Not Even Wrong

Witten is giving a colloquium talk next week at Princeton on the topic of “Supersymmetry Pro or Con”. His talk is a last-minute replacement for one about “Recent Results from WMAP” by Lyman Page. WMAP was supposed to report the results from the analysis of the second year’s worth of satellite data early this year, but this has been delayed quite a bit already, and evidently is being delayed even more. Does anyone know why?

This weblog thing is getting out of control. It seems that Frank Wilczek’s wife has one, as well as his daughter. What about you, Frank?

Witten’s talk this morning at the KITP on “The Future of String Theory” is now available. He only talked for about fifteen minutes and then took some questions. I thought it was a rather weird performance. Not only did Witten not really have anything to say about the future of string theory, he didn’t even discuss the present state of the theory. The most recent thing about string theory he mentioned is the now seven year-old AdS/CFT correspondence. He drew the standard picture of Feynman diagram vs. string world-sheet, claiming it indicates that space-time is an “emergent phenomenon”. He even noted that he has been drawing the same picture for nearly twenty years now and he still doesn’t know in what sense this “emergent space-time” idea is true, although AdS/CFT is the closest thing to the kind of thing he is looking for. Now not only space-time is supposed to be “emergent”, but so is the string itself, although he admits he doesn’t know what this means.

Instead of looking optimistically to the future, Witten’s talk was extremely defensive. He started off trying to defend why string theorists work on string theory (basically because it is a non-trivial extension of QFT, contains gravity and has lead to important mathematical results). Much of his very short talk was taken up by mentioning criticisms of string theory and giving unconvincing responses to them. He didn’t say anything in the bulk of his talk about the Landscape or twistor string theory, or anything else going on these days in the field.

There were several questions from the audience. Someone asked him if he would still believe as strongly in string theory if the LHC didn’t find supersymmetry. He somewhat evaded the question, saying he would be less optimistic about how well we can ever understand the world, but implying that he wouldn’t consider this as evidence against string theory itself, repeating the same defense of why he did string theory that his talk started with.

The last question was about the anthropic principle and the Landscape. He began his answer with something like “Well…..(nervous laughter)… uh…..” then finally said more or less “I’d be happy if it is not right, but there are serious arguments for it, and I don’t have any serious arguments against it.” So I guess he comes down on the Weinberg side (“I don’t like it, but maybe we have to accept that our fundamental theory can’t explain any of the things it is supposed to”) vs. the Gross side (“people who think this way have given up doing physics”).

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.

Well, my prediction of who would win this year’s Nobel prize in physics turned out to be correct. No, I didn’t have any inside information about this at all. I suppose I should mention that many of my friends will not be so impressed by this feat since they have heard me make this same prediction incorrectly every one of the last 15 years or so. Sooner or later I had to be right, and it was dumb luck that it happened the first year I had a public forum in which to make this prediction.

Congratulations to Gross, Politzer and Wilczek!

Last week I was in a bookstore and ran across a new book by Emanuel Derman called My Life as a Quant: Reflections on Physics and Finance. Derman got a particle theory Ph. D. here at Columbia in 1973 when he was one of Norman Christ’s first students. He then went on to post-docs at Penn, Oxford and Rockefeller and a tenure track job at Boulder. By 1980 he had decided he didn’t want to stay in Boulder, partly because his wife couldn’t get a job there, so he left academia for a job at Bell Labs.

In 1985 he went to work in the financial industry at Goldman Sachs, staying there until 2002, interrupted by a one-year stint at Salomon. He’s now back at Columbia, teaching in the Financial Engineering program run by the IEOR (Industrial Engineering and Operations Research) department of the Engineering school. This kind of master’s program is extremely popular; besides IEOR, the math and stat departments collaborate on a separate MA program in the Mathematics of Finance which has been wildly successful. Each year we get more and better applicants, and they seem to do very well on the job market when they get out.

The first half of Derman’s book gives a good view of what it was like to be a theorist of the phenomenological variety during the seventies and early eighties. The second half has a nice description of the mathematical problems involved in pricing options and mortgage-backed securities, as well as many comments on what it is like to work in the financial industry. He was one of the earliest particle theorists to do this, but many others have followed him there in recent years, some of whom are regular commenters here.

Over at sci.physics.strings there’s the scary sight of Lubos Motl agreeing with me in a posting about “Stringy Naturalness”. Well, maybe he isn’t directly saying he agrees with me, but “It would be too difficult for me to pretend that I disagree with these Woit’s remarks” is pretty close. Lubos is criticizing the new sort of “naturalness” critierion advocated by Miichael Douglas in a preprint reviewing his recent work on the “Landscape”. By this criterion a low energy effective QFT is more “natural” when there are more supposed string theory vacua that have this low energy limit. As Lubos points out, the danger with this criterion is that it tends to lead you to the conclusion that the most “natural” effective field theory is the one that is least likely to be able to predict anything new.

The posting immediately before Lubos’s is from Michael Douglas himself, responding to an earlier thread. In it he explains the goal of his work as follows. He wants to estimate N_SM, the number of vacua consistent with the observed known Standard Model behavior, then

“Based on this information, we can decide whether we should continue the search for the right vacuum directly (appropriate if N_SM <= a few), look for additional principles to cut down the number (if N_SM is large), or give up and start making anthropic arguments or whatever (if N_SM is ridiculously large)." The posting immediately before Douglas’s asks for “what would cause string theory to become nonviable and abandoned”, but hasn’t gotten any responses. An obvious response would be that if it becomes clear that string theory has so many consistent vacua that it can’t ever predict anything, the theory would have to be abandoned. Neither Douglas nor others working on the Landscape seem willing to mention this possibility in public, the closest he gets is the line about having to “give up and start making anthropic arguments or whatever”.

There’s an interesting new preprint by the historian of mathematics Erhard Scholz about the early history of the use of representation theory in quantum mechanics. Immediately after the beginnings of quantum mechanics in 1925, several people started to realize that the representation theory of the symmetric and rotation groups was a very powerful tool for getting at some of the implications of quantum mechanics for atomic spectra. One of the main figures in this was Eugene Wigner, who was trained as a chemical engineer, but worked on this topic with his fellow Hungarian, the well-known mathematician von Neumann.

Equally important was the role of the mathematician Hermann Weyl, who in 1925 had just completed his main work on the representation theory of compact groups, perhaps the most important mathematical work in a very illustrious career. Weyl was in close communication both with the group at Gottingen (Heisenberg, Born, Jordan) who were developing matrix mechanics, as well as Schrodinger who was working on wave mechanics. Weyl and Schrodinger both were professors in Zurich and knew each other well (Schrodinger’s first paper on quantum mechanics thanks Weyl for explaining to him some of the general properties of equations such as the Schrodinger equation). In 1927/8 Weyl gave a course on quantum mechanics and representation theory, which became the basis of his extremely influential book “The Theory of Groups and Quantum Mechanics”, first published in 1928.

Scholz has also posted another preprint about Weyl’s work, one that focuses on how his conception of the relation between matter and geometry evolved from 1915 to 1930. Weyl worked on general relativity and wrote an influential book about it (Space-Time-Matter, 1918). At that time he, Einstein and others believed that matter could somehow be described by a unified theory expressed in terms of some generalization of Riemannian geometry. Perhaps particles were some specific singularities or special solutions to the non-linear equations for the metric. The advent of quantum mechanics convinced Weyl (unlike Einstein), that this was a misguided notion, that matter should be described by a complex wave function. The right mathematics was not the geometry of a metric, but (in modern language) the geometry of gauge fields and of sections of a vector bundle with connection. The close connection between the basic ideas of representation theory and of quantum mechanics was quite clear to him, so, unlike Einstein, he enthusiastically adopted the new point of view of quantum physics.

One part of the close connection between Weyl and the history of quantum mechanics isn’t mentioned by Scholz. Weyl was not only a close friend of Schrodinger’s, he was Schrodinger’s wife’s lover. Schrodinger didn’t believe much in monogamy; it’s a well-known story that he discovered the Schrodinger equation while on holiday in the mountains with a girlfriend.