Ask a String Theorist! Or an Atomic Physicist.

By Sean Carroll | August 21, 2007 2:53 pm

Over at Uncertain Principles, Chad Orzel is on vacation and has handed the keys to the blog over to Aaron Bergman and Nathan (last name mysterious), specialists in string theory and atomic physics, respectively. Good luck to them as they experience what the blogosphere is like from the other side.

Aaron has begun to talk a little about the multiverse — here, here. He has thereby earned grumpy mutterings, rolled eyes, and “help” from some sensible physicists, some crackpots, some curmudgeons, his guest co-blogger, and even himself. I don’t quite understand what all the angst is about. (Actually I do understand, of course; this is one of those times when you adopt a rhetorical stance of pretending not to understand some alternative position in order to emphasize how unimpeachably correct your own position is.)

People are very welcome to disagree with the presuppositions or conclusions of anthropic reasoning; that’s just how science goes, and is perfectly healthy. But in addition to the substantive disagreements, there’s a widespread urge to express dismay that it’s even being talked about all the time. Now, that urge can’t be sensibly directed toward the actual research being done, because on that score multiverse-type stuff is a tiny percentage of all the work that goes on. Peek at any day’s worth of abstracts on hep-th, hep-ph, gr-qc, or astro-ph; you might find something anthropic here or there if you’re lucky, but it’s a tiny minority. This stuff is not dominating science, or physics, or theoretical physics, or high-energy theory, or even string theory.

No, the complaint is that considerations of parts of the universe that we can’t possibly see tend to receive an inordinate amount of attention in public discussions — on blogs, in books, in magazines and newspapers. Which is completely true, as a factual statement. At the risk of revealing a trade secret: the public discussion of different avenues of scientific research does not faithfully reflect the amount of research effort being put into those questions. Eek! I’d be willing to bet that it has always been like that. And yet, science marches on.

You may ask why something like the multiverse exerts such an outsized pull on the public imagination. So let me break it down for you here: it’s fun. People like talking about other universes, and whether we could be living in a simulation, and what happened before the Big Bang. For one thing, anyone can dive in; you don’t need to be an expert on twistor space, or two-loop counterterms, or BRST invariance in order to pontificate about the conditions under which life could exist if the laws of physics were very different. (Comments from people who are more informed and thoughtful about the subject will generally be more useful, but anyone can say something.) For another, it’s just cool to contemplate these way-out possibilities. The lure of crazy ideas is what draws a lot of people to science in the first place.

And that’s … okay, as Stuart Smalley would remind us. It would be very bad indeed if unmoored philosophizing about other universes became the dominant paradigm in science, or any subset thereof, but there’s zero danger of that. Really. But there’s no reason why people can’t have fun contemplating some of the more provocative and accessible ideas out there. On this very blog we will occasionally write lengthy discourses on some piece of technical work related to observations — and not get anywhere near the number of comments that a two-minute toss-off about the anthropic principle gets. And yet, science has not ground to a halt. I think the enterprise is sufficiently healthy to survive a few more posts about the multiverse.

CATEGORIZED UNDER: Internet, Science
  • Dima

    I completely agree!
    In fact, just recently, a friend of mine I took a course with, who is as far from science as anyone could be (although I convinced him very quickly that religion is not what he used to think it was) randomly started pontificating about other universes and my comment on the possibility that multiverse might not be how nature operates kinda threw him to a tailspin – he was surprised that the universe might be less interesting than he wanted it to be.

    It’s fairly interesting when people, who are not very knowledgeable (mildly speaking) about a subject as intriguing as the universe go on a pedestal and pipe in with their own two cents – that’s indeed the draw of science and of religion too by the way – they’re also drawn to the incredibly complexity and beauty of our universe, but unfortunately come up with empty and nonsensical explanations.

    Either way, the enterpris is indeed sufficiently healthy to endure any dose of speculations about multiverses, simulation arguments, etc.

  • Neil B.

    Hmmm. What I like to ask: If you want to explain why things are like they are, what would you hang it on? If “existence” is not a predicate and does not logically support any preferred way to be among all possible descriptions or “model” universes (how could it?) then there’s no logical foundation for a “this way” instead of “that way” universe. That’s why the multiverse comes up. I already explained the problems with that in other threads here and at Uncertain Principles. Sure, just using what we know to construct theoretical entities from here on down makes sense, but it really can’t be scientifically done from the ground up.

  • Michael T

    Perhaps the inordinate attention the public pays to the so-called “fun” ideas is due to the inordinate attention many credible scientist place on them.

    You guys give this stuff a lot of ink so to speak. Blogs, public lectures, etc. all seem to encourage such flights of the imagination which are arguably fascinating but in the end is it really doing the public a service? Is anybody really learning anything? Is it possible that all of this chatter is actually doing a disservice by characterizing scientific discourse in such a way where facts are unnecessary? What is the difference then between say the multiverse and intelligent design (just a straw man argument don’t take this literally).

    I really don’t think you bloggers with degrees can walk away from this without taking any responsibility and just chalk it up to harmless fun. Would you consider that it may actually have a negative impact on society contributing in a sad way to scientific ignorance leading to three Republican candidates for President saying they don’t “believe” in evolution.

    Hey, I’m just asking!

  • Jim Miles

    “two-minute toss-off”


    You put these in deliberately, I think.

  • rudy mcgoody

    i know what you mean, but:

    suppose we are trying to explain an experimental fact, A. We might reason anthropically, and say that if A wasn’t true, we wouldn’t be here wondering about it because human life couldn’t have evolved. And that’s fine. But then suppose someone realises that A is an inevitable consequence of preceding cause B. It now becomes clear that, regardless of the existence or otherwise of human beings, A must be true.

    Do we now throw away our original anthropic explanation? Surely the 2nd explanation, which i would call the scientific one, is much “better”? I understand that for some things, anthropic explanations are all we’ve got. But that doesn’t mean we should be satisfied with such theories. I get the impression that in string physics there is a satisfaction with anthropic theories, and that we’ve given up on non-anthropic scientific ones – but there’s no reason to think that scientific explanations don’t exist. Obviously the fact that we’re having a hard time coming up with them is no evidence for their non-existence!

    opinions on the above welcome…

  • Dr Who

    Sean: thank you, thank you for finally injecting some common sense into all this. It is painful, and perhaps politically incorrect, to say this, but the fact is that some ideas are more interesting than others — and not just to the general public. Come on, face it: what the interior of a black hole is like is simply *more interesting* than the use of AdS/CFT to compute quantities in certain gauge theories that vaguely resemble QCD. The fact that the universe is accelerating is *more interesting* than the fact that brown dwarfs exist. One shouldn’t rub it in; but equally, one should not talk as if multiple universes, and even talk about multiple universes, are like some kind of scientific pornography.

    It is painful, in particular, to see string theorists saying again and again: hey, we don’t spend all our time on this crazy stuff! We do lots of other interesting things! Yeah? Well, if that is the case, why don’t you blog about them?

  • Sean

    Dr. Who, I know what you mean, but I don’t agree. It isn’t true that some ideas are intrinsically more interesting than others; that’s not a matter of political correctness, it’s just a fact. “Interesting” is a quality that describes the relationship between an idea and a person, not one that inheres in the idea itself. A person might find one idea more interesting than another one, but that’s fine; it’s a personal judgment, not something that might be right or wrong.

    The whole point of my post was that the set of things that most people are interested in is just not the same as the set that professional physicists are interested in. If someone working on AdS/QCD tells you that they find that more interesting than thinking about the interior of a black hole, you have no reason to believe they are being anything less than honest. And also vice-versa, which is the point of the post. Interestingness depends radically on context, which is perfectly understandable.

    Michael T, there is a question here of demand as much as supply. As I pointed out, posts about more representative nitty-gritty stuff don’t draw nearly as much attention as the more speculative stuff. The point (as I will repeat once again) is that there’s nothing wrong or surprising about that. There is no moral compulsion on the part of scientists or journalists to give emphasis to different kinds of research in precise proportion to the amount of effort that scientists are putting into them. There just isn’t, nor should there be.

    If there is a great unmet demand out there in the public for highly technical blog posts on the kind of dense and difficult work that makes up the overwhelming majority of research in string theory or cosmology or any other kind of science or academia, I am sure that someone will soon take advantage of the situation to write a spectacularly popular blog.

  • Count Iblis

    Well, in this paper they point out that by messing with time you can map a particular set of laws of physics to any other laws of physics. By taking this ambiguity into account, you can just as well work with a random Hamiltonian.

    The process of identifying a time variable in time reparameterization invariant theories results in great ambiguities about the actual laws of physics described by a given theory. A theory set up to describe one set of physical laws can equally well be interpreted as describing any other laws of physics by making a different choice of time variable or “clock”. In this article we demonstrate how this “clock ambiguity” arises and then discuss how one might still hope to extract specific predictions about the laws of physics even when the clock ambiguity is present. We argue that a requirement of quasi-separability should play a critical role in such an analysis. As a step in this direction, we compare the Hamiltonian of a local quantum field theory with a completely random Hamiltonian. We find that any random Hamiltonian (constructed in a sufficiently large space) can yield a “good enough” approximation to a local field theory. Based on this result we argue that theories that suffer from the clock ambiguity may in the end provide a viable fundamental framework for physics in which locality can be seen as a strongly favored (or predicted) emergent behavior. We also speculate on how other key aspects of known physics such as gauge symmetries and Poincare invariance might be predicted to emerge in this framework.

  • Dr Who

    Sean said: “If someone working on AdS/QCD tells you that they find that more interesting than thinking about the interior of a black hole, you have no reason to believe they are being anything less than honest. ”

    I’d like to believe this, I really would. Sadly, all the evidence is against you. A large part of academic politics consists of people saying, “Hey, the theory of left pseudo-heaps is every bit as important as the proof of the Poincare conjecture! Promoting that guy just because he has done something more “important” than I have is just discrimination!” The fact remains that a proof of the Poincare conjecture will get you a job at Princeton [if you want it!]. A major advance in left pseudo-heaps won’t. Some fields really are just more important than others. Naturally everyone feels that his own work is interesting. That feeling may be semi-delusional, however.

    However, I don’t want this to distract from the service you have performed in asserting that there is nothing disreputable about working on [or blogging about] fields that happen to attract a lot of public interest. The proper response, if one feels that a certain field deserves more attention than it has hitherto received, is to blog about it and try to convince outsiders that left pseudo-heaps or organic chemistry are not as boring as they look….

  • Ellipsis

    I agree with Michael T. Of course you should post entirely what you like — it’s your blog, but note that the number of comments from a thread is an incredibly poor metric of either how much the public has learned from a post, or of the “demand” for such a post. (For example, you could consistently generate huge numbers of comments from a post about what a horrible devil-worshipper Hillary Clinton or Mitt Romney is, but would anybody be learning anything about science, or about anything for that matter? Or do most people really want such posts? No, generating minor religious wars is not progress. Nor do most people really want minor religious wars, despite the fact that they get large numbers of comments — in large part from extremists and not-so-well-informed people on both sides.)

    And furthermore, I think atomic physicists deserve an exclamation point just as string theorists do — and perhaps an extra one!! 😉 Where would the world be today without lasers, for example? Unfortunately at this point in time we can’t say the same thing about string theory — not to say there won’t be incredible things in the future.

  • jw

    You guys might enjoy this (or maybe not):

    Modern Cosmology: Science or Folktale?

  • Ted

    Sean, (7), said “I’m sure someone …”

    Well a few have, at various levels of esoterica. I like Baez’ This Week’s Finds and The Unapologetic Mathematician for starters. Frankly I come here, or to NEW, mostly for the occasional links to the deeper golden nuggets, for which I thank you for providing.

  • Mark

    It’s true, there are always issues of dogma, derision, and the danger of myopia from supposition taken as truth. Just as surely as there are wildly implausible and downright erroneous conclusions, regardless of the passion behind them, in whatever form that passion might take.

    It can hinder “progress” greatly. But it also acts to check the validity of any progress. I think it’s probably worth slowing down history’s progress into the future a bit, as long as it’s not individual egos that are hindering new ideas. But since this is, regardless of Science, a human endeavor, I have a feeling we’ll always be stuck with the crazy human factors in play.

    From my perspective, I think it’s amazing and wonderful to receive these glimpses into the inner workings of a discipline, in its fullest range, from the down-to-earth “what we had for lunch” to the more exactingly abstract. I even enjoy the self-indulgent pontificating, and the interesting and useful dialog it so often brings. I trust that. And I consider it very worth-while, at least from my own selfish perspective.

    I particularly appreciate the visibility it brings to a traditionally closed discipline — I appreciate the opportunity to examine in more detail what these maniacs are up to. It fosters an interdisciplinary forum, not even limited to the strict disciplines of Science.

    Barring the many cans of worms that accompany such things, it seems inspiring.

  • Peter Woit

    The problem with the recent craze for discussions of the multiverse and the the anthropic principle is that what is going on is something significantly more disturbing than the usual phenomenon of scientists having some fun engaging in overly speculative diversions from their everyday serious work. The phenomenon of papers appearing on hep-th every week or so concerned with the sizes of the giraffe necks or Brontosaurus brains is a new one; this just didn’t happen before a few years ago. It’s driven by the fact that, even if most string theorists are not working on such things, the anthropic landscape philosophy is increasingly used as the theoretical underpinning for string theory research. It justifies the much larger fraction of research being conducted into the details of complex compactification schemes for getting unified theories, despite the apparent impossibility of using such things to make any sort of conventional scientific predictions.

    This is really not innocuous, for two related reasons:

    1. Propping up a failed massive research program by abandoning conventional ideas about what is science and what isn’t doesn’t further the advance of science at all, quite the opposite.

    2. There is heavy promotional activity of this to the general public (e.g. Susskind’s book), and to the rest of the physics community by some of the most prominent people in the field from places like Stanford, Berkeley and Harvard. You can argue that this may get some people interested in science who wouldn’t otherwise pay attention, and after they get interested, they’ll move on to the sensible stuff. But it seems equally likely that this will just drive away sensible people from the field, and actually do damage to the public’s understanding of science and respect for scientists. As for the effect on the rest of the scientific community, you really need to pay attention to the reaction of some of your colleagues when they are subjected to a colloquium talk promoting this stuff. This reaction often could be characterized as visceral disgust, and if particle theorists find that they are getting little support from other members of their departments in the future, this will be one of the main reasons.

  • island

    jw said:
    You guys might enjoy this (or maybe not):

    Modern Cosmology: Science or Folktale?

    HEY… somebody who publically agrees with me!

    In its original form, an expanding Einstein model had an attractive, economic elegance. Alas, it has since run into serious difficulties, which have been cured only by sticking on some ugly bandages: inflation to cover horizon and flatness problems…

    Oh, no wonder…
    Michael J. Disney is emeritus professor

    The historian of science Daniel Boorstin once remarked: “The great obstacle to discovering the shape of the Earth, the continents and the oceans was not ignorance, but the illusion of knowledge.”

    Ain’t that the truth though…

  • Torbjörn Larsson, OM

    I agree with the post.

    To the list of reasons why multiverses comes up we can add discussions with creationists and others with antiscience sentiments.

    It is much easier to use as an example to show bystanding fence sitters that one can answer how creationist misconceptions about finetunings fail in natural settings. (Admittedly, analogies can be easier yet. But this is more convincing.)

    So multiverses are useful as well. 😛 All in all, I doubt discussing them will go away from the blogosphere.

  • tyler

    Sean, just FYI, as a card-carrying member of the Public I personally find the very technical articles you post much more interesting and valuable than the philosophy ones. I don’t post in them because I have nothing of substance to add and don’t want to cloud the waters with smartass jokesterism or observational metacommentary, which is about all I have to offer there. But I’ll gladly start posting “wow that’s interesting” comments so you don’t feel like you’re talking to the void.

    Many of those posts are, of course, largely above my head in their details, but I do have enough knowledge to glean something of interest from most topics. And if not, I store as much of the content as I can in the back of my head; and over the long term, often that kind of un-integrated data hoarding eventually leads to some later moment of clarity or understanding. I’m still waiting for my Higgs moment, but so are a lot of people…


    Yes, interested laypeople’s attention is drawn towards physics/astronomy/cosmology by two things: cool looking images and articles with punchy headlines that seem to address ontological topics (without using the word “ontological,” which would get you at least mocked if not beaten in many quarters). Whether this is a good thing or not is beside the point, it is what it is, and to bemoan it is a waste of time. The question is: can you, as scientists interested in educating the public, then provide hooks to more rigorous, but still interesting topics for the subset of this group that might be willing to follow you?

    There lies the value (in this regard) of a blog such as this one. A person might follow a link to a philosophical, political, or beer related post, and scroll down a bit and find themselves reading something with more substance.

    Which, I can guarantee you, will work a lot better than the tiresome internet trollery demonstrated by some of the folks who regularly come here looking to pick a fight. Seriously, nobody likes a troll.


    I’ve read Susskind’s book, I’m working on the more recent Smolin one and have Woit’s coming in from the library at some point in the near future. It’s an interesting debate I guess, but only in a metaphysical way; the interest is in the debate itself, the smart people arguing, not in the subject so much. It all seems like kind of a sideshow. The main reason I’m reading those is that I have trouble finding accessible-to-me books about more concrete current topics that I’d find more compelling. Morowitz’s book on emergence was OK, but very uneven with conspicuous stretches of handwaving at key junctures…well, back to Powells I guess, though they have Tao of Physics and crap like that mixed in with real books in the science sections, which irks me to no end….

  • Neil B.

    First, a reminder about back-engineered/Bayesian probability: the really important thing is, not the chance you’d get to stage one, but what to expect once you’re already there. As they say, someone had to be the Queen of England, so it’s silly for her to be surprised that “Hey, I’m the Queen of England! What was the chance it would be me?!” The interesting questions come with, if you find yourself already the Queen, then what else is most likely to be the case? There are various applications to the questions at hand, I will leave them for now.

    I do think multiverses and their implications have an unavoidable role in hard physics, given the condition: If the underpinnings of our world promote variation in kind (different kinds of laws, etc.), then Bayesian type reasoning (about what more to expect given what we already see) seems unavoidable. For example, if there’s a “Landscape” of possible ways for the universe to turn out, given “strings” as the fundamental building block, etc., then we have to ask: if we are in a certain region that’s possible from that matrix, what likelihood for other features. I mean, if 5% of universes with our currently known properties should also have property X, and correcting for their chance of occurrence (for example, that those would have twice the chance of coming into being as the others), then “at random” there’s a 10% chance our world has property X – ? That isn’t too far off the usual practice of doing an experiment and talking of likely errors etc. It can even be tested to some extent: See how many of the predictions come true, of course.

  • Quasar9

    Star Trek, Star Wars Science Fiction, Harry Potter, Fantasy … have all captured the imagination amillions and stimulated the imagination of next generations
    Speculation about Life on other planets & galaxies or even life on other universes and parallel worlds opens up possibilties untold, whereas life on earth is more a matter of food or foe, can we eat it do we farm, or is it a pest /enemy something we must be weary of and destroy. Dolphins are simply lucky they are not viewed as cat food just like Tuna – Japan still hunts Whale meat.

    But though the big bang may have now entered the vocabulary of most people on earth, whether there was a big bang and how big the bang was, whether the universe is an accelerating pancake or expanding pizza, whether the universe is 13.7 billion years old and how many billion light years the furthest galaxy is, is only of relative interest (or importance) to a few. Whether there is dark matter, dark energy, a higgs field or strings, and how nuclear energy works, only really matters to joe public if it can improve his life, make his car go faster and pour the perfect pint. And we are not likely to be going on tourism to the Moon or Mars anytime soon – never mind anywhere beyond the solar system.

    Though never say never – some people out there think mankind is at the cusp of some major discovery (like the wheel, telecoms, the combustion engine? the internet?) about to propel human knowledge into some dimension or realm hitherto unknown – to the next level – in gamespeak or computer jargon.

  • Neil B.

    To clarify what I said about universes: That “5% of universes” meant percent of denumerable kinds, or the continuum equivalent. Then, one must consider likelihood of those possibilities coming into existence (which may already be complicated by interactive issues, but just imagine “as is.”) For example, a graph showing the range of possible fine structure constant and then the chance each interval would be represented. Then the portion actually existing doesn’t have to equal the portion of the description space. Of course the phrase “5% of universes” in the context of already meaning the net outcome, implies that the chance of our universe having X would be 5% not 10% etc.

  • Hag

    Very sensible post Tyler. If you’d like something intermediary to read, I’d recommend Penrose’s A Road to Reality. It has everything in it, but of course, you can nit and pick the topics of your interest. The mathematical chapters are quite good and demanding, and amongst the physics chapters there are some good and some not so good. I found his criticism on inflationary theory(!!) quite interesting, whilst the one on QFT is a little poor.

  • Roman

    Sean, just FYI, as a card-carrying member of the Public I personally find the very technical articles you post much more interesting and valuable than the philosophy ones. I don’t post in them because I have nothing of substance to add and don’t want to cloud the waters with smartass jokesterism or observational metacommentary, which is about all I have to offer there. But I’ll gladly start posting “wow that’s interesting” comments so you don’t feel like you’re talking to the void.

    Absolutely, that’s very well said.
    You guys have somewhat distorted view of the Public.
    The Public reads things like A Road to Reality and the Public don’t necessary believe that Reality TV is real.
    I will conjecture that to the Public most of so called popular discourses about science by “the media” is naive.

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  • tyler

    Thanks Hag. Penrose is a great suggestion, I have only read Shadows of the Mind which I found interesting (in an utterly speculative sort of way)

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  • Ben

    Dr. Who said:

    The fact that the universe is accelerating is *more interesting* than the fact that brown dwarfs exist. One shouldn’t rub it in; but equally, one should not talk as if multiple universes, and even talk about multiple universes, are like some kind of scientific pornography.

    I would find this assertion about accelerating universes > brown dwarfs depressing, not because I disagree but because of the finality with which it’s stated. Fortunately, I am confident that there is some other universe among the zillions in the multiverse, where a bunch of astrophysicists are posting to a blog to talk about how brown dwarfs are really cool but dark energy is a boring old crock that even Einstein gave up on.

  • Dave S

    I noticed you avoided talking about teleportation, which has arguably received a tonne of public attention, albeit by science geeks and fictional writers – I guess it isn’t as catchy of a fringe science as the multiverse?

    Speaking of teleportation, what are your thoughts on the recently published “Progressive field-state collapse and quantum non-demolition photon counting”?
    I’ve given a brief summary
    and the press release can be found here

  • MattB

    RE: Post 8

    Regular reader, not regular poster, but just wanted to drop a note of thanks to Count Iblis. The paper you linked to just happened to feed in to a short SF story I was writing – even though I didn’t follow the maths (I’m a biologist by training, so…) it put some conceptual meat on the central concept.

    So, ta.

  • Arch Little II

    Shouldn’t gravity crush a massive imploding star into a string?
    Kerr used GR with a dash of conservation of angular momentum to show that a star does not collapse into a point singularity since a star spins and naturally bulges at the equator. This would cause the star to spin downward, like water going down a drain, and form a ring shaped singularity instead. The ring would be infinitesimal, spin in one direction at near the speed of light and the surface of the ring would wriggle with quantum foam. It doesn’t take much imagination to see this as a closed loop string. Wouldn’t this be proof that strings do exist?

  • Arch Little II

    Well, this is great! Anyone know a site called “Get an answer after you ask a string theorist”?
    To continue, wouldn’t gravity compact all of the google strings in a star right onto each other. Since they are one dimensional, this shouldn’t be a problem, although the frequencey of the compacted strings would increace considerably. Then you would essentially have a closed loop string vibrating at an incredibly high freqency representing a”particle” with the mass of a star known commonly as the Kerr ring singularity. I’m not a string theorist. It just seems that it would be ironic if GR actually predicted string like structures.

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About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson. Here are some of his favorite blog posts, home page, and email: carroll [at] .


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