The KITP in Santa Barbara is having a conference in honor of its 25th anniversary on the topic of “The Future of Physics”. Some of yesterday’s talks are already online. I’ve been watching Weinberg’s talk on “Where do we Stand?” this morning (a commenter also wrote in a little while ago while I was watching to recommend it). Weinberg gives a good summary of the present state of conventional wisdom about particle theory. He goes over the standard arguments that the standard model should be thought of as an effective low energy theory, and that doing so explains many of its features, with the two big exceptions of the scale of the vacuum energy and the electroweak symmetry breaking scale.
He promotes his “prediction” of the cosmological constant, and recalls that supersymmetry is the standard way of dealing with the low electroweak scale or hierarchy problem. But he then explains the problems with all known ways of breaking supersymmety, concluding that “no satisfactory theory of supersymmetry exists, where supersymmetry breaking is accounted for in the framework of particle physics.”
As for the “Landscape”, he notes that Gross hates it, says that “I don’t love it”, that it’s a disappointment, but one that we may have to get over. He makes some extensive comments about string theory, saying that it has had a history of advances leading to momentary optimism, but ultimately disappointment, with the bottom line that after 20 years we understand string theory much better but are no closer to contact with physics. He ends his comments about string theory with a rather weird remark that maybe it is wrong to look for a “guiding principle” behind string theory, that all there is to it is that it is the only way of extending the standard model to include gravity in 4d. I guess he is implying that string theory is not a fundamental beautiful theory, but, like S-matrix theory just a general framework imposed by consistency.
In general, Weinberg sounded to me old, tired and discouraged. Like just about all the leaders in the field, he refuses to publicly acknowledge the obvious possibility that the explanation for why string theory doesn’t predict anything or have any known fundamental principles is that it is just a wrong idea. He’s so discouraged about string theory that he has stopped working on it himself for the last fifteen years, but doesn’t have the energy or optimism to envisage any alternatives. He ends his talk with some real downers, one of which he calls the “LHC nightmare”, that the LHC will just see a single new scalar particle and nothing else. The second nightmare is that observations of the CMB will never see anything that tells us more about the early universe, just a 1/f spectrum, no evidence of the effects of gravitational waves.
All in all Weinberg ended up not giving a very optimistic view of the “Future of Physics”, but something closer to John Horgan’s argument about the “End of Physics”.
Tomorrow there will be a panel on “Field Theory and Mathematics” which should be interesting. Also, Witten will be talking on the “Future of String Theory”. It will be interesting to see if he is any more optimistic than Weinberg, and more specifically if he’ll come down on the Gross (“I hate it”) or Weinberg (“I don’t love it, but maybe it’s right”) side of the Landscape issue.