Quick Links

Posted on May 7, 2006 by woit

I’ve been much too busy the past few days, so haven’t had time to write anything new here. One thing that has been keeping me busy is going over the copy-edited version of the American edition of my book, which will be published in September by Basic Books. The British edition, published by Jonathan Cape, should be available June 1, both in Britain and Canada, and presumably one can order it from the British or Canadian versions of Amazon. The American version will have a somewhat different preface, and has been separately copy-edited, so there will be minor changes (beyond just changing British spellings back to the American ones I first wrote down…). Late last week I was sent an early copy of the British version of the book itself, and I’m very happy with how it looks.

Last week I also spent a significant amount of time at my colleague John Morgan’s 60th birthday conference, which was held here in the math department. Morgan is one of the leading figures in topology, and over the years has worked on a wide range of different kinds of mathematics, often bringing the subject together with other very different parts of mathematics. At the moment he’s involved in at least two projects, one involving Calabi-Yaus with Chuck Doran, another an ambitious attempt with Gang Tian to work out the details of Perelman’s proof of the Poincare conjecture. He’s also doing a stellar job as chair of our department.

Morgan has collaborated with and interacted significantly with Witten over the years, and Witten gave a wonderful talk at the conference on Gauge Theory and the Geometric Langlands Program. This was really just a taste aimed at mathematicians of his recent work on geometric Langlands and gauge theory. He explained some of the history of Montonen-Olive duality, some of the relevance of supersymmetry to mathematics, and then explained what an ‘t Hooft operator in gauge theory is, and that it is related to the Hecke operators studied in geometric Langlands.

Here are some quick links to interesting things I’ve run across recently:

John Baez has a new edition of his proto-blog “This Week’s Finds in Mathematical Physics”. It contains a beautiful exposition of the circle of very different sorts of mathematics that all gets related via Dynkin diagrams.

Greg Moore and his recently graduated student Dmitriy Belov had a beautiful new paper on self-dual field theory in 4l+2 dimensions.

Christianity Today has an article entitled Science in Wonderland, which mentions Susskind and string theory and notes:

This theory has not met with, shall we say, universal approbation, not least because it can’t be empirically tested. You could even say it’s not science, and some have said that, but they don’t hiss the way they do when they talk about Intelligent Design.

The AMS has a new web-site devoted to Mathematical Imagery.

In the comment section here, Bert Schroer pointed to some web-sites I wasn’t aware of that contain all sorts of links to various material related to the algebraic approach to QFT. These include the home page of Stephen Summers and the Local Quantum Physics Crossroads” hosted at Gottingen.

Update: If you want to know why the mathematics associated with Dynkin diagrams can’t be usefully explained or viscerally understood without string theory, as well as why John Baez is a proto-human, you can consult the blog of a prominent Harvard faculty member. He also notes that

Peter Woit is another proto-human who eats everyone who dares to look in between the clouds. Be afraid. Be very afraid.

and explains in great detail why

it is important not only to learn string theory well but also to emphasize that and explain why people like Peter Woit are intellectual barbarian cannibals. 😉

Posted in Uncategorized | 40 Comments

Hype from the Swampland

Posted on May 1, 2006 by woit

Over the last twenty years there has been an endless stream of hype about “tests of string theory”, pretty much all of it complete nonsense. For some examples just from the first few months of this year, see here, here, and here. Most of these examples seem to have been generated by confused PR people who misunderstood carefully worded comments by various physicists about the relation of their work to string theory. The average person just finds it hard to believe that it really could be true that there is no way to test a theory that has gotten so much attention for so long from so many prominent people.

Today there’s new nonsensical hype about testing string theory, but this time it’s due not to a clueless press relations person, but to several physicists, including the one who decides what gets into the hep-th arXiv and what doesn’t. The hype isn’t buried in the article somewhere, it’s in the title: Falsifying String Theory Through WW Scattering. In their abstract, the authors claim to derive a bound on coefficients of operators in the effective electroweak Lagrangian such that “a measured violation of the bound would falsify string theory.”

The first striking thing about this paper that purports to show that string theory is falsifiable is that there’s actually nothing about string theory in it. It’s only four pages long, and the first three pages consist of an introduction followed by some calculations in the non-linear sigma model one might want to use as an effective low-energy theory of pions. This is just a warm-up exercise for the real calculation that the authors want to make some claims about, which involves the low energy effective action for a non-linear sigma-model coupled to gauge fields. This is the model that one expects to describe the low-energy behavior of the Higgs field coupled to electroweak gauge fields, if one takes the Higgs mass to be very large.

The authors go on to just copy the terms in the relevant Lagrangian down from a 1993 paper by Appelquist and Wu, then stop and promise to actually calculate the relevant bounds in a forthcoming paper. Unless one wants to try and sit down and do oneself the calculation the authors haven’t done yet, it’s hard to know what these bounds will actually say and whether they will really be non-trivial. It’s also unclear to me exactly how all of this depends on the Higgs mass, which I guess is being assumed to very high, thus violating the known indirect experimental bounds from precision electroweak measurements (which assume the standard model). Very hard to tell about any of this, since it’s dealt with in a paragraph with no equations.

It turns out that the author’s proposal isn’t a proposal to falsify string theory at all, but a proposal to falsify the idea that physics satisfies Lorentz invariance, analyticity and unitarity at high energies. This would falsify our standard ideas about QFT, but it wouldn’t falsify current ideas about string theory. The authors don’t define what they mean by “string theory”, but presumably they mean some version of perturbative string theory. This involves a divergent series (even granting the conjecture that one can make sense of these amplitudes at more than two loops), so it’s unclear how one is going to “falsify” that. Standard ideology about non-perturbative string theory (“M-theory”) is that it will involve some new ideas about space and time, so I don’t see how one can assume that it won’t violate the analyticity and Lorentz invariance properties characteristic of QFT in flat space-time. I’m not convinced that the author’s proposal will falsify anything, but if it does, it will be QFT that is falsified, not string theory. After all, this paper is a QFT calculation (or, more accurately, a promise to do a QFT calculation), not a string theory calculation.

The authors note the problems of non-predictivity generated by the Landscape, and in the first version of the paper write:

Moreover, even if it is found to be difficult to generate the proper model from string theory, one would sooner accept the notion that it is the theorist’s imaginations which are insufficient than conclude that string theory has been falsified.

In the second version of the paper, they seem to realize that this attitude of “one” is kind of unscientific, and they change it to

Moreover, even if it is found to be difficult to generate the proper model from string theory, some would sooner accept the notion that it is the theorist’s imaginations which are insufficient than conclude that string theory has been falsified.

This new version leaves it unclear who this unscientific “some” is. In both versions they note correctly that:

This line of reasoning has resulted in sharp criticism of the theory.

This paper is motivated by the “swampland” program of trying to find effective field theories that can’t be the low energy limits of a string theory. I’ve written about the problems with this elsewhere, and blog postings by Distler have amply embodied what some of them are. In his first posting on the Swampland he gave as an example of a low energy effective theory that couldn’t come from string theory one with only one or two generations, only to be told by a commenter how to construct such things from string theory. He has a more recent blog posting called Avatars of Nonlocality? about the swampland work of Arkani-Hamed and collaborators that motivated this new paper. In a comment there, Arkani-Hamed takes him to task:

This post is a great illustration of what I dislike about blogs and more specifically trackbacks. As I explained to you when you were visiting Harvard last week, your first point about the RG running is standard effective field theory (with an abbreviated discussion in our paper because it is fairly common knowledge–read Georgi’s book). I of course don’t object to your writing a paper to clarify these points to yourself or others. But this is minor. More importantly, as I also explained to you both in email and in person, what you write about the DGP model is totally wrong…

Now, in general I don’t care about what is said on blogs, as I believe they largely fulfill the primate desire to look and see what the other monkeys are doing, and I think they are a big waste of time. But I do object to having a trackback, linked from my paper, to a post about it that claims that one of the central claims is wrong, when a 45 second computation, even done for the reader’s convenience in the paper itself, refutes the argument.

This whole subject really is a swamp, if you ask me, and has nothing at all to do with physics, including nothing to do with the supposed “falsifiability of string theory”. It will be interesting to see if a referee thinks otherwise.

Update: It has been pointed out to me that I’m being a bit unfair to the authors in characterizing the calculation in this paper as a “warm-up exercise”, since they claim that it is a correct first approximation to the actual calculation that they intend to do.

Posted in Swampland | 77 Comments

Scientists Speak Out About Guantánamo

Posted on May 1, 2006 by woit

I’ve been thinking there’s too much politics on this blog recently, and yet I still think the political activities of well-known theorists are worth noting here. As commenter Arun pointed out, this Sunday’s New York Times has a letter to the editor criticizing the human rights violations at Guantanamo, signed by many prominent particle theorists, including Susskind (whose name comes first, perhaps he’s the organizer), Bjorken, Deser, Dyson, Gaillard, Gross, Polchinski, Schwarz, Wilczek, Witten and Zumino.

Over at the science policy blog Prometheus, Roger Pielke has a posting called A Very Bad Dream Indeed, in which he strongly criticizes the authors of this letter for writing such a letter that has nothing to do with science policy. He seems to be worried about these scientists “transforming their privilege in the scientific domains into authority in non-scientific domains.” Somehow, I just don’t see the possibility of theoretical physicists grabbing political power and ramrodding through policies they support as being something much worth worrying about. My reaction to this particular letter was not “who do these people think they are to do this?”, but rather “how come everyone else isn’t doing this?” The situation at Guantanamo is a disgrace to this country and that the courts allow it to continue is shocking.

More about this at No Se Nada, the blog of Kevin Vranes.

OK, now, no more about politics for a while. I promise….

Posted in Uncategorized | 29 Comments

Yuval Ne’eman 1925-2006

Posted on April 27, 2006 by woit

Yuval Ne’eman died yesterday, from a brain hemorrhage caused by a recent fall. Science magazine has a story about this.

Together with Murray Gell-Mann, in 1961 Ne’eman co-discovered the SU(3) classification of strongly interacting particles. At the time he was both an Israeli military attache in London, as well as a graduate student of Abdus Salam (who was a devout Muslim). For some amusing stories of that period, see this web-page of fellow student Ray Streater.

In later years Ne’eman continued his research in theoretical physics, was president of Tel Aviv University, played an active role in the Israeli nuclear weapons program, and was the head of a far-right political party. He was definitely one of the most colorful characters in particle theory during the second half of the last century.

Update: There’s an obituary from the AP in the New York Times. It’s only comment about Ne’eman’s work in particle theory is that:

The Technion credited Dr. Ne’eman with discovering the principles of tiny subatomic particles, called quarks, although another scientist received the Nobel Prize for that discovery.

Ne’eman and Gell-Mann both realized that mesons and baryons could be classified as representations of SU(3), and some of the physics of the strong interactions could be understood this way. Gell-Mann won the Nobel because he later identified the fundamental representation of SU(3) with new particles, quarks.

Posted in Obituaries | 13 Comments

Revealing the Hidden Nature of Space and Time

Posted on April 26, 2006 by woit

The EPP2010 report by the Committee on Elementary Particle Physics in the 21st Century is out today, and it is entitled Revealing the Hidden Nature of Space and Time. This committee was convened to recommend priorities for high energy physics in the U.S. over the next 15 years. Its membership included non-physicists and it was chaired by economist and ex-president of Princeton Harold Shapiro. The inclusion of people from outside the field emphasized the need for wide support for funding of U.S. particle physics if it is to remain healthy. The latest issue of Nature contains an article about the report entitled US particle physics fights for survival, and an editorial Making collider endorsement count. A press release about the report is here.

At the press conference announcing the report (which was webcast), Shapiro emphasized that the non-physicists on the committee had not been fully aware of the difficult situation US particle physics was in. They were very sobered by the state of US HEP, which he described as facing a serious danger that it would be half its size in 4-5 years, as current programs ended without a compelling follow-on program. The most important recommendation of the committee was that construction of the ILC in the US, probably at Fermilab, be vigorously pursued and that:

The United States should announce its strong intent to become the host country for the ILC and should undertake the necessary work to provide a viable site and mount a compelling bid.

Constructing the ILC in the US would require an increase beyond the rate of inflation in HEP funding, and the committee considered a scenario of budget increases of 2-3%per year that would probably be required, although solid numbers for what the cost of the ILC would be are still not yet available. Emphasizing the ILC in this way was described as a “high-risk, high-reward” strategy, and that taking these risks was necessary for US HEP to retain any leadership role in the field.

More specifically, the committee recommended six action items, ranked by priority:

1. Realize the physics potential of the LHC experimental program.

2. Launch a major program of R and D for the ILC, significantly expanding current expenditures on this.

3. Announce US intent to become the host country for the ILC.

4. Increase the current share of the HEP budget devoted to studying dark matter, the CMB and dark energy.

5. Develop a staged program, with international cooperation, of neutrino experiments, with emphasis on neutrinoless double-beta decay, accelerator based experiments, and search for possible charge-parity violation. This last might involve large detectors that could also be used to search for proton decay.

6. Support (especially if they’re not very expensive) high-precision experiments that probe beyond the Standard Model physics, such as a future B factory, lepton-flavor violation and rare-decay studies, searches for electric dipole moments, and precision measurements of muon g-2.

The committee did a very good job of recognizing the difficult situation of US HEP, and coming up with a plausible strategy for how to make the best of it. I have my doubts about whether it’s really a good idea to sell this as “Revealing the Hidden Nature of Space and Time”, since it’s not especially likely that that is what is going to happen. There’s no particularly good reason to believe that extra dimensions will show up at the LHC or ILC energy scales, so over-selling this is dangerous. I do understand that it’s a lot harder to get people excited about the new physics that this is likely to really all be about: understanding the nature of electro-weak symmetry breaking.

This was a study of what to do about experimental HEP, so the problems of theoretical HEP were not addressed. Unfortunately, besides the usual arguments for supersymmetry, over-hyped ideas about string theory make an appearance as the committee calls for “Improved tests of general relativity to search for effects of extra dimensions or string theory” and “Measuring time variation of physical constants with spectroscopy of distant objects to search for effects of extra dimensions and string theory”, without noting that string theory makes no predictions about either of these. One other thing included in the report is new, improved verbiage about the status of string theory. In Witten’s biographical sketch, it is described as “one of the leading candidates for the grand unified theory of elementary particle physics”, which seems to me to be a downgrade from the phrase “the leading candidate” which until recently was often used to describe the status of the theory.

Update: More about this from Chad Orzel, Lubos, Clifford Johnson at Cosmic Variance, Tommaso Dorigo and The New York Times.

Update: Also from Alexey Petrov, who in a comment at Cosmic Variance links to a very different point of view about prospects for constructing the ILC in the near term: a recent resignation letter from Bill Foster, who was the Proton Driver project leader at Fermilab (the Proton Driver would be a high-luminosity, lower energy accelerator, useful for, among other things, producing a more intense neutrino beam).

Update: More from JoAnne Hewett at Cosmic Variance.

Posted in Uncategorized | 26 Comments

Dan Freed on Twisted K-theory and the Verlinde Algebra

Posted on April 26, 2006 by woit

Dan Freed recently gave the Andrejewski Lectures at the Max Planck Institute for Mathematics in the Sciences in Leipzig, and has put the slides from his first lecture on-line. These give a beautiful overview of his work with Hopkins and Teleman relating loop group representations and equivariant K-theory, and explain one aspect of the relation to topological quantum field theory. His second and third lectures aren’t available on-line. The second was supposed to cover the way they use Dirac operators, which is explained in their papers. The third lecture was evidently about the relation to Chern-Simons, which isn’t in their papers so far, and which I’d be quite curious to know more about.

This fall, Dan will be giving a graduate course on Loop Groups and Algebraic Topology, which should be quite interesting.

Posted in Uncategorized | 8 Comments

The Hype Goes On

Posted on April 23, 2006 by woit

Yet another example of the seemingly infinite supply of bogus “evidence for string theory” is a recent Slashdot posting about a claim to have measured a change in time of the proton/electron mass ratio. It is based on a New Scientist article that states:

If confirmed, the result could force some physicists to radically rethink their theories. It would also provide support for string theory, which predicts extra spatial dimensions.

The original PRL paper about this is here and it is free of anything about string theory. The string theory nonsense appears to come from the following press release, which says:

Standard physics does not have an explanation as to why Mp/me has this value, nor can it provide an explanation as to why it would vary. However, superstring and M-theories do provide qualitative explanations for the Mp/me value and also predict possible variations of the fundamental constants.

It’s unclear where the author got this particular piece of incorrect string theory hype. Not from Lubos evidently, who says that according to string theory the proton/electron mass ratio is constant, unless it isn’t.

Update: This particular piece of nonsensical string theory hype even makes it to USA Today:

Such changes to fundamental constants would lend support to modern-day versions of string theory, which has varying constants built into its basic equations. String theory holds that on the very smallest distance scales possible, strings or loops of energy vibrating at different frequencies are the components of sub-atomic particles. String theory has also been a hot topic in physics for decades among theorists looking for a better explanation than “that’s just the way it is” of why fundamental constants have their fundamental values. So far, string theory has more critics than results, it should be noted.

Update: The hype even makes it into Nature which is normally better at avoiding this kind of nonsense:

But various versions of string theory suggest that extra dimensions occupied by a particle might affect properties such as its mass. Subtle changes in these dimensions could make physical constants vary slightly, explains Barrow. However, “there’s absolutely no observational evidence to support this vast array of ideas,” cautions Fabian. The paucity of hard evidence for string theory may be partly responsible for the upsurge in interest in variable constants, Barrow adds; results like Ubachs’ could eventually provide a good way to assess the ideas. “I’m sure we’ll see some theory papers about this,” he says. “I might write one myself.”

Posted in This Week's Hype | 72 Comments

Witten Geometric Langlands Talk and Paper

Posted on April 22, 2006 by woit

I spent yesterday afternoon down in Princeton, and attended a talk by Witten at the Institute on his work relating gauge theory and the geometric Langlands program. He says that his paper with Kapustin is done, it’s about 220 pages long, and will appear on the arXiv in Monday’s listings. So Sunday night, this link to hep-th/0604151 should start working. He’s also working on a book on the subject, where he would be the sole author.

At the start of talk, Witten noticed that many of the Institute’s mathematicians were there, and warned them that they had come to the wrong talk, since it was one aimed at physicists. Pierre Deligne got up and left, but others, including Sarnak and Langlands himself, did stay for the whole thing, although I’m not sure how much they got out of it.

Witten began by giving an outline of the talk, emphasizing six main ideas that were crucial to what he wanted to explain. He also listed as number zero the idea of geometric Langlands itself, saying he would talk about it at the end if he had time (he didn’t). The six main ideas were:

1. From a certain twisting of N=4 supersymmetric Yang-Mills one can construct a family of 4d TQFTs parametrized by a sphere. The twisting is the same sort that occurs in his original TQFT for Donaldson theory, in that case coming from N=2 supersymmetric Yang-Mills. The TQFTs he considers have an S-duality, part of a larger SL(2,Z) symmetry.

2. Compactifying the theory on a Riemann surface leads to topological sigma models, based on maps from the Riemann surface into the Hitchin moduli space MH of stable Higgs bundles. The four dimensional S-duality corresponds here to a mirror symmetry of these topological sigma models.

3. Wilson and ‘t Hooft operators of the 4-d gauge theory act on the branes of the topological sigma models. Branes mapped in some sense to a multiple of themselves by these operators are called electric or magnetic “eigenbranes” respectively.

4. Electric eigenbranes correspond to representations of the fundamental group, this is one side of the geometric Langlands correspondence.

5. The ‘t Hooft operators of the gauge theory correspond to the Hecke operators of the geometric Langlands theory although these are now defined on the space of Higgs bundles, not G-bundles.

6. Using a certaing co-isotropic brane on MH, magnetic eigenbranes give D-modules on the moduli space of bundles. The electric-magnetic duality coming from S-duality in the gauge theory relates electric and magnetic eigenbranes, giving the geometric Langlands duality between representations of the fundamental group of the Riemann surface in the Langlands dual group, and “Hecke eigensheaves” on the moduli space of G-bundles.

By the time he got to the 6th of these ideas, he was running out of time and things got very sketchy.

Witten made clear that this work doesn’t directly give dramatic new physics or mathematics, but rather just explains some tantalizing relations between gauge theory and Langlands duality, ones that were first noticed in work of Goddard, Nuyts and Olive in 1976, and pointed out to him by Atiyah way back then. The geometric Langlands program is famous among mathematicians for its difficulty (I still have trouble getting my brain around the concept of a Hecke eigensheaf..), and for its tantalizing nature, bringing together a range of different mathematical ideas (many involving conformal field theory, although these seem to be different than what Witten is doing). The new relations between this subject and supersymmetric gauge theory and TQFTs that Witten has unearthed may very well lead to some very interesting new mathematical developments in the future. Undoubtedly it will take people a while to make their way through the new 220 page paper and absorb all that he and Kapustin have worked out since last summer.

Posted in Langlands | 105 Comments

Science Fantastic

Posted on April 20, 2006 by woit

Michio Kaku has joined the Talk Radio Network, where he will have a new radio show called “Science Fantastic” that will appear on 90 radio stations around the country. Topics that will be covered include “black holes, higher dimensions, string theory, wormholes, search for extra-terrestial life, dark matter and dark energy, the future of space travel, genetic engineering, the aging process, the future of medicine, the human body shop, artificial intelligence, the future of computers and robots, as well as topics from science fiction.”

The blurb at Talk Radio Network describes Kaku as “one of the world’s leading experts in theoretical physics, and according to New York Magazine, one of the ‘100 Smartest People in New York.'” It goes on:

Dr. Kaku is the co-founder of string field theory, one of the main branches of string theory, the leading candidate for the unified field theory. Many in the scientific field call this “The new Copernican revolution.”

Kaku’s appearance on Talk Radio Network is rather remarkable, given that many of the other talk show hosts there are extremist purveyors of right-wing sewage like Michael Savage and Laura Ingraham. In the past, Kaku has been known for his left-wing politics, hosting a radio show entitled Explorations on New York lefty radio station WBAI, rebroadcast on other Pacifica stations such as KPFA in Berkeley.

Posted in Uncategorized | 30 Comments

Susskind Turns Down Templeton Prize

Posted on April 18, 2006 by woit

OK, maybe they haven’t offered it to him yet, but over at the Edge web-site, in a comment about John Horgan’s recent piece about the Templeton Foundation, Susskind writes:

I don’t understand the idea that a convergence between science and religion is taking place. I don’t believe in any such convergence. Throwing huge amounts of money at scientists who claim to see such a convergence can only lead to a dangerous blurring of boundaries.

I hereby pledge to refuse any prize for advancing the so called convergence between science and religion.

I missed Susskind’s recent public talk here in New York, about his book which the New York Academy of Sciences describes as “revolutionizing the field of physics”. There is a podcast recorded just before his talk. He makes his usual points including claiming that the situation of the string theory anthropic landscape is similar to that of Darwin and the theory of evolution. He also claims that anyone who thinks it doesn’t have experimental implications is wrong, pointing to Weinberg’s “prediction” of the cosmological constant.

Posted in Uncategorized | 64 Comments