Not Even Wrong

Study of the string theory landscape seems now to have become the hot research topic that one should be working on in order to be taken seriously as a cutting-edge researcher in particle theory. Last week there was a workshop at Trieste on String Vacua and the Landscape that drew many researchers. Some of the talks from the workshop are available on-line.

Following on the heel’s of Susskind’s popular book promoting the landscape, which has received excellent reviews from particle and string theorists, there’s a new one on the same topic coming out later this month from cosmologist Alex Vilenkin, entitled Many Worlds in One: The Search for other Universes.

As string theorists in search of something to write papers about pour into the landscape, with its more than 10⁵⁰⁰ possible hot research topics to work on, Sean Carroll reports from a cosmology workshop at the Perimeter Institute that trouble may be ahead for the subject. Sean gives a short summary of the talks at the workshop, in the majority of cases ending with “Made fun of the landscape”, or “Made fun of the anthropic principle”.

The main argument for the landscape mania has always been that it justifies Weinberg’s “prediction” of the size of the cosmological constant. I’ve written elsewhere about why this is not a legitimate scientific prediction, and is off by at least an order of magnitude anyway. Evidently Steinhardt and Turok are about to put out a paper claiming that the situation is much worse than this, that if you take anthropic reasoning seriously, the natural “prediction” of the landscape is that:

the cosmological constant should be quite large (many times the matter density, although presumably not at the Planck scale), and we should live in a single lonely galaxy in an empty universe dominated by vacuum energy.

It will be interesting to see if landscapeologists will be willing to admit that the only supposed “prediction” of this subject doesn’t work at all, and that it is not only pseudo-science, but failed pseudo-science.

I ordinarily keep a short list on my desk of things I’ve seen recently that I’d like to write about here. The last few days this list has gotten way too long, so I’ll try and deal with it by putting as many of these topics as I can in this posting.

The June/July issue of the AMS Notices is out, with many things worth reading. The two long articles are one by Ken Ono about Ramanujan and one by Arthur Jaffe telling the story of the founding of the Clay Mathematics Institute and the million dollar prizes associated with seven mathematical problems. There’s also a book review of Roger Penrose’s The Road to Reality, news about the proposed US FY 2007 budget for mathematical sciences research, and an account of a public talk by Michael Atiyah, who evidently closed by explaining some of his very speculative ideas about how to modify quantum mechanics, then said:

This is for young people. Go away and explore it. If it works, don’t forget I suggested it. If it doesn’t, don’t hold me responsible.

The June issue of Physics Today is also out. In its news pages it reports that Robert Laughlin is out as the president of the Korea Advanced Institute of Science and Technology (KAIST), and will return to Stanford in July “where he plans to teach, research, and write ‘anything that brings income.'” The report gives conflicting reasons for why things didn’t work out for him at KAIST, but notes that “90% of KAIST professors gave him a vote of no-confidence and nearly all deans and department chairs quit their administrative posts to protest his continuing in the job.”

There’s an extremely positive review of Leonard Susskind’s The Cosmic Landscape by Paul Langacker, which ends:

The Cosmic Landscape is a fascinating introduction to the new great debate, which will most likely be argued with passion in the years to come and may once again greatly alter our perception of the universe and humanity’s place in it.

Why any particle theorist would want to encourage other physicists outside their field to read this book and give them the idea that it represents something theorists think highly of is very unclear to me.

Finally there’s an article by Jim Gates entitled Is string theory phenomenologically viable? Gates aligns himself with the currently popular idea that string theory doesn’t give a unique description of physics:

The belief in a unique vacuum is, to me, a Ptolemaic view – akin to that ancient belief in a unique place for Earth. As I wrote in 1989, a Copernican view, in which our universe is only one of an infinity of possibilities, is my preference, but there were very few Copernicans in the 1980s.

He seems to promote the idea that one should not use 10d critical string theory and thus extra dimensions, but instead look for 4d string theories, and that perhaps the problem is the lack of a “completely successful construction of covariant string theory.” For more about this point of view, see Warren Siegel’s website.

There are quite a few idiosyncratic things about Gates’s article, including the fact that he refers to non-abelian gauge degrees of freedom as “Kenmer angles”, after Nicholas Kemmer (not Kenmer) who was involved in the discovery of isospin.

Some of his comments about string theory are surprising and I don’t know what to make of them. He claims that “some aspects of string theory seem relevant to quantum information theory”, and the one supposed observational test of string theory he discusses is one I hadn’t heard of before and am skeptical about (observing string-theory-predicted higher curvature terms in Einstein’s equations through gravitational wave birefringence). His discussion of supersymmetry seems to assume that observation of superpartners is unlikely, since for reasons he doesn’t explain he expects their mass to be from 1 to 30 Tev. Finally, he worries that people will not investigate things like covariant string field theory since we are about to enter an “era that promises an explosion of data”. I certainly hope he’s right about the forthcoming availability of large amounts of interesting new data.

The Harvard Crimson has an interesting article about Ken Wilson.

John Baez is getting ever closer to having a blog in its modern form, now he has a diary.

Read about the tough summer life of theoretical physicists in Paul Cook’s report from Cargese (which reminded me of when I went there as a grad student), and JoAnne Hewett’s report from Hawaii (which reminded me of a very pleasant vacation I spent on the Big Island).

Science magazine has an article about progress on increasing luminosity at the Tevatron, hopes for getting enough events there to see the Higgs before the LHC, and the debate that is beginning about whether to run the machine in 2009.

Slides are available from the Fermilab User’s Meeting.

There’s a news story out from China (and picked up by Slashdot) about the new paper by Huai-Dong Cao and Xi-Ping Zhu soon to appear in the Asian Journal of Mathematics. This paper is more than 300 pages and is supposed to contain a proof of the Poincare conjecture and the full geometrization conjecture, filling in an outline of a proof due to Perelman, who used methods developed by my Columbia colleague Richard Hamilton. Other groups have also been working on this in recent years including my other Columbia colleague John Morgan together with Gang Tian; for another example, see the notes on Perelman’s papers recently put on the arXiv by Bruce Kleiner and John Lott. Cao and Zhu have evidently been explaining their proof in a seminar at Harvard run by Yau during the past academic year, and Yau will talk about this at Strings 2006 in Beijing later this month. When the paper appears it will be interesting to see what some of the other experts in the field think of it and whether there’s a consensus that the proof of Poincare and geometrization is finally in completely rigorous form.

Update: According to a blog entry from the Guardian, “Perelman seems to be active in string theory.”

I was up in Boston for a few days, and managed to attend a few of the talks at the conference in honor of George Lusztig’s 60th birthday. Lusztig started out his career in geometry and topology; his thesis was in the area of index theory, working with Michael Atiyah and using the families version of the index theorem. He soon turned his attention to representation theory, which is the field that he has worked in for most of his career, often from a quite algebraic point of view. His papers are dense and can be difficult to read, especially for someone like me who is not so algebraically inclined, but many speakers at the conference remarked on how their work had drawn important inspiration from one or another of these papers.

Among the things he is famous for are his work on quantum groups, on the representation theory of reductive groups over finite fields (called Deligne-Lusztig theory, for an introduction, see here), on a whole new field in Lie theory known as Kazhdan-Lusztig theory (for an introduction, see the article by Deodhar in the proceedings of the 1991 AMS summer institute on algebraic groups), and many other things.

Of the few talks I heard at the conference, two were really exceptional. One of these was by Michael Atiyah, with the title “Quaternions in Geometry, Analysis and Physics”. He began by explaining that not only was Lusztig 60, but, if he were alive, the Irish mathematician Hamilton would be 200. There’s a famous story about Hamilton’s discovery of the quaternions: this took place in a flash of insight on October 16, 1843, after which he supposedly engraved the defining relations of the quaternion algebra into a Dublin bridge. Atiyah described a piece of history I didn’t know, showing an extract from a 1846 paper of Hamilton’s in which he takes a square root of the Laplacian and essentially writes down the Dirac equation (in Euclidean signature, this was long before special relativity…).

Hamilton was very taken with quaternions as a generalization of complex numbers, and wanted to develop a “quaternionic analysis” that would be a generalization of complex analysis, a project he thought would take him at least ten years. It turns out that you can’t simply generalize the beautiful subject of complex analysis and algebraic geometry over the complex numbers to the quaternionic case. Because of non-commutativity, polynomials behave very differently. Atiyah explained that in his view the correct generalization of complex analysis to the quaternionic case was Penrose’s twistor theory. Here one considers all possible ways of identifying R⁴ with C², forming a 3 complex dimensional “twistor space”. Complex analysis on this twistor space is what Atiyah claimed should be thought of as the quaternionic analog of complex analysis (on the complex plane).

He reviewed the story of how solutions to various linear equations are related to sheaf cohomology groups on the twistor space, then went on to the non-linear case, where solutions of the anti-self-dual Yang-Mills equations correspond to holomorphic bundles on the twistor space. One can generalize twistor theory to what Atiyah claimed should be thought of as quaternionic analogs of Riemann surfaces: 4d Riemannian manifolds with holonomy in Sp(1)=SU(2), these are self-dual Einstein manifolds, what Penrose would call a “non-linear graviton” (although this is the Riemannian, not pseudo-Riemannian case). The twistor space of these 4d manifolds is a 3d complex manifold, and Atiyah considers complex analysis on this to be the quaternionic analog of complex analysis on a Riemann surface.

The quaternionic analog of higher dimensional complex manifolds are manifolds of dimension 4k, with holonomy Sp(k). Unlike in the complex case, there are few compact examples. Atiyah went on to discuss how examples (mostly non-compact) could be generated as quotients using the quaternionic analog of symplectic reduction. He described several different classes of examples, noting that this construction first appeared in work with physicists studying supersymmetric non-linear sigma models. While I was a post-doc at Stony Brook, Nigel Hitchin was visiting there and working with Martin Rocek and others on this, leading to the 1987 paper in CMP by Hitchin, Karlhede, Lindstrom and Rocek. Atiyah said that he wouldn’t try and describe the relation to supersymmetry, since “I don’t know much about supersymmetry, and if I tried to explain it, you would understand even less”. That Atiyah, after many years of working in this area, still finds supersymmetry to be something he can’t quite understand, is an interesting comment, reflecting the way the subject is still very imperfectly integrated into mathematician’s traditional ways of thinking about geometry and algebra.

Atiyah also commented that off and on over the years he had pursued the idea that quantum groups (which aren’t quite groups), are in some sense the quaternionification of a Lie group (which doesn’t quite exist). He said he hadn’t been successful with this idea, but still thought there was something to it, and hoped that someone else would take up the challenge of trying to make sense of it.

The second wonderful talk I heard was that of Igor Frenkel, from Yale, with the title “Quantum deformation, geometrization, categorification: What is next?”. Unlike Atiyah’s talk, which I pretty much completely understood, Frenkel’s covered much too quickly a lot of material I had never understood, but putting it into an intriguing perspective close to the unsolved problems that seem to me the most important ones for mathematicians and physicists to be looking at. Frenkel began by saying that for many years he had been trying to solve the problem of how to generalize the constructions of representations of loop groups that are related to 2d CFT to representations of 3d gauge groups that should be related to 4d QFT. Some of his thoughts about this are in the write up of his talk at the 1986 ICM. He described himself as having for a long time given up on this problem, moving on to simpler things that he could do: quantum groups which are deformations of the affine Lie algebra story. He went on to talk about “Geometrization”, by which he meant the principle that “all structure constants are Euler characteristics of some variety, all vector spaces are cohomologies”, then “Categorification”, to him the principle that “all structure constants are dimensions of vector spaces, all vector spaces the Grothendieck groups of an Abelian category”. Many of the examples he was using to flesh this out are not well-known to me, I need to do some serious work learning about them before I can say that I clearly understand exactly what he has in mind here.

The last part of his talk, the “What Next?”, went by way too fast but sounded fascinating. He claimed to have some new ways of thinking about the problem of what a representation of these higher dimensional analogs of loop groups should me. I hope to learn more from him in the future to get a better idea of what he has in mind here. He and collaborators at Yale have papers forthcoming, which I look forward to reading. When and if I ever better understand this stuff, I may try and write about it again here.

News about various colliders of various vintages:

The Tevatron has been shut down for the past two months for maintenance and various improvements. It should start up again this coming week, for latest news on its status, see here.

Seed magazine is starting a series of articles on the LHC. One prediction about the LHC that I feel confident making is that it is going to get a lot of press coverage.

A group called the LHC Theory Initiative has been trying for a while to get the NSF to fund new postdocs and graduate student fellowships for physicists working on LHC phenomenology. So far they have been turned down, with the panel that recommended not to fund this presumably concerned that money going to this purpose would be taken away from the standard NSF group grants that fund particle theory groups at many institutions. The full NSF proposal is available on-line.

Science magazine has an article about Barry Barish, who is leading the Global Design Effort for the ILC.

The same issue of Science has a paper by Steinhardt and Turok promoting their cyclic cosmological model as explaining the small value of the cosmological constant, together with an article by Vilenkin criticizing them and promoting the anthropic point of view.

Update: Experimentalist Michael Schmitt, sometimes commenter here, has an excellent new blog about accelerator-based particle physics at the Tevatron and LHC entitled Collider Blog.

Update: The Tevatron start-up was going smoothly until early yesterday morning when they ran into serious trouble. Here’s the report from the FNAL accelerator update page:

At 1:24 AM, Operations reported a raccoon attack on the Linac gallery. It seemed to be a coordinated effort. Fortunately, by 1:53 AM, a joint force of operators and Pbar experts managed to drive the raccoons out of their hastily made fortifications. Then at 4:18 AM, the raccoons made what some thought to be a counter attack on the Division Headquarters, but others believed it to be only a simple reconnaissance incursion. No raccoons were either injured or captured during these encounters. Operator losses were low.

Just upgraded to a new version (2.0.2) of WordPress, and as far as I can tell everything is working normally again. If not, let me know. The one change I plan to make here soon is to try out some of the new anti-spam features. The ones in the older version of WordPress were much better at rejecting valid comments than identifying spam, we’ll see about the new version…

Frank Wilczek has a new Reference Frame piece in this month’s Physics Today. It’s about the question of whether the parameters of our fundamental physical theory are uniquely determined by abstract principles, or “environmental”. He gives two reasons for suspicion about the idea that these parameters are calculable from a fundamental theory:

1. They have complicated, “messy” values and, despite much effort, no one has come up with a good idea about how to calculate them (an exception is the ratio of coupling constants in a supersymmetric GUT). He writes:

Could a beautiful, logically complete formulation of physical law yield a unique solution that appears so lopsided and arbitrary? Though not impossible, perhaps it strains credulity.

2. Some of the values are fine-tuned to make complex structures and thus life possible:

It is logically possible that parameters determined uniquely by abstract theoretical principles just happen to exhibit all the apparent fine-tunings required to produce, by a lucky coincidence, a universe containing complex condensed structures. But that, I think, really strains credulity.

Personally I don’t see the same degree of believability problems that Wilczek sees here. On the first point, it seems quite plausible to me that there are some crucial relevant ideas we have been missing, and that knowing them would allow calculation of standard model parameters, by a calculation whose results would have a complicated structure.

On the second, it’s not at all clear to me how to think about this. Sure, the fact that our universe has highly non-generic features means that it is incompatible with generic values of the parameters, but there’s no reason to expect the answer to a calculation of these parameters to be generic. I guess the argument is that there would then be two quite different ways of getting at some of these parameters: imposing the condition of existence of life, and a fundamental calculation; and if two different, independent calculations give the same result one expects them to be related. But the question is tricky: by imposing the condition of the existence of life in various forms, one is smuggling in different amounts of experimental observation. Once one does this, one has a reason for why the fundamental calculation has to come out the way it does: because it is has to reproduce experimental observations.

Wilczek avoids any mention of string theory, instead seeing inflationary cosmology and axion physics as legitmating the idea that standard model parameters are fixed by the dynamics of some scalar fields, or something similar. This dynamics may have lots of different solutions so:

We won’t be able to calculate unique values of the parameters by solving the equations, for the very good reason that the solutions don’t have unique values.

The fundamental issue with any such anthropic or environmental explanation is not that it isn’t a consistent idea that could be true, but whether or not it can be tested and thus made a legitimate part of science. It’s easy to produce all sorts of consistent models of a multiverse in which standard model parameters are determined by some kind of dynamics, but if one can’t ever have experimental access to information about this dynamics other than the resulting observed value of the parameters, why should one believe such a theory? It is in principle possible that the dynamics might come from such a simple, beautiful theory that this could compel belief, but the theories of this kind that I have seen are definitely neither simple nor beautiful. If you want me to believe in a complicated, fairly ugly theory, you need to produce convincing evidence for it, some sort of testable predictions that can be checked. Wilczek does believe that multiverse theories may provide such predictions:

Of course, the very real possibility that we can’t calculate everything in fundamental physics and cosmology doesn’t mean that we won’t be able to calculate anything beyond what the standard models already achieve. It does mean, I think, that the explanatory power of the the equations of a “theory of everything” could be much less than those words portend. To paraphrase Albert Einstein, our theory of the world must be as calculable as possible, but no more.

One can’t argue with this: if a model make distinctive predictions, and these can be compared to the real world and potentially falsify the model, one can accumulate evidence for the model that could be convincing. Unfortunately I haven’t seen any real examples of this so far. The kind of thing I would guess that Wilczek has in mind is his recent calculation with Tegmark and Aguirre that I discussed here. I remain confused about the degree to which their calculation provides any convincing evidence for the model they are discussing.

Unlike many theorists, Wilczek personally seems to be an admirably modest sort of person, and perhaps this has something to do with why the multiverse picture with its inherent thwarting of theorist’s ambitions to be able to explain everything has some appeal for him. Over the years during which particle theory has been dominated by string theory, Wilczek has shown little interest in the subject, perhaps partly due to its immodest ambitions. But I see two sorts of dangers in the way his article ignores the string theory anthropic landscape scenario which is what is driving the interest of much of the theory community in these multiverse models. As his advisor David Gross likes to point out, accepting this scenario is a way of giving up on the perhaps immodest goal he believes theorists have traditionally pursued, and one shouldn’t give up in this way unless one is really forced to. None of these models is anywhere convincing enough to force this kind of giving up.

The second danger is that what is happening now is worse than just giving up on a problem that is too hard. The string theory landscape anthropic scenario is being used to avoid acknowledging the failure of the string theory unification program, and this refusal to admit failure endangers the whole scientific enterprise in this area.

Update: It has been accurately pointed out to me that Wilczek does mention string theory briefly at one point in the article (“Superstring theory goes much further in the same direction”), and alludes to it at another place (when he talks about a “theory of everything”).