    It might seem that the question of whether some work constitutes a `major advance’ will often be controversial and not something that people can agree on. But I expect this will be less of a problem than people might imagine. The maths community seems to be at least as specialized and fragmented researchwise as physics, but they manage to reach agreement on such questions so I’m sure people in physics can as well if they put their minds to it. One important thing that I think is currently missing in physics though is a proper accreditation system for major advances. The mathematicians have this – the accreditation there comes through publication of the paper in a top maths journal. We could really do with something like that in physics as well and I hope people will consider it.

  • George Musser

    Gina makes a good point that automatic postdocs might merely put off the day of reckoning:

    Automatic five-years postdocs for all new Ph. Ds in physical sciences is problematic. For one thing, getting a postdoctoral position is an important step in the academic selection of the better Ph. D graduates towards academic positions. Delaying the time when people will know if they can get into academic life or have to quit can be bad for the researchers themselves as well as for the universities.

    Such a move will probably increase the overall number of people getting Ph. D in physical sciences. I am not sure if it is desirable and it can only magnify the problems it meant to solve. Of course, like in everything else we discuss the details are quite important.

    This might be addressed by combining the automatic postdocs with graduate “birth control”, i.e. fewer graduate-school admissions. To be sure, birth control has its own tradeoffs. Every system does; the question is whether it would be better than what we have now.

    One beneficiary of automatic postdocs would be lab heads. It would take off some of the pressure on them to bring in grants and maybe even let them do some research again.

    George

  • Thomas Dent

    ‘Light was predicted’? I thought light was already known of before Maxwell.

    Anyway, I wasn’t comparing EW theory or QCD to string theory; I was comparing *gauge theory*, in complete generality, to string theory.

    The gauge principle was first thought of by Weyl, and he used a real exponential transformation rather than an imaginary phase. Effectively, conformal transformations. Is this really a fundamentally useful thing to describe nature? We don’t know yet.

    Or take Yang and Mills. They invented a theory that, for several decades, seemed to be a total crock in terms of any relation to data – nonabelian gauge theory. They were lucky!

    T

  • Gina

    Dear George,

    It does not look that this modified idea is particularly good either. What is wrong with the current system?

  • Gina

    Dear Herbert

    I was impressed by your thoughtful and detailed comment. If I understand you correctly some of the smooth and inspiring steps that Moshe talked about are not so smooth for you as a mathematician. And you regard some of the steps (like the extra-dimensions and maybe also supersymmetry) as ad hoc and artificial. (Of course, different people may well have different tastes/point of view/etc.)

    I wonder if some of these difficulties or similar do not arise already for established physics theories like the standard model. (The usual interpretation of these difficulties is that mathematics is not quick enough to catch up with progress in physics.)

    You wrote:
    “I think that ultimately, there can only be two justifications for a physical theory
    1) direct experimental confirmation of central predictions not obtainable by existing theory,
    2) a logically consistent extrapolation of experimentally well-established theory.”

    It looks to me that ST is mainly aiming at item 2) (although not in a mathematics-rigor level) and there are also some (highly debated) thoughts in the direction of 1). There are also claims that any quantum gravity theory will have similar difficulties for item 1) as ST.

  • George Musser

    Gina asks: “What is wrong with the current system?”

    Lee and Peter have argued that string theory is a case of an instability in the system that overallocates resources to one field and starves others. Whether or not that’s the case, people do spend an inordinate amount of time writing proposals or postdoc applications. Hiring committees and grant review panels, faced with a huge oversubscription, tend to choose more conservative proposals from name researchers. The grant proposals themselves are sometimes written in a less-than-entirely-frank way. The whole system has a certain “prisoner’s dilemma” effect whereby individuals’ incentive is to submit as many proposals as they can, heightening the competition for each grant, even if collectively everyone would be better off with fewer proposals.

    Anyway, if anyone wants to continue this discussion with me offline, please send me email at gmusser@sciam.com. I’m really looking for viable alternatives to the present system.

    George

  • http://thecrossedpond.com adam

    George:

    I think that it really has to come down to a pit-fight. The younger, and often better physically conditioned, researchers will be able to use their youthful vigour to counteract the wilier street-fighting techniques of the more experienced rivals.

    Alternatively, a limited version of the ‘Quickening’ scenario from Highlander might be pursued, where everyone interested in a particular grant or position chases the others around the world with swords with the aim of beheading their rivals. There can be only one.

  • http://eskesthai.blogspot.com/2007/04/finiteness-in-string-theory-landscape.html Plato

    Gina:It looks to me that ST is mainly aiming at item 2) (although not in a mathematics-rigor level)

    I am not sure how you can write that knowing some technical issues presented.

    George from following the discussions, it seems to me to be a smoke screen that’s been put up by Peter and Lee that leads away from the issues. Knowing one’s perspective views on “another area” let’s say one’s version of the landscape” seem to me to indicate that such decisions based on that position would also develop from that point of view. Look to support that position. See all the “injustices” in the world?

    If you can show that the position Peter has adopted was just as flimsy as he purports of string theory and his forgone conclusion, then that has to be taken out of the equation?

    The merits of the landscape issues are still being worked out? String theorist have confronted Peter on the technical issues?

  • http://tyrannogenius.blogspot.com Neil B.

    No interest here in other approaches to the question of space dimensionality, despite the theme of skepticism about string theory? I hope some could at least check my blog, Tyrannogenius, for curiosity’s sake. I discuss how comparisons of E&M interactions in different spaces show preferability of three large space dimensions. This is not a rehash of existing facts of the specialness of 3-D space, but points to novel inconsistencies found in other spaces.

  • Lee Smolin

    Dear Gina,

    No doubt selection has to be done at some point, based on some criteria. The question is when it is best done, and what the criteria should be. There are basic requirements like, mastery of the material and tools of the subject, ability to do the research, produce correct results, write them up etc, all of which should be the criteria to get a Ph.D. Once you get past that stage and consider the group of people who are in fact contributing to research during their Ph.d. my view is that the most important predictors of future impact on science are intellectual independence, creativity, originality and originality. How many original ideas do they come up with which are aimed to solve key problems? How willing are they to take risks on their own ideas rather than follow others and do “me too science”? I once asked Stu Kauffman how you tell which scientists will have the original ideas that lead to breakthroughs, he said, “its easy, by the time they are a few years out from the Ph.D they have already had and published several highly original, in some cases, surprising ideas.” Some will work, some won’t but the ambition, creativity and originality will be clear. My observations after many years in research centers and institutes hiring postdocs is that this is correct.

    Here is one thing that gives me pause. The great generation that made American science dominant in the world, hired from the late 40’s to the 60’s faced a very different situation than we do. Before the early 70s there were in many fields more open faculty positions than new Ph.d.s. There was consequently selection for who went to the elite places, but much less overall selection for which Ph.D’s got to have a career in science at some university or college. Many people in this generation I’ve spoken to never applied for a job-even for a first job after their Ph.D.

    Now this generation did great science which dominated the world. Since the 70s we have faced a situation of vast over production of physics Phd’s relative to faculty jobs in research universities and institutes. So we spend a lot of time and effort on selection. My question is, do we do this well? Do we use the best methods and criteria, in the interests of the progress of science, or do we use methods and criteria that disadvantage the kind of people I described above in favor of people with less originality and independence? My thesis, which is defended in the book, and supported by many statements quoted there and elsewhere by senior scientists in different fields, is that we do not do a good job of this and that we make it too easy for careerists with lots of competitivity and little originality and too hard for those who are really original and independent.

    When there was little selection we naturally got a wide diversity of types of scientists, which was good for science. My view is that we need that diversity, we need both the hill climbers and the valley crossers, the technical masters and the seers full of questions and ideas. My worry is that having to institute narrow selection, we have done it badly, in a way that narrows the diversity of types of scientists we need for the progress of science. My conviction, however, is that this is easily fixed, by changing the criteria and methods of selection to ensure we get the full range of types and characters we need for science.

    Thanks,

    Lee

  • Mike

    @ Count Iblis #92
    I don’t think (at least I don’t hope as far as I am concerned), that string theory is loosing credit in the public, just because it
    was “overhyped” in the past. After all, this is about science and I never get bored by electromagnetism or general relativity. I rather agree with what you say in the second paragraph. To me loop quantum gravity looks more interesting than string theory, is because it addresses the question “what is space” in a fundamental way, whereas string theory just puts strings in the same old Minkowski space, where the point particles of field theory are sitting in. Out of the approach of loop quantum gravity naturally comes the question, to what accuracy Lorentz invariance describes nature. These are the kind of good experimental questions then, which bring science forward even in the case of a negative experimental result (Lorentz invariance confirmed in the experimental bounds). Admittedly string theory has a similiar merit by encouring experiments to check for the strength of gravity in the low distance regime and thus looking for extra dimensions. This is, why I perfectly agree with Smolin to have a diversity of theoretical approaches, especially in the present time, when nobody can clearly claim to know the way ahead.
    What also somebody from the public can do (and what every person does in his daily life, when he has to rely on “experts”), is to judge those experts from their social behaviour. And here I can’t see, why a person like Smolin is not invited as a speaker on the strings main conference. He can’t be such a bad scientist, that it is not worth for the string theorists to listen to him and therefore abandon one of the many talks on the “landscape” problem.

  • Marty Tysanner

    Jacques (#199),

    You wrote,

    That would, indeed, be tiresome (and none would find it more tiresome than I).

    That is reassuring, but I don’t understand why you would invite a pointed response by an unnecessarily antagonistic “aside” to Peter in your otherwise reasonable comment #192:

    But, in all likelihood, that would be futile. I hold no particular hope of convincing you of anything. […]

    Back to comment #199, you say

    But there’s an important scientific point at stake — one which cuts to the heart of Woit’s “untestability” argument. […]

    Good. And most of the rest of us would get a lot more out of your commentary and not be left a bad taste in our mouth if you and others just addressed those points and left the personal jabs and innuendo completely out of the discussion.

    I’ll get off my soapbox now.

  • Gina

    Dear Lee,

    Many thanks for your kind comment.

    One clear advantage of the American system (compared e.g. to continental Europe) is that scientists are becoming academically independent at an early stage. When a young scientist has a solid tenure track or tenured position she can pursue science in the way that suits her best. (Whether to solve hard problems by others or pursue her own agenda or one of many other possible ways to practice science.) Indeed, few years out of Ph. D. is often a good time to make the call.

    Probably nobody disagree that originality is an important merit of a scientist and an important ingredient in hiring decisions at all levels. Different scientists and different departments may have different weights on various criteria for hiring, (and this diversity is good) but I am quite sure that originality is always considered as important.

    I do not see a need for administrative measures giving extra incentives (say, for originality or risk taking) on top of the usual methods departments use in their hiring decisions. Moreover, understanding the precise incentives administrative methods like the ones proposed here (automatic 5-years post-docs), or in your book (and maybe also in Peter’s book, I do not recall right now) is often a tricky business. In the few examples I looked at, the specific proposals you and others suggested may well lead to an outcome opposite to the intended one.

    (BTW, the new terminology of valley-crossers and hill climbers is very nice.)

  • http://golem.ph.utexas.edu/~distler/blog/ Jacques Distler

    And most of the rest of us would get a lot more out of your commentary and not be left a bad taste in our mouth if you and others just addressed those points…

    OK … so, from your perspective, what more do I need to say?

    (If you want formulæ, perhaps we could move this over to my blog, where technical discussions are possible. Tell me what you want to know and, if need be, I’ll craft a blog post in response.)

  • Gavin Polhemus

    Peter,

    In #146 you responded to my question.

    Personally, I’m actually not so interested in a “consistent theory of the SM and gravity” if it is highly artificial, mathematically ugly, doesn’t explain much of anything about the world, and is completely untestable.

    Since we have no consistent model of SM and gravity at present, I’d be happy to see one even if it is as ugly as you describe. It would be a huge accomplishment, in my opinion, to have a single theory that is consistent with every piece of data that we have.

    Certainly, I will be happiest if that model is natural, mathematically beautiful, and unique so that it predicts the result of every future particle experiment and future cosmological observation as well. Do you see any avenues for achieving such a special theory? I don’t.

  • Clastito

    I saw a long physics documentary that continuously adressed string theory, so at least someone has done his job.
    I speak as someone who has not the mathematical knowledge to understand the coherences they claim they have discovered through string theory. If you say you’ve made the mathematical demonstration, that the numbers fit nicely, so it must be, but I still cannot tell for myself.
    So much enthusiasm in physics around this is important, I know many brilliant minds have pursued ST.
    Sometimes scientific movements like this end up “intellectually bankrupt” (for instance, haeckel’s fundamental biogenetic law). Some scientific movements use a basic idea or argument, a “truth” that can outshine the insufficiencies (which are eventually unavoidable).
    At least I am sure that has been a problem with some movements within the history of biology (look up the “dogmatic hardening” of the neodarwinians in the 50’s in Gould’s fat book)
    A diversity of points of view is most desirable. String theory will exist as long as it remains capable of attracting the minds of brilliant people.

  • bk

    Dear Jacques,
    There was an exciting post on the Reference frame about these papers
    which came out today:
    http://arxiv.org/abs/0704.0445
    http://arxiv.org/abs/0704.0444
    Could you please comment on this work?

    Thank you!
    BK

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    Gavin,

    The problem with string theory unification is not that it doesn’t predict the result of every future experiment. The problem is that it doesn’t predict anything. I might not be completely happy with it, but I’d accept an ugly unified theory that made some predictions that were confirmed. I just don’t see the point of an ugly theory that doesn’t predict anything. Just “consistency” (especially if it’s only “consistency” at the standard level of physics argumentation, which usually relies on experiment to keep things honest) is not enough.

  • Paul Valletta

    Stringtheory appeared on the scientific landscape, as a direct proposal to certain theoretical and physical unanswered questions. The “NEW” theory emerged with a mathematical formalism, that would take up the time and efforts of all fledgling genius’s, to the extreme.

    Out of the new theory emerged new maths, which branched out into the need for new institutions, where the priveliged few could be left alone to formulate the “answers” to the pressing fundemental questions.

    Answers were “not_forthcoming” with any real physical meanings, but what emerged were a plethora of “more” complex questions. For every question “early” stringtheory failed to answer, stringtheorists (who by now were looked upon as being Mathemagicians, or M-THEORISTS), created a vast pool of “More” questions, each question appeared, without the hope of having any real chance of giving a single answer, except in a “Magical”, or “Mysterious” way.

    The Anthropic Egg was layed, when hatched, this egg would grow with the appetite of a Steroid fed Rooster, that devoured all the available “corn” that was meant to be shared around the sustainable “scientific/experimental” farmyard.

    The Landscape was changed for ever, the cocks and hens that were reliant upon the corn for their existence in order to survive long enough to at least ask questions of stringtheory?, were reduced to the act of scavaging amongst the Rooster bird_droppings, this is no ordinary “humble pie”

    Having to eat_s*it for long enough, a few fledgling birds are starting to spread their wings, and have learnt to leave the nesting grounds and fly away to a more sustainable landscape. Soaring high above, they can look down and see that there is more than one farmyard landscape, in this “new emerging natural” landscape, questions are tackled on “first_come” first served basis.

    Stringtheory itself has a world “historical” line?..if they look at this historical timeline, then how can they defend the simple fact that the early reasons for their existence, have still not been addressed?..1984, and the “theory of everystring” has not been a good working hypotheses.

    It has raised more.. more…MORE!…. exponential questions than answers. Stringtheory, by it’s very nature, is mathematically unworkable.

    The Landscape needs to be turned into a new Garden. From it will emerge testable fruits that can be managed
    and regulated, so it’s produce are not just sweet smelling, but fodder proof !

  • Haelfix

    Peter.

    Assume for the sake of argument that in the midst of every possible vacua of string theory, one day someone found something that looked exactly like the standard model, with a rather pleasent phenomenological spectrum at low energies. (Say something like a supersymmetric SO(10) gauge group theory, with the right suppression of fcncs, 3 generations, and a low amount of exotics, etc etc).

    Assume also that someone managed to show that their was a mechanism that made the remaining vacua’s phenomenology extremely hard to deform into this particular one, so at the very least it looked somewhat unique.

    Would you still object so vigorously to the construction?

    You might claim its wishful thinking that we find such a thing, but do you object to scientists following their hunches and looking for precisely that?

  • Marty Tysanner

    Jacques invited:

    Tell me what you want to know and, if need be, I’ll craft a blog post in response.

    I’ll take you up on your offer. Since the issue of relevance was Peter’s objection to the landscape in this forum, it would be nice if you could answer my four questions/queries here first, at least briefly. If you think additional elaboration would be better on your blog, that’s fine with me.

    1. I don’t yet see the “standard model landscape” as a very compelling analogy to the string landscape. The standard model is (presumedly) an effective theory, developed with significant empirical input rather than derived as a logical consequence of a more general theory. Thus, we have no way to know at present whether most of the parameters of the standard model are derivable from a more fundamental theory that contains gravity. We also don’t know whether a more fundamental theory will contain the standard model as it currently exists or something much more extensive; hence, there is no way to know whether a landscape is inevitable. At least the way I understand it, the landscape was a very unwelcome addition to string theory, a consequence of a need to allow vacua that accommodate the observed accelerating expansion of the universe. So on the one hand it appears we have a conjectured landscape that might only exist if the more fundamental theory takes certain forms, while on the other hand the landscape is inherent if the more fundamental theory is to account for cosmological observations. Perhaps you can expand on this.

    2. You point out that it is far from clear that the 100+ independent couplings of the MSSM can be independently adjusted. It isn’t clear to me how a “minimal” supersymmetric extension with 100+ parameters is an improvement over the standard model which has far fewer parameters; in my mind a more fundamental theory should reduce the number of the existing theory by deriving at least some formerly unexplained inputs, but that may just be my sense of aesthetics. The hope I have heard from MSSM proponents is that constraints will be found that relate many of these parameters, and hence substantially reduce their number. Is this is the hope you spoke of, which seems to me to be independent of string theory, or were you referring to specific string theoretic reasons for believing that not all of the various couplings are independent?

    3. Are there any specific, string theoretic reasons for believing that only an extremely sparse set of vacua within the landscape can actually lead to universes that are compatible with life (whatever “life” is supposed to be)? That is, do any conjectures or other hints exist that indicate it is unlikely that two very similar solutions exist which equally well “predict” everything that we already know about our universe? Peter’s central point regarding the landscape seems to be that the answer is no, and will remain “no” regardless of any future experiments. (I’m excluding experiments that might show violations of Lorentz invariance, analyticity, and unitarity which, as commenters to an earlier post by Peter on the subject pointed out, are assumptions of almost all theories that people currently take seriously, not just string theory.) Do you disagree for specifically identifiable string theoretic reasons?

    4. Assuming you believe the overriding goal of the string program is to obtain a scientific theory that gives deep insight into the most fundamental nature of the universe, do you believe that if the answer to my third question is “no” that it would be wise to shift at least a small amount of resources from the string program to the exploration of other speculative approaches to the same goal? Do you think it would be wise to make it easier for grad students with new ideas of their own related to “fundamental physics” to explore their non-string ideas as a thesis topic, even within a department dominated by string theorists? (It may sound like I’m trying to lead you to a particular answer here, but I am actually interested in your perspective as a string theorist on this issue.)

    Thanks!

  • Alex Nichols

    Sean Carroll has suggested in “Spacetime and Geometry”, that a consequence of a string-based scalar-tensor theory of gravity would be unambiguous measurable departures from ordinary GR.

    He’s also suggested that detection of gravitational waves could provide a test for the proposed spin-2 graviton.

    Are the opponents of string theory suggesting that there is any reason in principle for such tests being invalid?

  • Gina

    Dear Lee,

    There is a claim in your comment and book which deserves further consideration

    You wrote: “My thesis, which is defended in the book, and supported by many statements quoted there and elsewhere by senior scientists in different fields, is that we do not do a good job of this and that we make it too easy for careerists with lots of competitivity and little originality and too hard for those who are really original and independent.”

    Certainly, this is a central thesis in your book and there are several anecdotal examples and quotes from prominent people which seem to support it. I cannot say that I see a solid case for your claim or even see a clear suggestion how to study it. Still, this claim is somewhat appealing so let’s take it for the sake of argument for granted.

    Suppose you have this great original young valley-crosser that you think deserves a position in Princeton or any other top place. Instead, because of the alleged bias he found a position in a second level university say Penn State. So what? He can make his original contributions from Penn State and when his ideas will prevail he will either move to Princeton or Harvard or else stay loyal in Penn-State and move his department to the highest level. And if he deserves a place in a second level university and will have to work in a third level one, again I do not see why it matters so much. Overall, the terms for doing theoretical resaerch are quite similar. (There is a difference in terms of students but having graduate students working on very original and high risk projects of their supervisors is a tricky matter anyway.)

    With the divesity and large number of research universities even if you are right in your thesis I cannot see how it makes a big difference.

    Perhaps something we can agree about is that the more bold, original and far reaching the scientific (and other) claims are the more careful and skeptical we need to be in studying them. For example, you mentioned Stu Kauffman here and also in the asymptotia thread where you referred to his idea to derive far-reaching conclusions in the theory of evolution from a result from mathematics known as the “no free lunch theorem”. This is certainly a highly original and bold idea. Do you really think Kauffman’s idea has any merit?

  • Pingback: Are there hidden costs of bad science in string theory? « Quantum field theory()

  • http://golem.ph.utexas.edu/~distler/blog/ Jacques Distler

    I don’t yet see the “standard model landscape” as a very compelling analogy to the string landscape. The standard model is (presumedly) an effective theory, developed with significant empirical input rather than derived as a logical consequence of a more general theory. Thus, we have no way to know at present whether most of the parameters of the standard model are derivable from a more fundamental theory that contains gravity.

    The vacuum structure of the Standard Model, coupled to gravity is entirely determined by the low-energy field content (the graviton, the photon and the massive neutrinos). It is utterly irrelevant what the high-energy completion is. Indeed, even the inclusion of the electron (the next-lightest particle) makes only exponentially tiny corrections to the vacuum structure.

    At least the way I understand it, the landscape was a very unwelcome addition to string theory, a consequence of a need to allow vacua that accommodate the observed accelerating expansion of the universe.

    Unwelcome, or not, the existence of an exponentially large number of metastable vacua (once one fixes the moduli) is a feature of String Theory. Some of these vacua have positive cosmological constant; others negative. This would be true, even had it turned out that we didn’t live in a universe with positive cosmological constant.

    You point out that it is far from clear that the 100+ independent couplings of the MSSM can be independently adjusted.

    “Adjusted” is, perhaps the wrong word.

    Let me remind you of a few salient facts about the Landscape.

    1) Consider an integer lattice Z^n. The number of lattice points inside a ball of radius R scales like R^n. In the IIB flux compactifications that people consider nowadays, n is the number of cycles on which one can independently place fluxes. The fluxes are quantized, and obey some tadpole cancellation constraint. So, to find the number of solutions, one is counting the number of lattice points inside a ball of some radius. Since n can be in the hundreds, this is a very large number.

    2) Another feature common to these models is that the degrees of freedom that give rise to the visible-sector gauge group and its matter content are localized on the Calabi-Yau. Most of the “n” cycles are disjoint from the locus where the Standard Model degrees of freedom are supported.

    In each of the R^n vacua, one has a low-energy effective theory. Most of these can (if we are particle physicists) be discarded immediately, because they look nothing like the real world. (It is exactly on these grounds that we ignore most of the landscape of vacua of the Standard Model.)

    What remains is still a very large number of vacua. These form a discrete set of points in the parameter space of (some supersymmetric extension of) the Standard Model.

    The fear is that they fill that parameter space “densely” (in the colloquial, rather than the Real-analysis use of the term “dense”). To within experimental accuracy, we would be able to “fit” any measurement of where we lie in that parameter space by one of these vacua.

    But there are solid reasons to believe that this fear is unwarranted. The vast majority of the “n” cycles are disjoint from the locus where the Standard Model degrees of freedom are supported. And so the precise distribution of fluxes on those cycles do not affect the renormalizable couplings of the Standard Model at all. Only n’ ≪ n cycles intersect this locus, and affect the Standard Model couplings. Rather than R^n points, densely filling the parameter space of the MSSM, we have a sparse set of R^n’ points.

    And thus, some real predictions…

    (Just to be clear, the cosmological constant, and possibly certain other soft operators, depends on the distribution of all n fluxes. So we still expect a dense set of values for it.)

    Are there any specific, string theoretic reasons for believing that only an extremely sparse set of vacua within the landscape can actually lead to universes that are compatible with life (whatever “life” is supposed to be)?

    I’m sorry.

    I am utterly uninterested in Anthropic arguments. Ask someone else.

    Peter’s central point regarding the landscape seems to be that the answer is no …

    Proof by assertion is not an argument.

    I’ve explained why I think it is likely that, when we manage to find a family of vacua which bear more than a passing resemblance to the Standard Model (so far, we haven’t), they will have a sparse distribution of values for the parameters — both those which have already been measured (which can, if you want, be used to further prune the vacua which bear looking at) and, more importantly, of the parameters we have not yet measured.

    Since we haven’t yet found the family of vacua we are looking for, my argument can hardly be called ironclad*. But it is a good deal more persuasive than the mere assertion than “You can get anything you want on the Landscape.”

    In any case, if you’re going to go around repeatedly making the latter assertion, then you have to explain why the above argument is wrong.

    Do you think it would be wise to make it easier for grad students with new ideas of their own related to “fundamental physics” to explore their non-string ideas as a thesis topic, even within a department dominated by string theorists?

    I am a firm believer in the proposition that graduate school is the time when you should work on all kinds of crazy ideas.

    Most students (even the very brightest) enter graduate school without much of an intuition for what will work and what won’t. Developing that intuition is a lot like learning to walk. You tend to fall down a lot. Graduate school is supposed to be a place where you can do that “safely.”

    I think it would be a terrible idea for graduate students to blindly follow some set of ‘marching’ orders from their professors.

    It sounds like you had a more specific proposal in mind. If so, you’ll have to explain what it is, if you want me to comment on it.

    * If we had, I wouldn’t be presenting you an argument, I would be presenting you a calculation.

  • Gavin Polhemus

    Peter,

    Do you see any approach to unification that will make testable predictions?

  • Gina

    Dear all,

    I like the analogy between scientists and mountain climber. Indeed, scientists are a little like mountain climbers. The sense of beauty of an unexposed territory, the loneliness, the prolonged difficulties, the need for stubbornness and flexibility. There are dangers in both occupations; For example, prominent hazards for mountain climbers are crevasses. Those (wikipedea tells us) are the slits or deep chasms formed in the substance of a glacier as it passes over an uneven bed. They may be open or hidden. In the lower part of a glacier the crevasses are open. Above the snow-line they are frequently hidden by arched-over accumulations of winter snow. The detection of hidden crevasses requires care and experience. Scientists’ crevasses are not deadly but they exist, and so is the danger of getting lost and of losing the skills.

    My approach (from my tea-cup VI discussion with Lee) that young scientists should not be encouraged to do high risk endeavors was part of my view that they should not be encouraged at all . In this spirit let me fantasize a meeting between Lee Smolin and a young Ph. D. candidate called Jeremy.

    Professor Lee Smolin: Please sit down. (Look at Jeremy’s file) I understand you graduated last year from Harvard University, .., straight A, … hmm junior thesis on the paper: “On the relationship between quantum and thermal fluctuation,” What bring you here, Jeremy.

    Jeremy: I would like to write a Ph D thesis under your supervision.

    LS: (looks at the file, this is the best file he saw for years…): I see. Let me tell you something right away Jeremy. A success as an undergraduate does not always mean a success in research, but looking at your file I am willing to take the risk and say that I think you will be able to write a good Ph D thesis.

    J: Thank you.

    LS: You must know that an academic job afterwards is not guaranteed. It depends on your success in research but also on many other factors.

    J: I am aware of that fact Professor Smolin.

    LS: (after a long pause). Young man, let me ask you a question. You did brilliantly at Harvard and you can really succeed in life. You can get out of here in one year with a Master degree and then go and become a successful man. If you want to be rich, you can go to business or high-tech and even to wall-street and if you want to build things you can go to engineering and if you want to help people you can go to med school. And whenever you go, you will be surrounded and work with real people, not mainly with formulas and computers. And, you know what, Jeremy, with a normal job, there is even a chance you will pay attention to your wife and children when they will talk to you rather than day dream about physics…

    J: But I want …

    LS (interrupts): Look, don’t give me an answer right away. Think about it. Take, two three weeks to think about it, Jeremy, and I will be happy to continue our conversation then.

    Lee of course knows that Jeremy will most likely come back, and will complete an excellent Ph D thesis. And then at times when he will be cold, wet and lonely on these mountains he will remember that graduate school was not something he was drugged to but truly his choice.

  • amused

    Hi Prof. Smolin, re.#217:

    What criteria do you propose to use to determine if someone is a support-worthy seer/valley crosser? One person’s seer may be another person’s crackpot. Where one person sees highly original, surprising ideas, another may see speculative, ill-founded nonsense. I don’t see how there could ever be an objective way to decide this. Even such eminent scientists as Feynman and Gell-Mann couldn’t agree about the merits of John Schwarz.

    For that matter, one person’s careerist may be another persons honest researcher who is just trying to do his/her best in the system they find themselves in. And I really don’t think you should invoke that kind of demeaning image to contrast against the type of people you would like to support. Criticizing sociological aspects is fine, and I also do it, but putting a question mark against the integrity of (some of) the people who succeed under the current system is just offensive. Without looking into their hearts you can hardly know whether careerism or desire to contribute to science is the underlying force that drives them.

    Please, rather than more social engineering (i.e. preferential weightings not only for research areas but now also for certain types of researchers) can’t we just agree that the thing that matters is to reward advances in physics in proportion to the size of the advance, regardless of whether it came in the form of an original surprising idea, a technical calculation, or whatever, and regardless of the topic the person is working on. If we can agree on that then I don’t think it would be so difficult to adjust the current system to implement it. The mathematicians have shown how it can be done. In exceptional cases accomplished senior people should have the possibility to step in and help a struggling youngster who they consider particularly promising (just as Gell-Mann did for Schwarz), but that possibility seems to be already there in the current system.

    Btw, I’m no historian but was under the impression that the rise of US science in the 2nd half of the last century was mainly due to the influx of many great scientist-refugees from Europe at the time of WW2. Are you sure it was not this but the availability of jobs that produced the rise in the US science level?

  • Thomas Dent

    Looking for ‘defence’ from string people?

    Then shouldn’t we already take into account the popular books written by them which, without specifically addressing the vocal critics, do attempt to give a good picture of the current state of research? For example those by Brian Greene, Lisa Randall, Lenny Susskind. I think this kind of book is a much better use of time and effort than pursuing “the intestine shock and furious close of civil butchery” which the public debate currently resembles.

    A big question here is whether it is worthwhile for any ‘string person’ to write a book and go on a long publicity campaign purely in order to provide a counterweight to Woit, Smolin, Horgan etc. There are a few factors coming in here. First, that would take several months, and few string-ers want to take such a time off from actually doing research. It seems to me the books and publicity blitzes are coming from people whose research field is rather less crowded and busy than strings, who therefore, on average, have more free time… Second, if the arguments being offered against string theory are sociological or irrelevant or highly subjective, and it seems that many (I don’t say all) of them are – judging a theory by the amount of nervous laughter? – is it worth anyone’s time and effort to go into detail rebutting them? Who on earth would read a book specifically devoted to answering or debunking everything said by Woit and Smolin?

    T

  • http://www.math.columbia.edu/~woit/blog Peter Woit

    Haelfix,

    What I think about this kind of hypothetical depends on the details. You conjecture something that looks just like the standard model, but describe something rather different. There are certain quite distinctive features of the standard model (gauge groups, representations, fermion mass matrices), which if you came up with a model which uniquely determined them, it might be convincing you were on to something (just getting the number 3 of generations is not like this). To be convincing, these would have to not be put in by hand, i.e. you’re not just looking at a huge class of models and picking out one that has desirable properties.

    If you found such a model, depending on exactly what it looked like, it might or might not be very exciting. If you could actually compute accurately some standard model parameters, or predict something beyond the SM that was tested and came out right, it would of course be highly convincing.

    The problem is that right now, if you look at any of the models people are studying, they are extremely far from this. I’ve looked at a lot of them, and all I see are things that don’t quite give the standard model, and are (unsuccessfully) being made more and more complicated trying to fit it. Maybe miraculously this will change and someone will find something very different. I just don’t see any reason to expect this other than wishful thinking, and wishful thinking is not a good motivation for a large-scale research program.

    Gavin,

    No, I don’t know of any really good ideas about how to get a testable unified theory right now. The best argument for string theory is that there aren’t other good ideas, but that’s not much of an argument for research on a speculative idea that clearly isn’t working. The crucial question for me is that of how to encourage people to try different things and look for new ideas, not keep pursuing one that isn’t working.

  • Lee Smolin

    Dear amused,

    I am sorry if I offended anyone, that was not the intention. It is better sometimes to speak plainly than to sound like a committee. It is simply true that there are people who try to game the system and pick their research topics based on an estimate of career advantage and there are people who have a deep desire to know and contribute and an aversion to playing competitive games. Granted many of us are mixes of both, I certainly was early in my career. Nonetheless, my claim is that something is wrong if the former easily succeed too often against the latter. We want the system to reward our best instincts, not our worse. This is an issue of values and I hope we can speak about them without seeming to offend people who may not share the values we advocate. The point is that any large system like the academy is not a law of nature, it is constructed in order to further the values of the people who build it and work in it. If we want to discuss how it works, we must discuss values.

    As to your points, of course people will disagree, this is one reason that decentralization is good. As to looking into people’s hearts, this is an unavoidable part of the process of selecting promising young people. One is opening up opportunities or not based on a bet on the long term success of someone, and motivation, ambition and character matter as much as the kinds of technical skills that can be tested objectively. One does this with a large dose of humility, knowing one can be wrong, but there is no way to avoid doing it. Every search committee and panel I’ve been on does it.

    It is true that sometimes senior people play the role of an angel (in venture capital terms) to protect a young person and a new idea. This is good. But it becomes harder to do as hiring and funding procedures become more formalized.

    I agree with you that what is required is not large changes to the system, but small adjustments. The kinds of things I and others propose in this direction is no more “social engineering” than the present system, and they are proposed mostly as additional initiatives. Indeed my point is that rather small changes could make a big difference. Small initiatives like founding one small institute, or starting a new foundation have in the last years made big impacts.

    Dear Gina,

    Of course one tries to discourage people, and conversations like the one you script have been part of the initial discussion with prospective grad students for decades. I do it and many people I know do it with all prospective students. The questions I am asking start a bit later, and concerns those who will not be advised or discouraged out of risky and ambitious attempts to contribute to physics. At some point, when a person has proved they have the ability to come up with new ideas that are ambitious and worth working on, they need our support.

    Lee

  • Gavin Polhemus

    Peter,

    The crucial question for me is “what should I study.” The lack of other good ideas may not be an argument for studying string theory, but “try different things” isn’t a very focused research plan.

    This isn’t an academic issue. I earned my Ph.D. and published a couple papers. Then I took several years off to be at-home dad while my wife established her career. Now my son is in school full time and my wife is a partner, so it’s my turn to pursue my interests. I’ve been talking to people in high energy theory about my options and they have two suggestions:

    (a) Do string theory
    (b) Don’t do string theory

    The people advocating (a) have some pretty specific ideas about what to do, but the prospects for experimental test are bleak. So I’m looking for some clarification on (b). Can we narrow that down a bit? Is there something I should read?

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    Gavin,

    Given that there’s no clear way forward at the moment, I think it’s hard to offer anything other than some very personal prejudices and guesses, and encourage other people to come up with their own, preferably new and different ones. I see a lot of interesting questions about the relation between QFT and mathematics that are waiting to be explored. One that has gotten attention is Witten’s recent work on the relations of QFT to the geometric Langlands program. There are lots of others, which I’ve tried to mention on the blog. Generically, I think it would be worthwhile if more people were just taking whatever aspect of QFT they had always found most intriguing and mysterious, and trying to learn more about it and seeing if they could come up with something new.

    On the less mathematical side of things, the LQG people do seem to be looking into a variety of different questions that seem worth pursuing. In QFT itself, chiral gauge theories remain extremely poorly understood outside of perturbation theory. For example, it’s remarkable to me how little interest there has been in the question of how to properly define the electroweak theory outside of perturbation theory, e.g. by finding a computationally useful way of doing calculations on the lattice.

    Peter

  • http://golem.ph.utexas.edu/~distler/blog/ Jacques Distler

    I wrote

    Let me remind you of a few salient facts about the Landscape.

    It’s worth emphasizing that, while I may have phrased the argument in terms of Type IIB flux vacua, it’s actually quite general and applies to any class of vacua which satisfy

    1) There’s an exponentially large number of vacua, corresponding to the different ways of distributing (quantized) flux among n different cycles.
    2) The Standard Model degrees of freedom are localized on the compact manifold, and only a much smaller number, n’≪n, of cycles intersect that locus.

    This describes Type IIA flux vacua, M-Theory on G_2 manifolds, … In fact, it describes all of the classes of vacua for which we currently understand moduli stabilization.

    So I see no merit to Peter’s ‘you can get anything you want’ claim, with regard to any of the known branches of the landscape.

    As to his fallback position that the string theorists’ constructions of these vacua are ‘complicated and ugly,’ I would ask you to reflect on whether this is an objective scientific judgement, or merely a symptom of Peter’s general distaste for string theory.

  • A.J.

    Gavin,

    Why not have a look at the particle physics via non-commutative geometry stuff that Connes, Marcolli, and others are doing? There’s a lot of interesting questions there, conceptual and computational.

  • amused

    Dear Prof. Smolin,

    I guess you must have in mind specific people who you are sure have achieved their success in the current system through gaming it. It surprises me that this is something that one can know for sure.
    I don’t suppose there’s any chance of you giving the names…

  • Jim Nammack

    I would like to offer a hypothesis, that if subjected to scientific scrutiny, would put string theory to shame.

    The proposed hypothesis is that reality is much like a spectrum of radio waves. Multiple radio stations, or realities, are available to us, but we only experience one wavelength at a time. We experience only the channel that we are focused on–or tuned into–at any given time.

    Perhaps reality is the same way. There may be an infinite number of realities, all of equal validity and “realness” as the one we live in, but if we simply had the ability to tune in to the others, we might learn that there is no end to them. Perhaps we would discover that there is an infinite number of alternative realities, all just as solidly real as the one we live in.

    As a lay person, it seems to me that much of what quantum physicists have discovered lately at least hints of this possibility.

  • Lee Smolin

    Dear Amused,

    Of course I won’t mention names, as my interest is not at all to attack or judge anyone, it is to have an open discussion of what values we think lead to the most scientific progress, and what values hinder it. Nor do I tend personally to judge individual people badly, we live in a very imperfect system and within the boundaries of ethics there are many strategies to a successful career.

    If it would help I can speak of myself. I made two major compromises in my career, which I believe hurt my contribution to science. First to not concentrate much on foundations of quantum theory till recently; even when I had tenure it would have endangered our group’s research funding. Second, I spent a long time working on different faint hopes for perturbative quantum gravity before striking out into what I knew from the beginning was more promising but more risky, which was developing non-perturbative techniques. Even if my first paper was on a non-perturbative approach, most of what I did the next six years was perturbative and while it advanced my career it did not lead anywhere.

    So I am talking from experience. I would have much prefered to work in a system where I could have dived into the problems I perceived were the deepest from graduate school on. Then I felt I had no choice, indeed there were peers of mine who were deeper and purer thinkers with much more talented than me who did not survive in academia. Now many years later I want to improve the system so other, better, people are not faced with the same choice. I do this not out of romanticism but because I believe there is lots of evidence that this would improve the progress of science. As I said, many very experienced people across the sciences appear to agree.

    Lee

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    “Peter’s ‘you can get anything you want’ claim”

    I don’t claim that it is possible to get absolutely anything out of string theory compactifications. Very specifically I do claim that I have seen no argument from anyone working in this area that these compactifications cannot lead to values similar to the SM ones for the data that characterize it (number of generations, gauge group and couplings, fermion representations and mass terms). Devotees like Jacques of so-called “swampland” studies are trying to show that certain kinds of effective field theories cannot occur this way. So far, they have only made arguments that turn out to be wrong (someone more knowledgable than them explains how to get what they said can’t occur), or are claiming to rule out theories very different than the standard model, ones that seem to be irrelevant to the real world.

    “As to his fallback position that the string theorists’ constructions of these vacua are ‘complicated and ugly,’ I would ask you to reflect on whether this is an objective scientific judgement, or merely a symptom of Peter’s general distaste for string theory.”

    Here I’m not relying on my aesthetic sensibilities, but quoting Lenny Susskind. In his recent book, he refers to these constructions as “Rube Goldberg machines”, and makes fun of the idea that string theory constructions are “elegant” or “beautiful”. If Jacques does believe these things are not complicated and ugly, instead of attacking me as prejudiced and not worth listening to, I suggest he go after my source, Susskind.

  • http://eskesthai.blogspot.com/2007/04/nurturing-creativity.html Plato

    Without taking up to much room I thought I would link this in terms of valleys and hills.

  • http://golem.ph.utexas.edu/~distler/blog/ Jacques Distler

    I don’t claim that it is possible to get absolutely anything out of string theory compactifications.

    You do claim that the Landscape renders string theory unpredictive. That means (if it means anything at all) that any values for the 100+ parameters of the MSSM can be accommodated (to within any foreseable experimental precision) by one of the vacua on the Landscape.

    If that’s not what you’re claiming, then please clarify your claim.

    I just gave a very general argument that if the Standard Model is found to be in the same general class of vacua as those which have been explored in recent years (an assumption which could, of course, be wrong, but one which is tacitly assumed by Susskind and, therefore one assumes, by you), then the above claim is wrong.

    If you have a counter-argument, please make it. Otherwise, stop going around making unequivocal statements like

    The problem with the landscape, and with the string theory framework in general if you believe that it includes the landscape, is that the nature of the vacua is so varied and complex that, as far as anyone can tell, you can get just about anything you want. …[A]s far as anyone knows, string theory has solutions with essentially any possible effective field theory at LHC scales.

    or

    The problem with string theory as a way to unify particle physics is not just at the electroweak breaking scale. It doesn’t predict anything at any scale up to the GUT scale.

    or

    [T]he framework is unpredictive and untestable.

    or

    The problem with “string phenomenology” is that no one has any idea how to make any predictions with it at all, much less precise predictions about electroweak physics.

    (All from this comment thread alone; you have made similar, but much more emphatic, statements elsewhere.)

    Obviously, no one has yet found a convincing candidate for the Standard Model, among the string vacua explored to date (in that sense, no one has made any predictions yet). But that’s not what you’re saying. You are claiming that the framework itself is inherently unpredictive.

    I have argued that claim is false.

    Do you have a counter-argument?

    If Jacques does believe these things are not complicated and ugly, instead of attacking me as prejudiced and not worth listening to, I suggest he go after my source, Susskind.

    Lenny and I agree that æsthetic judgements are not an objective scientific criterion. You’re the one claiming that the “ugly” nature of these vacua is reason-enough to abandon the whole field.

  • http://tsm2.blogspot.com wolfgang

    Jacques,

    > Obviously, no one has yet found a convincing candidate for the Standard Model

    so what about te claim of Eric Mayes in comment #22
    “we can now competely derive the MSSM from string theory [..]” ?

  • Joseph Conlon

    Hi Peter,

    It’s not clear that trying to reproduce the precise structure of the Standard Model is a useful way to go. There is lots of evidence that string theory can give models with the qualitative matter structure of the SM: chiral fermions, multiple generations etc, and there are a host of explicit models to this end. As a gauge group, SU(3) x SU(2) x U(1) seems born to come from an intersecting brane model.

    However it also seems that, supposing a string compactification does describe the real world, that the question of computing e.g. the Yukawa couplings will be isomorphic in difficulty to the problem of explicitly solving the Dirac equation on a full-blown Calabi-Yau and computing the resulting wavefunction overlap. This is a bloody hard problem, and maybe there’s a clever solution, but it’s not obvious a frontal assault on it is the best way to make progress.

    A nice thing about string theory is that it can relate physics which from a low-energy EFT point of view is very different. This is why I would say it is more useful to look at the inter-relations that arise in different compactifications rather than trying to ask `can string theory predict the electron mass? yes or no?’

    Best wishes
    Joe Conlon

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    Jacques,

    You are engaging in your standard tactic of deleting the part of what I write which contains my argument, then proudly saying that you have shown that I have no argument. I’m not going to bother with addressing the long list of out-of-context quotes with added formatting that you took the trouble to construct, the statements in them are accurate if sometimes requiring more detail to make clear exactly what the claim is.

    Here’s the argument again:

    1. Simple string compactifications that you can make real predictions with give wrong physics (e.g. no supersymmetry breaking, extra long range forces).

    2. In order to avoid this, string theorists are now studying complicated, ugly constructions. They are unable to extract predictions from this class of constructions and there are good arguments (e.g. Denef-Douglas) that extracting predictions is impossible due to the huge number and complexity of the constructions. This framework is not capable of any kind of conventional, testable, scientific prediction about particle physics: e.g. telling us explicitly what deviation from the SM will be seen at the LHC or higher energy accelerator, or explaining the value of any of the numbers that characterize the SM.

    You deleted this above, I’m including it again as part of this point:

    “Very specifically I do claim that I have seen no argument from anyone working in this area that these compactifications cannot lead to values similar to the SM ones for the data that characterize it (number of generations, gauge group and couplings, fermion representations and mass terms)”

    3. This is a classic failure mode of a wrong speculative idea. Simple versions of the idea disagree with experiment, you make things more and more complicated in order to avoid this, never actually having something predictive that can be successfully confronted with experiment. When it is clear this has happened, you are supposed to give up. It is clear that this is what has happened in this case.

    That’s precisely what I mean when I say the landscape is unpredictive, and it is so because it is ugly and complicated. I don’t always repeat all those words. If you want to argue with this, argue with points 1, 2 and 3 in their full form. Don’t construct some stupid straw man argument. I’m not an idiot making a stupid argument which is obviously wrong, no matter how much you would like to believe this.

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    Joe,

    I’m not asking for a computation of the electron mass. I’m asking for a computation of something, either something about the SM, or something that deviates from the SM and can be checked experimentally. This is just the standard request made of any scientific idea that purports to improve on the SM.

    You say you want to look at “inter-relations that arise in different compactifications”. Depends what these are. If they’re convincingly testable, e.g. “all particles will come with partners of the same mass and quantum numbers”, great, they’ll be real predictions. If they’re vague and make all sorts of assumptions which may or not be true, they’re not going to convince anyone the model reflects reality.

    By the way, I just don’t at all agree with “SU(3) x SU(2) x U(1) seems born to come from an intersecting brane model”…

  • http://golem.ph.utexas.edu/~distler/blog/ Jacques Distler

    1. Simple string compactifications that you can make real predictions with give wrong physics (e.g. no supersymmetry breaking, extra long range forces).

    String theory, just like the Standard Model coupled to gravity, has lots of vacua that don’t look like the real world.

    Who cares?

    As a particle theorist, you want to focus on those vacua that do look like the real world, and see whether you can extract predictions (about particle physics at accessible energies) from them.

    In order to avoid this, string theorists are now studying complicated, ugly constructions.

    String theorists are studying vacua in which the moduli are stabilized. I could care less whether you think those vacua are “complicated, ugly constructions.”

    They are what they are, and you can keep your æsthetic judgments to yourself.

    They are unable to extract predictions from this class of constructions and there are good arguments (e.g. Denef-Douglas) that extracting predictions is impossible due to the huge number and complexity of the constructions.

    Denef and Douglas are discussing a problem quite different from the one under discussion here. Please don’t drag them into this, unless you are prepared to explain why you think their results are relevant to the problem at hand.

    In particular, as a particle physicist (i.e, for the purpose of extracting predictions for accelerator experiments), I have no interest in figuring out how to tune the fluxes on cycles, disjoint from the locus where the Standard Model degrees of freedom are supported, so as to achieve an acceptable value for the Cosmological Constant.

    This framework is not capable of any kind of conventional, testable, scientific prediction about particle physics: e.g. telling us explicitly what deviation from the SM will be seen at the LHC or higher energy accelerator, or explaining the value of any of the numbers that characterize the SM.

    As a blanket statement, this is false.

    Since we have not yet found vacua that bear more than a passing resemblance to the Standard Model, no one can claim to have extracted such predictions.

    But there’s no a-priori reason why the relevant calculations should be un-doable.
    (Don’t bother invoking Denef-Douglas, as their results are not relevant to the calculations which need to be done here.)

    “Very specifically I do claim that I have seen no argument from anyone working in this area that these compactifications cannot lead to values similar to the SM ones for the data that characterize it (number of generations, gauge group and couplings, fermion representations and mass terms)

    There are too many negatives in that sentence. Could you please restate it in a fashion that I might have a fighting chance of understanding it?

    If you want to argue with this, argue with points 1, 2 and 3 in their full form.

    I just did. And I’ll ask you to extend the same courtesy to my arguments.

    Don’t construct some stupid straw man argument. I’m not an idiot making a stupid argument which is obviously wrong, no matter how much you would like to believe this.

    So you don’t disagree with the proposition that, when we finally do find the set of vacua compatible with the Standard Model, they will, very likely, give rise to only a sparse set of points in the MSSM (or some other, similar extension of the SM) parameter space?

    Because that proposition, if correct means that string theory is highly predictive.

    I don’t know that it is, in fact correct. The only conclusive way to settle the matter would be to present the relevant vacua. However, for the reasons I have explained, I believe the proposition is highly plausible, far more plausible than the contrary proposition, that string theory is entirely unpredictive about LHC-scale physics.

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    Jacques,

    you can keep your æsthetic judgments to yourself

    Not a chance, sorry. Simple, beautiful theories are predictive because a lot of non-trivial facts about the world follow from simple assumptions. Complicated, ugly theories are unpredictive because the input is as big as the output. The ugliness is part and parcel of what is wrong.

    Denef and Douglas are discussing a problem quite different from the one under discussion here.

    No, these constructions combine particle physics and gravity and predict the CC that you will observe. This has to come out right. If you write down a compactification and claim that it is a unified model of particle physics and gravity, compute the CC and it is 120 orders of magnitude off, you have the wrong compactification. You have to find one with the right value. The Denef-Douglas argument is that these are likely to exist, but you can never actually find them.

    But there’s no a-priori reason why the relevant calculations should be un-doable.
    (Don’t bother invoking Denef-Douglas, as their results are not relevant to the calculations which need to be done here.)

    Their results are relevant. It’s also true that, as Joe points out, doing something like accurately computing Yukawas is not something anyone has been able to do for a realistic model, or is likely to be able to do soon. What has happened, again, is that people are studying models so complicated that they can’t confront them with experiment. This is not because of convincing evidence that the vacuum state is complicated. It is what happens when you pursue a wrong idea, adding complexities to avoid wrong predictions, continuing to the point where you lose the ability to compute (although are still able to say “maybe with a few decades of effort we can do this complicated calculation..”).

    So you don’t disagree with the proposition that, when we finally do find the set of vacua compatible with the Standard Model, they will, very likely, give rise to only a sparse set of points in the MSSM (or some other, similar extension of the SM) parameter space?

    Because that proposition, if correct means that string theory is highly predictive.

    I have no idea what the set of all points of all possible EFTs derivable from string theory constructions and compatible with observed standard model and cosmological parameters looks like, and I don’t think anyone ever will, because of Denef-Douglas and other inherent computational difficulties with their origin in the huge complexity of these models. This set may be sparse or dense but we’ll never know. The set-up of the problem is inherently so complicated that you can’t ever identify this set. People keep coming up with new constructions that just make the problem worse and worse. The point of what I quoted that you didn’t understand is that it removes one reason for doing all this: one might argue that there are generic things about these models that imply that you can’t get something like the SM. There’s no evidence for this, thus little reason to pursue that hope of falsifying string theory in that manner.

    This is why string theory is unpredictive, because you can’t ever identify this set, not because I know for a fact that it is dense in the neighborhood of the SM parameters.

  • c

    “No, these constructions combine particle physics and gravity and predict the CC that you will observe. This has to come out right. If you write down a compactification and claim that it is a unified model of particle physics and gravity, compute the CC and it is 120 orders of magnitude off, you have the wrong compactification. You have to find one with the right value. The Denef-Douglas argument is that these are likely to exist, but you can never actually find them”.

    If we find a set of vacua where we predict the MSSM particle spectrum such that the terms in the soft lagrangian are independent of the value of the cosmological constant (there are explicit constructions where this is the case), we can just forget about the cosmological constant. I don’t understand this obsession with the CC problem. As long as we can derive the spectrum of superpartners or at least find some nontrivial relations between them, that is a real prediction. I can see that the CC problem is relevant for cosmology but as far as particle physics is concerned, it’s not that relevant.
    If string theory predicts the ratios between, say, the gaugino masses and they are confirmed by the LHC, that’s it! In this case I don’t care if the CC is tuned or whatever mechanism makes it small, it’s just a completely decoupled problem.

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    c,

    So, does this mean you have given up on string theory as a unified theory of particle physics and gravity, deciding to just pursue it as a way of doing particle physics, ignoring gravity?

    Funny, but there seem to be a lot of string theorists instead doing the opposite, deciding string theory is only useful for investigating quantum gravity, can’t tell us about particle physics.

    “If string theory predicts the ratios between, say, the gaugino masses and they are confirmed by the LHC, that’s it!”

    This is what I have in mind when I say that much string theory research is now based on pure wishful thinking…

  • anon.

    Peter, have you tried to understand the state of SUSY phenomenology? Broadly speaking, there are a few basic ways of mediating SUSY-breaking to the Standard Model fields, and they tend to be fairly robust in terms of the outcome for basic quantities like the ratios of gaugino masses.

    Many people have been trying to tell you that in the string theory constructions people have been building in recent years, the cosmological constant problem is essentially decoupled from the low-energy phenomenology. With given low-energy phenomenology you can find the CC you want, without disrupting the MSSM-ish sector you are studying.

    Jacques has been repeating this, and yet you don’t seem to want to acknowledge it.

    If the LHC sees superpartners, it will probably give us some strong clues about how SUSY-breaking is mediated, which in turn could give us strong clues about the sorts of string constructions we might be dealing with. It’s not “anything goes.”

    For that matter, even in field theory, it’s not true that there’s a wide variety of stuff we could observe at the TeV scale. You like to complain about how no one is doing anything predictive, but if you paid attention you might notice that precision constraints (from LEP, the Tevatron, B factories, etc.) are so strong that almost any model anyone ever tries to write down is either ruled out or must be very finely-tuned.

    Model-building — in effective field theory or in string theory — is not easy. Most of us could name at most a handful of reasonable possibilities for TeV-scale physics (and a handful of other unreasonable possiblities). And yet you seem to think there are zillions of possibilities, all of which can be realized in string theory. That’s hardly the case.

  • c

    “Many people have been trying to tell you that in the string theory constructions people have been building in recent years, the cosmological constant problem is essentially decoupled from the low-energy phenomenology. With given low-energy phenomenology you can find the CC you want, without disrupting the MSSM-ish sector you are studying.”

    Exactly!
    Thank you anon!

    “Funny, but there seem to be a lot of string theorists instead doing the opposite, deciding string theory is only useful for investigating quantum gravity, can’t tell us about particle physics.”

    Who said this?

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    anon.,

    I am aware of how tight the experimental constraints are that rule out most beyond standard model models or force them to be highly tuned. But the point is that these are EXPERIMENTAL constraints, not constraints coming from string theory (or even SUSY with various mechanisms for mechanisms for SUSY-breaking). While one can write down all sorts of string theory models that give just about anything at the TeV scale, virtually all of them are already ruled by experiment. Sure the CC constraint on viable unified string models is in practice far less relevant than the tight experimental constraints that pick out the part of the landscape not contradicting experiment.

    But this is an example of the kind of phenomenon that I’m trying to point out. As the experimental constraints get tighter and rule out various simple possibilities (e.g. mSUGRA), people are forced into more complicated things like non-minimal SUSY models. This is the sign of an idea that isn’t working: you’re forced into models with more and more parameters since your simpler ones with less parameters were falsified. The situation is nowhere near as bad for the MSSM as for string theory. A hundred or so parameters appearing in a simple way in a Lagrangian is something you can compute with, unlike the case of the string landscape, where you can happily throw in all sorts of very different things (brane worlds, anyone?) much more complicated that SUSY field theory.

    Personally I take these tight experimental constraints as strong evidence we’re not going to see SUSY at the LHC. The all too depressing possibility is a 160 GeV (or whatever the number is that makes the theory consistent at very high energies) Higgs. The exciting possibility is something we haven’t thought of. The possibility you mention, some form of SUSY, which by incredibly bad luck was such that we can’t see indirect evidence of it now, seems to me quite unlikely. Anyway, we’ll find out within the next few years.

    And, you know, even if you think I’m completely ignorant, it still might be a good idea to start off your comment with something more polite than obnoxious insulting rhetorical devices like

    “have you tried to understand the state of SUSY phenomenology?”

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    c,

    “Who said this?”

    Well, just starting to reread through the comments here I got as far as #20 before finding

    “I agree that string theory seems unlikely to tell us anything about electroweak scale particle physics(except perhaps through gauge/gravitational duality as applied to QCD). But it isn’t really fair to claim that it is thus dead in water. String theory excited many theorists by providing a quantum gravity candidate and, in the end, exploring that regime will be what determines if it sinks or swims.”

  • http://golem.ph.utexas.edu/~distler/blog/ Jacques Distler

    No, these constructions combine particle physics and gravity and predict the CC that you will observe. This has to come out right.

    Not for these purposes it doesn’t.

    The physics measured in accelerators is completely insensitive to gravity. The values of the cosmological constant and Newton’s constant are irrelevant to LHC physics.

    As I patiently explained, there is a huge degeneracy of vacua whose particle physics (at energies probeable at the LHC and beyond) which differ in the values of the cosmological constant and Newton’s constant, but whose particle physics is absolutely identical.

    For the purposes of making particle physics predictions, it doesn’t matter which of this exponentially large number of vacua you calculate in. You will get the same answers for all of them.

    Figuring out which of those vacua has the right value of Λ and G_N is a computationally hard problem, as argued by Denef and Douglas. However, the exponentially large number of such vacua virtually guarantees the existence of a solution. Computing the Standard Model Yukawa couplings may be a technical challenge, but it is not computationally hard (in the sense of Denef-Douglas).

    I have no idea what the set of all points of all possible EFTs derivable from string theory constructions and compatible with observed standard model and cosmological parameters looks like

    And you’re not interested in finding out either.

    Which is fine by me.

    What I take umbrage at is when

    1) You categorically declare (for æsthetic reasons, since you, apparently don’t have a physics argument) that, because of the Landscape, string theory is inherently unpredictive about particle physics at accessible energies.
    2) You excoriate an entire community of physicists for not abandoning this obviously “failed research program.”

    I don’t want to minimize the difficulty of the problem. It will require the combined efforts of many very smart people to solve it.

    But whatever may be “obvious” to you, you have failed to make any sort of a physics argument supporting that contention.

    I think you owe the community an apology.

  • http://golem.ph.utexas.edu/~distler/blog/ Jacques Distler

    Whoops! Sorry. One of the sentences above got spooged (curses cut ‘n paste!). It should have read:

    As I patiently explained, there is a huge degeneracy of vacua, which differ in the values of the cosmological constant and Newton’s constant, but whose particle physics (at energies probeable at the LHC and beyond) are absolutely identical.

  • c

    “While one can write down all sorts of string theory models that give just about anything at the TeV scale, virtually all of them are already ruled by experiment.”

    The standard N=1 D=4 SUGRA prescription through which one obtains the MSSM soft breaking terms from string compactifications results in some very nontrivial relations between them.
    One such example is the ratios of the gaugino masses. I’m unaware of any construction or a set of constructions where one can get “just about anything”
    for the ratios of the gaugino masses. This is completely independent of the experimental constraints from LEP, Tevatron, etc.

    “Well, just starting to reread through the comments here I got as far as #20 before finding

    “I agree that string theory seems unlikely to tell us anything about electroweak scale particle physics(except perhaps through gauge/gravitational duality as applied to QCD). But it isn’t really fair to claim that it is thus dead in water. String theory excited many theorists by providing a quantum gravity candidate and, in the end, exploring that regime will be what determines if it sinks or swims.” ”

    I don’t know if Josh is a string phenomenology expert but this statement does not reflect the current state of the field, that’s for sure. I know some string theory people who work on things like black hole entropy, ADS/CFT and are unaware of the recent progress in string phenomenology.

    I personally would not rely so much on the statements made by some other people and instead go and read some relevant papers myself.

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    Jacques,

    Sorry, but I’m just not completely convinced that string theory unifies gravity and the other known forces, but that then things are completely decoupled in the way you claim. I don’t doubt that in many of the string theory models people work with this is true, but there are others in which I don’t see it. What about those extra dimensions and black holes that we keep hearing might be showing up at the LHC? Also, presumably the same Denef-Douglas problem applies to anything that is fine-tuned, and if I believe Arkani-Hamed, the electroweak breaking scale may also be fine-tuned for our existence. Is the electroweak breaking scale also completely decoupled from TeV scale particle physics predictions? Maybe you’re right and this is not a problem, it’s a bit late at night for me to completely think this through.

    In any case, the Denef-Douglas problem, and other semi-theological problems of principle aren’t the main point that I keep repeating, and that you keep refusing to acknowledge or quote. I’ll happily stipulate that you’re right and Denef-Douglas is not a problem. You quoted my

    “I have no idea what the set of all points of all possible EFTs derivable from string theory constructions and compatible with observed standard model and cosmological parameters looks like”

    then deleted the rest of the sentence, so that you could go into your typical sneering personal attack mode:

    And you’re not interested in finding out either.

    the rest of the sentence wasn’t about how “I don’t want to find out”, it went

    “and I don’t think anyone ever will, because of Denef-Douglas and other inherent computational difficulties with their origin in the huge complexity of these models. This set may be sparse or dense but we’ll never know. The set-up of the problem is inherently so complicated that you can’t ever identify this set. People keep coming up with new constructions that just make the problem worse and worse.”

    This is the argument you absolutely refuse to ever acknowledge the existence of. I’ve made it at least twice more here, you continue to completely ignore it and claim I don’t have an argument. Here it is again:

    “3. This is a classic failure mode of a wrong speculative idea. Simple versions of the idea disagree with experiment, you make things more and more complicated in order to avoid this, never actually having something predictive that can be successfully confronted with experiment. When it is clear this has happened, you are supposed to give up. It is clear that this is what has happened in this case.”

    and

    “Simple, beautiful theories are predictive because a lot of non-trivial facts about the world follow from simple assumptions. Complicated, ugly theories are unpredictive because the input is as big as the output. The ugliness is part and parcel of what is wrong.”

    and

    “It’s also true that, as Joe points out, doing something like accurately computing Yukawas is not something anyone has been able to do for a realistic model, or is likely to be able to do soon. What has happened, again, is that people are studying models so complicated that they can’t confront them with experiment. This is not because of convincing evidence that the vacuum state is complicated. It is what happens when you pursue a wrong idea, adding complexities to avoid wrong predictions, continuing to the point where you lose the ability to compute (although are still able to say “maybe with a few decades of effort we can do this complicated calculation..”).”

    There’s not much point in reformulating this a fourth time. I think this is a fair characterization of the current state of the study of these backgrounds. They are just complicated enough to evade making predictions (simpler, predictive ones give wrong physics), and this ensures that people can’t calculate things reliably with them and get predictions out of them. There is no reason to believe that if you can do these calculations you would get predictions, much less ones that agree with experiment. This situation has every hallmark of a failed research program and I’m not going to apologize for pointing this out.

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    c, anon., Jacques,

    There are three of you, but only one of me. And I’ve just spent the entire evening thinking about what you have written and trying to carefully responding to all three of youl, so haven’t finished preparing a talk for Saturday. I’ll be on a plane most of tomorrow, busy at the event Saturday, on a plane Sunday, teaching Monday.

    It has been an educational argument, sometimes I do learn things, even if I’m not convinced by all of your claims. Since you all seem to consistently claim there are robust predictions about gaugino mass ratios, and I’ll freely admit that I am no expert on all details of possible supersymmetry breaking schemes, I’ll leave you with a question I’m curious about: What value of a gaugino mass ratio would falsify string theory. .1?, .01?

    Will try and return to this when I can….

  • c

    What value of a gaugino mass ratio would falsify string theory. .1?, .01?

    Read the “Gaugino Code” paper by Nilles and Choi.

  • http://golem.ph.utexas.edu/~distler/blog/ Jacques Distler

    Sorry, but I’m just not completely convinced that string theory unifies gravity and the other known forces, but that then things are completely decoupled in the way you claim.

    I’m not sure how to parse this sentence. Do you doubt that LHC physics is insensitive to the values of G_N and Λ? Surely not. Do you disagree with my argument that, the renormalizable couplings of the Standard Model are insensitive to the distribution of fluxes on cycles disjoint from the locus on which the Standard Model degrees of freedom are localized? Something else?

    What about those extra dimensions and black holes that we keep hearing might be showing up at the LHC?

    What about them?

    Nonrenormalizable couplings, usually suppressed by inverse powers of M_{pl}, are unsuppressed in that limit. That’s just a symptom of the fact that 4D effective field theory breaks down, not at 10^{16} GeV, but at 10 TeV.

    But, hey, if the large extra dimension scenarios are correct, we won’t be quibbling about computing Yukawa couplings. We’ll be directly probing stringy physics at the LHC.

    Also, presumably the same Denef-Douglas problem applies to anything that is fine-tuned, and if I believe Arkani-Hamed, the electroweak breaking scale may also be fine-tuned for our existence. Is the electroweak breaking scale also completely decoupled from TeV scale particle physics predictions?

    The Denef-Douglas problem arises because all n fluxes contribute (in some complicated way) to Λ and G_N. If there are other couplings that are similiarly affected by all n fluxes, I suppose they, too, will be cmputationally difficult to calculate.

    I don’t know of an explicit string theory realization of Arkani-Hamed et al’s idea. So I can’t say whether the Higgs mass falls into that cagegory.

    Good question, though!

    You complained that I failed to quote:

    “and I don’t think anyone ever will, because of Denef-Douglas and other inherent computational difficulties with their origin in the huge complexity of these models.

    Since I’d already explained why Denef-Douglas is irrelevant to the problem at hand, I didn’t see the point of quoting your repeated invocation of it.

    As to your other, unspecified, “inherent computational difficulties,” if you care to spell them out explicitly, I’ll be happy to try to respond. But I’ve learned not to make any assumptions about what you’re talking about.

    So, if you want me to respond, you’ll have to spell out your argument.

    This is the argument you absolutely refuse to ever acknowledge the existence of. I’ve made it at least twice more here, you continue to completely ignore it and claim I don’t have an argument. Here it is again:
    “3. This is a classic failure mode of a wrong speculative idea. Simple versions of the idea disagree with experiment, you make things more and more complicated in order to avoid this, never actually having something predictive that can be successfully confronted with experiment. When it is clear this has happened, you are supposed to give up. It is clear that this is what has happened in this case.”

    That’s not a physics argument. It’s an æsthetic judgement on your part (and a severe mischaracterization of the history of moduli stabilization).

    I’m really uninterested in your æsthetic judgements.

    In any case, they certainly don’t justify your conclusion that String Theory is inherently unpredictive.

    “It’s also true that, as Joe points out, doing something like accurately computing Yukawas is not something anyone has been able to do for a realistic model, or is likely to be able to do soon.

    There are no realistic models, at present. There are semi-realistic models. But no one is willing to invest the energy to work out all the details of a merely semi-realistic model (i.e., one that we know doesn’t describe the real world).

    (There are, in addition, some computations that people still don’t know how to do. They’re the subject of ongoing research. Somehow, though, I doubt that you intend your entire argument to hinge on those research efforts coming to nought.)

  • a

    c, some phenomenological models make specific predictions for the two ratios among gaugino masses (and combining them one can fit whatever will be measured), but I am not aware of any stringy prediction for gaugino masses.

    Jacques, the anthropic principle appeared when somebody noticed that the small electron, up and down Yukawas lie within the relatively narrow range that allows “life” (see astro-ph/9909295 for a review). So, it seems likely that anthropic selection plays some role even for Yukawas. I understand that computing Yukawas is difficult, but maybe it is possible to estimate if the number of different string predictions for Yukawas is or is not hopelessly large?

  • http://golem.ph.utexas.edu/~distler/blog/ Jacques Distler

    I understand that computing Yukawas is difficult, but maybe it is possible to estimate if the number of different string predictions for Yukawas is or is not hopelessly large?

    Well, that was the substance of my argument to Peter.

    The distribution of fluxes on cycles disjoint from the locus on which the Standard Model degrees of freedom are supported doesn’t affect the Yukawa coupling of the SM. So the number of models with distinct particle physics is R^{n’}, instead of R^n, where typically n’≪ n.

    Moreover, for the purpose of making predictions (as opposed to retrodictions), one could take the some of the values of known and well-measured SM couplings as given, and throw away all of the vacua which disagree with those.

    That should leave one with a small, manageable number of vacua, for which one wants to compute everything.

  • Joseph Conlon

    Hi Peter,

    One of the inter-relations I was thinking about was the relationship of gaugino masses, which various people have emphasised above. This is both reasonably easy to compute from the high-scale theory and reasonably insensitive to much of the model-building uncertainties that exist. Unlike the Yukawa couplings, it is also theoretically quite a clean observable. No gaugino mass ratio measured at the LHC is going to falsify `string theory'; it is going to falsify certain string phenomenology models of moduli stabilisation and susy breaking.

    One can also look at other relationships, such as the ratios of moduli and gravitino masses, the expected scale of the axionic decay constant, etc.

    Here is also a potential LHC measurement that would, I think, cut a massive big swathe through all the IIB flux models that people (including myself) study: a 1600GeV gluino with 400GeV first generation squarks.

    Best wishes
    Joe

  • Marty Tysanner

    Jacques,

    Thank you for your response in comments #233 and #242. I found it to be a pretty clear statement of a defensible point of view. I agree, anthropic arguments are very uninteresting. Although I personally disagree with the entire anthropic way of thinking for fundamental theories, I mentioned it as a way of phrasing a selection criterion for candidate vacua; you could substitute “compatible with life” with another selection method that is more physical. In any case I think you answered the bulk of the question in which it was embedded.

    The perspective about decoupling gravitational considerations from those of particle physics in vacuum selection is interesting, something I was unaware of. The exchange between you and Peter was also informative.

    I won’t press you to answer the rest of my fourth question, regarding resource reallocation to alternative approaches to a more fundamental theory, although I would still be interested if you decide to do so…

    In comment #254 it was my perception, but just a perception, that you discounted aesthetic judgements too much. I can only speculate that aesthetics were an important factor in your original choice to work in string theory. In my understanding of history, aesthetic considerations have been a valuable guide in theory building, although the earlier days of quantum mechanics would probably be an important exception. One could of course argue that “nature is what it is” and “nature doesn’t care about our sense of aesthetics,” but theories are necessarily human constructions and hence are strongly affected by our sense of what “feels” right.

  • Thomas Larsson

    Here is also a potential LHC measurement that would, I think, cut a massive big swathe through all the IIB flux models that people (including myself) study: a 1600GeV gluino with 400GeV first generation squarks

    What about the more likely scenario that the LHC finds neither gluinos, squarks nor any other sparticles at all? Would that be a problem for string theory?

  • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

    Wild (but highly amusing) rant by mclaren deleted, as it was twenty times longer than necessary. More importantly, I’m actually learning things from the string phenomenology discussion, occasional personal attacks notwithstanding, so I’d rather not derail that.

  • Cecil Kirksey

    Jacques:
    I cannot follow your detailed mathematical arguments with Peter, so if I can I would like you to answer the following questions from a very interested retired engineer.

    1) How many metasable vacua are consistent with the SM? 10^10?, 10^20?, 10^100???

    2) If you pick such a vacuum and make a “prediction” about some other paramater value and then experiments disagree with the prediction, then do you select some other vacuum that is now consistent with the new parameter value of the SM?

    3) If the prediction is incorrect do you then predict a value for a new parameter?

    4) Even if the prediction is correct in the first instance how can you be sure that the selected vacuum is the correct vacuum? Make anorther prediction about some other paramter value?

    String theory may be the correct theory. But the process of determining the truth seems unending if my understanding of what your suggesting is correct.

    Can you respond in a manner that a non-professional can understand. Thanks.

  • http://golem.ph.utexas.edu/~distler/blog/ Jacques Distler

    Cecil wrote:

    1) How many metasable vacua are consistent with the SM? 10^10?, 10^20?, 10^100???

    I don’t know. Maybe zero. No one has found any so far.

    If you find one, however, you will find a large number. But there will be a huge degeneracy, in terms of the predictions they make for particle physics. The number of independent particle physics models (i.e., neglecting the values of Newton’s constant and the cosmological constant) will be much, much smaller.

    This will yield a sparse set of points in the parameter space of (some extension of) the Standard Model. Either the real world corresponds to one of those points (to within experimental accuracy) or it doesn’t.

    Is that clear enough?

    Marty wrote:

    In comment #254 it was my perception, but just a perception, that you discounted aesthetic judgements too much. … In my understanding of history, aesthetic considerations have been a valuable guide in theory building

    Sure, æsthetics can be a useful guide. But, like everything else, our æsthetic sense is something acquired from experience, not some fixed fixed criteria that can be imparted to beginning graduate students and which will serve them for the rest of their professional lives.

    Concert audiences recoiled in horror when they first heard the music of Stravinsky. Only much later did they (well, most of them) learn to appreciate its beauty.

    Mother Nature is more oblivious, than any composer ever could be, of whether we appreciate what she is telling us.

    I can only speculate that aesthetics were an important factor in your original choice to work in string theory.

    String theory has proven to be a vastly richer and vastly more beautiful theory than anyone could have suspected in 1984.

    I’m sure you read my account of how I became interested in string theory on my blog. Aesthetics had little to do with it.

  • http://tsm2.blogspot.com wolfgang

    Jacques,

    I would like to repeat my question from comment #250:

    A long time ago, in comment #22, Eric Mayes made the statement
    “we can now competely derive the MSSM from string theory [..]” .

    You wrote later, “Obviously, no one has yet found a convincing candidate for the Standard Model”.

    How should one resolve this apparent contradiction?

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    Had a few minutes this morning before I leave for the airport to look into the literature about the claims being made here that were new to me.

    1. Last night before going to bed people here had me somewhat convinced that maybe there was more of a possibility of some weak kind of string theory prediction about ratios of superpartner masses than I had thought possible. Thanks to “c” for providing the reference http://arxiv.org/abs/hep-ph/0702146.

    Taking a look at it, I see pretty much the kind of “predictions” I’ve always seen in this area, which I think it is not unfair to characterize as “you can get pretty much whatever you want”. There’s nothing like a prediction that could be used to falsify string theory here (which I guess kind of explains what was bothering me last night, why I hadn’t seen that claim before, since I’ve certainly been looking).

    The authors identify 12 different classes of schemes to get supersymmetry breaking, mostly from string theory, and don’t claim the list is exhaustive. 10 different classes lead to 3 separate pattern of ratios (although one of these patterns involves an undermined parameter), and there are various questions about exactly how to relate these ratios to observed masses. For the other two classes (“volume moduli-dominated SUSY breakdown in perturbative heterotic string theory”, and “M-theory compactification on G2 manifolds with moduli stabilization by non-perturbative dynamics”, the authors claim that predictive power is lost.

    The claim is that this is actually the best situation as far as SUSY parameters goes. It looks just like I would expect. Lots of different complicated classes of models, with some sorts of predictions possible in a given class of models (Joe gives an example of this kind of thing), but no predictions possible independent of a choice of specific model. There’s enough complexity to get whatever you want, so you can’t use this to make a falsifiable prediction of any conventional kind.

    2. I took a look again at the Denef-Douglas paper (http://arxiv.org/abs/hep-ph/0702146), since I had read it, and didn’t remember seeing Jacques’s argument about independence of the CC there. I see that’s because it’s not in the summary section describing the signifcance of the paper, but is somewhat buried near the end of section 6, which I guess I didn’t read carefully enough. Denef and Douglas refer to it as “the optimistic hypothesis” and comment:

    “Do we believe in it? It seems fairly plausible for Standard Model observables, but is perhaps less obvious for other properties, for example the properties of the dark matter.”

    Off to catch a plane…

  • http://www.wsst.org/podcasts.asp Dale Basler

    James Gates, from Elegant Universe on PBS, gave a lecture last week at the national science teacher’s conference titled “Can String Theory Be an Educational Force Multiplier?”

    He talked about string theory and how it can be used as a bridge to educate the public about science.

    He wonders if the remarkable public interest in string theory can be used to bring science to the masses.

    See the slides from his talk and hear an interview at: http://www.wsst.org/labtable.asp?newsID=302

  • c

    “Lots of different complicated classes of models, with some sorts of predictions possible in a given class of models (Joe gives an example of this kind of thing), but no predictions possible independent of a choice of specific model.”

    Peter, nobody claimed that the patterns are model independent. However, there are not 10^100 CLASSES of models such that you can get 10^100 types of patterns of gaugino mass ratios. There are so far very few actual classes where the patters are pretty robust and a couple of models which are still in their early development such as the G2 compactifications, where additional threshold corrections have to be computed to make a more robust prediction. So if one of those patterns is confirmed by the LHC it would be a huge boost to string phenomenology. If none of those patters is confirmed then we’ll have to look for alternative ways to stabilize the moduli.

    “There’s enough complexity to get whatever you want, so you can’t use this to make a falsifiable prediction of any conventional kind”
    No, there is not enough complexity to get anything you want.
    As you said: “10 different classes lead to 3 separate pattern of ratios”.
    Note that “classes” of models makes this degeneracy much bigger. If a “class” , for example, the large volume Type IIB compactifications, has 10^100 models within it and predicts THE SAME ratios for the gaugino masses then that’s a prediction for this whole class of 10^100 models.

    The claim that “There’s enough complexity to get whatever you want, so you can’t use this to make a falsifiable prediction of any conventional kind” in this context basically implies that there is an infinite number of alternative CLASSES of models with different mechanisms stabilizing the moduli and vacua with spontaneously broken SUSY. Well this sounds quite implausible. It took many years to figure out how to fix the moduli in string theory. So far there are only a handful of ways, i.e. fluxes, non-perturbative corrections, alpha prime and string loop corrections. The few “classes” of models people have been able to construct so far where all the moduli are fixed and SUSY is spontaneously broken so that one can honestly compute the F-terms and hence the gaugino masses, scalar masses and the trilinears in terms of the microscopic parameters coming from the Kahler potential and the superpotential are hard to come by.

    The vast majority of the “string phenomenology” models don’t do these computations and instead set the F-terms and the moduli vevs to some ad-hoc values and do phenomenology with this stuff – and these are clearly not the types of models I was talking about.

  • Joseph Conlon

    Hi Peter,

    “Lots of different complicated classes of models, with some sorts of predictions possible in a given class of models (Joe gives an example of this kind of thing), but no predictions possible independent of a choice of specific model.”

    `Complicated’ is in the eye of the beholder, but otherwise – great! The LHC comes along, it skittles most or all of the models and ideas that exist, and we can all forget our theoretical prejudices, give up on the stuff that doesn’t work and instead follow the data and the models that fit it. To me this just seems to be normal science, and not a problem in any way.

    Actually, I think your comments above aren’t string-specific in any way: they could be applied, unaltered, to all BSM phenomenology. SUSY, technicolor, extra dimensions, little Higgs, invisible Higgs: doesn’t your complaint above apply equally to all of these, and other, scenarios?

    Best wishes
    Joe

  • Cecil Kirksey

    Jacques:

    Thanks for the reply. However, I am still left unclear as to the size of the vacua. You use terms like “large”, “huge” and “sparse” to describe the size of the expected vacua. You will admit these are relative terms. What I was hoping for was something more quantitative. The reason I say this is that if one is looking for this expected vacuum then it would be nice to have some idea of the potential difficulty. Agreed?

    Let me ask you: Do you believe that ST must produce a vacuum that is consistent with the SM, i.e., it is necessary in order for ST to be viable? If the answer is yes then shouldn’t it also be important to understand the difficulty of finding such a vacuum?

  • http://golem.ph.utexas.edu/~distler/blog/ Jacques Distler

    However, I am still left unclear as to the size of the vacua. You use terms like “large”, “huge” and “sparse” to describe the size of the expected vacua. You will admit these are relative terms. What I was hoping for was something more quantitative.

    I gave more quantitative estimates above, and you said “I cannot follow your detailed mathematical arguments.” So I a non-technical response.

    Make up your mind!

    In the discussion above, I had in mind n of order 100, n’ of order 1, and R of order 10. The parameter space of the Standard Model is 19 dimensional. Simple supersymmetric extensions of the Standard model can have parameter spaces of dimension ~100.

    10^{400} points in a 100-dimensional parameter space could be dense (and hence unpredictive). 10^4 points in a 100-dimensional parameter space is incredibly sparse (and hence predictive).

    These are all really crude estimates. (For instance, I need to put in what range of values one might expect to obtain for each of the parameters in question and with what accuracy we can hope to measure them. Otherwise “dense” and “sparse” have little meaning. Still, this should give you some idea.)

    OK?

  • mclaren

    Sean Carroll deleted my comment because I asked him to provide the journal title, article title, volume number, issue number and pages of any peer-reviewed HEP physics journal in which a falsifiable testable prediction from string theory has appeared.

    Do you really think you’re going to win the public debate on string theory, Sean, by deleting posts asking for falsifiable testable predictions made by string theory?

    That’s the scientific method.

    Censoring people who demand the application of the scientific method is not a winning debate strategy, Sean.

    I repeat my request.

    What are the journal titles, article titles, volume numbers, issue numbers and page number of the peer-reviewed HEP articles containing testable falsifiable predictions made by string theory?

    Can you even provide one published peer-reviewed testable falsifiable prediciton in all the string theory literature?

  • Haelfix

    One thing I think is safe to say. If the LHC and ILC does not see any tracers of SUSY and instead just sees a scalar Higgs and nothing else, a good percentage of phenomenologists will stop doing stringy constructions, and instead try to tackle the much more pressing problem of trying to solve the hierarchy problem. Forget about the CC, we will have a naturalness problem at accessible energies the likes of which will deeply shake the community.

    String theory won’t be falsified, but surely the intellectual and numerical dominance its had over the field will be lessened by that most troubling scenario.

    So science will proceed just as before, and Peter and Lees worries will not come to fruition in that case. Experiment ultimately is the trend setter, which is as it should be.

  • TimG

    Really interesting comments with regard to string phenomenology. Thank you all for giving us the chance to read them. Even if neither side can win the “debate” (in terms of convincing their opponent), it definitely helps to inform interested observers like myself.

  • http://www.math.columbia.edu/~woit/blog Peter Woit

    Back from an interesting time at the University of Central Florida, where I had the honor and pleasure of speaking together with Jim Gates. I think people were hoping for controversy and disagreement, but there was relatively little. In particular, while he should speak for himself, we didn’t seem to disagree about the string theory landscape. Will try and write something about this on my blog tomorrow or, in any case soon.

    c,

    You’re deleting the relevant parts of what I wrote, then making up something I didn’t write and arguing with it. I didn’t say anything at all about an infinite number of classes of alternative models.

    What I did do was point to the fact that the reference you gave says that two out of the twelve models described don’t actually predict a specific pattern of gaugino mass ratios. So, there are enough models to provide ones where you can get anything you want. This set-up is not falsifiable. No matter what you gaugino mass ratios you see, some model can accomodate it.

    Joe,

    For the LHC to decide between SUSY models, first it has to see SUSY. What do you think will happend to this whole field of model-building if the LHC doesn’t see SUSY? I’d like to believe that Haelfix is right that people will give up on it, but I’m not sure.

    As for the comparison to other ideas in beyond SM phenomenology, sure, none of them are very convincing, although some at least have more distinctive experimental signatures. Given the lack of a convincing idea, the best thing to do is to try and come up with new ideas. That’s hard, so sure, some people should continue to try and see if they can get something out of ideas that so far haven’t worked very well. But personally I think it’s not very healthy if one unpromising idea completely dominates the field the way “string phenomenology” does.

  • Cecil Kirksey

    Jacques:

    Thanks for the reply. I cannot follow the detail technical arguments that you use to arrive at a conclusion; however, I certainly am able to draw some opinion about the quantative conclusions of your technical argument.

    You said:

    10^{400} points in a 100-dimensional parameter space could be dense (and hence unpredictive). 10^4 points in a 100-dimensional parameter space is incredibly sparse (and hence predictive).

    These are all really crude estimates.

    I am a retired engineer and I can understand crude estimates. But really, 396 orders of magnitude difference!!!

    Look, Jacques, I have been an advid layperson follow of high energy physics, cosmology, gravity, etc, for 40 years. I have probably over 100 books on the subject, some very technical that I really don’t grasp, like GSW String Theory, and others not so technical like Guth, Feymann, Suskind, Randall, and Greene’s books, but I try, OK.

    Some ST critics like Woit do not believe in ST. I can be convienced by a simple argument which I have been searching for the last several years. After 22-23 years I would have thought that ST could make some connection with the real world. And reduce to GR and the SM (I guess GR is considered part of the SM) and actually make a single prediction that goes beyond the SM. This is the way all new physical theories have been developed. I am trying to understand why this is so hard for ST to do.

    So trying to understand the effort involved in reducing the magnitude of the crude estimate does not seem so unreasonable.

    So in the spirit of Sean’s suggestion that it would be more helpful to the ST cause if more ST researchers provided feedback to the lay public. I believe my question really gets to the heart of the matter. Just how difficult is it to connect ST to the real world?

    Thanks for your time and believe me I am very receptive to a straightforward argument that any lay person can follow.

  • c

    “What I did do was point to the fact that the reference you gave says that two out of the twelve models described don’t actually predict a specific pattern of gaugino mass ratios. So, there are enough models to provide ones where you can get anything you want. This set-up is not falsifiable. No matter what you gaugino mass ratios you see, some model can accomodate it.”

    At the end of the section about the G2 compactifications the authors state:
    “In this case, the gaugino mass ratios can be determined only when one can reliably compute the values of the highly UV sensitive Gamma_phi and Omega_{aphi}, which is not available with our present understanding of M theory compactification.”

    Peter, how many papers are there on those types of fluxless G2 compactifications? Did you check? There is only ONE paper, which came out in January. You are ready to make your claims that this class of models can accomodate “anything you want” based on the fact that nobody has computed the threshold effects for the anomaly mediated gaugino masses in those models? Well, there are plenty of very smart people around who will figure out how to compute those reliably and make predictions for the gaugino mass ratios.

    Your claim that “you can get anything you want”, based on the fact that certain effects have not yet been computed in a brand new class of models cannot be serious. The techical difficulty in comuting the quantities Gamma and Omega certainly does not imply that this class of models can accomodate any ratio for the gaugino masses. You do understand that there is a huge difference between a model which can IN PRINCIPLE accomodate anything you want and a model where a techical problem does not YET allow to make a robust prediction?

    In fact, if you check the original paper on these G2 compactifications, there is already a very interesting prediction from the entire class of the G2 compactifications without fluxes: light gauginos with masses

  • c

    The remaining part of the last sentence:
    light gauginos with masses

  • c

    OOPS, here it is:
    light gauginos with masses less than 1TeV and very heavy scalars with masses
    O(100)TeV. Hence, if the LHC discovers squarks or sleptons, this entire class of G2 compactifications will be ruiled out!

  • http://www.math.columbia.edu/~woit/blog Peter Woit

    c,

    You’re still ignoring the last class of models in which the authors say no prediction is possible and you aren’t providing any evidence that G2 compactifications will become predictive about this (whether they give predictions about something else is irrelevant). I think “a” a while back is a phenomenologist who is telling you what the informed consensus about this question is:

    “c, some phenomenological models make specific predictions for the two ratios among gaugino masses (and combining them one can fit whatever will be measured), but I am not aware of any stringy prediction for gaugino masses. ”

    I don’t think it’s at all helpful for the credibility of string theory to be making public claims of predictions which aren’t sustainable. There has been a lot of that going on…

  • c

    “There is only ONE paper, which came out in January.”
    Correction: To be more precise, there was a 4 page paper by the same authors which came out last summer, but it was a very short version of the one in January and had no analysis of the dS vacua Choi and Nilles are talking about in the “Gaugino Code”.

    By the way, now that I have thought about it, the UV sensitivity of the threshold correction to the anomaly mediated contribution (which is itself a one-loop effect) is not likely to change the final result by much, maybe a O(10-20)% at the most. Although this would not be the kind of “robust” prediction Choi and Nilles want to obtain, it would still be far from “anything you want”. If they are correct in their claim that the UV physics does affect the gaugino masses to some extent, this class of models would directly probe the UV physics! Don’t you think this is exciting?

  • c

    “c, some phenomenological models make specific predictions for the two ratios among gaugino masses (and combining them one can fit whatever will be measured), but I am not aware of any stringy prediction for gaugino masses. ”

    See, the G2 paper: hep-th/0701034 page 56 for the tree-level gaugino mass calculation and pages 58-60 for the anomaly mediated contributions. Those are pretty honest “stringy” calculations coming from M-theory on G2.

  • c

    “You’re still ignoring the last class of models in which the authors say no prediction is possible and you aren’t providing any evidence that G2 compactifications will become predictive about this”

    About the last class of models:
    For the specific toroidal compactification discussed in Nilles and Choi, the string threshold tilde M_a^()|_{string} has been computed in terms of the Dedekind function eta and the explicit expression is given. Hence the UV sensitivity is known for this particular model. Now, Nilles and Choi speculate that the more generic models (which have not yet been constructed) would also be UV sensitive. I don’t see why this would necessarily be the case. The reason for the UV sensitivity in the simple toroidal model is the suppression of the dilaton F-term F_s which contributes to the tree-level gaugino mass. Has anyone demonstrated that it will be suppressed in the general Calabi-Yau case? I don’t think that Choi and Nilles in their review paper have demonstrated this. So, their remark is a speculation about the general models which have not yet been constructed. The specific toroidal model they are discussing is predictive because the UV physics contribution is known.

    About the G2 models, in more detail, the authors cite the Friedmann and Witten paper hep-th/0211269 where the M-theory threshold corrections to the gauge kinetic function have been explicitly computed and they are actually constants, independent of either the moduli or the hidden sector matter phi. So, I don’t know what Nilles and Choi have in mind about Omega being dependent on phi. The assumption about the dependence of Omega on phi through e^(K/3)Z or the other coupling is a speculation which assumes that the heavy M-theory modes contribute via SUGRA type couplings like e^(K/3)Z. But we know, for instance, that in the heterotic example I discussed above, the string threshold corrections are expressed in terms of the Dedekind function in terms of the moduli which has nothing to do with N=1 D=4 SUGRA couplings.

    The bottom line is that the Nilles and Choi is a review of models where many classes of models make robust predictions about the gaugino mass patterns which can be tested by the LHC. The G2 model is less robust (this is excusable since this is a very new class of compactifications) but the corrections can be taken into account, i.e. using Friedmann and Witten’s work. Corrections to Gamma can be easily estimated and should not give more than O(10-20)% error to the total gaugino massess. You can just add terms with higher powers of phi to see this.

  • http://golem.ph.utexas.edu/~distler/blog/ Jacques Distler

    My apologies, Cecil. We really have been talking at cross-purposes.

    Peter Woit and I were arguing about the proposition that the Landscape renders string theory unpredictive even in principle (“you can get anything you want”). That is, about the proposition that there are “too many” SM-like vacua.

    You are asking why we have not yet found any vacua which are viable candidates for the SM (though we’ve found lots of vacua that come close). These are orthogonal issues and little of my argument with Woit has bearing on your question.

    The problem of constructing such vacua and calculating their properties is a hard one, and the technical tools are still under development (see, e.g., c’s comment above). None of the requisite tools existed 20 years ago. Some crucial ones did not exist 5 years ago.

    But, then, you’ve surely heard that before.

    The fact that the problem is hard does not make it unworthy of study (people have been studying the Navier-Stokes equation for over a century, with relatively little progress). I suppose one could review the progress that has been made on this, and explain why people continue to be optimistic.

    (Of course, a prerequisite to optimism is that the “you can get anything you want” argument is clearly wrong; but then you’ve heard that, too.)

    But, rereading your comments, it’s not clear to me that’s what you are really interested in either.

  • TimG

    Peter,

    Just out of curiosity, if the LHC does find superpartners (as I know you expect it won’t), would you reconsider your opposition to string theory? I know that supersymmetry is possible even without string theory, but it still seems like it would be one crucial element falling into place.

  • Cecil Kirksey

    Jacques:

    Thanks for the reply. That is EXACTLY what I would like to hear. It is hard, if not very hard, to find a single vacuum that is consistent with the SM. How hard is the problem?? Who really knows. It would be very helpful if ST researchers would at least attempt to explain how hard it is and exactly where in this quest is the current research effort and do it in layman’s language.

    I do appreciate your responding to my questions. Sometimes lay people can ask questions that really separate the wheat from the chaff if given the opportunity.

  • Joseph Conlon

    Hi Peter,

    “For the LHC to decide between SUSY models, first it has to see SUSY. What do you think will happend to this whole field of model-building if the LHC doesn’t see SUSY? I’d like to believe that Haelfix is right that people will give up on it, but I’m not sure.”

    Give up and go home :) No, seriously, if the LHC sees anything clearly BSM it’s obviously tremendously, hugely, career-definingly exciting. In that case, I say follow the data and enjoy the ride.

    But let’s not be too confident the LHC won’t see SUSY: there is after all > 3 sigma evidence for BSM physics in muon g-2, which would seem to be best explained by susy ;)

    “That’s hard, so sure, some people should continue to try and see if they can get something out of ideas that so far haven’t worked very well. But personally I think it’s not very healthy if one unpromising idea completely dominates the field the way “string phenomenology” does. ”

    I don’t agree that string phenomenology `dominates the field’. Certainly, hep-ph is not being smothered by stringy constructions of the MSSM. The ‘try to compute the superpartner mass spectrum’ part of string phenomenology is a relatively recent development, from 2005 onwards. It only makes sense to try to do this computation once you can stabilise the moduli, and moduli-stabilising constructions are relatively new. Even after this, it require lots of care, knowledge about the how the SM is embedded in the compactification, etc. I think the reason why there has been lots of work on this recently is that now the technical tools are sufficiently developed that there is a sporting chance of doing the computation and believing the result. There is real progress being made here, and I think this justifies the current interest in this topic.

    The other point to make is that, whatever the LHC ends up seeing, the best preparation for the data that will come out of the LHC has to be studying particular models in detail. Even if scenario X is wrong, thinking carefully about how scenario X manifests itself in a collider will massively help in understanding scenario Y which is actually relevant.

    Best wishes
    Joe

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    TimG,

    Just finding superpartners wouldn’t necessarily address the problems with the lack of predictivity of string theory. So, for generic values of the observed superpartner properties, no, this wouldn’t change my opposition (which is not to “string theory”, but to the way of using it to unify particle physics and gravity that people are pursuing). If the superpartners have properties that are explained by a reasonably simple string theory model (in the sense that the inputs to the model are simpler than the outputs it is matching to experiment) I’d certainly reconsider, and if the model makes testable predictions that were checked, of course I would agree that I had been completely wrong, highly foolish, and shut up about this for good.

    For any values of the superpartner parameters, I surely would start taking a lot more interest in the details of the various supersymmetry breaking schemes out there.

    c,

    People can read it for themselves, but I think the Choi-Nilles review is clear in its claims, and they are explicitly not claiming what you are, that string theory leads to specific values for the gaugino mass ratios. I’ve never seen in the literature a claim that string theory leads to solid LHC predictions, and the review just explains one aspect of why this is true. You argue that some of these models are very recent, so we need to wait before evaluating the situation. Extrapolating from the past, it seems likely that all that will happen in the future will be that there will be more models and more possibilities.

    Cecil,

    As usual, please don’t believe a word of what Jacques Distler tells you my argument is, without reading my actual argument, which is made all too extensively above. The problem with string theory unification is not the abstract problem Jacques would like to discuss (which I don’t think we’ll ever know the answer to), but the undeniable fact that string theory now makes no predictions about particle physics. There are clear reasons for this undeniable current failure, no good reasons to believe that further elaboration of this failed framework will change the situation.

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    Joe,

    I think we can agree that if the LHC sees something new, people will, if they can’t get their model to fit the data, drop it and start working on something that maybe will fit the data. But what if there is not something new (i.e. just a SM Higgs), then what?

    Sure, the best argument for string phenomenology is that by playing with these models people will learn things and come up with new possible BSM signatures for the experimentalists to look for. The best argument against it is that it may be covering only a wrong-headed piece of the space of possible new physics, experimentalists might pay too much attention to this, and make a huge mistake like design their triggers to look for the wrong thing.

    I agree with your explanation of why people are doing these calculations, just disagree that this is a good thing. Having some new tools that allow you to push forward down a direction that hasn’t worked means it’s possible to do this, doesn’t mean it’s a good idea.

  • Mark Srednicki

    The question I always come back to is, what if the landscape is essentially correct? That is, what if string theory is the correct theory of the world, that it has zillions of metastable vacua, and that inflation creates zillions of “pocket universes” (our universe being one of them), each with its own metastable vacuum?

    I’ve never heard an argument why this could not possibly be true. And if it is true, it simply does not matter that it cannot predict the details of our particular particle physics, just like it does not matter that the theory of planet formation cannot predict the details of our particular solar system.

    In this case, the thing to do would be to strive to narrow down the possible string vacua that are compatible with the Standard Model (as amended, if necessary, by whatever is found at the LHC), and then to look for predictions common to this class. Unless and until this is done, it is simply not possible to make blanket statements as to what it will or will not be possible to predict.

  • c

    “People can read it for themselves, but I think the Choi-Nilles review is clear in its claims, and they are explicitly not claiming what you are, that string theory leads to specific values for the gaugino mass ratios.”

    Peter, could you please point to my comment where I claimed that “string theory leads to specific values for the gaugino mass ratios.” I can’t seem to find where I said that this prediction would be model independent.

  • Cecil Kirksey

    Mark Srednicki:

    I agree with your comment. It is basically in the same vein as my commentary with Jacques. Can a ground state be found that is in fact consistent with the SM and future observations from the LHC?? Nobody seems to know the answer but some researchers such as Jacques apparently are still very hopeful and I wish them the best. What will it take to have them accept the reality of a landscape, IF it exists?? Beats me.

    I have thought about the same scenario as you Mark. It very well maybe that that is just the nature of the beast and we will just have to accept it. Zero predictability. This maybe the result of ANY TOE. Period. It can not be proved one way or the other.

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    c,

    “I’m unaware of any construction or a set of constructions where one can get “just about anything”
    for the ratios of the gaugino masses”

    “Peter, have you tried to understand the state of SUSY phenomenology? Broadly speaking, there are a few basic ways of mediating SUSY-breaking to the Standard Model fields, and they tend to be fairly robust in terms of the outcome for basic quantities like the ratios of gaugino masses.”

    OK, the last one was from “anon”, not you, and I guess I missed the weasel-word “tend”, and the fact that it allows for the fact that some models don’t give robust results for gaugino masses.

    Not clear that it’s worth arguing about the definition of “just about anything”, seems to me an accurate description of what Choi-Nilles say you can get out of two string constructions.

    For a while I actually did believe, based upon what you and anon were saying, that there actually were robust predictions of a sort about gaugino masses that I didn’t know about.

  • http://www.cgoakley.demon.co.uk/qft/ Chris Oakley

    Cecil & Mark,

    Excuse me, but harping on with questions like

    “What if [insert weird, untestable idea] is essentially correct?”

    is not the scientific method. Scientific method invariably consists in choosing the simplest possible explanation for the observational data.

  • Mark Srednicki

    Cecil, I think it is very unlikely that we will end up with *zero* predictability, though we may only be able to predict things that are too much of a technological challenge to measure (eg, superplanckian scattering cross sections). But we just won’t know until a lot more work is done.

    There is also the possibility that there are still key missing ingredients that will radically change the picture. For example, Lee Smolin says that he suspects that the possibility that ours is one of a vast collection of universes with random laws “is not in fact a logical possibility in the correct theory of quantum cosmology” and that “by the time we understand quantum cosmology the notion of time will have been so altered as to make [this possibility] either nonsense or uninteresting” and that this could all happen within the framework of string theory. (Quotes extracted from various comments by Lee at http://asymptotia.com/2007/03/23/questions-and-answers-about-theories-of-everything ) This, or something like it, could well turn out to be the case. But we just won’t know until a lot more work is done.

    Some people apparently think this work should not be done, because string theory has “failed”. I think that giving up on string theory at this point would be like giving up on the nebular theory of planet formation in the 19th century, because it could not predict the number and type of planets in our solar system.

  • Mark Srednicki

    Chris, if I knew of a simpler explanation than string theory for the observational data (Standard Model plus gravity), I would embrace it. But I don’t. (The various flavors of LQG do not qualify, in my view, because no one has shown that any of them has the required semiclassical limit, and my intuition [which could be completely wrong] is that none of them do.)

    Another point to remember: the Standard Model is not pretty. It’s got three different gauge groups with three different gauge couplings, fermions in five different irreducible representations, Yukawa couplings that range over five-and-a-half orders of magnitude. ANY correct theory must reproduce this mess. It’s not going to be easy, or pretty, for ANY theory to do this. ANY framework will either have to explain why this mess is the unique ground state, OR invoke a landscape-style explanation.

  • http://golem.ph.utexas.edu/~distler/blog/ Jacques Distler

    Compare and contrast:

    The problem with string theory unification is not the abstract problem Jacques would like to discuss (which I don’t think we’ll ever know the answer to), but the undeniable fact that string theory now makes no predictions about particle physics. [emphasis added]

    I guess I missed the weasel-word “tend”

    Not clear that it’s worth arguing about the definition of “just about anything”

    Sigh.

    I really have been wasting my time here, haven’t I?

    Oh well, maybe I’ll try again the next time I see the (even illusory) semblance of a physics argument again.

  • c

    Peter, you said: “People can read it for themselves, but I think the Choi-Nilles review is clear in its claims, and they are explicitly not claiming what you are, that string theory leads to specific values for the gaugino mass ratios.”

    How is my saying: “I’m unaware of any construction or a set of constructions where one can get “just about anything” for the ratios of the gaugino masses” equivalent to “string theory leads to specific values for the gaugino mass ratios”?.
    It seems absurd to say that I have claimed “STRING THEORY leads to specific values for the gaugino mass ratios” when I was taking about the existing classes of models where the predictions for the gaugino masses were DIFFERENT. I went through the relevant papers trying to give you some very specific technical arguments to reinforce my claim that the two models you said can give “just about anything” can be quite predictive by explaining the ways to address the uncertainties described by Nilles and Choi.

    “Not clear that it’s worth arguing about the definition of “just about anything”, seems to me an accurate description of what Choi-Nilles say you can get out of two string constructions.” Can you get M1

  • c

    “Not clear that it’s worth arguing about the definition of “just about anything”, seems to me an accurate description of what Choi-Nilles say you can get out of two string constructions.” Can you get M1 smaller than M2 smaller than M3 in the G2 compactifications? No, you cannot because the anomaly mediated contribution to M1 is always smaller than the tree level value, even when the threshold effect to the anomaly mediated piece are taken into account.

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    Jacques,

    Your tactic of taking what I write out of context, deleting parts of it, and changing the rest by adding emphasis that wasn’t there in the original, then pairing the result with some sneering comments on your part is as charming as ever.

  • Jean-Paul

    Mark Srednicki, #302 and on. I can’t believe that I see it again. Here is what I commented on Peter’s blog just couple of weeks ago, referring to a comment made by somebody who claimed to be “a string theorist”:
    “Your argument about planetary orbits is yet another propaganda trick pulled by AP desperados, that appears in the introduction part of all Arkani-Hamed talks (at least of those that I attended). Yes, we do not understand initial conditions for many motions in the Universe, and its not a big deal that we do not understand them for the solar system which is in our nearest proximity. However, you cannot compare this ignorance to our lack of understanding of say electron’s mass which is relevant not only in our proximity, but everywhere that we know in the Universe.”

  • Mark Srednicki

    Jean-Paul, the point (which I’m sure you understand) is that, in the scenario under discussion, our universe is just one tiny piece of a much larger “multiverse”. In other universes, the electron has a different mass, or doesn’t exist at all. This is exactly analogous to our living in a single solar system that is just one tiny piece of a galaxy, with each solar system having different properties.

    Some may claim that the analogy is not precise, because there is (as far as we know now) no way to observe the other universes, whereas we can observe the other solar systems (to some limited extent). I don’t think this objection is very strong, however, as we can easily imagine intelligent life in (say) the atmosphere of a gas giant, with no hope of building technology that could see through their clouds. Yet any hopes they might have of explaining their world based on its (to them) unique properties would be hopeless, because their world was in fact produced by random initial conditions.

    We might be in the same situation with regard to the particle physics we see in our universe. I personally think this is rather likely, precisely because the Standard Model is such a mess; it’s hard for me to see how it could emerge as the unique ground state of any “nice” theory, other than in a landscape scenario.

  • Mark Srednicki

    And, it would be nice if the critics of string theory would propose something else to work on. (I’m exempting Lee here, since he has his own well-articulated program.) Peter Woit has said that we should work on nontrivial representations of gauge groups, but it’s awfully hard to figure out what this would mean: in QED, the statement that the trivial representation is the correct one is equivalent to imposing Gauss’ Law. So a nontrivial representation would violate Gauss’ Law. Introducing states that violate Gauss’ Law just doesn’t seem helpful to me. And it certainly doesn’t seem to point towards any explanation of why the top quark is 5.5 orders of magnitude heavier than the up quark …

    It’s easy to throw stones at houses one doesn’t like, much harder to design and build one yourself …

  • Thomas Larsson

    And, it would be nice if the critics of string theory would propose something else to work on.

    QJT.

    The idea is simply that the algebraic structure underlying quantum gravity should be the combination of those underlying general relativity (background independence) and quantum mechanics (lowest-energy representations). As is well known already in 1D, interesting lowest-energy representations of the diffeomorphism algebra are necessarily anomalous (Virasoro algebra), and the higher-dimensional case is not different (multi-dimensional Virasoro algebra).

  • Gina

    Dear all,

    Overall, this seems to be a good discussion and it gives quite a good picture on the matter of how string theory will connect to empirical evidence. Two points which I was getting are:

    1) While string theory as a whole does not give at present (and there is no guarantee it will give in the future) concrete predictions (e.g. Gaugino mass ratios; whatever they mean) specific fragments of string theory do.

    Therefore, new empirical findings expected in the (5-10) years ahead may lead to developments within string theory. The role of such empirical evidence to establish the correctness of string theory seems rather questionable. So is the (related) issue if it will allow for concrete predictions from string theory on later empirical observations.

    2) It is somewhat premature to discuss it since we do not have yet a single example of a model from string theory that agrees with the standard model. (When one such model will be found there will be automatically many such models.)

    I hope I got the picture at least approximately right.

    (And people also discussed several scenarios/prophecies on what LHC will find. I can very cautiously offer the following prophecy: If the LHC findings will be depressing we will be depressed while if the findings will be encouraging we will be cheered.)

  • Gina

    Dear Peter,

    You wrote : “…and if the model makes testable predictions that were checked, of course I would agree that I had been completely wrong, highly foolish, and shut up about this for good.”

    I do not think we should regard this discussion as a “prophecy competition.” If you (or anybody else) make good (and novel) academic/scientific arguments “against” string theory then there is nothing to be ashamed of even if later the ideas turned out to be false. (And vice versa!).

    Maybe, I have an over-romantic view about science but the way I see it the quality of the arguments themselves counts a lot and not just the bottom-line.

  • Thomas Larsson

    in QED, the statement that the trivial representation is the correct one is equivalent to imposing Gauss’ Law. So a nontrivial representation would violate Gauss’ Law.

    The subcritical free string has a conformal gauge anomaly, but can nevertheless be quantized with a ghost-free spectrum (no-ghost theorem). So not all anomalous gauge theories are inconsistent.

    Of course, an anomalous gauge symmetry becomes a global symmetry on the quantum level, which acts on the Hilbert space instead of reducing it. So anomalies are a means to gauge symmetry breaking, possibly an alternative to the Higgs mechanism.

  • http://www.cgoakley.demon.co.uk/qft/ Chris Oakley

    Mark,

    I am no expert on String Theory, but one does not need to be an expert to realise that Occam’s Razor does not apply to the vast majority of the efforts in this direction. See, for example, comment #204 here. The extra dimensions seem to be what leads to all the problems, but there was no interest whatsoever when a former colleague of mine advanced the possibility of a 4D version. As far as I can see, the attitude of ST practitioners has never been scientific – it has always been, “Gee, Wow! Let’s see where this amazing idea leads!” Which brings me on to your comment: “it would be nice if the critics of string theory would propose something else to work on”. This has been happening all the time – my own modest efforts being part of this – it is just that no-one notices because of the noise generated by the excitable children who do String Theory.

  • Thomas Larsson

    Chris, you don’t seriously think that somebody who knows The TRUTH is interested in alternatives? :-)

  • http://www.cgoakley.demon.co.uk/qft/ Chris Oakley

    Thomas,

    You’re right. All this scepticism … I feel terrible. Makes me feel a bit like Pontius Pilate – “What is truth?” Sorry I spoke. Maybe as I type this, the veil of the temple is being rent in twain – which I guess here in London would mean the Temple Underground Station – I’ll check the news when I finish work today.

  • Paolo Bizzarri

    Mark,

    I am referring to your comments #308 and #315.

    First and foremost, please note that I am no expert in theoretical physics. So, most of my comments will not be on your physics arguments (which I am not able to comment properly).

    You are saying:

    “And, it would be nice if the critics of string theory would propose something else to work on.”

    This is a weak argument, for at least two reasons.

    First, if I see a weakness in your theory, I can point it to you, and I am not required to provide an alternative theory.

    But, second, and most important, building a ST-like theory is an immense task. As far as I understand, it has required 20+ years of work of top level physicist.

    You cannot seriously ask for “something alternative”. Years of work by Witten and all the others string theorist(including, as I understand correctly, you) cannot be replaced by the work of one or two persons (unless they are true geniuses).

    If the problem was simple, you and your collegues would have already solved it, and everyone would be happ about the solution.

    I cannot judge your results. But you can. You have said “Chris, if I knew of a simpler explanation than string theory for the observational data (Standard Model plus gravity), I would embrace it”.

    The point is, you cannot find what you are not searching for. Don’t you believe it could be a worthwile effort to try to define an alternative to String Theory?

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    At first I was going to try and respond to Mark Srednicki’s comments about me and about representations of gauge groups, but decided that this would take this thread far off-topic. But then I realized that Mark’s comment is perfectly on-topic. Sean described string theory advocates as losing the public debate, because they won’t “Make some effort to explain to everyone why this set of lofty speculations is as promising as you know it to be”. Instead, Mark seems to think that he”ll convince people of the promise of string theory by attacking Smolin and me, including behavior like publicly jeering that Smolin is a “crackpot” (at an event being videoed for public distribution).

    Go right ahead and keep doing this if you want to keep damaging your own cause.

  • Gina

    Hi Peter,

    Mark and Lee had recently nice and very interesting physics exchanges on “asymptotia”. (They both made interesting points and I think they even agreed at the end on some issue.) It could have been nice to have a discussion on the usefullness of non-trivial representation of guage groups and their potential role. And how this can still be consistent with Gauss’ law. If you think it is off-topic you can simply ignore this remark. But bringing back this “crackpot” things seem counter-productive.

    Anyway, I do not think that questioning the role of non-trivial representations of gauge groups can be regarded as a personal attack of any kind. (Or perhaps we should work for a universal agreement that the only personal attacks from now on will be representation-theoretic.)

    Actually this point even looks like an interesting scientific issue.

  • Mark Srednicki

    Thomas:

    Am I correct that QJT is currently unable to predict the value of any parameter in the Standard Model (or any plausible extension thereof)? If so, it seems to me that it’s intellectual status is no different than that of string theory. I have no problem with you or anyone else working on it, or on anything else that you believe is worth pursuing. If anyone asked me my opinon of it, I would say “It doesn’t look promising to me, but I’ve certainly been wrong before.”

    I agree that violations of Gauss’s law are not mathematically inconsistent; they are inconsistent with experiment. Isn’t that supposed to be the ultimate test?

    I would be very interested in seeing a concrete proposal for replacing the Higgs field of the Standard Model with an anomalous gauge symmetry.

  • Mark Srednicki

    Chris:

    You complain that “there was no interest whatsoever” when William Shaw prospoed a 4D string theory. Perhaps that’s because he never wrote a paper on it, but only gave a talk on it (at DAMTP) in 2004, and first posted the slides for this talk on his personal web site (with no link from his home page) in January of this year (that is, three months ago). Furthermore, in a quick perusal of the slides, I could not find any discussion of the quantum Virasoro algebra for his twistor-based theory; only the classical Virasoro algebra is treated (as far as I could tell). It is the anamoly in the quantum Virasoro algebra that fixes the critical dimension. It seems extremely likely to me that his theory (if it’s consistent at all) is anomalous in all but 26 dimensions. If he (and you) want string theorists to pay attention, then I believe it is incumbent upon him to (1) write a paper demonstrating that the quantum Virasoro algebra is anomaly free in 4D, and (2) to submit the paper to the arXiv and to a journal. If he writes that paper, and it contains an argument for 4D consistency that I can follow and think is not obviously wrong, I hereby volunteer to act as endorser for the arXiv.

    Meanwhile, I think it is grossly unfair of you to complain that this obscurely posted set of slides has been ignored by the string community for the past three months.

    As for Occam’s razor, if you have a framework for fundamental physics that is closer to making a definite prediction for a parameter of the Standard Model (or a plausible extension thereof) than is string theory, please let us know.

  • Mark Srednicki

    Paolo:

    You are correct that “building a ST-like theory is an immense task” that “has required 20+ years of work of top level physicists.” You say that, therefore, I “cannot seriously ask for ‘something alternative’.”

    I believe it is fair to ask for an alternative from those who insist that string theory is not worth pursuing, who say that it has “failed” and that all this work should simply be abandoned. Abandoned in favor of what, exactly? That’s what I want to know.

  • Paolo Bizzarri

    Mark:

    “Abandoned in favor of what, exactly? That’s what I want to know.”

    Well, my understaning is that, if you scientists had a good alternative to String Theory (something that is beatiful, predictive, mathematically consistent, full developed and so on), you will be eager to throw ST to the dogs.

    But the problem is exactly this: from one side, you have a complex, rich theory with 20+ years of development behind it, that right now is not fully developed yet, and has no predictive ability; from the other, you have very little (ok, you have LQG, but I understand that also LQG has lots of problems).

    So, it is safe to say that if you throw away LQG, you are back to square one.

    You can’t ask for an alternative to ST. The only alternative for ST is rolling up your sleeves, and going back to the blackboard.

  • Mark Srednicki

    Peter:

    I would be happy to hear an explanation of how a nontrivial representation of the gauge algebra in QED can avoid looking like a violation of Gauss’ Law (or how such a violation could be made consistent with experiment).

    I believe that a key point in the public debate on string theory must be, “What are the alternatives?” and “What predictions do these alternatives make?” So exploring the proposed alternatives in a public forum seems to me like a good thing to do.

    Concerning your other point, relevant discussion can be found at http://asymptotia.com/2006/10/27/more-scenes-from-the-storm-in-a-teacup-v/#comment-3045

  • anon.

    “As for Occam’s razor, if you have a framework for fundamental physics that is closer to making a definite prediction for a parameter of the Standard Model (or a plausible extension thereof) than is string theory, please let us know.” – Mark Srednicki

    The basic standard model has only 19 parameters, the minimal supersymmetric (stringy) version of standard model has 125 tunable parameters! If you want to make string theory get closer to predicting something, start by dropping supersymmetry, which just drags it further from reality.

    The impression you are making is that string theory is going toward making predictions, when it’s actually going in the other direction. Supersymmetry is not science because there’s no experimental evidence that the standard model forces should all need to unify at 10^16 GeV, the Planck scale is dimensional analysis and hasn’t been empirically observed, nor is there any evidence for supersymmetric partners. (It’s like supergravity: start with the guess that there are gravitons, then invent an 11-d universe for those imaginary, unobserved gravitons. The framework that’s closer to reality is the 4-d GR and SM based on observables: LQG, representation theory, whatever.)

  • Mark Srednicki

    Paolo:

    When I was a grad student in the late 70s, a friend (not a physicist) said to me that he had heard that the great unsolved problem of physics was combining quantum mechanics and general relativity; he wanted to know if people were working on this.

    My answer was, not so much. The problem, I said, is you needed a good idea. You couldn’t just go into work in the morning, sit at your desk, scrunch up your forehead, and say “Now I will think about quantum gravity!” You needed an idea, something concrete to pursue. Yes, I said, some people were working on certain ideas, but none of them appeared all that promising, so mostly people were working on more tractable issues.

    So, yes, you can roll up your sleeves and go to your blackboard, but what will you write on it?

  • Paolo Bizzarri

    Mark,

    I understand that I am playing the easy part of the game. The problem, as you correcttly describe, is what you write on the blackboard.

    My answer is “I have no idea”. But this is not my problem. I don’t know if it is your problem.

    If you feel that ST is not working really, you should get some people in front of a blackboard, and then say: “ST is a mess! LQG is a mess! Every theory we are working on is a complete mess! Now, what we want to do?”

    Perhaps you could ask people like Peter and say “Ok, people, now you are in charge, which theorem are we going to demonstrate tomorrow?”. Or, in general, collecting people from different approaches and trying to come up with a new idea.

    Perhaps you should try to work on something simpler. Perhaps the unification that ST promised, long time ago, was too much. If you have to explore the whole space of theories in one step, it could be impossible (even if ST could be perfectly reasonable).

    Perhaps you should burn a picture of professor Witten, as some sort of rite in order to free yourself of his too much powerful influence :-)

    But I really don’t know.

    The real point is if you consider a worthwile task to spend time to find a new idea.

  • Mark Srednicki

    anon:

    You write, “The framework that’s closer to reality is the 4-d GR and SM based on observables: LQG, representation theory, whatever.”

    I’m not sure exactly what framework you mean. Of course we must end up with 4d GR and the Standard Model (or whatever extension of it, if any, turns up at the LHC) as the low-energy limit. The question is, what happens in the high-energy limit? String theory is being criticized for not providing a definitive answer. This is a valid criticism, but it also applies to ALL proposed “alternatives”. I put “alternatives” in quotes because most of them are so undeveloped that the relevant questions can’t even be asked. I personally see extremely limited prospects for development of any of these alternatives to the point that the questions can be asked. Spin-foam LQG has the best prospects, in my view, though I would still bet heavily against it working out, and it presently has nothing whatever to say about the parameters of the Standard Model.

    As for representation theory, there seems to me to be no issue in the abelian case: nontrivial representations look like violations of Gauss’ Law, and these are ruled out experimentally (though I would be happy to be pointed to a source that explains why this is wrong).

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    Mark,

    Your idea that the way to deal with criticism of string theory is not to make the case for it, but to attack its critics remains remarkably consistent over time. On the physics issue, I’m not talking about QED, but about chiral gauge theories. You’re well aware of this, since you supposedly read the third post on my blog, more than three years ago, about exactly this topic. At the time you (like other string theory advocates in the blogosphere) thought the best way to deal with a string theory critic was to attack them as ignorant of basic facts about physics:

    “I came to your web site because I was told that you are a critic of string theory, and I wanted to see what you had to say about it. What I find is appalling ignorance. You really ought to spend some time learning some physics before you attack it. I recommend starting with Weinberg’s three-volume text on quantum field theory…

    …I’m horrified that the ideas of someone as ignorant as you can be so widely circulated without serious rebuttal. You haven’t gotten serious rebuttal because the serious people have better things to do with their time. If you want to learn some physics first, fine. Unless and until you do, please stop trying to tell funding agencies (all staffed with people far more knowledgable than you are) how to best use their meager sums.”

    Do you care at all why, as Sean Carroll notes, string theorists are losing the battle in the public marketplace of ideas? One big reason is because of behavior like this of yours and of other string theory advocates on various blogs. You’re doing far more damage to the cause of string theory than I or Smolin ever will. Go right ahead and keep it up.

  • Mark Srednicki

    Peter:

    So you agree that only the trivial representation of the U(1) of QED is allowed?

    I made my point in the context of QED only for simplicity. In the nonabelian case, non-trivial representations will violate (as far as I can see) the nonabelian version of Gauss’ Law. In terms of scattering amplitudes, this will lead to extra tadpoles in Feynman diagrams that can almost certainly be ruled out by precision electroweak data (unless the tadpoles conspire in some way; once again, I would be happy to be pointed to a detailed explanation of how this is supposed to work).

    Three years ago, you appeared to be confused on the fact that, in four spacetime dimensions, a left-handed Weyl field is a hermitian conjugate of a right-handed Weyl field. I found this rather surprising, though I admit that I expressed my surprise in overly strong language.

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    Mark,

    I’ve never said anything anywhere about this being a physically interesting question in QED. Whatever you may think, I am well aware of basic facts about quantum field theory (such as basic facts about Weyl fields, and that Gauss’s law is the expression of infinitesimal gauge invariance). If you had bothered to read the posting three years ago on my blog before launching into insults based on your conviction that a string theory critic must be an ignorant fool, you’d see that my speculation related to our imperfect NON-PERTURBATIVE understanding of CHIRAL gauge theories. Feynman diagram arguments can’t address this issue.

    I don’t think this is the place for a serious discussion of the issue of possible holes in our understanding of nonperturbative chiral gauge theories, and, based on your previous behavior, I personally don’t believe you have any interest in such a discussion. Again, I seriously urge you to reflect on the point Sean Carroll is making in his posting here: string theory advocates are losing this debate because they can’t defend string theory research in a positive way. If you want to continue this losing tactic, go right ahead. As for your claim that three years ago, you were just expressing “surprise”, well, you’re continuing to insult my intelligence.

  • Gina

    Dear Mark,

    I have an “off debate” question. (But these blogs have also “outreach” purposes, I suppose.) Is it possible to explain to a lay person why only the trivial representation of the U(1) of QED is allowed. (I feel with all the reading of popular descriptions that I may well be only a few sentences from understanding at least in some level this matter.) I will be very very thankful for an explanation.

  • Moshe

    Gina, off-debate answer…when quantizing higher spin fields in a Lorentz invariant theory one has to somehow eliminate the negative norm states one encounter (those are states that have negative probabilities, something not so easy to interpret). The only known way to do it is to impose local gauge invariance- since those negative norm state can have arbitrary spacetime dependence, the symmetry imposed to eliminate them must also be local. This must be a symmetry of everything, including the observables. In other words everything should be invariant (aka the trivial representation) under gauge transformation.

    I don’t see anything specific to QED, or to perturbation theory, in this argument, but I am definitely going to stay off-debate.

  • anon.

    anon:

    You write, “The framework that’s closer to reality is the 4-d GR and SM based on observables: LQG, representation theory, whatever.”

    I’m not sure exactly what framework you mean. Of course we must end up with 4d GR and the Standard Model (or whatever extension of it, if any, turns up at the LHC) as the low-energy limit. The question is, what happens in the high-energy limit? – Mark Srednicki

    It just isn’t the case the existing understanding of 4-d GR and the Standard Model must be the complete and correct at low energy: there are a lot of outstanding questions about both, to be resolved better before these theories are properly understood in the low energy limit. Issues include electroweak symmetry breaking, dark energy (70% of universe), dark matter (25% of universe). If you assume that the existing understanding of the universe at low energy is complete and accurate, when it accounts for only 5% of the mass-energy and there is no confirmed theory of how mass arises or how electroweak symmetry breaks, then you’re speculating. You might as well be basing your final theory on Maxwell’s aether just because his equations for electromagnetism are well checked.

  • Mark Srednicki

    Peter:

    When I brought up representation theory, I was not referring to your post of three years ago (which does not mention representation theory at all), but rather to your recent talk in Orlando, where you wrote (full set of slides at http://www.math.columbia.edu/~woit/orlando.pdf ):

    “There are two main technical difficulties associated with properly defining QED and doing calculations with it:

    “1) Fields carry degrees of freedom for every point in space-time, thus an infinite number. Naive calculations are plagued by infinite results. Properly handling this is known as ‘renormalization’ and was not carried out for QED until the late 1940s.

    “2) The group of gauge symmetries is infinite dimensional. To this day, the representation theory of this group is not understood. Physicists generally believe this doesn’t matter, that only the ‘trivial’ representation matters, not the rest. In other words, one just needs to understand the ‘gauge-invariant’ part of the theory.”

    I don’t know how to reconcile this with your claim above that “I’ve never said anything anywhere about this being a physically interesting question in QED.”

    Once again, the only meaning I know how to attach to a “nontrivial representation of the gauge group” involves violations of Gauss’ Law (in both the abelian and nonabelian cases, irrespective of whether the matter is chiral) that would definitely show up in perturbation theory. If you know how to attach some other meaning to this phrase, I would appreciate being pointed to the explanation.

    As for “defend[ing] string theory research in a positive way”, I gave my take on the current situation above. To briefly recap: The Standard Model has lots of ugly features that ANY more fundamental theory will have to explain. To me, this makes “landscape” style explanations more plausible. No framework other than string theory comes anywhere close to explaining any feature of the Standard Model; every one of these alternative frameworks is significanlty less predictive than string theory. (In string theory, if we knew full details of a compactification that reproduces the Standard Model, we could in principle predict scattering amplitudes at superplanckian energies.) Finally, as Lee Smolin anticipates, there could well be deep surprises remaining that totally change the picture, and (as Lee concurs) this could well happen within the string framework.

    So, whatever the current demerits of string theory, it’s the best theory we have. I don’t know how to think up a better one. I’m very much open to hearing of a better one from someone else, but I don’t expect to; I think quantum gravity is a very constrained problem, and that string theory is very likely to be the only solution to this problem. If it is the only solution, abandoning it now would be a foolish thing to do.

  • Mark Srednicki

    Gina:

    Tell me how much physics you know (popular books, high school, 1st-year college, college major, 1st year grad school, PhD) and I will attempt an explanation at that level. (I would say that Moshe’s answer is PhD level.)

  • Mark Srednicki

    anon:

    I was implicitly including dark matter as something that might show up at the LHC (eg, as the lightest supersymmetric particle), but of course it might not; it might be condensed axions or some other moduli. Then we’d have to make sure our low-energy theory includes a suitable field. (Axions might be found in the current searches.) I’m assuming dark energy is the cosmological constant, anthropically selected from the landscape to be small. All this might result in enough uncertainty to prevent predictions at high energies, but we won’t know without a lot more work.

  • Gina

    Dear Moshe and dear Mark

    Many thanks for the explanation, Moshe. A few sentences away from some understanding was a little optimistic on my part. Based on the popular reading (+ a college degree with some physics +math and some later academic experience of little relevance) what you wrote sounds appealing and not completely cryptic but indeed also somewhat above my head. I will be happy to learn more.

    BTW, Is the negative norm state that force you to forget all other representations similar to the unpleasant gadgets that force you dimensions 26 (10) for strings? (I vaguely recall the term negative norm states from that story as well.)

  • http://www.cgoakley.demon.co.uk/qft/ Chris Oakley

    Mark,

    I am not qualified to comment on the merits of William Shaw’s work on 4D superstrings – the reason for mentioning it was just that he had felt that the talk at DAMTP had not gone down well at all. This I found surprising. I should point out, though, that the slides have been available on his web site for some years, although not always in a very “friendly” format (i.e. very large PDF files).

    As for Occam’s razor, if you have a framework for fundamental physics that is closer to making a definite prediction for a parameter of the Standard Model (or a plausible extension thereof) than is string theory, please let us know.

    I have tried to, and will continue to try to accurately reflect my own perception of the issues, and their possible solutions, on my web site. Yes, it would be very nice to explain SM parameters, but establishing a mathematical framework free of inconsistencies has to be done first.

  • anon.

    Mark Srednicki on Apr 10th, 2007 at 4:34 pm
    anon:

    I was implicitly including dark matter as something that might show up at the LHC (eg, as the lightest supersymmetric particle), but of course it might not; it might be condensed axions or some other moduli. Then we’d have to make sure our low-energy theory includes a suitable field. (Axions might be found in the current searches.) I’m assuming dark energy is the cosmological constant, anthropically selected from the landscape to be small. All this might result in enough uncertainty to prevent predictions at high energies, but we won’t know without a lot more work.

    Mark, thanks for your reply in the string theory context. The idea that supersymmetric partners, whose masses aren’t theoretically predicted, might be dark matter is very neat: a typical “heads I win, tails you lose” type forecast. There’s a catch 22 when you defend string theory by saying a lot more work needs to be done on it to see what it really says about dark energy, dark matter, etc. Henry Kissinger replied, when someone told him the Vietnam War was like a bottomless pit for money and human lives: “Every pit has a bottom.” It’s weird that sometimes people believe so much in things that they have a convenient answer to any objection. Any complaint that string theory is a complete failure as physics is responded to by saying it just needs a lot more work. Plus more funding…

  • Mark Srednicki

    Gina, I think I may have been a little optimistic in claiming I could explain it at any level, but here goes …

    The three components E_i, i=x,y,z, of an electric field the three components B_i of a magnetic field can be expressed in terms of the three components A_i of a vector potential via E_i = -(d/dt)A_i and B_x = (d/dy)A_z, B_y = (d/dz)A_x, B_z = (d/dx)A_y. (Note to cognoscenti: I am working in the partial gauge A^0=0.) The vector potential that yields particular electric and magnetic fields is not unique; it can be changed from A_i to A_i + (d/dx_i)g, where g is any function of x_i (and not time), without changing E_i and B_i.
    This is a gauge transformation.

    Without any charged matter around, Gauss’ Law is (d/dx_i)E_i = 0, where the repeated i is summed. Physically, it means that electric flux is conserved; electric field lines don’t end. (With charged matter, electric field lines can end on charges, and Gauss’ Law is modified to (d/dx_i)E_i – rho = 0, where rho is the electric charge density.)

    In the quantum theory, because E_i = -(d/dt)A_i, E_i and A_i obey equal-time canonical commutation relations of the form [E_i(x,t),A_j(x’,t)] = i delta_{ij}delta^3(x-x’).

    Now we define G, the generator of gauge transformations, given by the integral over all space of g(x)(d/dx_i)E_i(x). Then we have the commutators [G,A_i(x)] = i(d/dx_i)g(x), which (except for the factor of i) is the added term in the gauge transformation. This is why G is called the generator of gauge transformations.

    If Gauss’s law holds for a quantum state |s>, then G|s>=0. This is equivalent (in the usual meaning of the terminology) to the statement that |s> is in the trivial representation of the gauge group. In any nontrivial representation, G|s> would not vanish, which is only possible if Gauss’ Law is violated.

    All this still works when we add charged matter and/or go to the nonabelian theory, but the formula for G changes.

    The relation of this explanation to Moshe’s is highly nontrivial. And yes, negative norm states of a single string are what force you to 26 (or 10) dimensions. (My version of the explanation also has a counterpart in string theory, where one tries to prove the Lorentz algebra, and finds that it only works in the critical dimension.)

  • http://www.math.columbia.edu/~woit/blog Peter Woit

    Mark,

    In the next page after the one you quote, I refer to the problem of gauge symmetry as being solved in QED, and later solved in 1967 for Yang-Mills theory. I don’t anywhere say anything about the lack of understanding of gauge group representations in QED leading to a physical problem in that theory.

    The theory where the question is more interesting is the standard model. There, if you throw away the electroweak sector, pure QCD is non-chiral, and the lattice appears to provide a satisfactory non-perturbative formulation, with gauge invariance achieved by integrating over the gauge degrees of freedom. In the continuum, even in this theory, there are poorly understood aspects of gauge invariance outside of perturbation theory (e.g. Gribov ambiguities).

    If you add in the electroweak sector, the theory is chiral and lattice regularizations are problematic (there are claims that overlap fermions solve this but the situation seems unclear to me, and I haven’t seen anyone able to do actual non-perturbative SM lattice calculations). Chiral theories generically are anomalous gauge symmetry, but we understand how anomalies cancel in perturbation theory in the SM case. The fact that we don’t have a well-understood non-perturbative formulation of exactly this theory that would allow a clear understanding of how gauge symmetry works there seems to me an interesting problem, and it is not unreasonable to notice that it is exactly in this case that we need the Higgs mechanism to deal with the gauge symmetry properties of the vacuum state.

    In 1+1 d one can actually hope to understand exactly what is going on since one does know what states look like as representations of the gauge group, and the representation theory mostly determines what goes on. Various interesting phenomena occur here, I’ve written about some of them and their relation to twisted K-theory and the Freed-Hopkins-Teleman theorem, but there is still a lot I don’t understand about this situation, hope some day to get sorted out and written down. Maybe some of it will give some insight into higher dimensional theories.

    Your claim that string theory is better than alternatives because other theories are “less predictive” is just not true. String theory explains nothing about the SM and makes no predictions. You don’t even know the string scale or string coupling (who says it is small enough to make string perturbation theory valid?), so you don’t even have the predictions you claim about super-planckian scattering amplitudes.

    If string theorists want to believe, after a few bong hits, that somehow magically a compactification that describes the world will be found, will be predictive, get tested and verified, they’re welcome to do so, although they should admit there is no argument about why this should happen. If others want to believe, after some other, possibly lesser, number of bong hits, that better understanding of gauge symmetry will explain the Higgs mechanism and allow computation of Yukawas, that a dynamical triangulation will produce the right kind of particle states, or that a 4d consistent string theory that explains the SM will be found, they also should be welcome to do so. I don’t think one can sensibly claim one of these is more likely to work out than the other. The only distinguishing characteristic of the string compactification unification scheme at the present time is that it has received vastly more attention, a much greater amount of work has gone into it, and its problems (the landscape..) are now rather well understood. This is an argument for encouraging people to try to do other things.

  • Diogenes

    *”If you add in the electroweak sector, the theory is chiral and lattice **regularizations are problematic (there are claims that overlap fermions solve this **but the situation seems unclear to me, and I haven’t seen anyone able to do **actual non-perturbative SM lattice calculations).”

    The computational cost of doing calculations involving fermions, chiral or otherwise, is well known, and it is only recently that there has been sufficient computing power to go beyond the quenched approximation in QCD simulations, for example.

    But this is different from the claim that we do not know, in principle, how to define chiral gauge theories on the lattice. What is it specifically about the overlap fermion proposal that you believe is incorrect? Is there a publication that I can refer to for your analysis?

    Thanks for your assistance!

  • onymous

    Peter, it has always seemed to me that the difficulty with chiral fermions on a lattice is really an issue of the topology we choose when going to finite volume. If we knew a good regulator on the sphere, for instance, we presumably wouldn’t have any difficulty nonperturbatively defining a chiral gauge theory on the sphere. So I don’t see it as being really a feature of the theory itself that makes it problematic, I see it as a bug in the choice of regulator. I would think that one direction to go in for trying to nonperturbatively define chiral gauge theories would be trying to construct a theory on the fuzzy sphere and showing that the continuum (zero-fuzziness) limit is good.

  • gs

    off-debate physics question, regarding gauge-invariance in QED. Isn’t it correct that Gauss’ law only says that physical states should be invariant under local gauge transformations that are trivial at spatial infinity?

    Specifically, if I write the Gauss’ law constraint as C(x)=0 where C(x)=div E(x) -rho(x), then G=int C(x)theta(x) is a generator of a U(1) gauge transformation with parameter theta(x) only when theta(x) goes to zero at spatial infinity. For example, take theta(x) equal to a constant. In this case, the Gauss law constraint G=0 just gives (Electric flux = Q). So physical states do not have to be invariant under global U(1) transformations generated by Q (otherwise how do I get charged states in QED?).

    Is this correct?

  • http://www.math.columbia.edu/~woit/blog Peter Woit

    Diogenes,

    I’m no expert on chiral gauge theories on the lattice, and would appreciate hearing from one about the exact state of this. My own experience doing lattice calculations involved several iterations of thinking I knew how to properly define something, only to find that there was a problem I hadn’t thought of once I coded the algorithm and started simulations. This is one reason I’d like to see an actual calculation of something. The literature I’ve tried to read contains various claims and the situation seems to me, as I wrote, unclear. Here’s Mike Creutz’s 2004 summary (in hep-lat/0406007) of the situation:

    “While a lattice regularization of a full chiral gauge theory such as the standard model remains elusive, we may not be far off.”

    I’m not aware of any major breakthroughs in this area since 2004.

    onymous,

    Again, I’m no expert, and haven’t thought much about this in a long time, but from what I remember, the global topology of the finite volume is not the problem, rather it is what is happening at the scale of the cut-off.

  • Moshe

    gs: right, gauge transformations that don’t vanish at infinity should be thought of as global transformations that act on the Hilbert space of the theory. The generator of those transformations is the (total) electric charge. Related issues are the definition of mass in GR, and that of the theta angle in QCD, where gauge transformations not vanishing at infinity are important.

  • onymous

    Peter, it looks like the issue is more subtle than I had realized. Nielsen and Ninomiya first gave a proof using homotopy theory, relying on the topology of the Brillouin zone (Nucl.Phys.B185:20,1981). This is what I was (somewhat) familiar with. Later, they gave a more general argument (Phys.Lett.B105:219,1981) that claims to apply to any regulator satisfying some basic assumptions that one would not want to give up (gauge invariance, the right anomaly, an action bilinear in the fermions). The obvious perturbative regulators (dim reg, Pauli-Villars) each violate one of these assumptions.

  • Hendrik

    Mark Srednicki, #347 and Moshe:

    I can flesh out the mathematical side of the problem of the Gauss law constraint and its relation to indefinite metric representations (+ a different option).

    First, one needs to know about the following two theorems:

    1) Strocchi 1967:
    If A_mu(x) is an operator valued distribution (on a Hilbert space) which transforms covariantly w.r.t. the Poincare group, then
    Box A_mu =0 (field eq’n) and
    partial^mu A_mu =0 (Gauss law)
    implies that F_{munu} = 0 where F_{munu} = partial_nu A_mu – partial_mu A_nu

    2) Barut + Raczka 1972:
    A J-unitary representation of the Poincare group which is of zero mass and on tensor valued functions (e.g. Fock rep), must have J not equal to I, i.e. it must be on an indefinite metric space.

    For the electromagnetic field, these two theorems force you (for the Fock representation) to go to an indefinite metric space, and hence the Gupta-Bleuler method of enforcing both the Gauss law and the field equation as state constraint conditions.

    The justification is that after constraining, the final physical space is again a Hilbert space (i.e. the indefinite metric is eliminated), so the indefinite metric only appears for the nonphysical part of the theory.

    However, as I have argued (with my co-author) in Rev. Math. Phys. 12, 1159 (2000), the indefinite metric can be avoided. The point is that there are implicit regularity assumptions for the representation of the two theorems above, and there is no reason to require regularity on nonphysical objects. So, if one takes the field algebra of observables, and allow (Hilbert space) representations to have nonregular behaviour on the nonphysical objects, then the theorems above do not hold anymore, and one can enforce the Gauss law constraint and field equation without any problems. In particular, we have done this for Gupta–Bleuler electromagnetism, and we obtained the same results than what one obtains via indefinite metric Fock rep. Moreover, the final physical algebra has a perfectly sensible Fock rep with all the right properties, but importantly, it did not come from constraining a Fock rep on the original field alg.

    So the moral of the story is that for gauge theories one should not be married to indefinite metric representations in constraint problems, they can be avoided.

  • Mark Srednicki

    Chris,

    Looking at Shaw’s slides, I’m not surprised the talk didn’t go well. There don’t seem to be any clear conclusions. Is he claiming to have constructed previously unknown string theories? I can’t tell …

    And I don’t agree at all with your statement that while “it would be very nice to explain SM parameters, but establishing a mathematical framework free of inconsistencies has to be done first.” Historically, progress in physics has almost never been made this way. It almost always came by somebody futzing around with some not-fully-baked theory, until something interesting popped out. QED, for example, almost certainly does not exist as a stand-alone theory. Waiting around for some UV completion of it before calculating a few orders of g-2 would have been a very bad idea.

  • Mark Srednicki

    Peter,

    I’m now completely mystified as to what that comment on gauge-group representations in your Orlando talk was supposed to mean if you agree that only the trivial rep has physical significance. But never mind.

    For the benefit of those who might not know, I would like to point out that there is a huge literature on the possibility that the Higgs is dynamical, stretching back to the seminal late-70s papers of Weinberg and Susskind on technicolor (Susskind’s term). Technicolor models were extensively studied and developed, then slowly abandoned as they got pushed into tighter and tighter corners by observations. Susskind jumped off the ship pretty early (presumably sensing that it wasn’t going to float much longer), despite the fact that if technicolor had panned out, he would almost certainly have gotten a Nobel Prize for it.

    I also don’t see how further knowledge of nonperturbative behavior of chiral gauge theories is going to help with this program, since the model-builders of old were willing to assume just about any minimally plausible behavior that would get them a workable model.

    And I’m glad to learn that you think that “If string theorists want to believe … that … a compactification that describes the world will be found, will be predictive, get tested and verified, they’re welcome to do so.” I don’t know that I believe this will happen, but I do think it’s an open possibilty, and one with much greater promise than that offered by any other framework that is known today.

  • Thomas Larsson

    gs: right, gauge transformations that don’t vanish at infinity should be thought of as global transformations that act on the Hilbert space of the theory. The generator of those transformations is the (total) electric charge.

    Moshe, one should be careful about which version of the algebra of gauge transformations one considers. In the polynomial or compact support version, one can combine nonzero charge with local triviality, because the local transformations generate an ideal. However, if one considers the Fourier or Laurent polynomial versions, as one does in string theory, no part of the gauge algebra can act trivially in the presence of nonzero charge.

    This is easy to see for the centerless Virasoro algebra. Since

    [L_m, L_-m] = 2m L_0,

    a nonzero charge L_0 != 0 implies that all L_m != 0, and unitarity the requires an anomaly. In the polynomial version, where m >= 0, we can have L_0 != 0 and all other L_m = 0, but in that version there is no such thing as a central charge. Other gauge algebras work in exactly the same way. Thus, there seems to be only three alternatives:

    1. Laurent polynomials are always allowed. Then there are new gauge anomalies, and string theory is wrong.

    2. Laurent polynomials are never allowed. Then there is no such thing as a conformal anomaly, and string theory is wrong.

    3. Laurent polynomials are allowed in string theory but not in Yang-Mills. This is clearly a case of double standards, aimed at hiding the fact that string theory is wrong.

    I agree that violations of Gauss’s law are not mathematically inconsistent; they are inconsistent with experiment. Isn’t that supposed to be the ultimate test?

    Mark: Nonzero charge is an experimental fact, and string theory teaches us that Laurent polynomials are ok.

  • http://golem.ph.utexas.edu/~distler/blog/ Jacques Distler

    However, if one considers the Fourier or Laurent polynomial versions, as one does in string theory, no part of the gauge algebra can act trivially in the presence of nonzero charge.

    If you’re quantizing on the circle (as in string theory), then there is no “spatial infinity” where bona fide gauge transformations are supposed to go to the identity.

    Sheesh!

  • Paolo Bizzarri

    Mark,

    “I don’t know how to think up a better one. I’m very much open to hearing of a better one from someone else, but I don’t expect to;”

    if you are searching for new ideas, start speaking with people outside the ST community. Organize a conference with people from LQG, twistors, whatever. Take the proposals of Peter Woit in a constructive way.

    “I think quantum gravity is a very constrained problem, and that string theory is very likely to be the only solution to this problem. If it is the only solution, abandoning it now would be a foolish thing to do.”

    The key is the if.

  • Thomas Larsson

    If you’re quantizing on the circle (as in string theory), then there is no “spatial infinity” where bona fide gauge transformations are supposed to go to the identity.

    So quantize in a Fourier basis on the n-dimensional torus. The algebras are isomorphic.

    Sheesh!

  • http://www.cgoakley.demon.co.uk/qft/ Chris Oakley

    Mark,

    And I don’t agree at all with your statement that while “it would be very nice to explain SM parameters, but establishing a mathematical framework free of inconsistencies has to be done first.” Historically, progress in physics has almost never been made this way.

    I did not word this very well. Try this: “particle physicists are used to using a calculational framework that is as full of holes as a Swiss cheese. So-called “effective” field theory is not a theory, it is just recipe whose success in a limited sphere (QED) has led physicists to believe that it will also work for other types of interaction. Success here, though, has been limited, quantum gravity being a notable failure. The response of the vast majority has been to explore higher levels of abstraction, hoping that, whilst leaving it largely intact – they will be able to “explain” effective field theory and – hopefully – also solve some of the mathematical difficulties.

    “I never felt optimistic about this program, but more than twenty years on, I feel even less optimistic. I believe that it is high time that “effective” field theory was abandoned altogether. Accurate values of g-2 and the Lamb shift may, possibly, elude us temporarily, but for mathematical consistency it is a price worth paying.”

    Alright?

  • http://www.math.columbia.edu/~woit/blog Peter Woit

    Mark,

    The significance of the comment was:

    1. We don’t understand non-trivial representations of the gauge group for any gauge theory in 3+1 d.

    2. There’s no indication this matters for QED, little for QCD, but maybe it is important for completely understanding the SM, since it is a chiral gauge theory, and we don’t fully understand it non-perturbatively.

    One way of seeing the problem is to think about it in Hamiltonian form. BRST then becomes essentially Lie algebra cohomology, where you construct the invariant, trivial piece of a representation by cancelling a sequence of non-trivial representations against each other. To do this, maybe you actually need to understand what those representations are.

  • amused

    Wow, this thread must have smashed all length records!

    Since it came up above, here is a bit about the current situation re. chiral gauge theories on the lattice. To actually get to the stage of being able to calculate anything there are two main things that need to be done: (i) An acceptable lattice formulation of chiral gauge theories (and in particular the SM) needs to be developed, and then (ii) an appropriate phase transition in the lattice model needs to be found where correlators diverge and a continuum limit can be defined. Both of these things have been done in lattice QCD; there is a phase transition for bare coupling g -> 0 where a continuum limit can be defined, and the hadronic masses etc which have been extracted so far are in very good agreement with experiment.

    For chiral gauge theories we have not yet progressed beyond (i). For a long time there was a major obstacle to even getting started on (i), namely the Nielsen-Ninomiya no-go theorem. The naive lattice discretization of the Dirac operator gives rise to “doublers” (spurious fermion species) and N-N basically says that there is no way to fix this without ruining the chiral nature of the theory, i.e. ruining the possibility to decompose the massless lattice fermion action into decoupled left- and right-handed pieces. In the ’90’s there was a major breakthrough though, and this problem got solved. The developments came from two directions, going by the names “overlap formulation” and “Ginsparg-Wilson (GW) formulation” respectively, which converged into two mathematically equivalent ways of formulating chiral gauge theories on the lattice. From the GW perspective, the solution to the original problem is that the notion of chirality gets modified on the lattice: Lattice Dirac operators satisfying the so-called GW relation (with the overlap Dirac operator being the main explicit example) break usual chiral symmetry but have instead an exact lattice-deformed version of chiral symm which can be used to decompose the action into left- and right-handed pieces as in the continuum. Thus a not-obviously-inviable lattice formulation of chiral gauge theories is obtained.

    To be acceptable though, the formulation should reproduce the things we already know about continuum chiral gauge theories; in particular the chiral gauge anomalies and their cancellation in certain fermion representations. This is actually a big challenge. In the continuum there is a beautiful connection between chiral gauge anomalies and families index theory for the Dirac operator coupled to gauge fields. In particular, there are obstructions to the vanishing of anomalies corresponding to non-trivial topological structure of the index determinant line bundle over the orbit space of gauge fields. It would seem at first sight that a lattice formulation could never reproduce this, since in finite volume (e.g. on the 4-torus) the space of lattice spinor fields is finite-dimensional but to have a non-trivial index theory the operators generally must be acting on an infinite-dimensional vectorspace. Amazingly though, the the overlap/GW lattice formulation is able to handle this; an index bundle can be defined in a natural way over the orbit space of lattice gauge fields, connected to anomalies in the lattice model in the same way as in the continuum setting, and the obstructions to vanishing of anomalies are found to reproduce the continuum ones. For me this is a very powerful indication that the overlap/GW formulation must be the right approach to chiral gauge theories on the lattice and is deserving of interest and attention.

    The resolution of (i) in the overlap/GW formulation is not yet compete though. We need to explicitly construct a “chiral fermion measure” as a function of the lattice gauge field such that the resulting chiral fermion determinant is gauge invariant in fermion representations satisfying the usual anomaly cancellation conditions. This has been done so far only for gauge group U(1); the non-abelian cases remain. It’s a hard technical problem. Let’s imagine that it eventually gets solved though, and consider the challenge of (ii). Unlike lattice QCD, the lattice chiral gauge theories are likely to have a complicated phase structure and it might not be obvious which phase transition to use to define the continuum limit. In fact this is already known to be the case for lattice QED. Another big problem will be that the chiral fermion determinants are complex-valued – numerical lattice simulation methods require real (positive) fermion determinants. My own hope (no doubt naive and perhaps completely wrong) is that both of these obstacles may be overcome as follows. First, I would expect that there should be a phase transition in the limits where the bare couplings g’ and g” of the U(1) and SU(2) gauge fields of the lattice electroweak theory both go to infinity, and that this would be the appropriate phase transition for defining the continuum limit. (In fact I would expect the analogous thing to be true for lattice QED, but I don’t know the current state of knowledge on that.) Then, it should be possible to analytically make strong coupling expansion in g’ and g” to get expressions for the quantities of interest which don’t directly contain the chiral fermion determinants and can therefore (hopefully) be calculated via numerical lattice simulations (and maybe even analytically in some cases for electroweak theory without QCD).

    At any rate, this is one example of a non-string formal particle theory topic which seems pretty interesting but is career suicide to work on in the present string era.

  • http://golem.ph.utexas.edu/~distler/blog/ Jacques Distler

    Larsson wrote:

    So quantize in a Fourier basis on the n-dimensional torus. The algebras are isomorphic.

    There’s no spatial infinity on an n-torus either.

    So that case is entirely irrelevant to the situation that had been under discussion (until you tried to hijack it into a discussion of your pet theory), namely the status of “gauge” transformations that don’t go to the identity at spatial infinity.

    Normally, I don’t bother responding to your ceaseless self-promotions. But there was a serious physics discussion going on, and your remarks promised to hopelessly confuse it.

  • Thomas Larsson

    Mathematically, embedding the algebra of local gauge transformation into the larger algebra also containing global and divergent transformations is the most natural thing in the world to do. If you do that, gauge anomalies are forced upon you. But you can of course insist that embedding local transformations into a larger structure is an evil and illegal thing to do. After all, why on earth should a string theorist be interested in new mathematics with obviuos connections to gauge symmetries?

  • Thomas Larsson

    As everyone has surely noticed, the crucial point is the existence of a two-sided grading with the global charge generators at degree zero. E.g. on the torus, the gauge generators are J^a(m) = exp(im.x)Q^a, where Q^a are the global charges. Since [J^a(m), J^b(-m)] = if^abc Q^c, nonzero charges imply that the whole shebang is nonzero; no ideal of local transformations which can be represented trivially. Divergent transformations have really nothing to do with it.

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    amused,

    Thanks a lot, that’s exactly the sort of informative explanation of the situation I was hoping for!

  • Mark Srednicki

    Chris,

    Presumably you understand that abandoning effective field theory means abandoning everything we know about particle physics.

    I also don’t see why quantum gravity should be considered a failure of effective field theory. Effective field theory predicts that, below the Planck scale, general relativity should work just as it does.

    The situation is analogous to that of the V-A theory of weak interactions; this works just fine below the scale of the W mass. Above that scale, you need an ultraviolet completion.

    Ignoring gravity, the Standard Model provides you with one, up to a much higher scale (wherever the first Landau pole is).

    So, we need an ultraviolet completion of gravity. That’s what all string theorists and LQG theorists are trying to construct.

  • David B.

    Dear Thomas:

    When one studies string theory one always finds L_0=0 for all physical states.
    This equation is part of the Virasoro constraints for the total conformal algebra that includes the ghosts.

    Your algebraic argument, although correct, is irrelevant for physical situations in string theory. In fact, in string theory the total central charge vanishhes.

  • Mark Srednicki

    Thomas,

    You say that “Nonzero charge is an experimental fact.” Of course it is! And it’s always observed to be carried by dynamical particles (e.g. electrons), consistent with Gauss’ Law.

    You say that “Mathematically, embedding the algebra of local gauge transformation into the larger algebra also containing global and divergent transformations is the most natural thing in the world to do.”

    OK, as a mathematically challenged physicist, I’m happy to agree that this is mathematically natural.

    “If you do that, gauge anomalies are forced upon you.”

    Oops! This is bad! Maybe it’s natural, but now I sure don’t want to do it!

    “But you can of course insist that embedding local transformations into a larger structure is an evil and illegal thing to do.”

    Well, if it leads to anomalies in gauge symmetries that I’m trying to preserve, then, yes, it’s illegal.

    “After all, why on earth should a string theorist be interested in new mathematics with obviuos connections to gauge symmetries?”

    Because, according to you, it leads to bad physics, which I have no interest in constructing.

  • Mark Srednicki

    Paolo,

    You wrote, “if you are searching for new ideas, start speaking with people outside the ST community. Organize a conference with people from LQG, twistors, whatever.”

    Already done!

    KITP Miniprogram: The Quantum Nature of Spacetime Singularities (January 8-26, 2007); Martin Bojowald, Robert H. Brandenberger, Gary T. Horowitz, Hong Liu. organizers. http://online.itp.ucsb.edu/online/singular_m07

    I didn’t organize it, but I attended as much as I could. (For those who don’t know, Bojowald is a LQG theorist, Horowitz is a general relativist and string theorist, Liu is a string theorist, and Brandenberger is a cosmologist.)

  • Mark Srednicki

    Paolo,

    In response to my statement that “”I think quantum gravity is a very constrained problem, and that string theory is very likely to be the only solution to this problem. If it is the only solution, abandoning it now would be a foolish thing to do,” you replied, “The key is the if.”

    Of course! Those who think string theory is not worth pursuing, should not pursue it. Those who think it is, should.

    Ever Peter now appears to agree with this.

  • anon.

    “Those who think string theory is not worth pursuing, should not pursue it. Those who think it is, should.
    Ever Peter now appears to agree with this.” – Mark Srednicki

    If you’d read Not Even Wrong or The Trouble with Physics, maybe you’d see that the problem is somewhat different: a tyranny of failed ideas which just demands more research and more money every time it fails.

    The problem is that it’s celebrated in advance of actually achieving anything. This was how aether went wrong. You need to check the theory in advance of acclaiming it (however, that’s easier said than done because the failures get renamed anomalies, i.e., the failure to predict the cc, and the failure of supersymmetry to predict the observed strong SU(3) force from the other forces at low energy).

  • Mark Srednicki

    amused, very interesting. Is there a review article available on this? Or a standard set of papers?

  • gs

    amused,
    Regarding (ii), is there any reason to believe that a continuum limit can be taken, given that perturbation theory gives you Landau poles? In QCD asymptotic freedom comes to the rescue.

  • Mark Srednicki

    anon,

    I’ve read The Trouble with Physics. I disagree with most of it, especially the accusations of blatant racism and sexism.

    As for the failure of string theory, allow me to stipulate that. Yes, string theory has so far failed to make a definite prediction. But so has every other appraoch to the problem of quantum gravity. Lee has pushed the idea that violations of Lorentz invariance might turn up in one particular flavor of LQG. But there are versions of LQG that are Lorentz invariant from the start, so this cannot be said to be a prediction of LQG. It seems to me that this is exactly analogous to statements that certain classes of compactifications in string theory make certain predictions, but when all possible classes are considered, no prediction is common to all. Similarly, LQC makes no predictions that are common to all versions of it that are currently under investigation.

    There is then a subjective issue of which framework is closer to making a prediction. Peter evaluates this in terms of the number of bong hits needed to believe any particular scenario, which is as good a measure as any.
    For me, string theory currently needs about 2 bong hits, the Lorentz-invariant flavors of LQG maybe 4 (though if one of them works I would expect it to also have a string interpretation), and I’m passed out before we get to anything else.

    Your opinion may differ. Lee’s certainly does.

    So, how are we going to fund things? I believe it is an intellectually defensible position to say that none of this stuff should be funded. It’s all useless fluff that is not going to feed the hungry or house the homeless.

    Assuming you don’t agree with that, I think the current system, while far from perfect, is pretty good. In his book, Lee says that there are about 200 people working on LQG. There are maybe 2000 (I’m guessing) working on string theory. I think this ratio is about right, when translated to the bong-hit scale (which I see as logarithmic). This sounds like an awful lot of people overall, and it is, but the difficulty is that it’s awfully hard to figure out which people to keep, if you’re going to cut some. The current system has many flaws, but it does have the virtue that many different people are making hiring decisions at many different institutions.

  • Gina

    Dear Mark,

    Many many thanks for the explanation (and for the optimism) on the Gauss law and non trivial representation. Let me try to think about it. (The “off debate” fragments are very nice, in my opinion. In this thread also some of the debate part seemed interesting.)

    Gina

  • amused

    Mark,

    Thanks. The standard paper for the overlap formulation is hep-th/9411108; for the GW formulation see hep-lat/9811032 and hep-lat/9904009.

    For reviews, see, e.g, hep-th/0102028 and hep-lat/0009033. The stuff about anomalies and index theory that I mentioned was subsequent to these reviews but it should be easy enough to track down by a literature search if you are interested.

    A small comment on the general debate here: The discussion often gives the impression that there is nothing else interesting and worth working on besides quantum gravity and Theories of Everything. In fact there are plenty of interesting “bottom up” things to do. For example, the QCD dynamics responsible for confinement and spontaneous breaking of chiral symmetry still seems far from understood. E.g. there is so far no definitive explanation for why the phase transitions in finite temperature QCD where deconfinement and chiral symm restoration set in occur at the same critical temperature (which lattice simulations have revealed to be the case). Isn’t it an interesting problem to try to explain that? I guess it’s pretty mundane compared to the glamour of quantum gravity, but on the other hand there’s surely a much better chance of making some real progress in understanding physics.

  • amused

    gs, re. #376:

    To tell the truth I have no idea how things will work out regarding (ii). My guess, for what it’s worth, is that it will be possible to take a continuum limit but that the theory might not be in the phase that we would like it to be in, e.g the electroweak part in a confined phase. In that case I guess we would have to move on to lattice formulation of GUTs or maybe supersymmetric extensions of the SM…

  • Diogenes

    “Mark

    ….A small comment on the general debate here: The discussion often
    gives the impression that there is nothing else interesting and worth
    working on besides quantum gravity and Theories of Everything. In
    fact there are plenty of interesting “bottom up” things to do….”
    -amused-

    Dear amused

    I think that you’re preaching to the choir here. If you take a look at Mark’s publications (you can search for him on the Stanford Public Information Retreival System (SPIRES); go to: http://www.slac.stanford.edu/spires/ and type in your search), I think you’ll find that while he has done some (important: see his paper “IIB or not IIB”) work on string theory, this work represents only about 6 of his 100+ papers. His thesis was on lattice gauge theory, and since then he has done important work on axions, technicolour models, Grand Unified Theories, supersymmetric model building, early universe cosmology and inflation, baryogenesis, black-hole thermodynamics (see his paper “Entropy and Area”), temperature anisotropies in the cosmic microwave background radiation, and cosmic reheating after inflation.

    He is an acknowledged world expert on the particle astrophysics of dark matter, having coauthored the first paper computing neutralino relic densities in the full susy standard model, and he has continued to be a leading authority in the field over the succeeding quarter century, with over thirty papers on the subject to date. He is also the author of an exceptionally clear and pedagogical textbook on Quantum Field Theory, which just appeared this last February.

    You should not assume that just because someone defends the value of continuing to work on understanding string theory, that they work primarily (or even at all) on string theory. There is considerable interest in string theory among cosmologists, astrophysicists, particle phenomenologists, and heavy-ion nuclear theorists, because it acts as an “imagination stretcher” (to use a phrase first coined by Bjorken) for the fields with which it interacts.

  • Mark Srednicki

    amused,

    Thanks for the references. I agree completely that there’s plenty of interesting “bottom up” stuff to do. So do all the string theorists that I talk to. I don’t know anyone who wouldn’t be very interested in results on properties of strongly-coupled chiral gauge theories from lattice simulations. (And let’s not forget that we learned a tremendous amount about strongly coupled supersymmetric gauge theories from the work of Seiberg and other string theorists, all of whom would be thrilled if they could extend their results to nonsupersymmetric cases.)

    As for Landau poles, I wouldn’t think that they would be much of a problem; they mean you won’t be able to go all the way to the continuum limit, but you never do anyway (in an actual simulation).

  • Hendrik

    Dear Peter, concerning your comment #363:

    “…is to think about it in Hamiltonian form. BRST then becomes essentially Lie algebra cohomology, where you construct the invariant, trivial piece of a representation by cancelling a sequence of non-trivial representations against each other.”

    Do you mean this comment:
    1) For classical BRST (which is rigorous via Stasheff e.a., so I won’t comment), or

    2) For quantum BRST, but within the physics understanding of it (for which my understanding falls short, so I won’t comment), or
    3) For quantum BRST, but from a mathematical point of view?

    If it case (3) could you please give me a reference? The maths of quantum BRST (one of my pet projects) may be a point of argument.

    My apologies for adding noise to the string debate (I’m also an opponent – see my post #204), but the BRST-issue is something which matters to me independently.

  • Mark Srednicki

    Diogenes,

    I’m blushing. Yes, I like to work on lots of different things; apparently I have a poor attention span. For the past few years I’ve mostly been working on quantum chaos theory, work that doesn’t show up on spires.

    I haven’t done much work on string theory because I’ve haven’t had many good ideas about it. (The IIB or not IIB stuff was a lucky exception.) But the people I know who do work on it are all incredibly smart, in all the best ways. I’m offended by the ridiculous caricature of an insular community of blinkered blowhards that some people seem to hold to.

    String theory feels right to me. I didn’t always think that way. I first heard about string theory in 1982. I was a postdoc at Princeton, and one day Ed Witten and I were the only two people who showed up. (I think it was a Monday holiday and we were the only ones who didn’t notice.) At lunch, Ed asked me if I’d ever read any of the papers of Green and Schwarz. I replied that I’d never heard of Green and Schwarz. He then told me about string theory, that there were three different versions, one that gave phi-cubed theory in 26 dimensions, one that gave N=4 U(N) supersymmetric gauge theory, and one that gave N=8 supergravity. “I admit that it’s hard to see the charm of phi-cubed theory in 26 dimensions,” he said, “but you’ve got to admit that the other two cases are interesting!” So, after lunch, I went to the preprint library and found the latest paper of Green and Schwarz. It was about computing the mobius amplitude in Type I theory. It was horribly technical and completely incomprehensible to a neophyte. “No way can this stuff be relevant for real physics,” I thought. I made no more effort to understand string theory.

    Some time after the November Revolution of 1984, I had a job in Santa Barbara, and Ed came to town. There had been recent papers with a solution of the doublet-triplet splitting problem in stirng-based models. (If you don’t know what that is, it doesn’t matter.) I told Ed that I found that impressive. He laughed. “That it’s a finite theory of quantum gravity doesn’t impress you, but a solution to the doublet-triplet splitting problem does? Well, I expect that everyone will soon be working on it, for one reason or another!” He went on to say that he thought the next major advance would be a solution to the cosmological constant problem. “We’ve been trying to solve it without having the right theory of quantum gravity,” he said. “Now that we do have the right theory, it should be much easier.” (All quotes from ancient memory and almost certainly not perfectly accurate.)

    Well, Ed was right about some things and wrong about others. Time will tell what’s right and wrong about our current ideas.

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    Hendrik,

    I do mean quantum BRST, but as far as I know in the case of 4d gauge theory all that exists are physicist’s arguments, no well-formulated mathematical theory. There’s a long story about different versions of BRST, and their precise formulation in QM and 1+1 d QFT, and it would take a long posting to say sensible things about this topic. My only point was that, no matter what your version of quantum BRST, you are using homological techniques to isolate an invariant piece of some non-trivial representation, and understanding how this works out requires working with non-trivial representations.

  • amused

    Diogenes,

    Don’t worry, I know who Prof. Srednicki is and that he has made many important contributions across a wide range of topics. My comment was mostly sparked by his amusing description of the relative number of bong hits needed to believe in string theory and LQG. After reading it I thought: hey, there are still topics that are interesting to work on without any bong hits, right? I’m sure Mark and many others knew this, but it still seems worth mentioning now and again since otherwise an impression gets created that it has to be either strings or LQG.

  • amused

    Mark,

    Thanks for your remark about Landau poles and the continuum limit – that’s good to bear in mind in this business.

    As for string theorists also being interested in non-string bottom-up work, that’s definitely my impression as well, at least for the more senior ones. On the other hand, the reality is that if you want a string/brane theorist to hire you then you had better be working on their topic. (That is of course true across other topics as well.) Since most people in formal particle theory are doing strings/branes, that leaves very few possibilities for someone working on something else. I would have liked to continue working on lattice chiral gauge theories, but felt obliged to drop it some time ago and focus on other things to have a chance of remaining employable. This isn’t a moan about my own situation (which is actually ok for the time being); I just think it is a shame that there are interesting non-string topics in formal particle theory but young people would be putting themselves at a disadvantage careerwise by working on them.

  • Hendrik

    Dear Peter,

    Thanks, I appreciate your reply.
    I know there are many BRST’s, some ill-defined & inequivalent. I asked the question because Hamiltonian BRST is defined independently from gauge theories (e.g. by Henneaux) purely as a constraint reduction algorithm, and in this form can be analyzed mathematically.

  • anon.

    “I’ve read The Trouble with Physics. I disagree with most of it, especially the accusations of blatant racism and sexism.
    As for the failure of string theory, allow me to stipulate that. Yes, string theory has so far failed to make a definite prediction. But so has every other appraoch to the problem of quantum gravity…” – Mark Srednicki.

    As Not Even Wrong points out, even the few things string should predict in an ad hoc way are totally wrong: using the measured weak SU(2) and electromagnetic U(1) forces, supersymmetry predicts the SU(3) force incorrectly high by 10-15%, when the experimental data is accurate to a standard deviation of about 3%.

    It’s also not true that no other theories make definite predictions in gravity; what you should right is that the only other approaches string theorists take seriously and actually read are failures. It’s a big difference, mainly focussed on the idea that gravity is definitely due to spin-2 gravitons which interact with one another, creating massive problems at very high energy. There’s no evidence for that. So the framework of ideas you are interested in is entirely speculative, and not necessarily scientific.

    I’ve had a paper published in a peer-reviewed journal (not a gravity-related journal!) which in 1996 predicted the 1998 observational discovery that there is no cosmological slowing down on the expansion, because any quantum gravitational mechanism should suffer from gauge boson redshift (energy degradation) when exchange occurs between rapidly receding masses, over large distances in this universe. It also post-dicts the gravitational coupling constant acurately. Even Nobel Laureate Phil Anderson points out that the simplest resolution of the cc is that it is zero:

    “the flat universe is just not decelerating, it isn’t really accelerating” – http://blogs.discovermagazine.com/cosmicvariance/2006/01/03/danger-phil-anderson/#comment-10901

    Supporting a cc is zero, so exchange radiation redshift effects weaken the gravitational coupling constant and cause the lack of gravitational deceleration, there is Lunsford’s unification of electromagnetism and general relativity http://cdsweb.cern.ch/search?f=author&p=Lunsford%2C+D+R which was censored off arxiv without explanation despite being published in a peer-reviewed journal, Int. J. Theor. Phys.: 43 (2004) no. 1, pp.161-177. This shows that unification implies that the cc is exactly zero.

    This is why the whole stringy framework is harmful. I can’t imagine Smolin censoring out alternatives to the degree that string theory does. The accusations of racism and sexism are not blatant: where they are made in every case a reference is given. They’re not invented accusations. Face the facts, please.

  • ymous

    anon. said

    “The accusations of racism and sexism are not blatant: where they are made in every case a reference is given. They’re not invented accusations. Face the facts, please.”

    This is absolutely and demonstrably false. I quote from TWP:

    “There are rules and ethics of confidentiality that prevent me from giving examples, but there are several detailed studies that tell the story (2).”

    (2) references the important and useful MIT study on women in science, but it certainly does not document the “blatant prejudice” claimed by Lee.

    Lee is using a cheap rhetorical device by trying to associate LQG with women and minorities and critics of LQG with sexists and racists. I find it one of the more deplorable parts of his book.

  • Mark Srednicki

    anon,

    You wrote “As Not Even Wrong points out, even the few things string should predict in an ad hoc way are totally wrong …”

    I have no idea what “should predict” and “in an ad hoc way” are supposed to mean. Either string theory makes a prediction, or it doesn’t. Currently, string theory, considered as a general framework, does not make any definite predictions for the parameters of the Standard Model (or any plausible extension thereof). There may (or may not) be one (or more, maybe many more) compactifications of string theory that are consistent with the Standard Model. Each of these (if one or more exists) will make definite predictions (in principle) for all observable physics. I say “in principle”, because we will only be able to do the relevant calculations in a regime where there is a suitable expansion parameter, and it is logically possible that there is no such regime, other than the low-energy limit where weakly coupled field theory works. (On the other hand, even strongly coupled string theory might eventually be tackled with numerical methods, just as we can now tackle certain strongly coupled gauge theories.)

    You write, “[Smolin’s] accusations of racism and sexism are not blatant: where they are made in every case a reference is given.”

    Lee does not give any details of any of case he has personally witnessed, citing confidentiality rules. His references (that, he says, “tell the story”) are http://web.mit.edu/fnl/women/women.html and http://www.aps.org/educ/cswp . The latter page no longer exists; CSWP is the Committee on the Status of Women in Physics, and their reports can now be found at http://www.aps.org/programs/women/reports/index.cfm .

    I invite everyone to compare these reports with what Lee says in his book.

  • Gina

    Dear all,

    I found the off-debate discussion on non trivial representations, QED and Gauss laws very interesting and also the related more advanced comments. (Also there are quite yummy off debate comments like Mark’s memories and comments about Witten, Susskind and others.)

    I feel very fortunate to have received three different explanations #339 #347 and #355 on why non-trivial representations cannot occur in QED without violating Gauss’ rule. (It looks from what Moshe and Mark said that their argument applies in much greater generality, but I am happy to think just on the “simple” case of QED.)

    Mark commented that his explanation is not just an elaboration of Moshe’s but rather a different one and that the connections between these two explanations is actually quite deep. This type of different explanations for the same phenomenon and then deeper relations between the explanations themselves that sometimes lead to further understanding always stroke me as a very nice feature of science.

    (Actually, I did not understand the bottom line of Hendrik’s #355 comment, beyond some technical statement from mathematics that of course I did not understand. Is it a different explanation why non trivial representation would violate the Gauss law or perhaps a different view? I do not mind not understanding the mathematics, of course, but please please Hendrik do explain what is the bottom line of your comment.)

    Everybody (including Peter) seem to agree that invoking non-trivial representations is not a good idea to proceed in the context of QDE (and Moshe and Mark point out that this seem to apply also to cases where Peter original suggestions may refer to.)

    So let me ask the following: Is it actually impossible (or perhaps, why is it impossible) to offer a mathematical model for QED which will involve non trivial representations and will give precisely the same empirical predictions as the current model (including Gauss law, of course)?

    If I understood Mark’s explanation such a possibility will require a large amount of “cancellations” because individual terms will go contrary to Gauss’ law; perhaps it also follows from what Mark said (but I am not sure about it) that such a model is not possible under the roof of QFT. From Moshe’s comment I find it hard to understand if this is impossible or just “unlikely” or “unknown”. Moshe uses the words “The only known way to do it is to impose local gauge invariants…” so it not clear to me if not “known” means “mathematically impossible” or really just unknown.

    Why do I think this question may be interesting?

    First of all, there is a rare consensus from Peter to Mark that it is not interesting, so by some sort of Marphy’s rule maybe this may be a place to look again :) .

    Second, while such a possibility will make no difference for QED, it may make some difference for cases where similar arguments are not only more complicated but also are more questionable.

    Third, of course, QED seems the simplest, for this case (as I remember from Peter’s book) the frightening name “representation theory” is just plain old “trigonometry”.

    (Also a fourth reason may be that I vaguely remember reading somewhere that there is no fully accurate mathematics model for QED.)

    Two little less off-debate remarks:

    I would like to support what Mark said about string theorists. I doubt if anybody really knows if string theory is the theory, but there are very good reasons to say that string theorists are the theorists; in terms of their wide horizons, intellectual and technical power, and creativity. Of course, there are very bright people in other fields of science and outside science as well. Perhaps even in wall street (but I do not think the smartest people go, as Horgan and G. Johnson would like us to believe, to wall street). There is something special about string theorists.

    Another small comment is that I looked at the slides of Peter’s talk. It looks like a very good talk which refer mainly to the first half of his book which is not about string theory. (I do not like Peter’s anti string polemic and repeatedly criticized various aspects of it but the the first half of his book is, in my opinion, very good.) There is no harm if among the 40-60 slides there is one slide with some of Peter’s own ideas (or even wild speculations) on what direction he feels it is fruitful to proceed.

  • Thomas Larsson

    “But you can of course insist that embedding local transformations into a larger structure is an evil and illegal thing to do.”

    Well, if it leads to anomalies in gauge symmetries that I’m trying to preserve, then, yes, it’s illegal.

    Mark´#371,

    I don’t understand this comment. By also probing our system with divergent transformations, we can learn more about it than if we only use local and global transformations. Why is it illegal to learn more about the system?

    Consider CFT as an example. If we wish, we can restrict attention to positive conformal transformations – L_m with m > 0. There is nothing inconsistent with this restriction, and the positive L_m in isolation generate a gauge symmetry; there is no anomaly in the positive sector and thus a nilpotent BRST operator. If you insist on preserving this gauge symmetry, introducing the negative L_m is illegal; it leads to an anomaly. The reason is that we must now consider a tower of systems, where your original anomaly-free system is the ground state. Your original gauge generators still annihilate this vacuum, but not the tower above it.

    At least in CFT, the introduction of this gauge-violating tower leads to much non-trivial information. One should also observe that this line of reasoning has led to dramatic discoveries: the multi-dimensional Virasoro algebra, lowest-energy representations thereof, and a formulation of physics which takes the quantum nature of the observer into account. One feels that with such a spectacular track record, this idea must be an important part of The TRUTH.

  • Diogenes

    Re: Thomas Larsson Comment 393

    Dear Dr. Larsson

    In the case of two dimensional critical phenomena (statistical field theory) the conformal symmetry is a global symmetry of a conventional field theory, and the scale anomaly can give anomalous scaling at the critical point (ie. a representation of the Virasoro algebra with c not equal to zero).
    This symmetry is not gauged so there is no problem with an anomaly in it.

    In the case of the string world sheet the conformal symmetry is a (conformal) gauge fixed remnant of local general coordinate and Weyl symmetries. As such it is a gauge symmetry and we do not allow it to be anomalous. That is the origin of the critical dimension in string theory, which arises from requiring that we have enough world-sheet “matter’ fields contributing positive central charge, to cancel the contribution of the reparametrization ghosts which contribute negative central charge, to give total central charge zero and cancel the anomaly.

  • anon.

    You wrote “As Not Even Wrong points out, even the few things string should predict in an ad hoc way are totally wrong …”

    I have no idea what “should predict” and “in an ad hoc way” are supposed to mean. Either string theory makes a prediction, or it doesn’t. Currently, string theory, considered as a general framework, does not make any definite predictions for the parameters of the Standard Model (or any plausible extension thereof). …

    – Mark Srednicki

    Ad hoc is Latin “for the purpose required”, in other words, predicting something that we already know. This is no use unless it also predicts something else that can be tested.

    ‘It has been said that more than 200 theories of gravitation have been put forward; but the most plausible of these have all had the defect that they lead nowhere and admit of no experimental test.’ – Sir Arthur Eddington, ‘Space Time and Gravitation’, Cambridge University Press, 1921, p64.

    The problem with the standard model and string theory is not that string theory can’t predict any of the parameters, but that it increases the number of parameters from 19 to at least 125 (for the minimally supersymmetric standard model).

    So your statement that “string theory, considered as a general framework, does not make any definite predictions for the parameters of the Standard Model (or any plausible extension thereof” is plain misleading; you should be writing something more along the lines that string theory makes the empirically developed standard model uncheckable by creating a landscape of about 10^500 models; supersymmetry increases the number of fine tuned parameters from 19 to at least 125 without explaining any of them; far from even attempting to explain any physical reality, string theory makes a complete mess of physcs and due to the landscape has no possibility of ever achieving anything. This isn’t a new problem, Feynman was complaining about it just before he died nearly twenty years ago!

    ‘… I do feel strongly that this is nonsense! … I think all this superstring stuff is crazy and is in the wrong direction. … I don’t like it that they’re not calculating anything. I don’t like that they don’t check their ideas. I don’t like that for anything that disagrees with an experiment, they cook up an explanation – a fix-up to say “Well, it still might be true”. … All these numbers … have no explanations in these string theories – absolutely none! …’ – Richard P. Feynman, in Davies & Brown, ‘Superstrings’ 1988, pp.194-195.

  • Thomas Larsson

    Diogenes,

    In the case of two dimensional critical phenomena (statistical field theory) the conformal symmetry is a global symmetry of a conventional field theory, and the scale anomaly can give anomalous scaling at the critical point (ie. a representation of the Virasoro algebra with c not equal to zero).

    As I pointed out, the subalgebra generated by L_m with m > 0 contains no reference to the conformal anomaly. Hence this subalgebra admits a nilpotent BRST operator, and can be viewed as a gauge symmetry. The BRST operator for the full Virasoro algebra is not nilpotent, and hence a global symmetry.

    In the case of the string world sheet the conformal symmetry is a (conformal) gauge fixed remnant of local general coordinate and Weyl symmetries. As such it is a gauge symmetry and we do not allow it to be anomalous.

    What seems to be little known among a younger string theorists is that also the subcritical free string can be quantized consistently, despite the conformal anomaly. Look at the first sentence of section 2.4 of GSW, which clearly states that the free string can be quantized with a ghost-free spectrum for all D <= 26. That is D <= 26, not D = 26. The interacting string runs into trouble when D < 26, but the free subcritical string is a nice example of a consistent, anomalous gauge theory. More precisely, a classical gauge theory which becomes a non-gauge theory after quantization.

  • amused

    Correction to something I wrote in the discussion of lattice chiral gauge theories in #364: The part in the discussion of (ii) starting with “My own hope (…) is …” is complete nonsense! I guess I must have been thinking about the possibility to investigate strongly coupled chiral gauge theories via strong coupling expansion in the lattice model and forgotten that I was supposed to be talking about the SM. Instead of what I suggested, the sensible thing to do re. (ii) would be to explore the phase structure of the lattice model and hopefully find a phase that has the right properties for the real world (confined quarks and gluons, deconfined leptons photons and W,Z bosons…; it should certainly not be a phase where everything is confined, which is where you would end up if my mistaken suggestion in #364 was followed). Then look for points at the boundary of that phase region in the space of couplings at which correlation lengths diverge and a continuum limit can be defined.

    I suppose it could happen that there is a whole family of points where a continuum limit can be taken. This would give a “landscape” of possible continuum theories, and we would have to find which (if any) describe the real world. Well, at least that landscape would be easier to explore than the string theory one!

    As mentioned in #364, a practical difficulty is that chiral fermion determinants are complex-valued and therefore cannot be handled by numerical lattice simulation methods. However, it may be possible to still investigate the the theory qualitatively in a “quenched approximation”. In lattice QCD the quenched approx is setting the fermion determinant equal to 1 – that might sound drastic and ad hoc, but there are theoretical reasons for why it is quite reasonable, and quenched lattice QCD has shown itself to give quite a reasonable description of the real thing. However, in an anomaly-free chiral lattice gauge theory, setting chiral fermion determinants equal to 1 might not be as justifiable as in QCD – something more elaborate may be required. (I have an idea for what the `something’ should be, and I’m sure you’re all just dying to know, but this isn’t the time or the place…)

  • David B.

    Dear Thomas:

    The book by GSW was published in 1987. A lot of the non-critical strings have been studied since. It would seem by your comment that your information is somewhat out of date.

    The modern resolution for those theories (subcritical) is that the Lioville mode does not decopule. When you take it into account you get a non-trivial CFT on the worldsheet, and the criticality of the string is restored by the Liouville mode.

    Also, the so-called linear dilaton backgrounds are studied
    as examples of “non-critical” string theories. This is an active topic of research and many young string theorists do study those setups. They might be using different language than the one you are used to.

  • Thomas Larsson

    The no-ghost theorem was, I believe, proven in the 1970s. That people have studied Liouville theory later does not invalidate it.

  • Thomas Larsson

    David B (erenstein?),

    In fact, Liouville theory is the reason why I believe that spontaneous symmetry breaking may be traded for anomalous symmetry breaking. Classically, the worldsheet metric has no physical components; it has three components but there are three gauge symmetries to cancel them, two diffeos and one conformal. After quantization, the trace of the metric becomes physical. Depending on your formalism, this can manifest itself in different ways:

    1. If you start by gauge-fixing diffeos, you get a conformal anomaly.

    2. If you start by gauge-fixing conformal transformations, you get a diff anomaly, cf hep-th/9501016 by Roman Jackiw.

    3. If you add a self-interacting scalar field with c = 26-D, the total anomaly cancels, but you have an extra Goldstone boson.

    Either way, you get one extra degree of freedom.

  • Mark Srednicki

    Damn! I missed making the 400th comment!

    Gina, I have to say that I have to disagree with your comment that “there are very good reasons to say that string theorists are the theorists … There is something special about string theorists.” I think it’s clear that there are brilliant people in all areas of theory, and all areas of science, and all areas of human endeavor in general.

    In one of his popular books, Feynman talks about almost getting into a bar fight, but then tensions are smoothly defused by another patron. “Every area has its geniuses,” Feynman says. (Or something like that: I’m relying on memory again.)

    amused, I had decided not to point out that your strong-coupling expansion scheme didn’t make sense, but I’m happy to see that you noticed it yourself.

    Now if only certain others posting here had similar powers of introspection …

  • David B.

    Dear Thomas:

    I got confused by your previous post #396. That is why I made my remarks. I’ll think some more about the last few comments.

  • Mark Srednicki

    Thomas,

    I took a look at your paper math-ph/0603024, which in comment #28 you say contains a “no-go theorem for string theory”. Elsewhere, you’ve complained that this paper has been ignored.

    Curiously, neither the abstract nor the conclusions of this paper even mention string theory. The abstract begins, “A local gauge symmetry can not possibly be a mere redundancy of the description, provided that 1. charge is nonzero.
    2. we also consider divergent gauge transformations, whose brackets with local transformations contain global charge operators.”

    I believe you have made a mathematical error in your discussion of Yang-Mills theory. The error consists of working on R^3 without specifying boundary conditions at infinity. Without boundary conditions, the theory is ill-defined.

    We can supply boundary conditions by working on T^3 or S^3 (or any other compact manifold). Then the divergent gauge transformations are not present, because there is no r->infinity limit where they can diverge. Also, only the zero-charge sector exists; I cannot put a single electron on a compact manifold, because there is no place for its electric field lines to end.

    So neither your first condition (nonzero charge) nor your second (divergent gauge transformations) holds when boundary conditions are supplied by working on a compact manifold.

  • Gina

    “I think it’s clear that there are brilliant people in all areas of theory, and all areas of science, and all areas of human endeavor in general.”
    Of course, I agree, Mark, and I even said so. Something special about string theorists is the required abilities (from the bulk of them not just the very best) to master so many things. One especially annoying aspect of the critique on string theory, in my opinion, was the fundamentally unfair critique of string theorists and the string theory community.

  • Thomas Larsson

    Mark, I agree that my no-go argument is not a theorem in the mathematical sense. There are also some tacit assumptions, e.g. that the gauge generators act as well-defined operators (possibly the zero operator) on a well-defined Hilbert space, something which presumably is not true in interacting QFT.

    And yes, I ignore boundary conditions, but I don’t believe that the essential physics resides on the boundary. Besides, you may object to CFT on similar grounds. If you fix boundary conditions at infinity on the complex plane, it does not seem to be a good idea to apply conformal transformations with singularities there. This never stopped anyone from using the full Virasoro algebra.

    Thus, I only have a heuristic argument, but it does suggest the existence of anomalies. That such anomalies are then found strongly suggests that my argument was essentially right in the first place.

    Note that the Kac-Moody-like anomaly does not arise in QFT, because it is proportional to the second Casimir rather than to the third; the two types of extensions are contrasted in eqns. (12) and (13). It does arise in QJT, however. The reason is that in QJT, we quantize not only the fields but also the observer, and the relevant anomalies in all known representations are functionals of the observer’s trajectory.

    It may be noted that the higher-dimensional affine algebra has appeared in string theory with a different physical interpretation, cf. hep-th/9511185. They also describe what happens globally and on the group level, something which I am unable to do.

  • amused

    Mark, thanks for giving me the chance to find that mistake on my own. (As a feeble excuse, my main interest in this stuff was with anomalies and index theory in the lattice model, and I never gave much thought to the more practical continuum limit issue before.) Related to this I have a physics question which maybe you or someone else can help me out with. What is the current status of the continuum limit issue in lattice QED? (It seems unrealistic to hope to get anywhere with the continuum limit issue in lattice formulation of the SM without properly understanding the lattice QED case first.) Lattice QED has two phases – a weakly coupled Coulomb phase and strongly coupled confining phase. So I guess the places where one could try to take a continuum limit are at the two boundaries of the Coulomb phase, namely e -> 0 and e -> e_c where e_c is the critical coupling separating the Coulomb and confined phases. I seem to remember reading somewhere that there is a possibility to take the continuum limit at e -> 0. But that seems wrong, since for small coupling we can use perturbation theory to find that the bare coupling e(a) as a function of the lattice spacing flows *away* from 0 for a -> 0. (This is the opposite of the situation in lattice QCD and is due to the fact that the leading term in the beta-function has the opposite sign.) That seems to leave e -> e_c as the only possibility for taking a continuum limit, but I never saw this possibility discussed in the literature… maybe there is some reason why it doesn’t work and lattice QED doesn’t admit a continuum limit?

  • http://egregium.wordpress.com/ Christine

    Gina wrote:

    “Something special about string theorists is the required abilities (from the bulk of them not just the very best) to master so many things.”

    They are not alone, definitely.

    Cosmologists for instance have to embrace almost every branch of physics, sometimes even chemistry and some other disciplines. Some cosmologists even embrace string theory besides all that. :)

    There are multidisciplinary scientists who work in many disciplines in order to investigate a given problem.

    But, yes, string theory deals with a lot of mathematics, if that is what you meant.

    Christine

  • http://arunsmusings.blogspot.com Arun

    Gina wrote:
    “There is something special about string theorists.”

    Exactly! The question so hotly contested is whether that something special is good or bad for physics.

  • Lee Smolin

    Mark asks (302), “The question I always come back to is, what if the landscape is essentially correct? That is, what if string theory is the correct theory of the world, that it has zillions of metastable vacua, and that inflation creates zillions of “pocket universes” (our universe being one of them), each with its own metastable vacuum?”

    If everyone doesn’t mind going back to this, I would like to make two comments. First this is two hypotheses. String theory could have a vast landscape of metastable vacua whether or not eternal inflation is true. The first question, how do we do science if string theory-or any other candidate for unification- gives a vast ensemble of vacua, was the question I asked in my first book, Life of the Cosmos (1997). I agree with you, this is a key question. I think the answer, as developed in that book at length, is that we are still obligated to falsifiable predictions by which we can test our theory. I showed in that book and related papers that this can be done, in the context of the cosmological natural selection scenario (CNS).

    Your second hypothesis is that eternal inflation is right. So far, when combined with the string landscape this does not yield any falsifiable predictions. I have explained in detail in that book and again in TTWP and recent papers why it cannot. Thus, I believe that while the string landscape may be true, its development within the eternal inflation scenario is problematic, because if there are no falsifiable predictions.

    Nothing that has happened since publication of LOTC in 1997 has changed or challenged the conclusions given there. CNS is still the only cosmological scenario within which it is possible to make falsifiable predictions (and btw its predictions remain unfalsified.) Alternatives based on the anthropic principle have failed for exactly the reasons I explained they must in LOTC and papers since.

    Now, you advocate, “strive to narrow down the possible string vacua that are compatible with the Standard Model (as amended, if necessary, by whatever is found at the LHC), and then to look for predictions common to this class.” My expectation would be that there are no interesting further predictions for accessible accelerator experiments, because I know of no reason the landscape should not evenly populate the space of standard model and post standard model parameters. The reason is the hierarchy problem itself. I see no reason why constraints imposed to get consistency at the Planck scale should imply any constraints on gauge groups, choices of fermion and scalar representations, and parameters of low energy effective field theories, apart from those that could be deduced by the principles of effective field theory, without string theory or quantum gravity. Nor is there any reason for eternal inflation, taking place at grand unified scales, to lead to probability distributions that favor any particular fine tunings in the standard or post standard model parameters.

    One can always hope, but this seems to me a faint hope. Better I would think to spend our time investigating cosmological scenarios that immediately leads to predictions for standard model parameters.

    Thanks,

    Lee

  • http://tyrannogenius.blogspot.com Neil B.

    Lee, and anyone else still here: What do you think of “modal realism,” the idea that every “logically possible universe” exists (or, that “existing” is not rigorously definable in any non-circular way anyhow, etc, as argued by Frank Tipler and apparently, Max Tegmark.) In such a case, there is no point in talking about string theory or any other such foundational business, since our world is just one of the infinite platonic universes…. However, there is a Bayesian self-selection problem that we would be unlikely to live in a possible world that had such consistency even if friendly to life, for there are “more” possible universes where the descriptions no longer follow the preceding order (just like there are more possible pixel arrangements that start out orderly, like a recognizable face, but then deteriorate into a mess, than the very few that are entirely recognizable.) Letting “everything” exist is more of a mess for that an other reasons, than its proponents realize or acknowledge.

  • Gina

    Dear Christine, what I meant to say (but perhaps did not succeed) is this: String theorists individually and as a group are extremely impressive even if string theory itself will eventually somewhat disappoint us. (Yes, yes, cosmologists are great as well!)

    Similarly, LHC is an amazing piece of technology and a great human achievement even if the outcomes will be somewhat disappointing. (And yes, yes, the Hubble space telescope is great as well!)

  • Gina

    Dear all, crossing the 400 comments line is perhaps a time for some foundational issues. (In addition to a most welcomed discussion on the Cosmological natural selection scenario.) Do we really have a public debate as the title of Sean’s original post suggest? Below is some very indirect evidence for a negative answer. My argument is based on a (very preliminary) comparative study of two cities in California, Gilroy and Santa Barbara.

    Gilroy is referred to as the “Garlic capital of the world”, indeed when you pass through Gilroy there are big signs stating precisely this. In Gilroy, you smell garlic everywhere you are offered garlic food at every corner, even garlic ice cream. It is not universally accepted that Gilroy is the garlic capital of the world: I heard of a city in Ohio with similar claims and I would not be surprised if some cities in Russia China or India can also be regarded as contenders to this highly desired title. Yet it seems that garlic is of central importance to the people of Gilroy as every visitor immediately realize.

    I expected something similar in Santa Barbara when I visited there as a tourist some years ago. I expected big signs “Santa Barbara the physics capital of the world!” or at least “Santa Barbara – the land of the asymptotically free”. I expected to smell physics everywhere in Santa Barbara. I expected to be offered “QCD-ice cream”, to see “string bars” instead of the traditional “noodle bars,” or at least to see “open strings pomodoro” or “brane-lasagna” dishes in local Italian restaurants. In turn, the only thing remotely related to physics I saw in the whole one afternoon touristic trip to Santa Barbara was the sign on the highway: UCSB next exit.

    In summary, my thesis is that this debate on string theory is not really a public debate and it is of interest just to a small part of the already very small academic swamp. In some sense, it is the projection of the serious and deep scientific debate within the string theory and high energy physics community itself on its shallow boundaries. (For a real public debate, we can try garlic.)

  • Lee Smolin

    Dear Neil B,

    I agree with you and deeply disagree with what you call modal realism, because I do not believe that mathematical objects and systems exist, in anything like the same meaning of existence that the physical universe exists. So I am a Platonist neither about mathematics or physics. I believe there is a lot of confusion generated by mixing notions of mathematical and physical existence, which has affected the notion of time in physics as well as notions of probability and possibility. This further corrupts how people try to think about the landscape, because they are tempted by the Platonic fantasy of timeless probability distributions on timeless spaces of mathematically possible universes. Eternal inflation restores the eternal timeless universe fantasy that GR superceded and suggests this confusion of mathematical and physical possibility. I suspect that these eternally static and infinite spaces of possible universes will come to be seen as quaint and theological as we now see medieval diagrams of the Ptolemeic universe with earth at the center and heaven above the stellar sphere. I very much admire Max Tegmark’s recent work about this because he takes to the logical reducto ad absurdum everything that I suspect is wrong with the Platonic notion of mathematical reality. My current project, with the philosopher Roberto Unger, is to sort this all out and give time, change and evolution central roles in cosmology.

    Thanks,

    Lee

  • http://backreaction.blogspot.com/ B

    Hi Gina,

    I expected to smell physics everywhere in Santa Barbara.

    This is funny :-) What do we learn from that? Strings don’t smell? When I was in Santa Barbara, I’ve been repeatedly asked if I know any Nobel prize winner, and if I’m working on that string stuff. I can’t say it happened all that often, but it happened (should stop reading papers at Starbucks). I have to say though that KITPs public outreach isn’t really impressive. This discussion is in so far public as that Peter, Bob and Paul from next door (and yes, also Alice) suddenly think they need to have an opinion about string theory and string theorists. When it comes to string theory, I find that not bad at all, it’s an opportunity to raise interest in theoretical physics generally. When it comes to string theorists, the issue among physicist is not whether or not the discussion is ‘really’ public, but how public they think it is – this does of course affect the way arguments are made, starting with complete denial of any problems, and is generally not beneficial for having calm discussions. I have to say that I don’t think blogs are really useful in this regard, neither do I think writing books is. I mean, seriously, what’s the next thing to happen? Regarding String Kings – someone is going to write a book praising the string community and deconstructing Loop-lers? Come on, that’s not going to work, we should really try to find a better way to deal with the present problems in research funding. Best,

    B.

  • anon.

    ‘I believe there is a lot of confusion generated by mixing notions of mathematical and physical existence, which has affected the notion of time in physics as well as notions of probability and possibility. This further corrupts how people try to think about the landscape, because they are tempted by the Platonic fantasy of timeless probability distributions on timeless spaces of mathematically possible universes.’ – Professor Lee Smolin

    So you disagree with Sir James Jeans, who for decades in the first half of the twentieth century was credited with the false ‘discovery’ that the solar system was formed by massive tides in the sun. Jeans wrote in his book The Mysterious Universe (Cambridge University Press, 1930, reprinted many times) that God is a mathematician:

    ‘The universe is built so as to operate according to certain laws. As a consequence of these laws atoms having certain definite numbers of electrons, namely 6, 26 to 28, and 83 to 92, have certain properties, which show themselves in the phenomena of life, magnetism and radioactivity respectively … the Great Architect of the Universe now begins to appear as a pure mathematician.’ — Sir James Jeans, MA, DSc, ScD, LLD, FRS, The Mysterious Universe, Penguin, 1938, pp. 20 and 167.

    It’s then an small step for a Harvard string theorist to write sixty years later to claim: ‘Superstring/M-theory is the language in which God wrote the world.’

    However, the problem for Jeans was that the special atomic numbers he lists aren’t special for reasons of pure mathematics. Those numbers aren’t primes or anything. Instead they come from quantum mechanics, with the way electrons are arranged in orbits according to phsyical effects like the exclusion principle. Jeans’ claim about radioactivity being just due to the atomic number being 83-92 was a complete deception.

    Professor Eugene Wigner argued:

    ‘The observation which comes closest to an explanation for the mathematical concepts’ cropping up in physics which I know is Einstein’s statement that the only physical theories which we are willing to accept are the beautiful ones. … A possible explanation of the physicist’s use of mathematics to formulate his laws of nature is that he is a somewhat irresponsible person. As a result, when he finds a connection between two quantities which resembles a connection well-known from mathematics, he will jump at the conclusion that the connection is that discussed in mathematics simply because he does not know of any other similar connection. It is not the intention of the present discussion to refute the charge that the physicist is a somewhat irresponsible person. Perhaps he is. However, it is important to point out that the mathematical formulation of the physicist’s often crude experience leads in an uncanny number of cases to an amazingly accurate description of a large class of phenomena.’ – E.P. Wigner, On the Unreasonable Effectiveness of Mathematics in the Natural Sciences, Comm. Pure Appl. Mathematics, vol. 13, No. I (February 1960): http://www.dartmouth.edu/~matc/MathDrama/reading/Wigner.html

    The role of maths in string theory contrasts with Wigner’s account of why mathematics is useful in physics generally. String theory spectacularly successful in explaining unobservables in terms of other non-observables: an example is how Nobel Laurate Brian Josephson was able to use string theory concepts without a single equation in his paper unifying ESP and what he calls the ‘special mental vacuum state’ used by string theorists when doing their mathematics, see: http://arxiv.org/abs/physics/0312012

  • E.

    Is there anybody else out there that believes that the reason for the existence of the landscape and extra dimensions is due to the fact that string theory starts with a classical object which is then quantized? The role of compactifcation is to eliminate these classical degrees of freedom. Perhaps if we had the correct quantum starting point rather than modeling things on a classical string + quantization+compactification, we would be free of the landscape. Presumably, this correct starting point would correspond to one of the string vacua, and we would be able to see how it is special if we ever find it.

  • Moshe

    Hi Bee, we seem to have converged on more or less the same opinion…I like the way you phrased it, indeed everyone seems to be in urgent need of a strong opinion. For something you are not an expert on and does not have direct influence on your life, wait and see approach seems to me sensible, but I’m sure I’ll be corrected…

    It is sad though that this endless ongoing debate derails almost any discussion of either funding structures or string theory content (the actual physics), by mixing the two subjects together, such is life…we can always discuss garlic.

  • Mark Srednicki

    amused,

    The standard lore is that lattice QED has a quasi-continuum limit (I’ll say what I mean by that in a moment) for any lattice coupling e_0 in the range 0 0 is only possible if you also take e(k) -> 0; that is, you can only get free field theory in a true continuum limit.

    More interesting is what happens if you start with e_0 > e_c, and approach e_c from above, in the confined phase. At least some of the people, some of the time, thought there was an interesting continuum theory here; I once heard Mike Peskin remark that perhaps this theory would be useful in technicolor models. But today I don’t think there is an interesting continuum limit. You would like to get a spectrum of mesons and lightballs, but there is no guarantee that their mass ratios stay fixed as e_0 -> e_c. I think the most likely possibility is that these mass ratios all become infinite, and that the continuum limit is a free field theory of the lightest meson/lightball (which presumably has spin zero). Not too exciting.

  • Mark Srednicki

    Thomas,

    I agree that the essential physics does not lie on the boundary at spatial infinity, but that’s just where your argument puts it! A robust argument would also work on a compact spatial manifold, and yours (as far as I can see) does not.

    Incidentally, the analogy with the conformal plane of the string world sheet is flawed as well. The conformal coordinate z is to be identified as exp(tau + i sigma), where tau is euclidean time, and and 0 < sigma < 2pi is the periodic coordinate along the string (for closed strings). Therefore, z -> infinity is the same as tau -> infinity, and we typically do not want to impose boundary conditions in the infinite future.

    At any fixed time (say, tau = 0), the usual Laurent-Taylor expansion of the stress tensor into Virasoro modes corresponds to an expansion into plane waves on the sigma circle. Then, with L_0 identified as the hamiltonian (the generator of time translations), the Virasoro algebra fixes the time dependence as well, and this yields the Laurent-Taylor expansion in powers of z.

    So I see no argument for new anomalies, no paradoxes, and certainly no reason to expect a “no-go theorem” for string theory.

  • Mark Srednicki

    oops, in my comment to amused, somehow several lines got lost. The first paragraph should read

    The standard lore is that lattice QED has a quasi-continuum limit (I’ll say what I mean by that in a moment) for any lattice coupling e_0 in the range 0 0 is only possible if you also take e(k) -> 0; that is, you can only get free field theory in a true continuum limit.

  • Mark Srednicki

    Arg! It happened again! I now notice that the instructions above this box (rendered in a lovely light-gray font on a light-gray background) say that I shouldn’t use less-than and greater-than signs, even if they appear in the preview. Nothing like a user-friendly interface, I always say.

    OK, once again, with feeling:

    The standard lore is that lattice QED has a quasi-continuum limit (I’ll say what I mean by that in a moment) for any lattice coupling e_0 in the range 0 < e_0 < e_c. For any momenta k << 1/a (where a is the lattice spacing), we end up with electrons and photons interacting with a gauge couping e(k), computed via the (exact lattice) beta function starting at e(1/a) = e_0. This means e(k) < e_0, so if you want a particular e(k) at some scale k, you must start with a larger e_0. And you cannot go all the way to the continuum limit (that’s what I mean by there being only a “quasi-continuum” limit), because ka -> 0 is only possible if you also take e(k) -> 0; that is, you can only get free field theory in a true continuum limit.

  • Gina

    Damn! I missed making the 400th comment!

    Guys, Let’s keep the 500th for Mark!

  • http://backreaction.blogspot.com/ B

    @E # 416

    Is there anybody else out there that believes that the reason for the existence of the landscape and extra dimensions is due to the fact that string theory starts with a classical object which is then quantized?

    Yes, me.

    If someone can convince me that the necessity for extra dimensions does not arise from quantization, please go ahead. If it does, let me ask, why do you trust it?

  • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

    I edited some comments so that the < and > signs appear where they should. Glad everyone thinks our color scheme is lovely!

  • anon.

    E, B, I’m afraid I don’t understand what you mean. There are certainly string theory vacua that are not all that close to the weakly-coupled, higher-dimensional strings. For instance, there are nongeometric compactifications. But the existence of these points in the landscape doesn’t make the other, extra-dimensional-looking points go away.

    Maybe I should point out that points that are self-dual (and hence, in some sense, deepest in the interior of the moduli space) often have some enhanced symmetry. There was a paper by Faraggi suggesting that such points are really preferred vacua. But as far as I can tell no real mechanism to select such points was suggested, aside from some strange-looking (to me, at least) reformulation of quantum mechanics. A related, but more mainstream, idea is that beauty is attractive.

  • http://backreaction.blogspot.com/ B

    @ anon
    thanks for the answer. I don’t know exactly what E referred to, but my question was much more basic. what I mean is roughly: does the necessity for extra dimensions exist for the classical string? if not, isn’t it then caused by quantization? if so, couldn’t it be the reason is that we don’t understand quantization?

  • E

    The need for extra dimensions is a direct result of quantization, in particular anomaly cancellation. My point is that we build string theory by quantizing a classical object. Shouldn’t we really start with something which is inherently quantum? I think that by quantizing a classical object, we are modelling whatever this true quantum starting point is, however classical degrees of freedom come along as extra baggage, e.q. extra dimensions. By compactifying the extra dimensions, we are restricting these extra classical degrees of freedom. So, what I’m saying is that the true theory will correspond to one of the vacuum states, while the other vacuum states are just mathematical gargabe. Thus, quantizing a classical string in 10 dimensions and compactifying the extra dimensions is nothing more than an approximate description which models the true theory. Essentially, this is what I believe Alon and others have in mind with compactifying on self-dual points.

  • Thomas Larsson

    Mark # 421,

    In critical phenomena, which is more important than string theory because it is a physically successful application of CFT, we do have an infinite plane with boundary conditions at infinity. Any argument against Laurent polynomials in r is an argument against Laurent polynomials in z. Any argument against Fourier polynomials on the torus is an argument against Fourier polynomials on the circle. CFT seems to be doing fine despite these objections.

    Anyway, the positive part of my message is that the mathematics of gauge symmetry in multi-dimensions now exists, and is ready to be applied to the physics of gauge symmetry in multi-dimensions. The most striking feature is that we must quantize the observer’s trajectory. This is philosophically very appealing, because every physical observer obeys the rules of quantum mechanics.

    With an alternative available, there is no reason to believe in string theory, since nobody has managed to connect it to reality in the past 39 years.

  • http://eskesthai.blogspot.com/2006/12/against-symmetry.html Plato

    Gina:I expected to be offered “QCD-ice cream”, to see “string bars” instead of the traditional “noodle bars,” or at least to see “open strings pomodoro” or “brane-lasagna” dishes in local Italian restaurants. In turn, the only thing remotely related to physics I saw in the whole one afternoon touristic trip to Santa Barbara was the sign on the highway: UCSB next exit.

    Let’s not forget tomato soup?

    It is always good to know how Lee is lining his point of view up? Against Symmetry?

  • amused

    Mark.

    That was very useful – thanks! Some things which had been a bit muddled for me have suddenly become very clear. From your explanation I can deduce that lattice QED could only be useful for calculations at large momentum scales – but with unphysically small coupling (it would have to be no larger than e_c, but in the real world e(k) would no doubt be much larger than that for large momenta). By the way, is the exact beta function for lattice QED actually known for all values of the coupling below e_c? I have only heard of perturbative calculations at small coupling.

    The situation for a lattice formulation of the SM will no doubt be similar in that only a quasi-continuum limit is possible there as well. (And my suggeston of a “landscape” of continuum limits in #397 is looking a bit silly at this point – I better take that back.) Still, I imagine that it would still be interesting to have a lattice formulation of the SM, to look for and investigate a phase with spontaneously broken electroweak gauge symmetry when the Higgs is stuck in. Also interesting is your suggestion in #382 to study strongly coupled chiral gauge theories, where the lattice is able to provide a full nonperturbative definition of the theory (i.e. a continuum limit is attainable).

  • Mark Srednicki

    amused,

    The exact beta function for lattice QED is not known. (If it was, we wouldn’t need all those computers!) But the physical coupling e(m_e) = 0.302, where m_e is the electron mass, is actually very small; a good point of comparison is the pion-nucleon coupling, which is around 13. In general, the loop expansion parameter (which is roughly g^2/16pi^2) should be of order one in a strongly coupled theory; so I would expect e_c ~ 13. So there’s plenty of room for the physical QED coupling below e_c. Another way to say this is that the Landau pole (the scale M where e(M) formally becomes infinite) is predicted by the lowest-order beta function to be at M = exp(3pi/2alpha(m_e))m_e = 10^280 m_e. (Here alpha(m_e) = e^2(m_e)/4pi = 1/137.)

    I do think it’s important to have a nonperturbative formulation of chiral gauge theories (or even non-chiral gauge theories with a controllable number of flavors). Lenny Susskind once remarked, decades ago, that not having such a formulation “will one day come back and bite us in the ass”. (Usual disclaimer on ancient quotes.)

    Given such a formulation, and an arbitrarily large and fast computer, I suppose the first question I would try to answer is whether or not Seiberg duality holds for nonsupersymmetric theories.

  • Mark Srednicki

    Thomas,

    You wrote, “With an alternative available, there is no reason to believe in string theory, since nobody has managed to connect it to reality in the past 39 years.”

    However, your alternative, like string theory, and like all other proposed alternatives, has made no definite predictions for what will be seen at the LHC, or in any other experiment. Thus other criteria must be used to decide what is worth working on.

  • Thomas Larsson

    Mark,

    It is true that QJT makes no definite testable prediction. If this is still true 20,000 man-years from now, I will be seriously worried. In lack of predictions, here are some alternative criteria:

    Mathematical beauty. The algebraic structures underlying string theory are either one-dimensional (chiral algebras, Gelfand-Kirillov dimension = 1) or classical (no extension). QJT involves algebraic structures which are both four-dimensional and quantum in the above sense, as appropriate for a 4D quantum world.

    Experiments. Although string theory makes no definite predictions, it makes several natural ones – supersymmetry, extra-dimensions, 496 gauge bosons, a large and negative cc, etc. Taken at face value, these predictions are wrong. Maybe God is giving us a hint here.

    Logical consistency. A fundamental part of QJT is a quantized observer, which leads to quantized time. Time is what is measured by a clock, but clock time has a sharp value only in an eigenstate of the proper time operator. This is an obvious consequence of QM, yet it cannot be formulated in QFT. It is a natural consequence of QJT which explicitly involves the clock’s worldline.

    I think that these are good reasons to think about QJT. Even if people don’t agree, they should know about them.

    Good night.

  • http://tyrannogenius.blogspot.com Neil B.

    Lee: Thanks for the thoughtful reply which I am honored to get from you. I never trusted that platonic pan-realism either. As for features themselves, I happen to think “as a philosopher” that the fine structure constant is about 1/137 is so “we” (intelligent life of some kind) can be here, more than any intrinsic “physical” reason. However, I understand that physicists will by definition want to explore naturalistic avenues. As for some other facts about the universe’s features, I think classical considerations play a larger role than is generally appreciated, which I can elaborate on if asked.

    PS, a bit OT, but I give my condolances to the students and others killed in the horrific shootings at VA Tech.

  • http://tsm2.blogspot.com wolfgang

    Thomas,

    > clock time has a sharp value only in an eigenstate of the proper time operator.
    > This is an obvious consequence of QM

    I am sure you are aware of the fact that there is no ‘time operator’ in QM.
    Pauli pointed out that a (self-adjoint) time operator is incompatible with a Hamiltonian spectrum bounded below.

  • Mark Srednicki

    Thomas,

    you wrote “Although string theory makes no definite predictions, it makes several natural ones – supersymmetry, extra dimensions, 496 gauge bosons, a large and negative cc, etc.”

    I’m not sure what you mean by a “natural prediction”. Either a theory makes a prediction, or it doesn’t. It is true that some phases of string theory have full supersymmetry, extra-dimensions, and 496 gauge bosons, but these phases also have a cosmological constant that is exactly zero.

    Other phases have different features. The problem, as emphasized by Peter, is that (as far as we know right now) there is no feature that is common to all the phases, and hence qualifies as a prediction of the string framework.

    But, as I keep pointing out, there is currently no framework for particle physics that does any better.

  • Thomas Larsson

    Mark,

    I think the lack of definite predictions is a worse problem for an old, well-established field than it is for a new idea. Speculative ideas take time to grow.

    Wolfgang,

    Reading a real clock is a physical experiment to which QM applies.

    In QJT, all fields are expanded in a Taylor series around a 1D curve q(t), and everything is reexpressed in terms of the Taylor coefficients. This curve is parametrized by a c-number t. Energy is bounded from below in the sense that the vacuum is annihilated by negative frequency modes, where frequency is defined wrt t. However, one can write down a natural proper time operator tau(t), which is a quantum operator. The c-number t itself never runs backwards.

    The reason why QJT differs from QFT is that q(t) is operator-valued. This is necessary for a well-defined action of diffeomorphisms.

  • amused

    Mark,

    Thanks for your points. I wasn’t worried so much about whether the physical QED coupling was smaller than e_c, but there was a misunderstanding (once again) in my last comment which made it a bit incomprehensible. Rather than go into the details of that I’ll just mention that what I had forgotten at the time, but later remembered, is that the size of the lattice spacing `a’ needed to perform a reasonably accurate lattice calculation only needs to be smaller (by, say, an order of magnitude) than the inverse of the relevant energy or momentum scale for the stuff you are calculating. (I.e. 1/a needs to be larger than that scale.) Taking that into account, what I should have written in my last comment is that lattice QED can in principle give a good description of QED physics at all scales k that are at least an order of magnitude less than k_c, where k_c is the scale at which e(k_c) = e_c. (Taking the bare lattice coupling e_0 to be e_c (or a bit less than e_c – just to make sure we are properly in the Coulomb phase) then corresponds to lattice spacing a bit more than 1/k_c.)

    Provided I got that right, the situation in a lattice formulation of the SM will no doubt be similar in this regard. So there will be some energy scale below which the physics can well described by the lattice model. Hopefully this will include the stuff to do with electroweak symm breaking.

    Hopefully I got this more or less right this time, but if not I’ld appreciate being put straight. Thanks for your patience!

  • Gina

    It is nice to see discussions about QED. Somehow I have the feeling that QED is somewhat neglected and yet there may still be fundamental and important issues concerning QED which may reflect on more advanced topics.

    Let me repeat (and slightly rephrased) the thought from #392.

    1. The idea:

    What we need to find is a landscape of mathematical options regarding QED: Namely a vast number of mathematically different theories giving precisely the same predictions. (By mathematical theories I mean theories in the physics non rigorous standards. Among all these we will hopefully find some day, some theories consistent with rigorous mathematics)

    And yes, we should embed QED in a theory involving non trivial representation of U(1), in a way that will not effect any empirical prediction.

    2. Roots of the idea

    The immediate root of this idea is Mark’s understanding (#330,#336) of Peter Woit’s rather vague ideas regarding non trivial representations of gauge groups. (Peter strongly objected (#335 #337) to the way Mark understood his ideas, and regard it as just a way for Mark to claim that Peter is not on top of things.)

    Not very promising, I admit, but we have seen worse.

    (But, of course, similar suggestions are floating around in blog discussions and perhaps even in more serious forums.)

    3. Wasn’t it examined before and isn’t it precisely what physicists are doing?

    Actually, I do not know (and be happy to learn) but I tend to think with little evidence that QED is somewhat neglected.

    Let me mention something I learned from a paper by David Corfield, when I hanged out in the n Category cafe blog (while being on exile from Peter’s blog.) David described in a paper the “divorce” between mathematics and physics caused mainly by the non rigorous nature of QED. (Like any divorce there could have been other reasons.) An idea like the one above could have appealed more to mathematicians than to physicists, but it could have fall between the chairs because of the non rigorous mathematical nature of QED and the related “divorce” between mathematics and physics.

    It is true that math and physics are dating again but it seems that the topic of conversation is much more advanced theories which now appeal more to both.

    4. Isn’t Mark, Moshe and Herbert already explained that non trivial representations may not occur?

    Maybe. I could not understand Herbert’s comment and even could not tell if he agrees with Moshe and Mark. I am not sure and I certainly cannot tell if Moshe and Mark’s appealing and kind explanations do not already rely on some extra math or physics assumptions.

  • http://www.cgoakley.demon.co.uk/qft/ Chris Oakley

    Re: the QED divorce, I believe that Mathematics initiated the proceedings against Physics, and won the case on the grounds of Mental Cruelty.

  • Gina

    Chris, It is always much much more complicated. After centuries together it is only natural that some period of seperation and individual soal-searching was called upon. No point to raise old difficulties now, after all math and physics are dating again, and there is some sense of happiness in the air. And certainly string theory got them close together and deserves a lot of credit. (And what other options do they really have?)

  • http://www.cgoakley.demon.co.uk/qft/ Chris Oakley

    Hi Gina,

    What other options do they really have?

    Where do you want me to start?

  • Gina

    Chris, You did not understand me. Math and physics have no other options in terms of partners. As for the precise nature of the relation, there are many options and possibilities but let them find the right way. We should not interfere at this delicate time.

  • http://www.cgoakley.demon.co.uk/qft/ Chris Oakley

    Gina,

    I am not really in much of a position to “interfere at this delicate time” anyway. As Dr. Arnold Neumaier of Vienna University has accurately pointed out in one of the Usenet discussions, no-one cares what I think, especially as I have been out of academia for nearly 20 years.

    HOWEVER, having said that, I grieves me to see the subject of fundamental physics at such a low ebb. Whole departments dedicated to a highly speculative idea and unwilling to even listen to alternatives. Fine if they were part of the Templeton Institute, but they are not. They are part of physics departments of once-great universities. I hope for a better future, but the only optimistic signs I see at the moment are that relative String theory outsiders, such as Peter Woit, seem to be able to bring pressure to bear. Note that this is EXTERNAL pressure. The fact that the criticism has had to come from outside cannot be a good sign.

  • Gina

    Dear Chris, Your voice is heard on these weblog discussions, and your anti-renormalization stance is quite something; but I simply disagree with you. HEP and string theory had glorious achievements in the last two decades (and so are other areas), and Peter Woit, while coming across as a nice guy with good intentions, does not really have a case. (But the first part of Peter’s book which does not deal with string theory is very good!) Let’s agree to disagree!

  • http://tyrannogenius.blogspot.com Neil B.

    Speaking of renormalization, which always seemed a bit fishy to me (a mathematical trick, but what *does* it in nature?): What is the “physical mechanism” of renormalization? What in nature makes it happen? I never heard any good answers, although I didn’t dig in far enough to maybe find out. Maybe string theory could help with that? Even then, I wonder how we can deal with the integration of field energy around an electron far exceeding its mass, even tho’ not infinite, as included radius goes below the classical electron radius (an electrons are “points” to far below that size….)

  • http://www.cgoakley.demon.co.uk/qft/ Chris Oakley

    Gina,

    I think you’re right – we will have to agree to disagree.

    Neil,

    Despite the fact that finiteness was one of the aims of the String Theory program, the best they aspire to nowadays is just reproducing effective field theory, a package which includes renormalization. So no, String Theory does not help. As regards classical models/analogies, I do not see that they are of much use, either. There is no obvious way to treat the infinities that appear when one has classical pointlike charges, whereas there are things one can do in the quantum world.

  • Aaron Bergman

    Speaking of renormalization, which always seemed a bit fishy to me (a mathematical trick, but what *does* it in nature?): What is the “physical mechanism” of renormalization? What in nature makes it happen? I never heard any good answers, although I didn’t dig in far enough to maybe find out.

    Renormalization is understand these days in the context of effective field theory. Nothing in nature does it. Instead, it arises as we try to better approximate nature with a given theory. The infinities just reflect our lack of knowledge about the UV physics.

  • Joe Polchinski

    Niel B –

    In fact there is a very physical interpretation to renormalization, which is presented in most modern textbooks (e.g. the second half of Weinberg ch. 12), but which is somewhat overshadowed by the historical (and efficient) cancellation-of-infinities presentation.

    First, a historical note relevant to your question: Weisskopf showed in 1939 that the infinite classical self-energy of the electron is largely cancelled by the contribution of virtual antiparticle states, so that it exceeds the observed mass not at the classical electron radius, but at a scale beyond the Planck length. That said, the modern interpretation is that these energies are real, but ultimately cut off in a more complete theory. Thus, in some grand unified theories the difference of the tau and bottom masses is accounted for rather precisely by the difference of the self-energies up to the GUT scale. String theory is an example of a more complete theory in which all these diverges are cut off: a given string vacuum leads to calculable [modulo steadily improving technical capabilities] and finite values for the masses and other parameters.

    But if there is ultimately a cutoff, what do we need renormalization for? In fact, it just parameterizes our ignorance of what the high energy theory is, so we can relate quantities measured at observed energies. In practice, however, it is simplest in calculation just to pretend that one is cancelling infinities, rather than making a long-winded statement about what one is really doing.

  • http://www.cgoakley.demon.co.uk/qft/ Chris Oakley

    But if there is ultimately a cutoff, what do we need renormalization for? In fact, it just parameterizes our ignorance of what the high energy theory is, so we can relate quantities measured at observed energies.

    This may be what effective field theory is about, but I do not see that it is anything to be proud of. We do not have a theory of classical mechanics or classical electrodynamics that merely “parameterises our ignorance of what the high energy theory is”, we have principles from which are derived results which then turn out to have wide domains of applicability. The problem with QFT as currently practised is that the principles do not work. Rather than starting again, people choose to do meaningless infinite subtractions, calling their kludges “quantum field theory” when they are in reality much less than this.
    .

  • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

    Chris, that’s more or less the opposite of the truth. In classical mechanics or electrodynamics we precisely have theories that parameterize our ignorance — they work in the classical domain, and stop working when quantum mechanics becomes important. And it doesn’t really matter what happens when quantum mechanics does become important; classical theories will still work.

    It’s exactly the same with QFT. Things happen at all scales; we don’t know what happens at the highest energy scales; but we don’t need to, since there exist a distinct set of useful rules that operate at low scales. That’s what renormalization is all about. And it works spectacularly well, as has been demonstrated repeatedly by comparing with actual data.

  • Mark Srednicki

    Here is my capsule take on renormalization:

    In a harmonic oscillator, the energy difference between the ground state and the first excited state is hbar w, where w is the classical frequency of the oscillator, which appears in the potential energy as V(x) = m w^2 x^2/2.

    If we add extra terms to the potential energy (such as g x^4), then the relationship between the energy gap and the classical frequency is altered; the corrections can be expressed as a power series in g.

    If we have many coupled oscillators, all contribute to these corrections; the more oscillators there are, the bigger the corrections.

    Now consider quantum field theory. Without infrared and ultraviolet cutoffs, quantum field thoery consists of an infinite number of oscillators. In this case, the corresponding corrections are infinite (without cutoffs in place).

    In field theory, the first excited state consists of a single particle at rest, and so the energy gap (between the first excited state and the ground state) is mc^2, the rest energy of the particle. The parameter that plays the role of the classical frequency is the so-called “bare” mass m_0. Since it is m (and not m_0) that is physically observable, and since m is observed to be finite, and since the corrections that give m in terms of m_0 become infinite in the limit that the cutoffs are removed, we conclude that m_0 must also become infinite in this limit.

    To quote one textbook, “It may be disturbing to have a parameter in the lagrangian that is formally infinite. However, such parameters are not directly measurable, and so need not obey our preconceptions about their magnitudes.”

  • http://tyrannogenius.blogspot.com Neil B.

    Thanks for various replies and sub-replies. So, simply speaking, “virtual particles” do the renormalization? I know, I have heard that before, but some people consider VPs a bit hokey (see the Wikipedia articles…) In any case, that still doesn’t work all the way down to “a point”, am I right, in which case you still need “strings” to keep things from getting absurd in the case of a “literal point” – ?

  • http://www.cgoakley.demon.co.uk/qft/ Chris Oakley

    Sean,

    Yes – I suppose that any physical theory is parameterizing ignorance of what happens at the scales when the theory breaks down (unless of course it really is the ultimate theory).

    But I do not find this notion helpful.

    The reasoning that leads to phrases like “parameterizing ignorance” is that perturbation theory involves divergent integrals on account of the integration being over infinite ranges of momentum. Since an infinite result is considered undesirable, a cutoff is introduced. The cutoff then becomes a parameter that represents our lack of knowledge about what happens at high momenta.

    This theory, which includes the cutoff, is then a possible result of subtracting infinity from infinity. A possible result, but not a unique one. The mathematical reality is that by subtracting infinity from infinity we can get any functional form we want, including theories that cannot yield the required experimental numbers.

    Since none of this jiggery-pokery is needed for classical mechanics or electrodynamics, I do not see how you can say that such theories are no different.

  • Mark Srednicki

    Neil, yes, simply speaking, virtual particles do the renormalization.

    And it’s the Wikipedia article on “virtual particles” that’s a bit hokey, not the virtual particles themselves! But their link to Gordy Kane’s answer to the question “Are virtual particles really constantly popping in and out of existence?” is worthwhile.

    And for most field theories, it indeed does not work all the way down to a point, in which case you do indeed need strings (or something; but strings is really the only concrete proposal so far) from getting absurd in the pointlike limit. I said most, because the so-called “asymptotically free” theories have interactions that disappear in the pointlike limit, and so in that case the limit is OK. (David Gross, David Politzer, and Frank Wilczek got the Nobel Prize in 2004 for showing that nonabelian gauge theories can be asymptotically free).

  • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

    Chris, the whole point of renormalization is that the result is extremely unique, or at least depends on a small number of parameters (the “constants of nature”), not on an arbitrary function. We don’t introduce new parameters every time we test QED or the Standard Model. Theories that are “renormalizable” are precisely those for which only a small number of parameters are needed to make a wide variety of predictions. There is a cutoff, as Joe mentioned, that might very well represent new high-scale physics; but the nice thing is that such physics is completely irrelevant to our low-energy predictions.

    People need to get over this discomfort with “subtracting infinity from infinity.” It’s called “taking a limit,” and is a perfectly respectable procedure.

  • http://www.cgoakley.demon.co.uk/qft/ Chris Oakley

    Neil,

    I am not sure what you mean by “doing” renormalization. Virtual particles form loops in Feynman graphs and these loops are most often divergent integrals. So virtual particles lead to the need to renormalize … they don’t actually “do” them, though, as the renormalization is carried out by tree graphs with counterterms attached.

    Read up on this (& not just on Wikipedia). Try, for example, Mark’s text book … you might find it enlightening.

  • Mark Srednicki

    Chris,

    You wrote, “The mathematical reality is that by subtracting infinity from infinity we can get any functional form we want, including theories that cannot yield the required experimental numbers.”

    This is just wrong. In, say, QED, you can get any value of the electron charge that you want, or any value of the elctron mass that you want, but that’s it. There’s no more freedom to adjust the predicitons (up to corrections suppressed by powers of E/Lambda, where E is the experimental energy and Lambda is the the ultraviolet cutoff).

  • http://www.cgoakley.demon.co.uk/qft/ Chris Oakley

    Sean,

    I am not arguing about the accuracy of renormalized perturbation theory for QED when done “correctly”, i.e. according to the recipe.

    I am merely saying that if, perversely, I choose not to follow the recipe, then I will get a different answer, despite starting with the same assumptions.

    Subtracting infinity from infinity is exactly what it is. It is not a limiting process – the limit, in this case, does not exist.

  • Aaron Bergman

    Chris, the recipe isn’t magic. Subtracting infinity from infinity is not what’s done; it’s a shorthand for a limiting process that we understand (or, at least, we understand how to deal with what we don’t understand.) Ugliness like MSbar and other ad hoc regularizations are just tricks that make it easier to get the answer that arises from the limiting procedure.

  • http://www.cgoakley.demon.co.uk/qft/ Chris Oakley

    Mark,

    There is no theoretical requirement that Λ should be a constant. It could depend on anything: momenta, energies, positions, variables that never entered the equations in the first place: anything. You choose it do be a constant, but its purpose is just to parameterize a divergent integral. I can use this freedom to get all sorts of wrong theories.

  • http://www.cgoakley.demon.co.uk/qft/ Chris Oakley

    Aaron,

    You say, “Subtracting infinity from infinity is not what’s done”, but that is what is in the text books.

  • Gavin Polhemus

    Chris,

    An example where you use the freedom to chose Lambda to get a wrong answer would be interesting. I suppose you could also make electric charge, particle masses, and Planck’s constant functions of momenta, energies, political preference and hair color, also generating wrong answers. What fun! However, getting wrong answers isn’t really the goal. Constant Lambda gives right answers, so that’s what we do (likewise for charge, etc.).

  • Mark Srednicki

    Chris,

    You can let Lambda depend on anything you like, but all effects of the cutoff (now matter how it varies) will be suppressed from the standard textbook calculations by powers of E/Lambda_min, where E is the energy scale at which the experiment is carried out (equal to the electron mass for “low energy” experiments like the anomalous magnetic moment), and Lambda_min is the minimum value of the ultraviolet cutoff Lambda.

  • Moshe

    Chris, what is missing in your discussion I think is the notion of universality: in renormalizable field theories there are certain quantities that, when expressed in terms of a small number of physically measured parameters, become independent on the details of the cutoff procedure. Those are precisely the quantities that are compared to experiment with such spectacular success, the universal ones. Incidentally, this is not specific to perturbation theory, lattice calculations do precisely that as well.

    I think the viewpoint of “subtracting infinities” is not a useful one. Maybe a more useful way is the view that renormalization is a process of systematically eliminating the dependence on unknown short distance physics.

  • Mark Srednicki

    Oops; “now matter how it varies” should have been “no matter how it varies”.

  • Moshe

    Also, the process of renormalization is so efficient that it is usually useful to eliminate the dependence on short distance physics, even in cases when it is known…

  • http://tyrannogenius.blogspot.com Neil B.

    Hmmm… BTW, the need to renormalize would come first anyway from the integration of field energy below the classical electron radius, so it is not just a problem that arises from quantum mechanics. But what about the virtual electrons and positrons themselves being either real points, or strings, does that make a difference? And, the virtual particles should have their own infinity issues, and virtual-upon-virtual particles, etc. It looks like a mess, and I don’t know much about it. If string theory can deal with that, then we would have a reason for it to be true?

  • Aaron Bergman

    This reminds me of a question that I had today that I probably ought to know the answer to. Does anyone know the bounds on the coefficients of various dimension 5 operators in the standard model?

  • onymous

    Aaron, that’s a pretty broad question. There are fairly strict bounds on just about any dimension 5 or 6 operator you could write down. (Things involving the top quark are the least constrained, as a rule.) What specific operators do you have in mind? I don’t know of anywhere that you can find all the bounds collected, though the PDG is probably a good place to start looking. Otherwise, key words to look for would be “electroweak precision”, or “compositeness bounds” for four-fermion operators. Not to mention all the flavor physics results….

  • Aaron Bergman

    I was mostly curious about to what scale we can rule out new physics that interacts with the standard model (beyond the electroweak symmetry breaking sector, of course.) But I suppose I should have realized the PDG would be a good place to look.

  • onymous

    This really depends on how it interacts with the Standard Model. In general, the bounds are really uncomfortably strong; I’m sure you’ve heard of the little hierarchy problem, or the problem with FCNCs in SUSY, etc…. This is why model-building is nontrivial.

    I think a lot of the strongest bounds are for four-fermion operators. Certainly these are among the easiest to understand the experimental results for: LEP measured e+e- going to various things rather precisely, and some of these operators must be suppressed by a scale of 10 or 20 TeV. (Of course, the actual scale depends on how large the couplings of the new physics to the SM are; e.g. a light Z’ is possible, if it couples very weakly.)

  • Joe Polchinski

    #461 There is no theoretical requirement that Λ should be a constant. It could depend on anything: momenta, energies, positions, variables that never entered the equations in the first place: anything. You choose it do be a constant, but its purpose is just to parameterize a divergent integral. I can use this freedom to get all sorts of wrong theories.

    A good challenge, to which there is good answer (basically already given in 464).
    Highly off-shell particles don’t propagate very far (the uncertainty principle). Thus their effects are essentially a delta function in spacetime (up to systematic corrections), which is a constant in energy-momentum. More formally, if you differentiate a graph enough times with respect to the external momenta, it becomes convergent (the BPHZ formalizsm). Dependence on position is forbidden by translation invariance.

  • http://www.cgoakley.demon.co.uk/qft/ Chris Oakley

    Gavin & Joe,

    You are only reinforcing my point. The principles of the subject (i.e. quantization of classical electrodynamics plus the Dirac field, interaction picture, time-ordered products, Wick-ordered products, Feynman graphs, renormalization) do not lead uniquely to the answer you want. They do not lead uniquely to any answer. As Joe has pointed out, you could even – using the freedom inherent in subtracting infinity from infinity – construct theories that violate translation invariance. So why bother with the “first principles” part at all? Why not just say that effective field theory, post-renormalization, as presented in the text books, is the theory and not pretend that it follows from anything deeper?

  • http://www.cgoakley.demon.co.uk/qft/ Chris Oakley

    Moshe,

    Same point. The clay from which you are shaping your required theory is infinitely malleable. A posteori choices of “reasonable” requirements for the theory (such as independence on Λ after having decided that it is a constant) are exactly that: they are choices you make because the original theory was not sufficiently rigid.

  • http://www.cgoakley.demon.co.uk/qft/ Chris Oakley

    Oh, sorry – I meant to close the italics after “a posteori”. BTW you can get Λ by typing this: &Lambda;

    Mark, I’m thinking about it, but my initial reaction is that if you know nothing about Λ then you are not entitled to expand in powers of E/Λ.

  • Hendrik

    On Renormalization (posts 446-468)

    Renormalization is an active area in mathematical physics,
    with a long history (starting with Glimm & Jaffe’s phi^4 theory, via constuctive field theorists e.g. Rivasseau, Froehlich, and more recently Fredenhagen & Brunetti). Ideally one should ask one of these people to discuss this issue on this blog.

    Until one of them arrives, here is my take on it.

    If one accepts that a quantum theory is a representation
    of some algebra of observables (usually C*), then:
    1) Whilst for a canonical quantum theory with finitely many
    degrees of freedom there is essentially only one
    irreducible representation (cf. the Von Neumann uniqueness
    theorem), for canonical quantum field theory – which has
    infinitely many degrees of freedom – there is a vast number
    of inequivalent representations.
    2) It is known from a range of models that even mild interactions
    cannot be unitarily implemented in the Fock representation, i.e.
    time evolution moves you out of it
    (cf. e.g. J.Math.Phys. 26(6) p1264, 1985 and others)
    3) By Haag’s theorem the Hamiltonian of an interacting QFT together with an invariant vacuum vector cannot exist in the representation of the free field (hence the interaction picture only exists if there is no interaction, cf. this survey paper in Erkenntnis 64 p305, 2006)

    So one knows from the outset that when you construct a perturbation series for the dynamics of an interacting QFT in the usual Fock representation that the mathematics will not allow it, something will go wrong. Unless you have a procedure for leaving the Fock representation to go to another inequivalent representation, and that is where renormalization comes in.

    Here’s a sketch of how it works. If one starts e.g. from the situation in Mark Srednicki’s post #452, i.e. an infinite lattice of quantum oscillators with e.g bounded nearest neighbour interactions. Then make a chain of regions in the lattice, increasing to the full lattice, and for each region say R, choose a ground state v_R for the operator

    h_R := H_R – E_R

    where H_R is the “partial Hamiltonian” of R, i.e. it involves only the lattice points in R, and E_R is its smallest eigenvalue. These vectors v_R through their expectation values define states on the algebra

    w_R(A) := (v_R, A.v_R)

    and as the set of states is w*-compact, there is a w*-compact
    accumulation point w which can therefore be written as a
    limit
    w(A) = lim_n w_{R_n}(A) for all A

    The state w defines a new representation for the algebra
    (GNS-construction) in which there will be a selfadjoint
    Hamiltonian producing the desired dynamics, and with a ground
    state. This is interpreted as renormalisation because
    when
    lim E_{R_n} = infty

    it looks like an infinite subtraction procedure. But the point is that you have left your original representation for this new one.

    So one can look at renormalisation as a way of moving out of the Fock representation to a different representation where one has a well-defined dynamics and vacuum.

    __________________________________________________________

    Whilst there is a good interpretation for (some) renormalization
    procedures, there still remain serious problems in the
    mathematics of perturbation series, for instance, the renormalised
    perturbation expansions of QFT in general do not converge
    (it is an `asymptotic series’ i.e. the terms seem to converge up
    to some point, but beyond that it diverges).
    So it still does not define a time evolution mathematically.

    Of course there is also the problem of what the algebra of
    the interacting QFT should be, and how to interpret the
    pointwise products of distributions which occur in many expressions
    (some recent advances by Fredenhagen & Brunetti on that one).

  • anon.

    Chris wrote:

    Mark, I’m thinking about it, but my initial reaction is that if you know nothing about Λ then you are not entitled to expand in powers of E/Λ.

    There might be two issues that are being conflated here. The first is that there might be a physical cutoff scale, Λ, at which there are new particles, etc. For instance, in the SM this might be TeV-ish. In that case you can expect relatively large contributions from higher-dimension operators, but (see above) experimentally these aren’t seen, so it seems to be safe to use a larger cutoff for most things.

    The other point is that there is an unphysical renormalization scale, μ, which is not physically meaningful and in fact does not enter the predictions because of the Callan-Symanzik equations. (If you truncate perturbation theory at a small order, μ can have an important effect, but computing loops will reduce this.) This scale μ can get transmuted into a real, physical cutoff, Λ. In abstract QED coupled to no other physics, this is the Landau pole, and you can only make predictions up to corrections in powers of (E/Λ). This Λ is not arbitrary, but physical. Of course in real-world QED the cutoff is lower — it’s where the rest of the SM starts to matter — so your predictions are valid up to corrections suppressed by that cutoff. In QCD, the physical scale Λ is small, and you can make corrections for high-energy processes that are undetermined in perturbation theory up to powers of (Λ/E). (Nonperturbatively, since QCD is asymptotically free we expect that it exists and that these power corrections are actually determined.)

    The idea of universality is really key here, and you really should try to understand it instead of arrogantly insisting that you understand these issues better than the large community of people who work with them every day.

  • http://www.cgoakley.demon.co.uk/qft/ Chris Oakley

    Hendrik,

    I do not believe that these complicated constructs are necessary to get around Haag’s theorem. AFAIC the theorem means that we have to abandon hope of doing perturbation theory in QFT in the same way that we did for QM, but this is not the end of the world. One may construct interacting fields from sums of tensor products of free fields, and obtain non-zero matrix elements for real processes that agree with experiment because of the interference between free fields at different orders. A contribution to e+e–>γγ, for example, can arise from a product of free fields (γ cr)(γ cr)(e+ annih) in the expansion of the interacting e- field. This matrix element cannot be reproduced by a system where H = H_0 + V, except as an approximation, which is what one would expect on account of Haag’s theorem.

    Anon.,

    I am certainly not insisting, arrogantly or otherwise, that I understand the issues in building effective field theories better than the people who work with them full-time. I do not want to build effective field theories. I would rather see it all derived from first principles.

  • Mark Srednicki

    The problem with trying to find a rigorous mathematical construction of quantum field theory (in four dimensions) is that there is considerable evidence that such a construction does not exist: with the exception of nonabelian gauge theories, all 4d quantum field theories are believed to be “trivial”, that is, they become free-field theories in the limit that the cutoff is removed. (See, e.g., “On the Triviality of Textbook Quantum Electrodynamics” by S. Kim, J. B. Kogut, and M.-P. Lombardo, hep-lat/0009029.)

    As explained by Hendrik, Haag’s theorem (that a free field cannot be turned into an interacting field by a unitary transformation) is also an artifact of the infinite-cutoff limit. Since one must do perturbation theory with a cutoff in place, Haag’s theorem does not invalidate the conventional interaction-picture approach.

    And constructing 4d nonabelian gauge theory rigorously is thought to be a very hard problem; you can get a million dollars from the Clay Foundation if you solve it.

    Even within pure mathematics, it is often useful to assume unproved results, and proceed. A huge amount of work has been done in analytic number theory assuming that the Riemann hypothesis is true. But that’s unproven, and another hard problem that you can get a million dollars for solving.

  • Thomas Larsson

    Hendrik,

    Although interacting fields are not unitarily equivalent to some Fock representation, all need not be lost. A key lesson from CFT in 2D (key = important to me) is that non-Fock representations may be constructed as factor spaces: a minimal model is a Fock rep modulo singular vectors. What seems to remain true is that energy is bounded from below also in interacting models. Put bluntly, the position and momentum representions are wrong in field theory, because energy is not bounded from below there. Unlike the Bargmann rep.

    The lowest-energy property is inherited by symmetry groups acting on the Hilbert space. This is why we are interested in lowest-energy reps in quantum theory. Non-trivial unitary lowest-energy reps of diffeomorphism and gauge algebras are necessarily anomalous, and a quantized observer jumps right out of their representation theory.

  • Joe Polchinski

    #474 As Joe has pointed out, you could even – using the freedom inherent in subtracting infinity from infinity – construct theories that violate translation invariance.

    You are correct: I am assuming that the high energy theory respects translation invariance. There is again an interesting general lesson: I can also make the opposite assumption and see where it leads. The effect would be that the low energy effective theory would also violate this symmetry. So I can conclude that the second alternative is false. I can do the same thing for Lorentz invariance, and conclude that the high energy theory respects Lorentz invariance (or some symmetry that reduces to it at low energy, but none such is known). That is, Planck-scale breaking will feed into the low energy theory. So approaches to quantum gravity that give up give up Lorentz invariance at the start are, I believe, doomed.

    On the subject of axiomatic quantum field theory, I note that this has largely gone over to the effective field theory point of view, where quantum fluctuations are considered scale-by-scale. See for example the review math-ph/9902023 by Rivasseau. In fact, if the only issue in the Clay prize were the UV limit of non-Abelian gauge theory, Tadeusz Balaban would probably already have won the million (see references in above review), using renormalization group methods. However, to get the Clay money one also has to prove a mass gap, which is a much harder problem.

  • http://tsm2.blogspot.com wolfgang

    > The effect would be that the low energy effective theory would also violate this symmetry.

    But what about lattice-QCD etc. (simulated in the Euclidean sector). Rotation symmetry is broken, but restored at large distances.

  • Diogenes

    “You say, “Subtracting infinity from infinity is not what’s done”, but that is what is in the text books.”
    Chris Oakley on Apr 19th, 2007 at 6:06 pm

    That is only a reflection of the fact that many textbooks are still written for the purpose of introducing students to the calculational tools of the subject, and do not explain the revolution in the conceptual understanding of the subject resulting from the work of Ken Wilson (for which he won a Nobel prize). An outstanding exposition of the modern understanding of renormalization and quantum field theory is the text:
    “Quantum Field Theory and Critical Phenomena” by Zinn-Justin [Oxford, 4th ed, 2002]
    A simpler exposition of the same ideas is in part 2 [“Renormalization”] of the text:
    “An Introduction to Quantum Field Theory” by Peskin and Schroeder [Harper-Collins 1995]
    An older article (“from the horses mouth”) is the review::
    “The Renormalization Group and The Epsilon Expansion” by Wilson and Kogut
    [Phys.Rept. 12, 1974, p.75-200]
    As noted by Joe Polchinski above, modern constructive quantum field theory is done by these methods as well. As well as the Rivasseau review quoted, an older reference is:
    “Quantum Physics: A Functional Integral Point of View” by Glimm and Jaffe [out of print].
    Good luck

    On another matter, you stated above that:
    “Since none of this jiggery-pokery is needed for classical mechanics or electrodynamics, I do not see how you can say that such theories are no different.”
    Actually this is not correct. The classical theory of charged point electrons interacting with the classical electromagnetic field is completely pathological. There is a divergent self-energy for the electron due to the energy of its coulomb field that diverges much faster (power law) in the classical case than in the quantum case (logarithmically), considered as a function of the cutoff on the “size” of the electon. Attempting to remove this by putting in a bare mechanical mass that adds to the electrostatic self-energy (for finite electon size) to give the physical mass, and including the internal stresses in the electron to maintain the finite size (with hopes of taking the size to zero at the end of the calculation), was done by Lorentz. The resulting theory is pathological. The electron motion obeys a third order ordinary differential equation with solutions that reduce to the standard solutions of the naive second order differential equation experiencing an acausal “preacceleration” *before* the application of the force producing the acceleration. This is explained in the last chapter of the text “Classical Electrodynamics” by Jackson [second edition; that’s the one I used in graduate school when I learned this…I don’t know if/where this is in later editions]. This in addition to the impossibility of forming stable atoms in the classical theory, and the liberation of an infinite amount of energy as an electron falls in to a (pointlike) classical proton destroying the observable universe with its radiation… It’s really classical mechanics and electrodynamics that are seriously pathological (though we largely hide this from our undergraduates), and quantum theories that ameliorate the situation (cf. the much more gentle growth of the electron self-energy as a function of the cutoff electron radius, as it goes to zero, in the quantum as opposed to the classical theory). Misplaced nostalgia should not blind us to how much better behaved are our quantum theories than the classical theories that they replaced.

  • Thomas Larsson

    I am sure you are aware of the fact that there is no ‘time operator’ in QM.
    Pauli pointed out that a (self-adjoint) time operator is incompatible with a Hamiltonian spectrum bounded below.

    Wolfgang #435,

    I maintain that time is the reading of a clock. If time is a c-number parameter rather than a quantum operator, it must mean that clocks in QM are classical and thus macroscopic. In contrast, clocks (or test particles) in GR are assumed light, so we can ignore their self-interaction with gravity.

    This gives a fresh angle on why QM and GR are incompatible: clocks are macroscopic in QM and microscopic in GR. Hence clocks in QG should be mesoscopic; a clock’s position and velocity do not commute.

  • http://tsm2.blogspot.com wolfgang

    > This gives a fresh angle on why QM and GR are incompatible
    I think this is indeed pretty much the core problem, but not really “fresh”. Pauli’s argument is from the 1920s and Wigner and Salecker discussed clocks in QM in the 1950s…

  • Hendrik

    Mark (#480)

    Concerning your point:-

    “The problem with trying to find a rigorous mathematical construction of quantum field theory (in four dimensions) is that there is considerable evidence that such a construction does not exist: with the exception of nonabelian gauge theories, all 4d quantum field theories are believed to be “trivial”, that is, they become free-field theories in the limit that the cutoff is removed.”

    This argument is of course not a general mathematical proof, so there is still hope. As far as I see, it only says that 4d-QFT cannot be obtained by a limit procedure from lattice QFTs in a very specific form. There are many possible frameworks in which one can try to model QFT rigorously, and I cannot see how they can all be excluded by the lattice QFT approach. For instance, the approach which I follow – through C*-algebras and their representations – can solve many problems of QFT (e.g. constraint problems – see my posts #204 and #355 above) by using the more extensive representation theory available to you. If the limit of lattice QFTs take place in one specific representation, then it excludes some of these representations. On the other hand, lattice QFT cannot approximate the C*-algebras in the operator norm because the lattice algebras are separable whilst the CCR-algebra is nonseparable.

    I also think this is a strange position want to defend;- it seems to say that there is no logically consistent theory underlying 4d-QFT. In other words, the framework is contradictory in an essential way. Given the strong connection of the Standard model with experiment, I would say that that is strong evidence for some consistent underlying mathematical theory for 4d-QFT, or at least for the more observable parts of it. Of course that is an article of faith in the consistency of nature.

    “Haag’s theorem (that a free field cannot be turned into an interacting field by a unitary transformation) is also an artifact of the infinite-cutoff limit.”

    I don’t think I understand this – it looks rather the other way round to me: Haag’s theorem forces you to go to other representations for interacting QFT, and the infinite-cutoff limit takes you to another representation. (That’s what happened in the toy model of my last post #477)

    “Even within pure mathematics, it is often useful to assume unproved results, and proceed.”

    Certainly, but all this work will disappear at the blink of an eye if the result gets disproved. In the case of physics, one requires both experimental support as well as logical (mathematical) consistency. The first often takes precedence over the latter, but eventually the logic must be sorted out. Especially when there are clear contradictions. Moreover, when you extrapolate an inconsistent theory into an unfalsifiable domain, (such as for some first-instant cosmology, or possibly string theory) there can be no justification for your conclusions.

    _____________________________________________________________

    Thomas (#481)

    “Although interacting fields are not unitarily equivalent to some Fock representation, all need not be lost. A key lesson from CFT in 2D (key = important to me) is that non-Fock representations may be constructed as factor spaces: a minimal model is a Fock rep modulo singular vectors.”

    I don’t know the details of your construction, but perhaps it is related to the standard way of constructing a representation from a given state on a C*-algebra (GNS-construction) which is also a factor space construction. But the main lesson remains, for interacting QFT one needs to leave the Fock representation.

  • http://www.cgoakley.demon.co.uk/qft/ Chris Oakley

    I also think this is a strange position want to defend;- it seems to say that there is no logically consistent theory underlying 4d-QFT.

    … or it means that the interacting theory in 4d is built from free field states, which satisfy the axioms.

    As for Haag’s theorem, one of the ingredients is Lorentz invariance. Since this is violated by introducing a cutoff, Haag’s theorem probably does not apply in this instance. So what?

  • Thomas Larsson

    I think this is indeed pretty much the core problem, but not really “fresh”. Pauli’s argument is from the 1920s and Wigner and Salecker discussed clocks in QM in the 1950s…

    But the connection between quantum clocks and anomalies is fresh. In projective representations of the diffeomorphism algebra, the Virasoro-like extension is a functional of the clock’s worldline (in 1D there is only one worldline and the extension becomes central). That’s why we cannot formulate this kind of diff anomaly in QFT proper, where the observer and her clock are not in the picture.

  • Gina

    What are Fock representations?

  • Hendrik

    Chris #479 and #488

    “I do not believe that these complicated constructs are necessary to get around Haag’s theorem…”

    Actually, in the toy model in which I described renormalisation, Haag’s theorem does not apply – the model need not even be translation invariant w.r.t. the lattice (e.g. by adding different bounded potentials to each point). The need for renormalisation came from the fact that the total ground state energy of an infinity of quantum oscillators is infinite in the original representation (infinite tensor product of Schroedinger reps of the oscillators), as pointed out by Mark Srednicki in his post #452 , and hence in this representation we do not have an invariant vacuum vector. One needs to go to a different representation to get such a vacuum, and this is what the limit of renormalisation accomplishes.

    “AFAIC the theorem means that we have to abandon hope of doing perturbation theory in QFT in the same way that we did for QM,”

    Structurally, the problem is this:- We have an algebra of observables together with an automorphic action of time evolutions on it (and possibly some symmetry groups). There is an initial representation of the algebra given (in which it is defined). Then one demands for a physical representation that the time evolution be unitarily implemented, that the generator of this unitary group be bounded below, and that the lowest point in the spectrum be discrete (i.e has an eigenvector=vacuum). For interacting theories there is no guarantee that the original representation has these properties, and a range of examples – including my toy example above – show that this is not the case. In fact even unitary implementability can fail. Haag’s theorem proves that under some natural general assumptions for interacting 4d-QFT, if the original representation is the Fock representation then it does not have the required physical properties. However, the general problem is more general than Haag’s theorem, and in fact is a separate issue from perturbation theory.
    The (mathematical) techniques of renormalisation are methods for finding new representations with the correct physical properties from the data of the original representation. In my toy model, the dynamics can be defined perfectly well without any perturbation theory, however, renormalization is still necessary.

    “One may construct interacting fields from sums of tensor products of free fields, and obtain non-zero matrix elements for real processes that agree with experiment because of the interference between free fields at different orders.”

    I had a quick look at your paper;- if you can make your claims mathematically rigorous, you would have solved one of the biggest outstanding problems of mathematical physics. May be worth a try.

    “or it means that the interacting theory in 4d is built from free field states, which satisfy the axioms.”

    I don’t know what you mean by “is built from free field states”. Since from an irreducible set of normal operators I can construct any other normal operator on that Hilbert space, in a sense I can already build any interacting field (once they are properly defined as operator-valued distributions) from free fields, but this notion is too general to be useful.

    “As for Haag’s theorem, one of the ingredients is Lorentz invariance. Since this is violated by introducing a cutoff, Haag’s theorem probably does not apply in this instance. So what?”

    It depends what you want;- if you regard Poincare transformations as physical (on Minkowski space) I would have thought in your final QFT that you require it. Else, what do you mean by a relativistic theory? Anyway, as I argued above, it is not just Haag’s theorem which produces problems for interacting theories – the representational problem is more general.

  • http://www.cgoakley.demon.co.uk/qft/ Chris Oakley

    Hi Hendrik,

    I don’t know what you mean by “is built from free field states”. Since from an irreducible set of normal operators I can construct any other normal operator on that Hilbert space, in a sense I can already build any interacting field (once they are properly defined as operator-valued distributions) from free fields, but this notion is too general to be useful.

    OK, but also I am making no distinction between the free and interacting vacuums. In the presence of interactions, the annihilation parts of the free field operators still annihilate the vacuum. This means, of course, that the Hamiltonian of the interacting theory is bounded below in the same way as in the free field theory, so this at least is not an issue.

    It is useful because (i) knowing the free-field (anti-)commutators enables one to read off matrix elements directly & (ii) the expansions of the interacting field in terms of free fields are determined by the equations of motion. This gives one a full calculational framework.

    The basic ideas of this approach have been around since 1934, and I think that – in most ways – it is simpler than the interaction-picture based perturbation theory in the text books.

    In regard to mathematical rigour, the main issue, as I see it, is this: local field equations always seem to result in infinities. One can remove them by normal ordering at each order of a power-series expansion in the coupling, but this still seems like a cheat. It could well be that there is a way of getting to the quasi-local, infinity-free expansion by solving the spacelike commutativity/anticommutativity requirement directly, but if there is, I have not found it yet.

  • http://www.cgoakley.demon.co.uk/qft/ Chris Oakley

    Hendrik,

    I had a quick look at your paper;- if you can make your claims mathematically rigorous, you would have solved one of the biggest outstanding problems of mathematical physics. May be worth a try.

    I think so.

    I might add that honesty/transparency is much the best policy. As long as the mathematical chicanery in QFT as currently practised is regarded as a lovable foible, there will not be the will to defeat it. Apart, of course from a small minority, which includes yourself.

  • Thomas Larsson

    Hendrik, I referred to a standard construction in CFT due to Feigin and Fuks. The Virasoro algebra acts on a fermionic Fock space and preserves certain subspaces generated by singular vectors; this means that the factor modules are well defined. There is a discrete set of factor spaces where two independent singular vectors have been modded out. The unitary ones are physically relevant in statistical physics.

    These minimal models are not Fock spaces, but they do have the property that there is an energy L_0 bounded from below.

  • Mark Srednicki

    Hendrik,

    I agree that it may be possible to construct phi^4 theory in 4d; my views on this are the same as those Weinberg expresses in his QFT book. If it is possible to construct it, I think it would be very interesting to see how the scattering amplitudes behave above the Landau scale.

    But since the Standard Model does not include gravity, and QFT of gravity has obvious problems, I feel that there is no physical reason to expect a rigorous construction of the Standard Model to succeed. What we really need is a formalism that (1) includes gravity, (2) includes particles and fields of the usual sort (scalar, fermion, vector), and (3) is renormalizable or (better!) finite.

    Hmmm … where might we find such a formalism, I wonder? If such a formalism could be found, it would probably trigger intense worldwide interest for decades …

  • Gina

    Dear all, certainly one of the fascinating aspects of the very interesting discussion on renormalization is the connections between mathematics and physics and the non rigorous nature of current physics theories as well as of the method of normalization.

    One thing that I learned in these (and earlier weblog) discussions and did not know before is that there is a whole spectrum of levels for non-rigorous mathematical constructions and computations used in physics. Trying to improve the level of rigor is on physicists mind even if a full mathematical rigor is not at sight.

    One possibility regarding this difficulty of incomplete rigor is that as the physics theory will be developed this will provide the framework, insights, and even technical tools for the rigorous mathematics which will then follow. Lubos Motl discussed this view in several very interesting posts on his blog. His view, if I understood it correctly, is (in short) that a successful string theory once completed may well settle all (or most) mathematical difficulties on the way and perhaps also other famous problems in mathematics.

    This sounded to me very nice but a little fantastic but one has to say that there are examples in this direction: E.g. the Seiberg-Witten story (nicely described in Peter’s book). Another example is mentioned in the comment #484 of Diogenes: According to Diogenes quantum physics resolved or at least mellowed difficulties in the mathematical foundation of classical physics. (I find this very beautiful.)

    Still, in spite of these examples, the idea that humanity will have to “wait” to a complete physics theory of everything to start understanding rigorously old very solid and special cases like QED still sounds a little unreasonable. (Chris’ idea that humanity has to wait to a full mathematical rigor before proceeding with the physics is even harder to accept.)

    According to Mark in order to have a mathematical rigorous theory for QED, string theory or “something like string theory” is needed. What is not clear to me is whether it is really necessary to study non abelian gauge theories to settle the case of QED. Isn’t it possible to develop (or perhaps it was already been developed) “something like string theory” just for the special case of the group U(1)? So why not solve the mathematical difficulties for QED or at least make them more mallow without solving them completely, by a little “something like string theory” for U(1), forgetting all the other gauge groups? (Maybe this was already done or tried.)

    And what does “something like string theory” mean? Sean referred to “something like string theory” in his original post, referring to his promised and much-hoped-for future post and so did Mark. String theory looks rather developed and rather “pointed” so when talking about “something like string theory” it is not clear what Mark and Sean are willing to give up in the current theory.

    Herbert referred to “moving away from Fock representations”. I did not find a wikipedia item on “Fock representations” (It is waiting to be written, guys) but there is one on Fock spaces which give some vague ideas on what it is about. Should we regard “moving away from Fock representation” that Herbert talks about as a synonym to “something like string theory” that Mark and Sean talk about? Or perhaps “moving away from Fock representations” is related to theories that do not have perturbative versions at all (like LQG?).

    Another question: Is it really the case that the easy half of finding a mathematically rigorous QCD theory was fully settled as Joe #482 pointed out? This sounds like big news!

  • Gina

    Mark asked: “The question I always come back to is, what if the landscape is essentially correct? That is, what if string theory is the correct theory of the world, that it has zillions of metastable vacua, and that inflation creates zillions of ‘pocket universes’ (our universe being one of them), each with its own metastable vacuum?”

    This possibility and related issues like the role of the anthropic principle was discussed quite substantially by Lee. Somehow, while seeing nothing wrong with the landscape issue and even with considering the anthropic principle, these aspects never strike me as being as terribly interesting as many other aspects of this debate. However, I have a little remark.

    Lee regards his approach on the landscape and his questions and suggestions about time as being in deep contrast with the anthropic principle.

    I am not convinced. It may well be the case that the two approaches are very similar if not identical. (Let us unify Smolin and Susskind! This may be a Grandiose Unification indeed :) )

    The anthropic explanation asserts that we should regard our universe and its rules as something (random) conditioned on life being possible. More precisely (and less contentiously), conditioned on sufficient irregularity in the structure of matter. (Irregularity that will allow life, if you wish).

    Lee strongly rejects this idea and says (among other things) something like: probability requires a notion of time; Lee (as various other physicists) asks if time itself is an emergent parameter, and see high prospects for the understanding what time is. (Mark pointed out that new understanding of “time” may well be positive or neutral to string theory and not necessarily negative.)

    So we can revise the anthropic principle and demystify it just as saying that we should condition our universe’ rules not on life but on time and then the A.P. reduces to something rather mundane.

    A sort of recreational version of Lee’s question is this: Given a picture (of the universe), Guess a formula for the emerging time! So we need a formula for the time (or rather for dT) in terms of the picture. Any suggetions?

    (You can let the picture be described in any way you wish, e.g. like a TV picture by a large array of pixels, and if you feel more comfortable to consider quantized picture this is fine too.)

    The principle should be: “when it is interesting time flies quicker.” (And maybe first identify cases where you want dT to be zero.)

    A similar question can be asked about Hollywood Movies. Given a frame in the movie find a formula estimating the movie-story-time passed from the picture one minute before (in actual movie time) to that one minute after. (I suspect the Hollywood version will be more difficult than the universe version, as the Hollywood pictures are probably more “interesting”.) Maybe in Geology and Archaeology one can find similar problems.

  • Gina

    oops, I meant Hendrik not Herbert. Sorry!

  • Mark Srednicki

    Gina wrote,

    “According to Mark in order to have a mathematical rigorous theory for QED, string theory or ‘something like string theory’ is needed.”

    Actually, as I said in #495, I’m agnostic on this. For QED, there’s probably (an infinite number) of technicolor-like theories that could provide an ultraviolet completion.

    It’s worth noting that standards of mathematical rigor are much lower in other area of theoretical physics, where it is well understood that all theories are effective. In condensed-matter theory, people will do things that they cheerfully admit don’t make any fundamental sense, soley because they give the right answer. (“Right” means, agrees with experiment.)

    In particle theory, only the final theory has to be mathematically rigorous.

  • Mark Srednicki

    500th comment!

    Do I get a prize?

  • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

    You get a free lifetime subscription!

  • Mark Srednicki

    Wow! Great!!

  • Aaron Bergman

    You killed the thread. Someone needs to say something provocative or we’ll never beat Hank Aaron’s record.

  • V.

    String theory is the devil!!!!

  • Aaron Bergman

    I think that’s on the right track; it just needs a little tweaking:

    Not only does god exist, but so does the devil. String theory is the invention of the latter.

  • Gina

    Dear all,
    I think this was (is) a very nice thread with good discussions on some specific issues. There are certainly various matters we can further discuss. Eg Lee’s (409) comment following Mark (302) and the issues of landscape, anthropic principle, time, are we typical?, and isn’t it premature to discuss these issues at all. We can slao have a look at falsifiability again. Remember – before the notion of falsifiability, there were various notions of “verifiability” which were dominant in philosophy of science. And on the more technical matters, if somebody can explain what are the technicolor methods that Mark refers to this can be great.

    “Someone needs to say something provocative ”

    We can also talk about the tendency for provocation and extreme views which is quite common also in this debate.

  • Gina

    And who is Hank Aaron? Any family relation, aaron?

  • V,

    Hank Aaron was a baseball player who currently owns the record for most career home runs. His record should be broken this year by Barry Bonds.

    Back to string theory, does anyone know if it’s possible to stabilize all of the moduli without using fluxes, even for a special case? I think fluxes are ugly and give us the landscape, which I personally don’t like.

  • http://realityconditions.blogspot.com Alejandro

    Re 505, I think the proper conclusion of the thread is:

    “God exists since string theory is true, and the devil exists since we will never be able to test it.”

    (originally said by Andre Weil on the consistency of mathematics, I’ve replaced “prove” with “test” which seems more adequate here.)

  • http://tsm2.blogspot.com wolfgang

    > I think the proper conclusion of the thread is:
    “God exists since string theory is true […]

    I am not convinced that Sean would like your conclusion 8-)

  • amused

    “Someone needs to say something provocative or we’ll never beat Hank Aaron’s record.”

    Ok, how about this:

    String theory = alchemy

    Newton devoted himself to alchemy, Witten to string theory…

    Discoveries made in the pursuit of alchemy turned out to be useful in chemistry;
    discoveries in the pusuit of ST might be useful for heavy ion physics…

    Btw, what is Hank Aaron’s record?

  • Gina

    Actually, the nice thing about this thread was that it was not provocative, and instead rather nice and modular. For example, the word “string” is mentioned only a handful of times in the recemt 50-comment interesting discussion on renormalization. Another novel thing was Mark looking and commenting om Thomas Larsson’s theory. (I always hoped somebody will do it.) There are plenty of things we can discuss (e.g., beyond my previous suggestions also we can discuss “skepticism” in general and in this case.)

  • Mark Srednicki

    The thread that wouldn’t die!

    Wikipedia to the rescue for Gina’s questions:

    http://en.wikipedia.org/wiki/Technicolor_%28physics%29

    http://en.wikipedia.org/wiki/Hank_Aaron

  • Aaron Bergman

    Now, if we could only get Lee to post his latest screed here, we’d easily make it!

  • Gina

    Dear all,

    As for topics for discussion here are two which are related to our discussion and yet we can explore without even mentioning the S-word.

    1) Symmetry: Is symmetry what it’s all about or perhaps just a cheap mathematical trick.
    (Of course, there are many possibilities in between)

    This is a very interesting issue on which I suspect that Peter Woit and Lee Smolin sharply differ. Peter sees, as far as I can tell from his book, that symmetry is in the essence of things and he gives an unflattering description of physicists (from the pre-QCD bootstrap time,) that dared thinking otherwise. Lee , on the other hand, has an interesting lecture called “against symmetry” that plato linked and referred to in #429.

    2) Time: Given a movie or a musical symphony played on a crooked video tape or audio tape. How can we find an “correct” internal clock for the piece?
    Perhaps there are known methods that engineers already use? This can help if we want to define time as an emergent feature.

    Aaron: “Now, if we could only get Lee to post his latest screed here, we’d easily make it!”

    Dear Aaron, Any comments by Lee will be most welcomed, as he makes a lot of interesting contributions and in a gentle style. It looks that you like Peter but not Lee, why is that?

  • Thomas Larsson

    It looks that you like Peter but not Lee, why is that?

    The only thing worse than a string critic without alternative ideas is a string critic with alternative ideas.

  • Aaron Bergman

    Dear Aaron, Any comments by Lee will be most welcomed, as he makes a lot of interesting contributions and in a gentle style. It looks that you like Peter but not Lee, why is that?

    I think I’m going to take a break from answering that. I can’t guarantee that I won’t be sucked in again, but I can’t imagine I have anything new to say at this point.

  • c

    “Back to string theory, does anyone know if it’s possible to stabilize all of the moduli without using fluxes, even for a special case? I think fluxes are ugly and give us the landscape, which I personally don’t like. ”

    It is possible to stabilize the moduli without fluxes in M-theory compactified on singular manifolds with G_2 holonomy. See hep-th/0701034 for the details.

    In this class of models the racetrack-type superpotential is purely non-perturbative and the hierarchy problem can be naturally solved via the dimensional transmutation. Moreover, surprisingly, in this construction the tuning of the CC results in a constraint which completely fixes the scale of gaugino condensation at ~10^14 GeV which in turn results in O(1-100)TeV scale superpartners.

  • Gina

    LHC prophecies

    One interesting part of this discussion in LHC prophecies and interpretations of various scenarios.

    Peter Woit wrote (#260): “The all too depressing possibility is a 160 GeV (or whatever the number is that makes the theory consistent at very high energies) Higgs.”

    In this case, Peter’s opinion that discovering the Higgs and no-more-and-no-less scenario is disappointing (even depressing) appears to be that of quite a few physicists. Looking at it well from the outside, I beg to disagree.

    It is a possibility (to which I will give a substantial but small probability) that LHC will fail. (And it also seems likely that the time schedule will not be as expected; Setting the expected date for definite results to 2012/3 rather than 2009/2010 seems reasonable.) But once LHC will succeed to run it is a win/win/win situation.

    If “only” the Higgs will be discovered this will be an amazing success for the scientific endeavor. (This is especially clear if you regard empirical verification of a scientific theory a major ingredient and not just a nuisance.)

    Sure, like any major achievement it will raise the question, what is next. But as is the case after the Everest was reached, or the Moon, or the Poincare conjecture solved (in the affirmative as most people expected) the question of what is next is of secondary importance.

    Of course, evidence for suppersymmetry will be another amazing success. Many physicists would not bet even money on this possibility but still regard it as a probable possibility. The stakes are so high that it certainly worth the wait.

    In any case, there is a very good chance that in 5-6 years we will replace some tentative theoretical beliefs with a firm knowledge. This is what science is all about isn’t it? And if we will get a conformation for more speculative insights, and some unexpected data to keep are busy in the future this will be welcomed too.

  • Gina

    Can beauty be debated?

    The issue of beauty and physics is quite prominent in this discussion. Lee Smolin warns against adopting a physics theory based on aesthetic consideration and bring Kepler’s theory relating the five planets and five platonic solids as an example. Peter Woit makes (repeatedly, here e.g. on #145, and #252,) the claim that string theory is simply ugly, very ugly.

    Well, beauty is a subjective matter. I remember my dear grand uncle Lena telling me:” Gina, aren’t we very lucky that people see things in a subjective way? If men were objective they would have all fallen in love with my own beloved wife (here name was incidentally also Gina,) who is clearly the most beautiful woman, and this could have caused all sort of complications.”

    I, for example, regard string theory as very beautiful. Supersymmetry which grew up from string theory is an extremely beautiful notion. (In my view, suppersymmetry has a natural form of beauty while string theory has an exotic and peculiar beauty.)

    But the really interesting question in my mind is how to debate beauty. Can beauty be argued and debated at all?

    Here is a story about arguing beauty in court, which may be of use. It was a case were the defendant was accused of a terrible crime.

    The attorney for the defendant said in his opening speech: “Look at the defendant. Looks how beautiful she is and look at her eyes of an angel. Do you really think she is capable of committing this ugly crime?”

    At first, The prosecutor thought to ignore this remark altogether, but then the remark was repeated and similar sentiments were expressed by some witnesses. The prosecutor watched how this non-issue is becoming an issue and was worried that the beauty claims may convince some jury member.

    The dilemma was not a simple one. Trying to argue that the defendant is not beautiful may convince a few jurors but will the strengthen the belief that indeed beautiful eyes is an obstruction for being a criminal. Trying to argue that there is no connection between the innocent angel look and the crime may give this whole business some credibility and may cause those jurors who believe in this connection to take for granted that the defendant is indeed beautiful

    This is what the prosecutor said in his closing argument:

    “Ladies and gentlemen of the jury. There are two types of beauty. There is the beauty that reveal a beautiful soul and there is the beauty that covers us a corrupted and distorted personality. It is very difficult to distinguish between theses two types of beauty, and often our initial hunches and intuitions turn out to be wrong.

    We have carefully proved during this trial that the defendant committed the crime she is accused with, and therefore you must conclude that to the extent you find her beautiful this is a beauty of the bad kind, a beauty which covers a corrupt personality able to commit terrible crimes.”

    (The moral is that if you want to argue against the beauty of string theory your best chance is, as Clifford Johnson often say in his tea-cup series, to come up with a real scientific argument against it. Of course, in such a case, the whole beauty issue becomes of secondary importance.)

    BTW Woit’s blog (which recently contains a lot of cool stuff and relatively little dozes of boring string bashing,) has in the May 5 posting a link to an interesting discussion on beauty and physics theories.

  • http://backreaction.blogspot.com/ B

    Hi Gina,

    yes, beauty is definitly subjective. But both, Lee as well as Peter, have made it more than clear what exactly they mean with that. Best

    B.

  • Gina

    Dear Bee,

    You wrote regarding the beauty issue “Lee as well as Peter, have made it more than clear what exactly they mean with that”

    If Peter’s approach is more than clear, is it clear to you, B, if Peter regards supersymmetry as beautiful or as ugly?

    (Lee’s approach to beauty and physics is oveall quite reasonable.)

  • http://arunsmusings.blogspot.com Arun

    “(The moral is that if you want to argue against the beauty of string theory your best chance is, as Clifford Johnson often say in his tea-cup series, to come up with a real scientific argument against it. Of course, in such a case, the whole beauty issue becomes of secondary importance.)”

    If you want to argue FOR the beauty of string theory, a real scientific argument for it would be useful, too. (Science as in empirical reality and not just something that you wish to be true.)

  • http://backreaction.blogspot.com/ B

    Hi Gina,

    how about you ask Peter? You are the one who wrote he regards string theory as very ugly. I meant to say he has written a whole book that clarifies his opinion. That doesn’t mean you have to share it. In my subjective perception for example the length of this comment section is ugly. Best,

    B.

  • Gina

    Dear Bee and Anon,

    Bee, Peter Woit’s discussion of beauty in physics (Chapter 13 in his book) is also quite reasonable, although I do not agree with his opinion that superstrings are not beautiful. In this thread, Peter refers to string theory as “ugly” ten times. (While criticism and skepticism are overall healthy and welcomed, the amount of repetitions here and elsewhere makes Peter skeptical style (also regarding other parts of the debate) a sort of “skeptical harassment,” which is, in my opinion, a rather problematic style of skepticism.)

    I think that seriously thinking about the role of beauty in physics or science can be of interest. The evaluation of supersymmetry can be a good test case. If Peter indeed described a clear approach regarding beauty of physics theories, as you said, Bee, we should be able to predict Peter’s answer on this particular matter without asking him. (But, of course, I did ask him and he just did not reply, (which is perfectly OK).) Peter’s description of supersymmetry (Chapter 12 in his book) is very good and support my view that this is a very beautiful idea/theory.

    Anon wrote: “If you want to argue FOR the beauty of string theory, a real scientific argument for it would be useful, too. (Science as in empirical reality and not just something that you wish to be true.)”

    The issue is precisely how to discuss beauty. If ‘beautiful’ is just the same as ‘empirically valid’, there is no point to talk about beauty at all. If ugly is a synonym for difficult or complex, again there is no point to discuss it as a separate concept.

    Bee wrote: “In my subjective perception for example the length of this comment section is ugly.”

    I am not sure, B. It may be true that we are well ‘over the hill’ here, but it is always nice to hope otherwise, no?

  • http://backreaction.blogspot.com/ B

    as you said, Bee, we should be able to predict Peter’s answer on this particular matter without asking him.

    I definitely did not say that. In fact, most of the time I ask questions for the reason that I can not predict the answer. The reason why I don’t ask Peter whether or not he considers something ugly is that it doesn’t matter to me. I want to hear the scientific arguments. Whether or not somebody perceives these as ugly or beautiful is a subjective judgement. I didn’t count the amount of times he used the word ‘ugly’, and the repetitive use of the word is probably not a very good writing style, but then he never meant to qualify for the Nobel Prize in literature.

    Best,

    B.

  • Eric

    I think that Woit considers most models derived from string theory to be ugly and contrived, not necessarily stirng theory itself. I generally disagree with this, although it may be true of some flux compactifications, which seem rather unnatural to me.

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  • http://www.mth.kcl.ac.uk/staff/w_shaw.html William Shaw

    Caught this discussion just now. I will write up the complexified string quantization via twistors at some point – I should point out meantime that there is indeed a quantum Virasoro algebra that matches the classical Poisson brackets precisely, and that arises from considering complexified strings and their first quantization in twistor space. The seminar where this is discussed is downloadable from:

    http://www.mth.kcl.ac.uk/~shaww/web_page/strings/strings.pdf

    One should also note the point of view discussed there that the standard bosonic string quantization is incomplete: the classical phase space is missing the complex forms of the classical ground state , i.e. complex null geodesics corresponding to spinning systems.

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Cosmic Variance

Random samplings from a universe of ideas.

About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson. Here are some of his favorite blog posts, home page, and email: carroll [at] cosmicvariance.com .

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