Strings 2014 ended today, with five separate “vision” talks, giving a good picture of where the leaders of the string theory community see the subject going. I saw the talks on streaming video, presumably they should appear on the conference website in the next few days.
- Michael Green led off by noting that string theory had at one point been intended as a unified theory, but now has “blossomed into something much more significant”, a framework covering all sorts of things. He went on to say that he would avoid discussing the grand questions, and instead just give a summary of what he found interesting about work reported at the conference. The main area that he covered in the talk were the many different kinds of results about scattering amplitudes that are under study. He seemed to be somewhat of a skeptic about Arkani-Hamed’s widely publicized “Amplitudehedron”, saying it had some ways to go before it was useful for computations (unlike other methods).
- Juan Maldacena gave a talk that had nothing to do with string theory, mainly about the conceptual issues of black holes and quantum theory. He claimed that the BICEP2 results showed that quantum gravity was now an experimentally-based subject, answering those who were skeptical about studying an untestable subject.
At the end of the talk he gave an answer to the question “What is String Theory?”:
Solid Theoretical Research In Natural Geometric Structures
- Andy Strominger gave his own answer to the “What is String Theory?” question:
anything that anybody in this room or any of their friends has ever worked on.
He did note that there were hardly any strings anywhere to be seen at recent string theory conference talks.
About the LHC and any conceivable follow-on higher energy accelerator, his comment was that it was now highly unlikely that string theory could make predictions relevant to them, and that he didn’t want this to be a defining goal of the field. Clearly, the failure to find SUSY at the LHC has now pretty much killed off most hopes that string theory unification is relevant to particle physics in any testable way. Like Maldacena, he pointed to BICEP2 as showing that quantum gravity was now an experimental subject.
He ended by explaining that he had sent around emails to a hundred people asking for their suggestions about what problems there would be progress on over the next 5-10 years. He got 80 responses, and quickly put up some slides with them. No time to really read these, but he says that they’ll be posted online soon, and that should be a quite interesting document
- The last talk was by David Gross, who pointed out that he has given many of these things before. He then went on to discuss Paul Steinhardt’s impassioned talk earlier in the week, which included a video of Richard Feynman discussing “Cargo Cult Science” and theories that were too vague to be testable. Steinhardt had been arguing that inflation was so vague and flexible a theory that it could not be tested and so was not science. Gross like many others realized that you could replace “inflation” by “string theory” in Steinhardt’s argument. He then gave a long and very defensive discussion of why string theory might still be science, invoking the recent book by Richard Dawid and telling the audience they needed to read it so they could defend their subject against the accusations it is facing.
I wrote here last year about the Dawid book, including an explanation of Dawid’s three main arguments for string theory. Gross went through these in detail, and I think what I wrote last year also responds to what Gross has to say. He did include in the “Meta-Inductive Argument” the argument that SUSY is a related research program to string theory and that it will be vindicated at the LHC in the next few years. It will be interesting to hear what he has to say at a future Strings 20XX after this hasn’t worked out. He announced that Strings 2015 will be in Bangalore, Strings 2016 in Tsinghua, Strings 2017 in Israel, Strings 2018 in Japan and Strings 2019 in Belgium.
He explicitly addressed the fact that many in the field were experiencing depression and anxiety due to things not working out, pointing out that even if the first derivative of progress in a field is negative, there can be jump discontinuities. So, although things don’t look good, maybe a big piece of progress will come along out of nowhere.
There was one more vision talk, but I’ll discuss that in a separate posting.
Update: Strominger’s slides are available here, and include the 80 responses he got from others about the open problems of the field.