Strings 2011

Strings 2011 began today in Uppsala, with presence quite a bit lower than in the past (259 registered participants, versus 500 or so on some of the past such conferences). One reason for this may be the cost of the Conference on high (discussed here), another possible that excellent video of the talks is available, so why bother travel to Uppsala?

The opening talk was by David Gross, who tried to address the question "where do we stand?" for string theory. He claimed that the field is "very healthy", "lively and exciting", "enormous progress in a variety of areas", with "huge progress" in N = 4 flat nr. At the same time, he acknowledged that it was "very disappointing" that string theory was 43 years old.

Strings XXXX conferences featured in the past, often a call for progress towards making predictions which could be tested on the LHC. With LHC data now, gross acknowledged that this has been a failure: there are no string theory LHC predictions. He put a positive spin on this by noting that the absence of any BSM signal on the LHC so far not a concern for string theory, since string theory cannot be tested on the LHC. As for the absence of any supersymmetry signal so far, he says that "I personally am not still concerned", while acknowledging that some people are becoming increasingly pessimistic. While no SUSY not a concern for string theory is, he feels that "it would be very nice for string theory as SUSY appeared". Presumably, he bets on SUSY at the LHC, but he gave no indication of when he would begin to worry (or the bets pay) as SUSY remains there are not.

The main area of progress he sees is the usual gauge-gravity duality that has dominated the field for years, along with progress in N = 4 SYM amplitudes. He sees the Verlinde "entropic Gravity" as an "exciting development I find immensely interesting". Apparently later this week to discuss Verlinde his latest ideas which supposedly an explanation of dark energy and dark matter.

Gross went on quickly the questions about string theory he first raised in a similar talk 26 years ago, which usually are unanswered, including the basic "what is string theory?". The supplementary questions raised by attempts to understand the emergence of space time in the background of a deSitter were a factor that inspired him to end up with the quote that:

The main product of the knowledge is ignorance.

To which he added "after 43 years of string theory, it would be nice to have some answers."

Surprisingly, not a word of gross on great ape or the multiverse. I assume that he is still an opponent, but perhaps feels that there is no point in beating a dying horse. Susskind is not there and oddly enough, the only multiverse-related conversations are from the two speakers brought to do public lectures (Brian Greene and Andrei Linde, hawking's health has kept him from a scheduled appearance of). So is the multiverse with a large proportion of the public profile of the Conference, but pretty well suppressed on the scientific sections. It is also pretty well suppressed "string phenomenology", or any attempt to use string theory to do integration. From 35 or so conversations I see only a few related to this, which is still the advertised primary objective of string theory.

I'm curious about the discussions of Witten, Gaiotto and Gukov, which I hope provides a gentle introduction to their intriguing recent long papers on the arXiv. As far as I find time to watch discussions this week and have comments about them, I will try and add updates to this post.

Update: after most of the discussions online look, is the most notable thing about Strings 2011 how little there is about string theory. One of the speakers, Chris Hull, began his speech with the comment:

During the lunch today was one of the organizers observe that my talk was unusual in one of the few actually talks about string theory. It would be interesting to speculate about what that could mean about the condition of the field, but it would be shameful to do here.

One of the main themes of the Conference so far has been the study of mathematically interesting supersymmetric QFTs in 3, 4, 5 and 6 dimensions, often obtained from a specific class of 6 d theories, which itself remain poorly understood (what is known about them was reviewed by Greg Moore). Witten gave an overview of his work relating Khovanov Homology and QFT, where a chain of different 6 d, 5 d, 4 d, 3D and 2d QFTs. Nati Seiberg reviewed the technology used for the construction of these theories over different backgrounds, noting that this was all about "rigid" SUSY theories and Supergravity, string theory create no appearance.

Update: the videos of the talks are all now. I took a look at the Verlinde spoken, and the ideas he sets still seems to me pretty much empty of all important content. In Jeff Harvey's summary of the Conference he notes that many people have noted that the Conference has not been a lot of string theory. About the landscape is his comment that "personally, I think it's probably not possible to do science in this way." He describes the situation of string theory unification as the Monty Python parrot "no, he is not dead, he rest." while some hope that a miracle will take place on the LHC or in the study of string vacua, revival of the Parrot to speak out.

That the summary main speaker at the Conference for a field the State of the main public motivation for the field as similar to that of the parrot in the Monty Python sketch would compare is pretty remarkable. In the sketch, the whole joke is the Parrot's seller reluctance, no matter what, admit that what he sold was a dead parrot. It is a good analogy, but surprisingly that Harvey would use.