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.