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.
March 31st, 2007 at 3:57 pm
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.
March 31st, 2007 at 4:07 pm
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!
March 31st, 2007 at 4:15 pm
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.
March 31st, 2007 at 4:15 pm
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!
March 31st, 2007 at 4:19 pm
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).
March 31st, 2007 at 4:34 pm
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!
March 31st, 2007 at 4:39 pm
God forbid scientists should have a sense of humor.
March 31st, 2007 at 4:40 pm
“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.
March 31st, 2007 at 4:41 pm
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…
March 31st, 2007 at 4:46 pm
[...] Update: Sean Carroll has a posting about this over at Cosmic Variance entitled String Theory is Losing the Public Debate. Probably best if people join the discussion over there, which so far includes John Horgan and others. [...]
March 31st, 2007 at 4:50 pm
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.
March 31st, 2007 at 4:58 pm
I think Jacques Distler did a very good job, explaining the Motivation(s) for string theory in this blog post.
March 31st, 2007 at 5:02 pm
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?
March 31st, 2007 at 5:24 pm
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…
March 31st, 2007 at 5:41 pm
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?
March 31st, 2007 at 5:55 pm
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.)
March 31st, 2007 at 7:27 pm
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.
March 31st, 2007 at 7:32 pm
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.
March 31st, 2007 at 10:18 pm
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”.
March 31st, 2007 at 10:59 pm
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?
March 31st, 2007 at 11:14 pm
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.
March 31st, 2007 at 11:54 pm
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.
April 1st, 2007 at 12:00 am
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.
April 1st, 2007 at 12:21 am
Eric,
Your paper sounds very exciting. How about a hint. What is the mass of the Higgs and the what particle is the LSP?
April 1st, 2007 at 12:26 am
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.
April 1st, 2007 at 1:01 am
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.
April 1st, 2007 at 1:34 am
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.
April 1st, 2007 at 2:32 am
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.
April 1st, 2007 at 3:48 am
String Theory is Losing the Public Debate
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 agains…
April 1st, 2007 at 4:35 am
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.
April 1st, 2007 at 5:08 am
“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.
April 1st, 2007 at 6:52 am
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.
April 1st, 2007 at 7:21 am
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…
April 1st, 2007 at 7:44 am
I suspect the Eric Mayes remark is in reference to a follow up paper to hep-th 0612087, but I could be wrong.
April 1st, 2007 at 7:47 am
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
April 1st, 2007 at 8:50 am
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?
)
April 1st, 2007 at 9:41 am
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.
April 1st, 2007 at 9:50 am
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.
April 1st, 2007 at 10:06 am
Josh wrote
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.
If only it were that easy …
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.
April 1st, 2007 at 11:54 am
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.
April 1st, 2007 at 12:17 pm
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.
April 1st, 2007 at 12:19 pm
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
April 1st, 2007 at 12:25 pm
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.
April 1st, 2007 at 12:47 pm
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.
April 1st, 2007 at 12:57 pm
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:
…as reference to the position mclaren takes in (32):
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?
April 1st, 2007 at 12:59 pm
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.
April 1st, 2007 at 1:04 pm
Josh wrote:
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.
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.
April 1st, 2007 at 1:05 pm
CIP, no problem.
April 1st, 2007 at 1:08 pm
“Pushed” (on both sides) would have been a better choice of word than “tested”…particularly in a science forum
April 1st, 2007 at 1:18 pm
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?)
April 1st, 2007 at 1:21 pm
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?
April 1st, 2007 at 2:38 pm
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?
April 1st, 2007 at 3:06 pm
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.
April 1st, 2007 at 3:08 pm
And I see that while I was writing, Tim G two posts above gets at my point in 1/4 the space, and better.
April 1st, 2007 at 3:15 pm
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.
April 1st, 2007 at 3:24 pm
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).
April 1st, 2007 at 3:30 pm
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.
April 1st, 2007 at 3:40 pm
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?
April 1st, 2007 at 3:42 pm
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.
April 1st, 2007 at 4:02 pm
“… 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.
April 1st, 2007 at 4:02 pm
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.
April 1st, 2007 at 4:07 pm
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
April 1st, 2007 at 4:08 pm
(sorry for the typo: aytpical should be atypical)
April 1st, 2007 at 4:18 pm
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.
April 1st, 2007 at 4:27 pm
“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’?
April 1st, 2007 at 4:31 pm
> Anxiously awaiting Mayes’ hep-th/0703280 to see if it explains the universe.
You can read it here.
April 1st, 2007 at 4:55 pm
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?
April 1st, 2007 at 5:06 pm
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.
April 1st, 2007 at 5:18 pm
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?)
April 1st, 2007 at 5:23 pm
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.
April 1st, 2007 at 5:27 pm
“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.
April 1st, 2007 at 5:46 pm
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…)
April 1st, 2007 at 5:50 pm
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.
April 1st, 2007 at 6:07 pm
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.
April 1st, 2007 at 6:22 pm
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.
April 1st, 2007 at 6:39 pm
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.
April 1st, 2007 at 6:52 pm
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.
April 1st, 2007 at 7:02 pm
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.
April 1st, 2007 at 7:02 pm
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.
April 1st, 2007 at 7:04 pm
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.)
April 1st, 2007 at 7:08 pm
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….
April 1st, 2007 at 7:10 pm
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!
April 1st, 2007 at 7:13 pm
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.
April 1st, 2007 at 7:19 pm
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.
April 1st, 2007 at 7:36 pm
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
April 1st, 2007 at 7:46 pm
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.
April 1st, 2007 at 7:47 pm
Hi Kostya,
We haven’t turned on any fluxes in doing the phenomenological analysis we present in the paper.
April 1st, 2007 at 8:01 pm
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
April 1st, 2007 at 8:11 pm
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.
April 1st, 2007 at 8:34 pm
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
April 1st, 2007 at 9:17 pm
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?
April 1st, 2007 at 9:29 pm
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.
April 1st, 2007 at 11:06 pm
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.
April 1st, 2007 at 11:49 pm
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.
April 2nd, 2007 at 12:06 am
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?
April 2nd, 2007 at 12:15 am
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
April 2nd, 2007 at 12:26 am
Yvette quoted members of the public saying:
…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.
April 2nd, 2007 at 12:49 am
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.
April 2nd, 2007 at 12:52 am
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.
April 2nd, 2007 at 12:58 am
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.
April 2nd, 2007 at 1:02 am
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).
April 2nd, 2007 at 1:09 am
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.
April 2nd, 2007 at 1:09 am
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.
April 2nd, 2007 at 1:14 am
Need to grade problem sets, so I’m going to have to leave this productive discussion — it’s been fun…
April 2nd, 2007 at 1:41 am
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.
April 2nd, 2007 at 3:34 am
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.
April 2nd, 2007 at 5:08 am
“… 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…
April 2nd, 2007 at 5:12 am
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.
April 2nd, 2007 at 6:31 am
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.
April 2nd, 2007 at 8:33 am
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.
April 2nd, 2007 at 9:21 am
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?
April 2nd, 2007 at 9:58 am
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.
April 2nd, 2007 at 10:24 am
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.
April 2nd, 2007 at 12:03 pm
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
April 2nd, 2007 at 12:14 pm
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?
April 2nd, 2007 at 12:31 pm
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.
April 2nd, 2007 at 12:44 pm
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.
April 2nd, 2007 at 1:03 pm
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.
April 2nd, 2007 at 1:43 pm
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
April 2nd, 2007 at 2:01 pm
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.
April 2nd, 2007 at 2:07 pm
Lee,
Any possibility that the worldsheet bosons and fermions of string theory are related to the spin networks of LQG?
April 2nd, 2007 at 2:36 pm
Getting String Theory funded to the levels that Theology is funded would probably be a good thing for String Theory.
April 2nd, 2007 at 2:47 pm
The most salient comment thus far, in my opinion, is that of the Count:
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.
April 2nd, 2007 at 2:50 pm
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!
April 2nd, 2007 at 3:27 pm
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.
April 2nd, 2007 at 3:39 pm
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.)
April 2nd, 2007 at 4:16 pm
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?
April 2nd, 2007 at 4:36 pm
Plato writes:
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
April 2nd, 2007 at 4:52 pm
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?
April 2nd, 2007 at 5:05 pm
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.
April 2nd, 2007 at 5:10 pm
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.
April 2nd, 2007 at 5:28 pm
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.
April 2nd, 2007 at 6:35 pm
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.
April 2nd, 2007 at 6:37 pm
JYI Article- String Theory
Interestingly, there is a long conversation right now going on over at Cosmic Variance on if String Theory is Losing the Public Debate. I’m going to go out on a limb and say yes- in my experience you have a lot of people who understand the scientific …
April 2nd, 2007 at 8:52 pm
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,
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
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.
April 2nd, 2007 at 9:24 pm
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.
April 2nd, 2007 at 9:25 pm
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?
April 2nd, 2007 at 9:28 pm
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?
April 2nd, 2007 at 9:30 pm
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.
April 2nd, 2007 at 9:32 pm
Moshe:
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.
April 2nd, 2007 at 9:40 pm
Ahh, the polyphyletic heresy! In the cladists view we *are* monkeys.
April 2nd, 2007 at 9:54 pm
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.
April 2nd, 2007 at 10:09 pm
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.
April 2nd, 2007 at 10:09 pm
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.
April 2nd, 2007 at 10:13 pm
[...] And then there’s this more recent post, where Sean responds to a recent Bloggingheads dialogue that trashed string theory. He also brings up some points that get lost in the transition from academia to the public. The fact that scientists have vocal disagreements over theories says nothing about the theories themselves. That’s just how science works, and we shouldn’t want it any other way. [...]
April 2nd, 2007 at 10:16 pm
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.
April 2nd, 2007 at 10:31 pm
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.
April 2nd, 2007 at 10:42 pm
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?
April 2nd, 2007 at 11:08 pm
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…
April 3rd, 2007 at 12:11 am
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.
April 3rd, 2007 at 1:33 am
“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?
April 3rd, 2007 at 2:03 am
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.
April 3rd, 2007 at 3:43 am
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.
April 3rd, 2007 at 5:16 am
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.
April 3rd, 2007 at 7:11 am
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.
April 3rd, 2007 at 8:24 am
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.
April 3rd, 2007 at 8:30 am
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!
April 3rd, 2007 at 8:36 am
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.
April 3rd, 2007 at 9:06 am
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
April 3rd, 2007 at 9:20 am
#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.”
April 3rd, 2007 at 9:30 am
Elliot,
Notice the “number comments-169″ versus the actually responses showing 160?
April 3rd, 2007 at 9:57 am
Eric Mayes writes,
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.
April 3rd, 2007 at 10:55 am
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.
April 3rd, 2007 at 11:05 am
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.)
April 3rd, 2007 at 11:26 am
This is boring. Let’s talk about something else or, you know, get back to doing physics.
April 3rd, 2007 at 12:07 pm
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.
April 3rd, 2007 at 12:38 pm
Peter, you wrote in response to my comment about funding:
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
April 3rd, 2007 at 12:41 pm
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.
April 3rd, 2007 at 12:51 pm
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.
April 3rd, 2007 at 1:00 pm
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.
April 3rd, 2007 at 1:03 pm
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.
April 3rd, 2007 at 1:16 pm
“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.
April 3rd, 2007 at 1:46 pm
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.
April 3rd, 2007 at 2:03 pm
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.
April 3rd, 2007 at 2:25 pm
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”?
April 3rd, 2007 at 3:31 pm
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.
April 3rd, 2007 at 3:58 pm
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.
April 3rd, 2007 at 4:14 pm
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
April 3rd, 2007 at 4:21 pm
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.
April 3rd, 2007 at 4:31 pm
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.
April 3rd, 2007 at 4:47 pm
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.
April 3rd, 2007 at 5:03 pm
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).
April 3rd, 2007 at 5:20 pm
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.
April 3rd, 2007 at 5:34 pm
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.
April 3rd, 2007 at 6:10 pm
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.
April 3rd, 2007 at 7:28 pm
[...] I’m about as far from being a physicist as it is possible to be, though I am fascinated by the history of science & the way it works within Western culture. I am, however, a veteran of the culture ward (if only a foot soldier), and I can tell you that the conservatives in the culture wars — those who oppose “post-modernism” in all its forms, who distrust the academy on principle, and who believe science exists somehow above or outside human culture — have taken up arms against string theory. This discussion thread at Cosmic Variance demonstrates my thesis. Reading through the comments, my head was spinning: I thought I was back in the early 1990s debating the politicization of the Humanities. There is just something about the language & rhetoric of cranks that distinguishes itself, whatever the debate. Could string theory be wrong? Sure, any scientific theory can be wrong: that’s what makes them scientific in the first place. But the speculations of the stringers clearly set off alarm bells among the end of history / end of science crowd. They respond with venom & derision. The mark of a crank is that he hates imagination. [...]
April 3rd, 2007 at 7:31 pm
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.
April 3rd, 2007 at 7:35 pm
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
April 3rd, 2007 at 8:18 pm
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.
April 3rd, 2007 at 8:51 pm
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.
April 3rd, 2007 at 10:36 pm
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.
April 3rd, 2007 at 11:42 pm
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.
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.
April 4th, 2007 at 12:59 am
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….).
April 4th, 2007 at 1:37 am
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.)
April 4th, 2007 at 2:03 am
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…
April 4th, 2007 at 2:13 am
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.
April 4th, 2007 at 2:20 am
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…
April 4th, 2007 at 3:01 am
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
April 4th, 2007 at 3:05 am
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.
April 4th, 2007 at 5:24 am
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.
April 4th, 2007 at 5:42 am
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
April 4th, 2007 at 5:51 am
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
April 4th, 2007 at 6:27 am
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.
April 4th, 2007 at 6:53 am
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.
April 4th, 2007 at 7:17 am
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?
April 4th, 2007 at 7:28 am
“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.)
April 4th, 2007 at 8:04 am
#205
>
hmmm….. is “theoretics” a valid research area without experimental verification?
April 4th, 2007 at 8:05 am
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.
April 4th, 2007 at 9:31 am
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.
April 4th, 2007 at 9:37 am
Gina makes a good point that automatic postdocs might merely put off the day of reckoning:
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
April 4th, 2007 at 9:59 am
‘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
April 4th, 2007 at 10:17 am
Dear George,
It does not look that this modified idea is particularly good either. What is wrong with the current system?
April 4th, 2007 at 10:43 am
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.
April 4th, 2007 at 11:07 am
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
April 4th, 2007 at 11:29 am
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.
April 4th, 2007 at 11:33 am
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?
April 4th, 2007 at 11:45 am
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.
April 4th, 2007 at 1:11 pm
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
April 4th, 2007 at 2:01 pm
@ 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.
April 4th, 2007 at 3:36 pm
Jacques (#199),
You wrote,
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:
Back to comment #199, you say
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.
April 4th, 2007 at 4:16 pm
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.)
April 4th, 2007 at 4:31 pm
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.)
April 4th, 2007 at 6:19 pm
Peter,
In #146 you responded to my question.
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.
April 4th, 2007 at 7:04 pm
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.
April 4th, 2007 at 8:31 pm
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
April 4th, 2007 at 8:40 pm
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.
April 4th, 2007 at 9:28 pm
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 !
April 4th, 2007 at 9:45 pm
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?
April 5th, 2007 at 1:49 am
Jacques invited:
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!
April 5th, 2007 at 1:55 am
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?
April 5th, 2007 at 2:34 am
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?
April 5th, 2007 at 3:24 am
[...] The entire industry had become indoctrinated in the philosophy of 1957, and there was no going back. Most of health physicists are employed by the nuclear or radiation industry at reactors or in medicine/research, so all these people have a vested interest in not rocking their own boat. The only outsiders around seem to politically motivated in one direction only (anti-nuclear), so there’s a standoff. Virtually everyone who enters the subject of health physics gets caught in the same trap, and so there is no mechanism in place to allow for any shift of consensus.  To see possible consequences of the general stagnation and old-fashioned poor standing of physics in the student community, try this report. When mentioning problem in Electronics World years earlier, my report was also ignored, and the problem became worse. There’s a peculiar ’shoot the messenger’ policy that deters you from pointing out why physics dictatorship by string theorists isn’t helping, and is in fact misleading almost everyone. Quietly publishing the facts doesn’t really start much of a debate or get anywhere, when there is so much hype about speculation taking precedence which claims falsely that mainstream electromagnetism, even though it needs serious corrections for quantum field theory, is completely accurate and well established. It’s the old story of people trying to run before they can walk: sort out electromagnetism, then you can start to build on that. [...]
April 5th, 2007 at 3:33 am
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.
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.
“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.)
I’m sorry.
I am utterly uninterested in Anthropic arguments. Ask someone else.
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.
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.
April 5th, 2007 at 4:22 am
Peter,
Do you see any approach to unification that will make testable predictions?
April 5th, 2007 at 4:52 am
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.
April 5th, 2007 at 6:28 am
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?
April 5th, 2007 at 6:33 am
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
April 5th, 2007 at 7:26 am
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.
April 5th, 2007 at 8:00 am
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
April 5th, 2007 at 9:03 am
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?
April 5th, 2007 at 9:56 am
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
April 5th, 2007 at 10:47 am
I wrote
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.
April 5th, 2007 at 11:17 am
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.
April 5th, 2007 at 11:40 am
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…
April 5th, 2007 at 12:02 pm
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.
April 5th, 2007 at 12:27 pm
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
April 5th, 2007 at 2:10 pm
“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.
April 5th, 2007 at 2:49 pm
Without taking up to much room I thought I would link this in terms of valleys and hills.
April 5th, 2007 at 3:58 pm
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
or
or
or
(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?
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.
April 5th, 2007 at 4:17 pm
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 [..]” ?
April 5th, 2007 at 4:25 pm
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
April 5th, 2007 at 4:58 pm
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.
April 5th, 2007 at 5:18 pm
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”…
April 5th, 2007 at 5:35 pm
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.
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.
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.
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.)
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?
I just did. And I’ll ask you to extend the same courtesy to my arguments.
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.
April 5th, 2007 at 6:41 pm
Jacques,
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.
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.
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..”).
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.
April 5th, 2007 at 7:55 pm
“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.
April 5th, 2007 at 8:05 pm
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…
April 5th, 2007 at 8:15 pm
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.
April 5th, 2007 at 8:30 pm
“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?
April 5th, 2007 at 9:13 pm
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?”
April 5th, 2007 at 9:18 pm
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.”
April 5th, 2007 at 9:38 pm
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).
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.
April 5th, 2007 at 9:51 pm
Whoops! Sorry. One of the sentences above got spooged (curses cut ‘n paste!). It should have read:
April 5th, 2007 at 10:35 pm
“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.
April 5th, 2007 at 11:04 pm
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:
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.
April 5th, 2007 at 11:18 pm
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….
April 5th, 2007 at 11:28 pm
What value of a gaugino mass ratio would falsify string theory. .1?, .01?
Read the “Gaugino Code” paper by Nilles and Choi.
April 6th, 2007 at 12:23 am
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 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.
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:
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.
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.
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.)
April 6th, 2007 at 2:09 am
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?
April 6th, 2007 at 2:28 am
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.
April 6th, 2007 at 3:38 am
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
April 6th, 2007 at 4:38 am
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.
April 6th, 2007 at 4:44 am
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?
April 6th, 2007 at 8:41 am
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.
April 6th, 2007 at 8:57 am
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?