String Theorists Finally Admit Defeat

The news that next week’s “Science Times” will run an article by NYT reporter James Glanz in which several leading string theorists say that they are giving up on the idea is rapidly spreading throughout the particle theory community. Evidently Glanz recently went down to Princeton to interview Edward Witten, who took the opportunity to announce that he has changed his mind about whether string theory will ever be a “Theory of Everything”. When Glanz contacted other string theorists and read to them what Witten had said, almost all of them told him that they too had been having their doubts about the theory.

Glanz quotes Witten as follows:

“One night a few weeks ago I was sitting at my kitchen table trying to make sense of Douglas’s latest work on the KKLT proposal and all of a sudden it really hit me that this is a completely lost cause. If perturbative string theory has any relation to Planck scale physics, then KKLT or something like it should work and string theory is vacuous since it can never predict anything. If perturbative string theory isn’t useful then we really don’t have anything since we’ve never been able to come up with a non-perturbative version that makes sense. Twenty years of this is enough. It’s time to give up.”

When Glanz asked him what he intends to do now, Witten responded:

“I don’t really know. There are still promising ideas about using string theory to solve QCD, and I could keep working on those. Maybe I should take up something completely different, like biology. I’m starting to worry that John Horgan was right about the ‘End of Science’. Right now I just definitely need a long vacation.”

When Glanz read Witten’s statement over the phone to David Gross, Frederick W. Gluck Professor of Physics at UCSB and Director of the Fred Kavli Institute for Theoretical Physics, Gross thought for a moment and then told him “Yeah, despite my quote last year from Churchill, I’ve also been thinking of giving up. Not sure though how I’m going to break this to the two Freds.”

The news of Glanz’s article has had dramatic effects at many universities and research institutes. At MIT yesterday, Prof. Barton Zwiebach shocked students in his Physics 8.251 “String Theory for Undergraduates” class by announcing that he wasn’t going to collect the homework due that day and was canceling his lectures for the rest of the semester. He also asked Cambridge University Press to halt publication of his new undergraduate textbook called “A First Course in String Theory”, the release of which had been planned for next month.

Search committees at several institutions that hadn’t finished their hiring yet this season held new meetings to decide how to react to the news. A prominent theorist at a UC campus told me in an e-mail that “our chair had the phone in his hand and had already dialed the number of a string theory graduate student from Princeton we were going to offer a post-doc to. I ran into his office as soon as I heard the news and stopped him just in time. Last week we were sure that string theorists were the smartest guys around and considered only them for jobs, but now there’s no way we’re going to hire any more, ever!”.

At the Institute in Princeton this year’s “Summer Program for Graduate Students in String Theory” scheduled for July has been canceled, with one of its organizers remarking “what graduate student would now be crazy enough to show up for a program like this?” Next week’s conference on “The Status of M-theory” at the Michigan Center for Theoretical Physics has also been canceled on very short notice. The director there, Michael Duff, commented “We had to do this because the status of M-theory is all too clear. It’s passed on! This theory is no more! It has ceased to be! It’s expired and gone to meet its maker! … This is an ex-theory!”

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16 Responses to String Theorists Finally Admit Defeat

  1. Peter says:

    Hi Urs,

    There are non-perturbative string theory calculations out there, but they have no known relation to the real world, so can’t be used to predict anything.

    I’m not sure what Douglas and Vafa work you are referring to. One guess would be toy d=2 string models and topological strings. Neither of these has any understood connection to 4d physics. Similarly with matrix models. There simply is no such thing as a non-perturbative formulation of string theory that allows one to calculate anything in the situation one cares about of four large dimensions.

    Even worse, you not only don’t have a theory you can calculate with, you don’t even know the energy scale of the mythical theory you want to believe in. Is it the Planck scale, is it 1 Tev? It could be anything as long as it’s not too small since then it would be ruled out by experiment.

    So, not only is there no prediction of an infinite tower of new states, there is no prediction of how many new states to expect from the theory, what their properties will be, or even at what energy scale they will occur.

  2. nnyhav says:

    Seems a shame the parrot sketch will only share space with the Holy Grail for a bit longer … but BBC4 chimed in on the latter …

  3. Hi -

    true, the full tower of massive states would only be observable for vanishing coupling. At finite coupling string self-interactions lead to a collapse of highly excited states as computed in papers concerned with string/black hole correspondence, e.g.

    Thibault Damour & Gabriele Veneziano, Self-gravitating fundamental strings and black-holes (1999)

    This effect leads to the creation of ‘string balls‘:

    Kingman Cheung, Black hole, string ball, and p-brane production at
    hadronic supercolliders
    (2002)

    (I recall that we had a very similar discussion before.)

    Yes, the above paper mentiones large extra dimensions such that the string scale would come into reach of next-generation colliders. If the string scale is further away, this means that these experiments will be possible only at higher energies. But it is possible in principle.

    Regarding the general criticism that only perturbative effects are known: Recent results by Douglas on D-branes and by Vafa and others are all concerned with non-perturbative effects. But I don’t understand these very technical paper well enough to say much more about them.

    Regarding the fact that Gross and Witten say that a full non-perturbative formulation is still not known:

    Sure. Robert Helling for instance (together with Nicolai and others) has shown that BFSS can only apply to a certain ‘sector’ of M-theory. But there it is a fully non-perturbative formulation. Helling tells me that the advent of the AdS/CFT ‘bandwagon’ has caused many people to reduce research in BFSS and concentrate on Maldacena’s conjecture. Hence counting number of people and papers in these fields doesn’t say much about the field itself.

  4. Peter says:

    Hi Urs,

    A few comments:

    About non-perturbative string theory: I did quickly look at the matrix model references you gave and saw no real evidence there of any hope of extracting realistic, 4d physics out of them. Maybe you or someone else can make progress on this, but it looks to me like a very unpromising idea to pursue. The statement that there is no known consistent non-perturbative formulation of string theory that gives realistic physics (only four large dimensions, recognizable particle spectrum) is not controversial. Gross and Witten for years have made clear in all of their general talks about string theory that they feel they don’t have a good idea about what non-perturbative string theory is.

    About Distler’s comments: He says that string theory “promises you” universal behavior of quantum gravitational effects at high energies. The problem is that this is still a promise, not reality, and will continue to be only a promise until either someone shows that perturbative string theory is a consistent approximation to something or finds a true non-perturbative theory.

    About the string theory “prediction” of an infinite tower of states:

    This is a “prediction” of perturbative string theory. Why should one believe that perturbation theory gets the properties of the higher mass states right but not the vacuum state? Isn’t this just because one can experimentally check whether a prediction of the vacuum state is right, but you can’t check “predictions” of higher energy states so you are free to claim them? Non-perturbatively you are going to have all sorts of things happening with these higher energy states. Won’t you start producing not just perturbative excitations of the string, but black holes, branes, and who knows what else? The high energy spectrum could be just about anything.

  5. Peter says:

    “Just wondering–and no disrespect meant–is this an April Fools Day joke?”

    Ummmm, yes. Some people think it was rather too subtle, some not.

    “I heard from Harvard yesterday that Lubos Motl has decided to take up professional wrestling now that his job there is being cancelled.”

    I had thought about including news about Lubos, but he is pretty hard to parody.

  6. Hi Thomas Larsson -

    I think it is a reasonable standpoint to say, as you implicitly do in your last comment, that quantum gravity as such is a problematic enterprise because it is not clear yet if and how the theory can be experimentally tested in practice.

    If anyone feels that this is reason enough for him or her not to be interested in quantum gravity then that’s fine with me. Similar comments probably apply to research for instance in theoretical quantum computing as well as some aspects of (classical) cosmology.

  7. Thomas Larsson says:

    >
    It’s not very subtle. String theory predicts for instance a tower of infinitely many massive particles.

    At the moment we cannot check this, just as we cannot check if the core of Pluto isn’t made of green cheese.
    >

    Hence this prediction is not falsifyable within a reasonable amount of
    time. Or is there any experiment that can produce this tower of
    infinitely massive particles?

    This is probably the most disturbing aspect of string theory. It may
    make predictions in principle, like LQG predicts quantization of area
    and volume, but no experiment will ever be able to disprove these
    predictions, so they are not falsifyable. As Dan Friedan points out,
    only large-distance physics is really science.

    I find it very disturbing that most string theorists simply don’t seem
    to understand that a theory is not testable unless there is some
    experiment that can test it, and falsify it, within a reasonable
    amount of time.

  8. raj says:

    Just wondering–and no disrespect meant–is this an April Fools Day joke?

  9. It’s not very subtle. String theory predicts for instance a tower of infinitely many massive particles.

    At the moment we cannot check this, just as we cannot check if the core of Pluto isn’t made of green cheese.

  10. Thomas Larsson says:

    >
    I can’t help but feel that the ‘doesn’t predict anything’ mantra is of the same quality as the ‘will give us particle masses in two months’ missaprehension was.
    >

    Please, Urs! Do you really claim that string theory makes hard
    predictions, that can be conclusively tested, and possibly falsified,
    within our lifetime or indeed within the present millenium? Would you
    then please tell us exactly which experimental result that would
    conclusively prove string theory wrong? No light Higgs at the
    Tevatron? No sparticles or extradimensions at LHC? No proton decay at
    SuperK? A positive cosmological constant?

    Unless you can give us an example of a falsifyable string theory
    prediction that can be tested within a reasonable amount of time, I
    think you should stop insinuating that there is.

    I agree with you that LQG cannot make such predictions neither, and
    that it has other problems as well, but at least Ashtekar and Rovelli
    don’t go around and claim that LQG is more predictive than QFT.

  11. Peter insinuated that string theorist’s have

    never been able to come up with a non-perturbative version that makes sense

    Last time that I tried to discuss this with you I didn’t hear back from you, unfortunately.

    I believe this could be a rewarding discussion for both sides, when done with care and focusing on the technical aspects. Over at the Coffee Table there are Robert and Lubos who have both worked on Matrix Models and Arvind is an expert on AdS/CFT. So if there really is any desire to discuss the status of non-perturbative formulations it should be possible. I’d enjoy it.

  12. Danny Ross Lunsford says:

    Serenus – ROFL!

    “Cage match – the ROCK vs. The Cancelled Czech!”

    -danny

  13. I can’t help but feel that the ‘doesn’t predict anything‘ mantra is of the same quality as the ‘will give us particle masses in two months‘ missaprehension was.

    I rather see more truth in this statement by Jacques Distler where it is pointed out that even with lots of vacuua string theory is more predictive than any other candidate theory we can currently think of.

  14. serenus zeitblom says:

    Yes, that’s very exciting. I heard from Harvard yesterday that Lubos Motl has decided to take up professional wrestling now that his job there is being cancelled.

  15. Sean says:

    You sense of humor may be too subtle, Peter. Didn’t I also hear that Bush “doesn’t feel right” about the Florida election fiasco in 2000, and has decided not to run for re-election this year?

  16. Danny Ross Lunsford says:

    Hmm, so much for the promising idea that dark matter is really made of stray lint and dust bunnies.

    Back to the loom for me, it is!

    -drl

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