String Theory, at 20 Explains It All – Not

This morning’s New York Times has a long and prominently placed article about the 20th anniversary of the “First Superstring Revolution”. The Times has a long history of producing overhyped uncritical articles about string theory, for a classic example, see “Physicists Finally Find a Way to Test Superstring Theory”. This one does allow some critical voices to be heard, including Lawrence Krauss, who is quoted as describing string theory as a “colossal failure” (which is different than a miserable failure)

Krauss is also quoted as saying “We bemoan the fact that Einstein spent the last 30 years of his life on a fruitless quest, but we think it’s fine if a thousand theorists spend 30 years of their prime on the same quest.”

Witten is quoted extensively, but he doesn’t sound very optimistic these days, saying “It’s plausible that we will someday understand string theory”, and making the rather weird statement that string theory is “so vast, so rich you could say almost anything about it” (for instance that it is a colossal failure?). He also seems to have given up on the idea that there is some fundamental new symmetry underlying string theory, instead putting his hopes on the existence of some new principle for constructing space and time.

The article also says that few theorists will give up on string theory when supersymmetry is not found at the LHC, with Witten interpreting this not as evidence that string theory is wrong, just that unfortunately it will be harder to get experimental evidence for it than he had hoped. String theorists in general seem to have trouble getting their minds around the idea that it is even possible the theory is wrong. Jeff Harvey does admit that sometimes he wakes up thinking “What am I doing spending my whole career on something that can’t be tested experimentally?”, but the question of “What am I doing spending my whole career on a colossal failure?” doesn’t seem to keep him awake nights.

The article ends by quoting an exchange between Steve Shenker and my colleague Brian Greene. Shenker quotes Churchill, describing the state of research into string theory as “perhaps it is the end of the beginning”. Brian seems to be one of the few string theorists around willing to actually consider the idea that the theory might be wrong, arguing that if string theory is wrong, it would be good to know this soon so physics can move on.

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81 Responses to String Theory, at 20 Explains It All – Not

  1. D R Lunsford says:

    Lubos,

    I’m sick of your attacks on Woit. You know, some of the gibing here and there, between us in particular, is harmless. But make no mistake, you don’t match up to Peter when it comes to having clues. Stop embarrassing yourself. Compared to Peter, you’re a nuisance ankle-biter.

    And I’m waiting for my ST-implies-SM-gauge-group paragraph.

    -drl

  2. Lubos Motl says:

    Dear Michael Nielsen,

    I think that you are confusing science and politics. Pro/con discussions don’t necessarily advance science in any way. Sorry, but I think that it is just a wrong approach from you if you rely on the pro/con discussions.

    The approach of a scientist is to find the relevant facts and data, and make his own conclusions using the brain. It’s certainly impossible to do so if you rely on low-brow discussions between the people like Peter Woit who like to talk about string theory, but who have almost no idea what it is.

    All the best
    Lubos

  3. Lubos Motl says:

    Dear “”,

    you’re choosing just the kindergarden mathematical toy model. String theory has much more impressive results than your brain is able to comprehend, and therefore it’s completely meaningless to discuss with you about these larger achievements.

    And yes, Cumrun Vafa’s discoveries are certainly and always based on string theory.

    Best
    Lubos

  4. Thomas Larsson says:


    Peter’s comment reminds me of that scene in Monty Python’s “Life of Brian” where they ask
    “What did the Romans ever do for us?”
    Yeah, what? Apart from…

    String theory undeniably brought a lot of popularity to the anthropic principle. This achievement makes at least some people happy. Though the same people are probably not overly fond of Lawrence Krauss, who has dared to criticize creationism despite being a layperson on Christian science.

  5. Peter says:

    Hi Michael,

    Thanks for your support!

    Peter

  6. Peter says:

    Hi Richard,

    Actually I’ve posted several things of the sort you suggest recently. Besides the comments on Khovanov homology (by the way I met Khovanov for the first time this week, he was here at Columbia giving a series of talks), I also wrote about the Baum-Connes conjecture and Witten localization. I certainly intend to do more of this and to when possible make more explicit the links I see between these kinds of mathematics and basic questions about quantum field theory.

    But you’ll also notice that virtually no one comments on those posts, and part of the reason for this I understand quite well, and it has to do with why I think it’s worth my time to complain about what string theory is doing to physics. It takes a non-trivial amount of time and effort to absorb new mathematical ideas and by so dominating the mathematical end of particle theory for twenty years, string theory has monopolized the time of the mathematically sophisticated members of the community. It has also quite literally driven out of the field a lot of people who were interested in other sorts of ideas about how to apply mathematics to questions in particle theory.

    The mathematically interesting aspects of string theory form an incredibly difficult and complex subject. Mastering this area at all is a full-time job and if you do that you’re not likely to have the time to learn other things (be they Khovanov homology, Baum-Connes, Witten localization or whatever). After many years I’ve become convinced that as long as string theory so thoroughly dominates the field, it will remain very difficult to get anyone to do the hard work and take the time necessary to learn other more promising subjects.

    So, I’ve decided to spend my time not only pursuing the ideas about mathematics and its relation to quantum field theory that seem promising to me, but also pointing out the “colossal failure” of the string theory project. If particle theorists acknowledge what has happened to their field, they may finally be able to move on to something more promising. More concretely, as long as smart young theorists who want to work on the interface of math and physics find that they can get a job if they work on something related to string theory, and can’t if they work on something not related to string theory, the field is going to continue to stagnate.

    Peter

  7. In reply to Richard:

    As a physicist who works in a field completely unrelated to string theory, I’m very interested to hear discussions (both pro and con) of the worth of doing string theory.

    In my opionion, people like Peter Woit, Urs Schreiber and Co are doing a useful service to the physics community by carrying on this sort of public debate in a spirited but relatively civil manner.

  8. Richard says:

    If you think string theory is crap – don’t tell us about it. Explain what you think is important in your area. What recent progress has there been in non-perturbative QCD? (quite a bit in lattice QCD, but I don’t think that’s what you reccomend everyone spend their time on) I found your article on Khovanov homology to be really interesting. Why don’t you focus your writing on similar uplifting topics?

    Just a thought
    – Richard

  9. Anonymous says:

    Lubos, are you saying that there is
    specifically stringy reasoning involved
    in things like TQFT, Donaldson/Seiberg/Witten
    theory, Gromov-Witten invariants and other
    much-admired offshoots of string theory?
    i.e. where you think in terms of the full
    string theory, get some idea/result and
    degenerate back to the purely topological or conformal theory?
    We can all admire Vafa et al, but it’s not
    clear to me how much (if at all) the spectacular
    successes in mathematical toy models have to
    do with strings per se.

    To put it another way, suppose topological
    M-theory is built tomorrow as a grand unified
    theory of the “interesting to mathematicians
    aspects of string theory”. Would string theory
    have anything further to say to mathematics
    or would we (mathematicians) only have to
    know about the topM-theory?

    All the best,

  10. D R Lunsford says:

    Dear Bon-Bon,

    Where exactly is this prediction? Just copy down the paragraph in which is appears.

    -drl

  11. Lubos Motl says:

    Dear “”,

    string theory has nothing to say about physics for those who don’t want to listen or those who can’t listen.

    Incidentally, the prediction of realistic string models for the low energy gauge group is SU(3) x SU(2) x U(1).

    As explained on my blog, the comparison of the rivalry between USA:Cuba could be more realistic than Microsoft:Apple.

    All the best
    Lubos

  12. Steve Esser says:

    I was entertained by the article’s bit on comparing string/LQG to Microsoft/Apple.

  13. Anonymous says:

    Dear Prof. Bully from Harvard,

    Come up with a definitive,*unique* prediction of the standard model gauge group and fermion content or parameters (promised by one of the string leaders in the mid-80s), then I will believe your sermons on string theory. Till then, string theory has absolutely nothing to say about physics. Mathematical beauty (some of it debatable) is not reality; otherwise the world would be superconformal.

    The so-called superstring phenomenology, such as the brane models, is a joke that may fool a few people all the time. Most have a brain, you know, and are not sheep uncritically following whatever a shill may say on the subject.

    The fact is that string theory ideas are being featured alongside religion in popular media as an explanation of the universe. Enough said.

  14. D R Lunsford says:

    Why our own pResident has given us the perfect description of ST:

    “Catastrophic success”.

    Logorrheically,

    -drl

  15. Lubos Motl says:

    Dear “”,

    thank you, even though there is only “” to thank for. The only thing I can say about your “” is “”. Zero. Ero. Ro. O. 😉

    Lubos

  16. Anonymous says:

    Lubos, your argument is deeply uninteresting and essentially superficial.

    Or is it deeply essential and superficially uninteresting?

  17. Lubos Motl says:

    On my blog (Unity of strings) it’s argued that Peter’s separation of string theory to “success” and “colossal failure” is inconsistent.

  18. Lubos Motl says:

    Let me be more specific why all of these effects of string theory on strongly coupled gauge theories and on mathematics ARE derived from string theory as a theory of quantum gravity including gauge theories with fermions etc. – such as the Standard Model:

    1. The strongly coupled limit of the gauge theory, according to the AdS/CFT correspondence, IS a theory of quantum gravity. For example, the N=4 d=4 super Yang-Mills is equivalent to type IIB on AdS5 x S5. In early 1998, you could have said that it is just type IIB supergravity, except that today we know a plenty of ways how you can see that the gauge theory is dual to the whole of string theory, including the excited strings. The strings are dual to operators like Tr(ABCDNBBBBCSB) where the letters are fields in the adjoint representation.

    The same statement holds for the strongly coupled dual of any other theories that are studied, and if you ask sufficiently deep questions, you’re guaranteed to need the whole string theory. The quantum gravitational phenomena that you can see from the conformal field theory include topology change inside asymptotic AdS spaces, see Maldacena et al. recent paper, as well as black hole thermodynamics and other things typical for “quantum gravity”.

    2. Mirror symmetry is a relation between two Calabi-Yaus that look geometrically different, but give you the same physics if you compactify string theory on them. By “physics” I mean that they will predict identical results for scattering of gravitons and Standard-Model-like quanta if you use the Calabi-Yaus as compactified manifolds. The Calabi-Yau compactifications are exactly the same compactifications that were used for 10+ years as the unique way to derive the real Universe – the Standard Model (or SUSY GUT) plus quantum gravity – from string theory.

    If you want to study some mathematical questions about the geometry of Calabi-Yaus only, you truncate the full string theory onto topological string theory. It still has a lot of stuff, but it’s clearly just a truncation, and all string theorists that work on topological string theory realize that there is a lot of stuff in string theory outside topological strings.

    All these dual pictures to tasks in mathematics and gauge theories are very specific configurations in the full string/M-theory, and it is absolutely impossible to understand their physics and mathematics correctly without knowing that there is a consistent theory of quantum gravity that admits 10- or 11-dimensional vacua but that also predicts gauge-theory-like matter in its various compactifications.

  19. Peter says:

    Hi Lubos,

    I don’t think I’ve made an error in logic. Thinking about 10 or 11 d strings/M-theory may lead one to interesting things (in math or gauge theory) even though your original motivation turns out to be a wrong idea.

    Actually, I think string theory has been such a success as math precisely because it has failed so badly in its original motivation. If in late 84-early 85 people had found some Calabi-Yau and some version of string theory on it that allowed the calculation of the parameters of the standard model, mathematically the whole field of string theory might have lead to a lot of information about one Calabi-Yau, and not much else.

    Because string theory doesn’t work as intended, string theorists have spent 20 years thinking about a wide array of mathematically very complex and rich structures. Coming at these structures from a very different perspective than the traditional mathematical one has lead to a lot of interesting new mathematics. The colossal failure of the string theory unification project as physics has ended up benefiting mathematics quite a bit.

  20. Urs says:

    Peter’s comment reminds me of that scene in Monty Python’s “Life of Brian” where they ask

    “What did the Romans ever do for us?”

    Yeah, what? Apart from…

  21. Lubos Motl says:

    Dear Peter,

    if you say that 1,2 are OK and 3 is wrong, then you must be doing an extremely trivial error with your brain, and I hope that you will be able to fix it. All the successes in 1,2 do follow from specific refinements (or truncations) of the vacua in 3 that you deny.

    Best
    Lubos

  22. Peter says:

    I suppose I should write a macro so that whenever I write anything about the disastrous effect of string theory on particle physics it includes the disclaimer:

    1. No, I’m not talking about the effect of string theory on mathematics, which, on the whole has been very positive.

    2. No, I’m not talking about the idea of using string theory to get information about strongly coupled gauge theories, which has had some real successes.

    3. Yes, I am talking about the idea that there is some fundamental 10 or 11 dimensional supersymmetric theory of extended objects which explains both quantum gravity and the standard model.

    It’s clearly point 3 that Krauss was referring to as a “colossal failure” and anyone who has read more than a few postings on this weblog would be well aware of points 1,2,and 3. The NYT article was not about whether string theory was successful as mathematics or whether it was promising as a way to solve QCD. It was very explicitly about the status of string theory as a unified theory and that is the issue to which my posting was addressed.

    The view, prevalent among more than a few mathematicians, that since important new ideas about algebraic geometry and other parts of mathematics have come from work motivated by string theory, there must be something to the idea of string theory based unification of gravity and particle physics, seems to me to be deeply superficial and essentially uninteresting.

  23. anon_mathematician says:

    As a working mathematician, I want to reiterate a point that has probably been made here many times—-string theory is a fantastically vibrant and deep mathematical enteprise, radically changing and increasing our understanding of basic mathematical objects (notably curves and higher dimensional algebraic geometry, but also impacting on representation theory, the social acceptibility of homotopy theory, and the relationship of hard analysis to understanding new algebraic structure—analysis is less useful these days, though that will eventually change).

    These insights come from a completely different intellectual tradition (often denigrated as “physical intuition”).

    It may be that string theory has no relation to the physical world; it clearly isnt testable yet. But mocking the whole enteprise is deeply superficial, and essentially uninteresting.

    And a field which has so greatly changed the way we understand fundamental mathematical objects (some studied for centuries) probably has something to say about the observable world too…

  24. Aaron says:

    It’s referring to a recent paper that claims that BF theory shows up in a conjectured thing called “topological M-theory”. BF theory shows up in relation to LQG, but i think it’s more than a bit of a stretch to say that LQG (which is a much wider construct than just BF theory) is part of string theory.

    The BF part of LQG isn’t the controversial part. It’s the quantization procedure that a lot of people have trouble with.

  25. Anonymous says:

    Interesting to read that now string theory considers
    LQG also to be a part of string theory. From the screed of in Wikipedia and elsewhere, it seemed that string theorits thought that LQG was complete garbage. What is going on??

  26. Anonymous says:

    Peter,

    Don’t you realize that whatever meaningful you and other naysayers will write, or will think about can all be explained by a speck in the vast rich holographic, hetorotic, D-brane landscape of conformally invariant matrix theoretic, dual of the compactified intersection of the F and M theories, upto a trivial combined S-U-T-duality that is unimportant for galactotrophic effects?

  27. Lubos Motl says:

    Hi Peter,

    i don’t think that the comment about “colossal failure” by L. Krauss – who has otherwise nothing to say – is a punch line of the article that one can use to create a meaningful review of the article.

    You’re confused if you’re combining the statement about the “colossal failure” with thinking of the string theorists. Of course that this is not how a physicist who continues to work in the field may be thinking. We’re just trying the best ideas we have, and this is why we still work on string theory.

    I agree with Brian that it would be great to know that string theory is a wrong theory of Nature if it were so. However I don’t think that this would mean that everyone would “move on”. String theory would still remain an important mathematical structure that would be investigated.

    I wrote an entry on my blog about this article, too.

    Best
    Lubos

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