Strings 2012

The big yearly string theory conference was held this year in Munich over the past week. Strings 2012 was the latest in a series of conferences that started more than 20 years ago. I’ve now written something about so many of these things that I’ve added a category for them, so you can review the last eight years of the history of these conferences by clicking here.

This year the conference drew 385 participants, a bit lower than the 400-500 that showed up at many of these things when held in Europe in the past, but higher than last year’s 259 (conference was quite expensive) or 2010’s 193 (conference was in the middle of nowhere in Texas, off-season). The week before Strings 2012 there was String-Math 2012, which brought nearly 200 mathematicians and physicists to Bonn. This is the second in a series, which seems intended to supplement or rival Strings 2XXX, with plans already in place for String-Math 2013 (Stony Brook) and String-Math 2014 (Alberta). Unfortunately the String-Math talks have not been posted yet, although I hear there are plans to do this.

One important aspect of Strings 2XXX conferences in recent years has been their role as PR events designed to promote string theory to the public and the media, and fight the perception of a failed subject. This year a press conference was scheduled last Tuesday, but there seems to be no publicly available record of it. About the only Strings 2012 story in the press that a quick search turned up was this one, which had nothing from the press conference, but Thomas Grimm explaining how everything is fine with string theory and maybe the LHC will find extra dimensions.

Another part of the PR activity at Strings 2XXX is promotional talks for the public, which this year included one from Witten about String Theory and the Universe. In honor of the Higgs discovery Witten said that he would add material at the beginning of the talk about particles rather than strings. He is still holding out hope for SUSY at the LHC, although now down-playing the fine-tuning argument and pointing to split supersymmetry as the thing to hope for, with answers to come “within a few years”.

The question session was unusually skeptical and challenging, beginning with a very hostile and long-winded question about whether he wasn’t worried that he had led physics down a 30-year path of failure. Unfortunately the questioner was intent on making a hostile speech, and much time was wasted trying to get him to shut up so that Witten could address the question. His answer was basically that 30 years wasn’t so long, the Higgs discovery had taken 50, and he gave other such examples. I don’t think any of his examples addressed the real issue, which is not that practical tests of string theory are far away, but that it makes no predictions, even if you had the technology to test it. To defend the falsifiability of string theory he gave the dubious argument that if table-top experiments showed quantum mechanics to be wrong, that would show string theory was wrong.

Mathematician Michael Hutchings was there, and he blogs about the public talks here, including a description of the question period:

The most interesting part was the question period afterwards. The first questioner launched into a very aggressive rant about how Witten was abusing his scientific responsibility by leading thousands of people to waste their intelligence on a theory for which there is no experimental evidence. The chairman basically needed to shut him up (and should have done so earlier)….

Anyway I was kind of shocked to see such an agressive attack from the general public. I’m glad I don’t have questioners attacking me because my work does not have enough real-world applications or whatever.

This was the first Strings 2XXX post-conclusive LHC evidence ruling out the discovery of SUSY in the form expected from arguments about “naturalness” and the “hierarchy problem”. Even the talks that tried to make some contact with the real world mostly ignored the SUSY problem, but the talk of Savas Dimopoulos on What Has the LHC Done to Theory? did address this head-on. On “naturalness” he quoted Samuel Beckett (“I’d wait till it was black night before I gave up”), arguing that one should hang in there with this until the bitter end, which he saw as coming late this year or early next year after the data from the 2012 run is analyzed. His basic point of view was that there are only two choices: versions of SUSY that solve the fine-tuning or naturalness problem (which are about to be ruled out), and versions of SUSY that don’t (e.g. split SUSY), which imply the multiverse to deal with fine-tuning. The only other option discussed was “high-scale SUSY” (SUSY broken up near the Planck scale). I guess the concept of SUSY extensions of the SM just being wrong is not within the realm of conceivability, given that they are part of the standard ideology of how to connect string theory with particle physics.

The slides from the talks are available here. I didn’t notice anything really new, just much the same topics as have been popular in recent years (e.g. adS/CFT and connections to condensed matter, amplitudes, higher spins). At Strings 2011 there was a lot of comment that few of the talks involved strings and string phenomenologists were shut out. This year’s conference had more stringy talks, as well as some on string phenomenology, possibly because it was organized by Dieter Lüst and his group in Munich, which does string phenomenology. Only one multiverse talk, Ben Freivogel on Predictions from Eternal Inflation, which, not surprisingly, had no predictions (but he did ask anyone who had one to get in touch with him, since his future employment would require some).

Hiroshi Ooguri’s summary talk reviewed his summary talks from 2004 and 2008, which featured many of the same topics and much the same story. The LHC results were completely ignored, and one of his slides seemed to me just delusional:

Significant progress has been made in understanding how to derive the Standard Model of Particle Physics from Superstring Theory.

Claims of such progress have been made at every one of these conferences for more than 20 years, with actual string theory predictions getting farther and farther away. There’s a reasonable case to be made for continuing interest in string theory, but I find it hard to believe that even many string theorists seriously believe there has been progress in recent years towards using string unification to predict anything.

The one talk that hasn’t yet been posted is David Gross’s Outlook and Vision. He has given such talks at a large fraction of these conferences, so one knows pretty much what to expect. I do wonder though if he’ll address the negative LHC results about SUSY, which at some point are going to cost him money, since he has made bets on this.

Update: I suppose I should ignore Lubos, but his reaction to the questions at Witten’s talk is pretty amazing. It seems that they are somehow all my fault (and Lee Smolin’s), and he gets into the spirit of Munich of a bygone era with his “endorsement of the creation of gas chambers for this scum” [this has now been removed]. The suggested way for Strings 2XXX conferences of the future to deal with this problem is to have all questions submitted in advance to make sure there aren’t any ones like this year’s.

Update: Video of David Gross’s “Outlook and Vision talk” is now available. It struck me as much more defensive and hype-ridden than versions of this from past years. We’re told that there is “every reason to be optimistic” that the LHC will discover how forces unify and how things fit into the string framework, with the standard arguments for LHC-scale SUSY given, no mention of the negative experimental results. About string theory, Gross claims “unbelievable progress every year”, and it includes everything that is “nice” and “consistent” about fundamental physics, including all consistent QFTs.

He echoes Witten’s argument that string theory is falsifiable since testing quantum mechanics tests string theory with his own claim that evidence for the SM is evidence for string theory (the SM is the “foundation” of string theory). He describes the press conference held last Tuesday as involving a lot of journalists complaining about the lack of testability of string theory, and Maldacena coming up with the argument that the LHC has successfully tested string theory since it hasn’t found anything incompatible with it.

The one substantive remark was that he thinks work on higher spin symmetries may provide a hint about what he sees as the fundamental problem with string theory: no one knows what the theory is, or what symmetry principle it should be built upon.

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54 Responses to Strings 2012

  1. Hansi says:

    I would find it a bit more interesting (and funny) to know what Lubos has to say on the talks which say that the MSSM would perhaps be ruled out by the LHC in the end of 2012.

    What does Lubos want to do with lecturers writing such plasphemic things, and what does Lubos want do with the LHC after it has ruled out the MSSM?

  2. Yatima says:

    *Cough*. Peter, that’s not Munich, that’s Wannsee. Officious bureaucrats and psychopaths setting up a “social improvement” scheme for the good of everyone.

  3. Klaus says:

    It is hard to recognize a person from his voice only, but the first questioner might be a known German physicist who wrote a book which is so critical and nasty about string theory that compared to it, “Not Even Wrong” is a laudatio of the string idea. He appears regularly in the media.

  4. Peter Woit says:

    Hansi,

    It’s not the MSSM that is getting ruled out, it’s the idea that supersymmetry “stabilizes” the weak scale, that it provides a “natural” way to avoid the “fine-tuning” problem introduced by the Higgs. That whole set of ideas is more general than the MSSM, and has always been given as one of the main motivations for SUSY. “Unnatural” versions of SUSY like split SUSY are still versions of the MSSM.

  5. Alexander Unzicker says:

    To avoid too many interpretations without the facts, here is what I actualy said after Witten’s public lecture:

    This was an impressive talk. I am sure many people are impressed. I am also sure that with your work you are making the best out of your extraordinary capabilities.

    I am not quite sure however that you are fully aware of the responsibility towards science, the search for the laws of nature…. It was Isaac Newton who said Nature created everything by number, weight and measure. Thus it is the theorist’s business to predict numbers the experimentalit’s business to measure these numbers. And as everybody can see supersymmetry and string theory in the past thirty years did not devliver a single result which Isaac Newton had called physics.

    So, aren’t you afraid of being the scientific leader of an entire epoch of physics that might lead to nowhere? Aren’t you afraid of misguiding the concentrated intelligence of seven billion people on a planet? (chairman tries to interrupt)

    Of course, nobody can prove you wrong, but it’s the history of science which gives a clear indication: the real revolutions of physics have always been pushed forward by skeptic individuals, never by the euphoria of the many. And this is where your problem lies.

    Your risk is that you are playing mathematical games of with their link to reality is still a promise, concepts of which the link to the physical realiy you do not understand. Thus I’d like to urge you to reflect upon your role in science. Please, get back to reality.

  6. Hansi says:

    Peter, maybe this is hairsplitting, but I thought MSSM means “Minimal Supersymmetric SM”. The name “minimal” would imply, I think, that split Supersymmetry is distinct from the MSSM. This naming convention is also the one in wikipedia:

    http://en.wikipedia.org/wiki/Split_supersymmetry

    “Split supersymmetry makes predictions that are distinct from […] the Minimal Supersymmetric Standard Model ”

    To me, this split susy model looks more a bit like a joke than a serious proposal anyway.

    And regarding to these “attacking questions”:

    Well, germans are often perceived not to be as “friendly” as people in other countries. For example, one almost can not! expect friendly questions in such a discussion in germany. I have seen Luest being asked similar questions (although shorter of course, and not only for self-distinguishing) by experimental physicists, when Luest hold an introductionary lecture at the technical university in munich.

    There are some experimentalists, especially experimental solid state physicists, who hold the viewpoint that mathematical physics (that is, to use physical ideas for doing mathematics) is not useful at all, and everything that does not lead immediately to an experiment should be abandoned. So, there is some hostility in germany against theorists. Especially against mathematical physicists.

    Historically, this may have to do with the early influence of Phillip Lennard and others in the 1930. They criticised the theory of relativity as “against common sense”. Because of Lennard and others, the official Nazi doctrine, to forbid those new theoretical ideas as “jewish physics” had a fruitful basis in german academia.

    Then, after 1945, most theorists were gone, and one had to staff the majority of physics chairs with experimentalists. In many physics departments, the experimental physicists successfully block the installation of new chairs for theoretical physics since those early days. As a result, the rare theoretical physicists are often watched with suspicion and hostillity in germany. In many of germany’s physics departments, experimentalists are quite fast to raise the question, whether a theorist uses money that could be better invested for some new experiment. And if a german theoretical physics professor retires, experimentalits often try to convert the chair into an experimental one. That is the situation in germany.

    That some persons in the general public have, like some of the more practically minded experimantal colleagues, very hostile views against mathematical physics, this is not that surprising, unfortunately.

  7. Hansi says:

    @Mr Unzicker:
    Physics does not only predict numbers. As physics uses mathematical modelling, it contains mathematical proofs. Mathematical physics is a scientific subject which takes physical ideas and does mathematics with it. This is most of what string theorists do. That is especially true for the research of Edward Witten, who won a fields medal in mathematics.

    By writing “you are playing mathematical games” you are saying that you, Mr Unzicker, do not like mathematics.

    Without doubt mathematics and mathematical physics is a wonderful science that proves interesting things. It is not just “some stupid game”.

    For this reason, Mr. Unzicker, nobody in the universe cares about whether you do not like mathematics. This is your own problem and so you should simply refrain from telling mathematicians, fields medal winners, and mathematical physicists that they should abandon mathematics.

    Also, as you seem to have problems to understand those mathematical Ideas, it seems it is you, Mr Unzicker, and not Witten who should get a grasp of reality. The reason is that reality obviously contains mathematics.

  8. vmarko says:

    @Hansi:

    Doing research in mathematics is not the problem. Selling this research as something that has physically observable predictions is the problem. String theory just doesn’t have any predictions. Spending 30 years researching this is ok when done by a moderate amount of people, but recruiting almost 90% of young and knowledgeable people to do this research is just unproportional to the possibility of string theory delivering those promised predictions. And Ed Witten, as an important figure in both physics and mathematics, a Fields medalist, helped in this recruitment.

    I believe Mr. Unzicker was just asking Witten to acknowledge his share of responsibility for this. Some others should too.

  9. P says:

    “I don’t think any of his examples addressed the real issue, which is not that practical tests of string theory are far away, but that it makes no predictions, even if you had the technology to test it.”

    It’s fine that you’re once again stating what you think the real issue is, Peter – and one can have a hearty debate about the ability to distinguish between string vacua and effective field theories at the TeV scale- but you’ve clearly spoken too strongly here, with the assertion that it makes not predictions even if one had the technology to test it.

    This is manifestly NOT true. ALL four dimensional string compactifications have a compactification scale and one will start exciting KK modes at energies above that scale. Moreover, probing with energies near the string scale one can begin exciting the infinite tower of string modes and these have observational signatures that have been studied in detail. They are also generic, as all string theories have them.

    So if one had the technology to access these scales, one would definitively be testing string theory.

  10. Hansi says:

    vmarko wrote:
    but recruiting almost 90% of young and knowledgeable people to do this research
    end quote.

    In germany, i bet around 70-80% of the physicists go into experimental physics, perhaps 10-15% in theoretical solid state physics, quantum physics and statistical physics. High energy theorists make in germany perhaps around 5% of all physicists. And they are mostly phenomenologists. Only a very very small fraction of the theoretical physicists in germany goes into relativity or quantum gravity research. The german chairs that are occupied with gravity or some form of quantum gravity or string theory can be counted with your fingers. And one must see this compared to dozends of solid state physics chairs.

    And no, the string theorists in germany do not sell anything. Selling is something that german professors traditionally do not do. However, as this Unzicker guy adressed this to Ed Witten: Well, Witten indeed has not much string phenomenology papers. However, Witten has articles on the geometric langlands program. Everyone who reads Witten’s papers immediately sees Witten’s research his is mostly of (very high) mathematical value, and not something that could be used for constructing a measurement device. Arguing, like Unzicker, that this kind of research would be “only a game” and therefore of no value is just stupid. Nobody cares if Unzicker does not like mathematics.

  11. vmarko says:

    @P:

    So if one had the technology to access these scales, one would definitively be testing string theory.

    I think that Peter is not talking about testing one particular variant of string theory, but about the fact that there will always exist some version of ST that will be compatible with any experimental data at any given energy scale.

    The problem is not in string theory having predictions, but in the fact that there are as many string theories as there are vacuua in the landscape.

    String theory is not a single theory, but a framework for theories. That is why it has no predictions. The similar situation is with QFT — it is a generic framework, and becomes a concrete theory only after one writes down some particular Langrangian (like QED, SM, MSSM, or otherwise). Only then one can give falsifiable predictions.

    So first go ahead and choose one particular vacuum from the landscape, one particular compactification scheme for extra dimensions, etc., and then you might get a testable string theory. And after it is tested against (hypothetical) Planck-scale experimental data, two things can happen:

    (1) the theory could be correct, or
    (2) the theory could be incorrect.

    But then in case (2) you could just change your initial choices about vacua etc., and create a new string theory (a model different from the tested one), which would be in accord with experiment.

    That is the lack of predictability of string theory framework. It is too general, you can fit it to any experimental data, just like QFT. There is no added value in it.

  12. vmarko says:

    @Hansi:

    I wasn’t talking about 90% of physicists in general, but 90% of hep-th/gr-qc physicists. You are indeed correct that the number of such chairs in Germany is single-digit or so. But even in Germany most of those are string theory (although statistics is lousy on a small sample, one should look planet-wide instead just Germany).

    As for Ed Witten, I am not disputing the importance of his work in mathematics. Nor am I saying that math should not be done. But still, selling pure math as physics (N.B. “selling as” = “advertizing”) does not always have merit, especially on such an unproportional scale.

    People often get confused by the concept called “mathematical physics”, and think that it is somehow a fusion between math and physics which sort-of creates a new scientific discipline. This is wrong. As a researcher in that area, I can tell you that there indeed is a fusion between the two, but in a very specific way (that I don’t want to elaborate here). And no new discipline gets created — mathematicians stay mathematicians, physicists stay physicists. We just interact a bit more than usual, to obtain some knowledge, ideas and tools (and sometimes manpower) from the other side.

    So, it is completely ok if Witten does research in math that may (or may not) be relevant to physics. But claiming that there is no difference between the two is not ok, IMNSHO. 🙂

  13. MathPhys says:

    Mr Unzicker,
    Some of us may disagree with E Witten on this or on that, but we all admire not only his intellect, but also his personal and scientific integrity.
    To achieve your 15 minutes of fame, you have attempted to corner and embarrass a very respectable man.

    You have also done damage to your cause. There were many better ways to do this. You chose the worst.

  14. Roger says:

    @MathPhys

    I think the question that was put to him was a valid one i.e. whether or not he should feel responsible for leading thousands of scientists down what may be a blind alley ? The problem was that the question was posed in a very confrontational way. This is a pity since a good discussion of the question can address useful topics, such as how a community of nominally free thinkers operates in practice and the roles of “leaders”.

  15. DB says:

    I like the idea of high-scale SUSY, close to the Planck scale. It will save me having to listen to promises that SUSY is just around the next corner, nonsense I’ve been listening to for thirty years.

  16. Peter, let me start by saying that I’m more sympathetic towards some of your arguments than you’d probably expect. But you could do without statements like the following:

    I don’t think any of his examples addressed the real issue, which is not that practical tests of string theory are far away, but that it makes no predictions, even if you had the technology to test it.

    If you had the technology to perform scattering experiments at the string scale you would see soft scattering. That’s a basic prediction made by every string model, and there’s no way around it. Do I think it’s likely that we’ll develop that technology? I doubt it; the string scale is probably too high.

    The claim that there are no “in principle” testable predictions of strings is wrong. The ongoing debate about strings isn’t advanced by presenting a misconception as if it were healthy skepticism.

  17. Bernhard says:

    Robert McNees,

    pardon my ignorance, but could you kindly point out any article (since this is so basic) where one can see the details of how a “soft scattering experiment at string scale” would look like? Are the possible phenomenological consequences of such an experiment unique to string theory? Are you talking about definite quantitative comparison or qualitative comparison?

  18. Peter Woit says:

    Hi Bob (this is also a response to P and Bernhard),

    I suppose I should get around to putting this question in the FAQ for the blog I started but haven’t gotten back to…

    You and I discussed this point almost exactly 7 years ago, on Sean Carroll’s blog, see here

    http://blogs.discovermagazine.com/cosmicvariance/2005/07/21/two-cheers-for-string-theory/

    and after a while even Sean seems to have agreed with me, see

    http://blogs.discovermagazine.com/cosmicvariance/2005/07/21/two-cheers-for-string-theory/#comment-260

    For those who don’t want to wade through the endless discussion back then, the point is that the “prediction” of soft scattering amplitudes once you get higher than the string scale suffers from the problems that:

    1. You don’t know what the string scale is.
    2. This prediction comes from a perturbative string theory calculation, but this is only reliable if the string coupling is small. Generically in M-theory this won’t be true and you don’t know what scattering amplitudes will be like.

  19. critical thinking says:

    I find quite bizarre the tone often adopted in discussions about the nature of string theory. I don’t necessarily agree with the line of argument by Unzicker (especially
    the social responsability arguments he advanced here), but I don’t see why skepticism about string theory should be considered out of the norm from a
    scientific perspective. Simplifying a lot, but I would like to confine myself to a few lines. Once there is widespread experimental confirmation of the predictions of a given theory, discussion normally ceases and the theory becomes — by most reasonable and informed people — acepted. Until then, skepticism is the norm, theories are work in progress and/or working hypotheses. In the end, it’s that simple. It can well be that Witten et al. intuition is outstanding, and that “his” theoretical program will prove the most fruitful. But we have no way of knowing it in advance. Furthermore I suppose no one contests the quality of his mathematical contributions. So I find all this outcry to Unzicker’s questioning as much ado about a completley expected scientific controversy. Unless someone thinks that dissent from the dominant theoretical approach should a priori be discouraged.

  20. Bob Jones says:

    Alexander Unzicker,

    I don’t know how much background you have in math and physics, but your comments at Witten’s talk suggest that you don’t completely understand what string theory is about. Like most critics of string theory, you focus on its failure to produce testable predictions, and you believe that scientists are wasting their talent on a failed idea. At one point, you even suggested that Witten’s ideas might “lead to nowhere”.

    I think you should seriously consider Witten’s response to your comments, especially the part where he explained how string theory has helped us better understand theories we already have. This is an aspect of string theory that has not been very well communicated to the public, but it’s one of the major reasons why there’s been such a sustained interest in the theory. In addition to providing a candidate for a unified theory of physics, string theory has provided valuable insights into other parts of physics and mathematics.

    In physics, the biggest success of the theory was probably the discovery of the AdS/CFT correspondence. This result provides a concrete realization of the “holographic principle” which appears to be a very generic feature of quantum theories of gravity. The correspondence shows that quantum field theory and string theory can provide equivalent descriptions of the same physics, and it can be used to understand qualitative features of certain condensed matter and QCD systems.

    In mathematics, the impact of string theory has been enormous. Ideas from string theory have led to important developments in mathematics like mirror symmetry, Gromov-Witten invariants, and the proof of the monstrous moonshine conjectures. In each of these subjects, string theory provides crucial physical intuition which has guided the development of the mathematics and led to new conjectures. Since you also mentioned supersymmetry in your comments, it’s worth pointing out that a certain supersymmetric field theory called Seiberg-Witten theory has led to revolutionary developments in the topology of 4-manifolds.

    Those are just a few of the applications of string theory, but it should be enough to convince you that Witten’s ideas have not led to nowhere…

  21. Peter Woit says:

    Bob Jones,

    I pretty much agree with you, that there’s a case to be made for string theory research based on other things it has led to, even though the unification idea has failed. If you look at what most “string theorists” are working on, it is typically such spin-offs, rarely string theory itself (Witten’s recent work is kind of an exception). “String phenomenologists” are now somewhat of a marginalized subfield, sometimes like last year even shut-out of the most prestigious string theory conference.

    That said, it’s remarkable that leaders of the subject keep trying to sell it with a hard-sell for string unification, ignoring the signs of failure of the idea. It is reasonable for members of an audience being sold this to question it, but too bad that Unzicker chose to speechify, since a real question expressed politely might have gotten a more interesting response from Witten, who surely is aware there’s a difficult issue for him here.

  22. M says:

    String theory degenerated into carpet selling when, 15 years ago, the most influential string theorists failed to acknowledge that the brane revolution ruined the predictive power of the theory. Hiring of string theorists could have been stopped at that stage. On the contrary, some famous institutions hired only string theorists, with the result that now they are almost outside from physics.

    I think that this a real responsibility.

  23. David Nataf says:

    I find it so unbelievably condescending that anybody would imply Witten is responsible for hundreds of young physicists going into string theory. It implies these young people are sheep with no internal direction, they’re simply feeling the wind and thinking “Witten, he’s the smartest, I’m going to go do whatever he’s doing!!”

  24. Hi Peter,

    Thanks for reminding me — I knew this discussion sounded familiar. Here is my take on the issue: I agree with both of the points you list, but I don’t agree with your interpretation of them.

    First, it’s true that we don’t know what the string scale is. For the sake of argument I am willing to accept a scenario where the string scale is taken to be near the Planck scale. If you don’t see some indication of soft scattering as you approach the Planck scale, then it isn’t there.

    Second, it’s true that I’m referring to the results of a perturbative calculation (As a note to Bernhard, you should be able to find this calculation in most string theory text books). But I don’t see this as nullifying falsifiability. If string theory is weakly coupled then near the string scale you begin to see soft scattering. If it is strongly coupled then it’s true that I don’t know what the physics looks like. But I know what it doesn’t look like: the same QFT that was used to describe the physics at lower energies. In a stringy framework the predictions eventually have to take a turn from the low-energy description, and if you don’t see that then the framework is falsified.

    For what it’s worth, I think everyone should be skeptical of strings. I just don’t agree with the claim that there are no in-principle falsifiable claims.

    P.S. Sorry it took so long to reply. Today was our first case of “vomiting five month old baby”.

  25. anonomous says:

    I think Strings 2012 falls into the category of high (human) drama that you mentioned several weeks ago, where everybody is looking for something to keep this field alive. Personally, if I had anything to do with string theory I don’t think I would have shown up at this conference – it sounds more like a consolation party.

  26. Anonyrat says:

    A 10^19 GeV collision can produce a huge number of say, 125 GeV higgses; I find it hard to imagine that such collisions will be dominated by the few particle amplitudes that are typically calculated in introductory texts. Therefore even in a weakly coupled string what should start appearing at the string scale is not clear to me.

  27. M says:

    Anoyrat, suppose you build a proton-proton collider at 10^19 GeV. As you need a radius as big as the Galaxy, turning it on would require at least 100,000 years. Before being able of computing string predictions, you need to find a string model that contains protons and all the SM physics. At the moment no example is known, and this might be as difficult as building the Planck collider. But presumably there are about 10^400 such models, that will give you about 10^400 different string predictions. In practice this means no prediction.

    PS: David, young people have internal directions, but in practice they need a stable position before they can work on what they like independently of the community.

  28. piscator says:

    M:

    Exactly wrong. The number of different realisations of low energy physics is irrelevant for what happens at high energy scales. Once you hit the high scale, you start hitting string excitations, which have a basic general structure – softness of scattering amplitudes, exponential growth in number of states with energy, Regge excitations, etc.

    Also note that soft scattering comes from the extended nature of the string – so the answer to Peter’s comment is that as long as your particle-like excitations become replaced by extended objects, which holds in all limits of string theory that I know, you should have soft scattering at high enough energies.

  29. Tmark48 says:

    Unzicker’s question is right. After 30 years people have the right to question the “social” and scientific cost of having had an entire generation of theoretical physicists waste their time on such a hopeless quest (unification of physics). And this was true after each “string revolution”, we went from bad to worse. And the situation right now is that String Theory (but should we be calling it String conjectures ?) is not in any sensible way a physical theory. By its very nature it cannot predict anything (it’s like having a logical model that is inconsistent, you can derive without any problem contradictory theorems).
    And who are more responsable for this situation than the leaders of this field ? A very unsettling question to be sure, but one which the powers that be should thruthfully answer.

    Now having some theorists work on ST is a good thing, as is a good thing having theoretical physicists work on other “speculative models of the universe”. But putting all your eggs in same basket is never a good thing. And sometimes fields in physics just die. I think ST is one of those. You simply cannot keep alive such a framework that has nothing to show for it after decades and decades. Saying that ST has helped to understand “superconductivity” etc… is all fine and dandy, but let’s get serious.
    The raison d’être of ST was to unify physics, and in this respect is has been a colossal failure.

    Witten was awared the Field medals for his mathematical acomplishments using ST. Good, so he is a very talented mathematician. Has he or will he ever be awarded the Nobel prize in physics ? That I think will never happen. So as a theoretical physicist he hasn’t done such a good job after all.

    Leave physics (experimental and theoretical) to physicists, and mathematics to mathematicians (or mathematical physicists).

  30. Bernhard says:

    Robert McNees,

    but then let us assume string theory is strongly coupled and that I don´t observe soft scattering at say, the Planck scale. Since we know nothing about Planck scale, saying how it does NOT look it´s not really very convincing. I have no trouble seeing QFT would break down there, but my understanding of your argument is the following: at the Planck scale we should see soft scattering (if string theory is weakly coupled) or ANYTHING at all that is not QFT, and this last “prediction” could be used to accommodate the non observation of soft scattering. If the case you were making was: no soft scattering = no string theory, OK, I agree this would be in principle falsifiable, but there seems to be, as always, a caveat that could be used to evade negative results.

  31. Tmark48 says:

    Hansi wrote :

    “For this reason, Mr. Unzicker, nobody in the universe cares about whether you do not like mathematics. This is your own problem and so you should simply refrain from telling mathematicians, fields medal winners, and mathematical physicists that they should abandon mathematics.


    It is ironic because no one is hitting Witten on the head for his mathematical accomplishments. But as you say, we shouldn’t ask mathematicians to abandon mathematics, but by the same token we sure as hell should ask or demand that mathematicians abandon physics research. Somehow theoretical physics departments have been inundated by wannabes mathematicians. And this is a disaster for physics and physicists.

    A mathematician has no problem dealing with a “physical theory” that offers 10^400 possibile solutions. He doesn’t care about physical predictions so anything is fair game. But try to pass this kind of “theory” to a real theoretical physicist (and if he isn’t senile or deluded) he will throw it out the window together with the person the presented it.

    Right now what theoretical physics is lacking are good PHYSICISTS.

  32. AcademicLurker says:

    Both Peter Woit and Lee Smolin have chapters in their respective books describing how hiring works in HEP theory and how this has had the effect of chocking off alternate, non-ST approaches.

    An interesting question now that ST seems no longer to be in the invincible position it once held is: will things change for the better? That is, if the sociology of the field remains the same – “Whatever the hot thing is today, that’s what everyone MUST work on if they want any chance at a job.” – will it matter if the hot thing is no longer ST but something else?

  33. Anonymous says:

    Tmark48:
    ” “social” and scientific cost of having had an entire generation of theoretical physicists waste their time on such a hopeless quest (unification of physics)”

    You should better ask about the social and scientific cost for wasting a whole generation of PhDs as quants in the financial bogus industry.

  34. MathPhys says:

    You know why string theory is a very attractive subject to work on, or even only to follow? It’s because, by and large, the smartest people in the physical sciences, including some of the brightest young talent, work on the subject, and it’s a great pleasure to listen and to talk to these people.

    I go to stringy meetings and to non-stringy meetings and the difference in average IQ, and in breadth and depth of knowledge of physics and mathematics, is palpable.

    Forget about the hype (which is infinitely less today than, let’s say in the mid 80’s) and forget about all pretensions to compute the mass of the Higgs and all that (very few people still talk this way, and they _are_ not string theorists). Just follow the intrinsic logic of the _theory_. It’s hypnotic.

  35. Peter Woit says:

    Hi Bob,

    Good luck with the baby!

    About the “string theory predicts soft scattering at high enough energy” prediction: I think here the bottom line is pretty clear. I’d describe the situation as an empty glass, Bob and others want to argue that there’s still a smidgen of moisture at the bottom (at some unknown scale, amplitudes will fall off exponentially in some unknown way).

    Tmark48,

    I think it’s incredibly unfair and unreasonable to blame the string theory debacle on mathematics and mathematicians. Of the large number of speakers at the conference none are mathematicians. Quickly scanning the list of nearly 400 attendees I don’t see any names that would be recognized by people in the math community other than Witten’s. The problem with string theory is not that it uses math or mathematical standards, but that it is based on a wrong physical idea about unification. The people pursuing this are physicists, trained in physics departments, hired by other physicists, funded by physics grant panels. If you listen to the arguments being made for string theory at this conference, they are about physics, not mathematics. There’s a healthy and interesting area of research going on at the boundaries of math and physics, inspired often by things that came up in string theory, but people doing this are not getting hired by physics departments.

    AcademicLurker,

    The problem of very few jobs in particle theory, leading to hiring only of people working on the “hot” topic, is independent of string theory. Lee Smolin made this very explicit in his book, I hope this point was clear in mine. For quite a few years now, physics departments in the US have stopped hiring string theorists, but instead only hired “phenomenologists” working on things like dark matter or BSM LHC physics. With nothing of this kind turning up at the LHC, this may be as much of a dead end as string theory. The backlash against string theory has also led to a trend of not hiring anyone doing anything mathematically sophisticated of any kind. This I think will turn out to be a big mistake, a complete misinterpretation of the string debacle as due to mathematics.

  36. AcademicLurker says:

    Peter,

    Both your and Smolin’s books were pretty clear that the “sociology” of HEP theory had origins independent of ST.

    I was just wondering whether the prospect that 90+ percent of the brightest folks in the field might have spent the last 30 years chasing a single idea into a dead end might result in a greater appreciation of the benefits of intellectual diversity.

    It sounds like the answer to that question may be “no”.

  37. Peter Woit says:

    AcademicLurker,

    Yes, the answer is a pretty definite “no”. The lesson physics departments are taking away from the failure of group-think about one trendy subject is just to change to a different trendy subject.

  38. M says:

    piscator,
    Planck-scale string states are just many particles.
    You don’t know how they couple to SM particles, unless you have a model of SM particles. All quantitative predictions depend on the unknown compactification.
    You can only have qualitative expectations, such as the presence of black holes and other effects that can be understood in semi-classical approximation.

    Notice that some people considered the possibility of extra dimensions and strings and the TeV scale: string theorists did not provide any solid prediction.

  39. Friedrich says:

    The problem of string theory is not that it makes no predictions; it is that string theory has no clear principles. The issue is usually avoided. But which alternative theory does? None. So the real failure is that hundreds of people with high IQ are not able, not willing, or not allowed to think about the principles for a unified theory.

    Yes, string conferences are full of really bright people. But they do not talk about the real issues. They squander their IQ. Every single day.

  40. Peter Woit says:

    Friedrich,
    Gross acknowledges explicitly the problem of no clear principles, and points to work on higher spin theory as an attempt to get some new insight into possible principles. Witten and many others have devoted a lot of effort to finding some foundational principles for string theory.

    The problem may be not the failure to acknowledge the problem, but that the problem may be insoluble. The conjecture that there is some wonderful M-theory based on some unknown symmetry principles that gives known string theories in various limits and can be used to unify physics may simply be a wrong conjecture. I’d argue that there’s now 20 years of evidence for this.

  41. Jack Lothian says:

    Last week I bought Smolin’s book for a $1 at rummage sale. It was a great buy – the first time I read it – it really helped me understand the debate on this blog. If there is another illiterate on this board other than myself, I strongly recommend it.

    As to Alexander’s intervention – I think the reaction was a bit over-the-top. Sure he was confrontational but I have been to dozens of symposiums/conferences & I have heard several extreme confrontational exchanges – often between well-known academics. Sure he unfairly lays the fault on the one person who happens to be most physicists’ choice for the greatest living physicists. But I bet Einstein also received some equally bad & unfair public attacks. We live in a free society & with freedom comes the right to say unpleasant things. While I recognize there are real limits to how uncivilized a person can act in a formal setting; I do not think Alexander really crossed that line. Witten’s purported response suggests that he accepted the factual content within the remarks & ignored the emotions – good for him.

  42. Peter Shor says:

    Tmark48: Mathematicians are generally kept down to earth by the need for rigorous proof. Theoretical physicists have generally been kept down to earth by the need to match experimental findings. When you remove both of these constraints, …

  43. Alexander Unzicker says:

    The comments on my question led me to reflect upon some points I’d like to clarify.

    I see that some people felt my comment was quite long. Actually I could not hear the chairman’s words but I had – and still have – good reasons to assume that it was the content which annoyed him, rather than the duration. For that, I continued.

    I don’t quite understand why some people saw a hostility on my side which I don’t feel. I didn’t question Witten’s integrity nor his mathematical intelligence. But maybe for that very reason, I think he is not interested in history or sociology of science, which I think are essential if one wants to evaluate the actual state of physics. And likely, for the same reason, he is plain uninformed about physics, e.g. about the missing evidence of gravitational waves (arxiv:0909.3583).

    That might all be fine, and I have no problem if string theorists do math in their
    meetings. But this was a public and highly publicized event which on purpose
    created the impression that the big science experiments – Heuers talk was just before – meet the top theories of physics. But string theory is not physics. It is a problem that string theory is not falsifiable, another problem that its reasoning is entirely metaphorical (see e.g. Bert Schroer’s papers), but the biggest problem is that it is still labelled as science.

    Yet I do not even blame Witten in first place for that false declaration. But as everybody else on the planet, he has to reflect upon the consequences of what he is doing. I am sorry that those who complained about inappropriate words havn’t been
    able to tell it to their friend in a nicer way. But that had to be said.

  44. Bob Jones says:

    Tmark48,

    “And sometimes fields in physics just die. I think ST is one of those.”

    I hate to disappoint you, but I think string theory is here to stay. For one thing, we know that it’s equivalent to interesting quantum field theories like the N=4 super Yang-Mills theory. In addition to equivalences such as this one, we know that string theory subsumes a wealth of interesting effective quantum field theories related by dualities. For these reasons, string theory has become an important part of the mathematical formalism of quantum field theory.

    “The raison d’être of ST was to unify physics, and in this respect is has been a colossal failure.”

    You realize that string theory was originally a theory of the strong force, right? Nowadays, many string theorists view their subject as a mathematical framework whose role in physics is not yet clear. Although unification was always the main advertized goal of the theory, I think it’s oversimplifying to say that unification is the “raison d’être” of string theory.

    “Witten was awared the Field medals for his mathematical acomplishments using ST. Good, so he is a very talented mathematician.”

    Here I think you’re oversimplifying the relationship between string theory and mathematics. None of the results that made Witten famous are “mathematics” in the usual sense. The concepts that string theorists work with are fundamentally nonrigorous because they are based on the notion of a Feynman integral, which doesn’t have any rigorous meaning. They are physical concepts, and I don’t think mathematicians would have discovered them without help from the physicists.

  45. Bob Jones says:

    “he is plain uninformed about physics, e.g. about the missing evidence of gravitational waves (arxiv:0909.3583).”

    Are you serious?? You think Edward Witten is uninformed about physics?

  46. Peter Woit says:

    Bob Jones/Tmark48,

    It’s simply not true that Witten won the Fields Medal for “mathematical accomplishments using string theory”, although this has been repeated so often that everyone seems to believe it. I’ve written about what actually happened here:

    http://www.math.columbia.edu/~woit/wordpress/?p=99

    Alexander Unzicker,

    You are behaving like a crank. The point of a question session after a public talk is not for everyone who feels like it to stand up and comment on what the speaker said. By doing this at length and refusing to shut up and let Witten speak you were rude to him and to the rest of the audience, who were there to hear what he thought, not your thoughts. You could have made your point with a concise question rather than a speech, which would have been a lot more interesting for everyone.

    By going on about gravitational waves and Witten not being informed about the absence of their detection, you remove all doubt in the minds of those suspicious about whether or not you are a crank. If you think you are doing the world a service by your behavior, saving us from string theory and its excesses, please be aware that you are doing the exact opposite, making people think that those skeptical of string theory are cranks who don’t know what they are talking about.

  47. Bob Jones says:

    Peter,

    Yes, you’re right. I didn’t mean to imply that Witten got his Fields Medal for work on string theory (though Chern-Simons theory is certainly related to string theory).

  48. Peter Woit says:

    Note to all,

    I’m not going to host any more discussion between Unzicker and other commenters here, that kind of thing is a crackpot magnet I want no part of.

  49. amused says:

    MathPhys wrote:

    “You know why string theory is a very attractive subject to work on, or even only to follow? It’s because, by and large, the smartest people in the physical sciences, including some of the brightest young talent, work on the subject, and it’s a great pleasure to listen and to talk to these people.
    I go to stringy meetings and to non-stringy meetings and the difference in average IQ, and in breadth and depth of knowledge of physics and mathematics, is palpable.”

    This is a familiar tune.
    If any of these brilliant young string theorists have anything interesting to say about physics, let them go publish it in Physical Review Letters.

    MathPhys, so that you can more fully appreciate the efforts the organizers of those high IQ meetings make to keep out the rabble, here’s a little story:
    Some years ago there was a Simons workshop on Geometry and Physics (or something like that). String theory was listed as one of the topics to be covered, but it was supposedly also open to other math-phys QFT-related topics. Young people who wanted to attend had to put in an application, listing 3 recent publications, and get a recommendation letter from a senior person. I decided to give it a shot, so I listed 3 of my papers on mathematical aspects of chiral gauge theories on the lattice, 2 in NPB and 1 in PRL, all single-author, and got a recommendation from a big-shot theoretical physicist at one of the major US universities with 7000+ citations (or maybe it was only 6000+ at that time) who was one of the main people working on that topic at the time.
    My application to attend was of course turned down. The organizer wrote “Sorry, that fact that you are not working on string theory shows that you are ignorant and have a low IQ, so we don’t want you at our meeting.”
    (OK that’s not what he really wrote, but I’m sure it’s what he was thinking 😉 )
    Afterwards I looked up the list of participants and they were all string theorists or mathematicians doing ST-related stuff. This of course just reflects the fact you mentioned that the smartest folks do string theory.

  50. piscator says:

    M: you are missing the physics of soft scattering. It is not something mysterious that requires pages of mathematics to understand, it is a feature of extended objects. Scattering at high energies probes structure at the corresponding inverse length scale, and if you have no structure at that scale – ie if all your objects are extended – then you cannot scatter hard. This is why Rutherford was surprised by hard scattering of alpha-particles, he thought the atom was some extended object rather than having a hard pointlike centre.

    With regard to models of TeV scale strings, it wasn’t string theorists who were responsible for the gross overhyping of these ill-defined and poorly motivated models.

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