Strings 2011 started today in Uppsala, with attendance quite a bit lower than in the past (259 registered participants, versus 500 or so at some of the past such conferences). One reason for this may be the high conference cost (discussed here), another may be that excellent video of the talks is available, so why bother traveling to Uppsala?
The opening talk was by David Gross, who tried to address the question “Where do we stand?” for string theory. He claimed the field is “extremely healthy”, “vibrant and exciting”, “making enormous progress in a variety of areas’”, with “stupendous progress” in N=4 planar SYM. At the same time, he acknowledged that it was “very sobering” that string theory was 43 years old.
In the past, Strings XXXX conferences often featured a call for progress towards making predictions that could be tested at the LHC. With LHC data now coming in, Gross acknowledged that this had been a failure: there are no string theory LHC predictions. He put a positive spin on this by noting that the lack of any BSM signal at the LHC so far is not a worry for string theory, since string theory can’t be tested at the LHC. As for the lack of any supersymmetry signal so far, he says that “I personally am not yet worried”, while acknowledging that some people are becoming pessimistic. While no SUSY is not a worry for string theory, he feels that “it would be awfully nice for string theory if SUSY appeared”. Supposedly he has made bets on SUSY at the LHC, but he gave no indication of when he would start to worry (or pay off the bets) if SUSY continues to not be there.
The main area of progress he sees is the usual gauge-gravity duality that has dominated the field for years, together with progress on N=4 SYM amplitudes. He sees Verlinde’s “Entropic Gravity” as an “exciting development I find enormously interesting”. Evidently later this week Verlinde will discuss his latest ideas about this which supposedly include an explanation of dark energy and dark matter.
Gross went over quickly the questions about string theory he first raised in a similar talk 26 years ago, which mostly remain unanswered, including the basic one of “What is String Theory?”. The additional questions raised by attempts to understand the emergence of spacetime in a deSitter background were one factor that inspired him to end with the quote that:
The most important product of 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 from Gross about anthropics or the multiverse. I assume he’s still an opponent, but perhaps feels that there’s no point in beating a dying horse. Susskind isn’t there and oddly, the only multiverse-related talks are from the two speakers brought in to do public lectures (Brian Greene and Andrei Linde, Hawking’s health has kept him from a planned appearance). So the multiverse is a huge part of the public profile of the conference, but pretty well suppressed at the scientific sections. Also pretty well suppressed is “string phenomenology”, or any attempt to use string theory to do unification. Out of 35 or so talks I see only a couple related to this, which is still the main advertised goal of string theory.
I’m looking forward to the talks of Witten, Gaiotto and Gukov, which I hope will provide a gentle introduction to their intriguing recent long papers on the arXiv. To the extent I find time to watch talks this week and have any comments about them, I’ll try and add updates to this posting.
Update: After looking at most of the talks online, the most remarkable thing about Strings 2011 is how little there is about string theory. One of the speakers, Chris Hull, started off his talk with the comment:
At lunch today one of the organizers was observing that my talk was unusual in being one of the few talks actually about string theory. It would be interesting to speculate on what that might mean about the state of the field, but it would be invidious to do so here.
One of the main themes of the conference so far has been study of mathematically interesting supersymmetric QFTs in 3,4,5 and 6 dimensions, often obtained from a specific class of 6d theories, which themselves 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, which involves a chain of various 6d, 5d, 4d, 3d and 2d QFTs. Nati Seiberg reviewed the technology used for constructing these theories on various special backgrounds, noting that this was all about “rigid” SUSY theories, with supergravity and string theory making no appearance.
Update: The videos of the talks are now all up. I took a look at the Verlinde talk, and the ideas he is putting forward still strike me as pretty much empty of any significant content. In Jeff Harvey’s summary of the conference, he notes that many people have remarked that there hasn’t been much string theory at the conference. About the landscape, his comment is that “personally I think it’s unlikely to be possible to do science this way.” He describes the situation of string theory unification as like the Monty Python parrot “No, he’s not dead, he’s resting.” while expressing some hope that a miracle will occur at the LHC or in the study of string vacua, reviving the parrot.
That the summary speaker at the main conference for a field would compare the state of the main public motivation for the field as similar to that of the parrot in the Monty Python sketch is pretty remarkable. In the sketch, the whole joke is the parrot’s seller’s unwillingness, no matter what, to admit that what he was selling was a dead parrot. It’s a good analogy, but surprising that Harvey would use it.