Not Even Wrong

Lots of conferences are going on right around now, here’s some of them, many with on-line versions of the talks.

Lattice 2005 in Dublin, with blogging from Matthew Nobes.

SUSY 2005 at Durham. See some comments by Clifford Johnson. There was also a Pre-SUSY 2005 workshop aimed at graduate students.

Also at Durham, a workshop on Geometry, Conformal Field Theory and String Theory, blogging from Paul Cook.

Introduction to Collider Physics, a summer program aimed at graduate students, taking place at the Institute in Princeton.

This year’s SLAC summer institute is on Gravity in the Quantum World and the Cosmos. Sean Carroll is lecturing there and may have more to say about it over at Cosmic Variance.

There’s a Summer Institute going on in Taipei, and a summer school in Dubna.

The summer meeting in Oporto has taken place. I’d love to hear from anyone who was there about Graeme Segal’s lectures.

The Simons Workshop in Stony Brook has started, leading off with a talk by Cumrun Vafa on The Swamp Surrounding the Landscape. He seems to be suggesting that theorists should be spending their time investigating the “swamp” of possible effective field theories for which it is unknown whether they can be the low energy limit of a string theory. Why he thinks its a good idea to try and lead the field into a “swamp” is very unclear to me, although one could argue it is already there anyway….

Update: A commenter properly takes me to task for ignoring what’s going on down under. There’s been a Conference in honor of Ross Street’s 60th birthday, together with one workshop on categorical methods and another one on noncommutative geometry and index theory, all covered extensively by bloggers over at the String Coffee Table.

This week I’m in Seattle, among other things attending a Summer Institute in Algebraic Geometry sponsored by the AMS. This is the latest in a series of large summer conferences on algebraic geometry that have taken place about every ten years. The last one was in Santa Cruz in the mid 90s, the one before that at Bowdoin in the mid 80s. This one is being billed as “the largest algebraic geometry meeting in the history of the world”, with about 320 mathematicians here this week, and a total of around 600 planning on showing up for at least part of the three weeks during which the conference is taking place. The full schedule of talks is on-line, and copies of speaker’s notes and transparencies should soon be appearing there.

The main topic of the first week is billed as “interactions with physics”, but there’s actually not a whole lot of that going on here. The organizers originally hoped that Robbert Dijkgraaf would be lecturing this week, but that didn’t work out. Kentaro Hori of Toronto is giving a series of three talks on mirror symmetry, and some of his lecture notes are already on-line. Rahul Pandharipande started off the conference with the first in what looks like it will be a very interesting series of lectures on Gromov-Witten invariants. This has now become a huge subfield of algebraic geometry, with many ramifications, some of which have been inspired by physics, and there continues to be active interaction between math and physics around this subject. Many of the talks in the afternoon parallel sessions are also related to this topic.

An unrelated note: Lee Smolin has a rather philosophical, but interesting, new preprint out entitled The case for background independence

Several months ago Erick Weinberg had told me that his recollections of the story of the calculation of the Yang-Mills beta function were different than David Politzer’s. Erick actually did independently do the beta function calculation (for the case with scalars). At the time we talked he thought he had gotten the sign right, but the coefficient wrong, but now he has checked it and says the coefficient is right. He has posted his thesis on the arXiv, equation 6.68 is the beta-function. From the comments after this equation, you can see that he was aware that this meant that perturbation theory would break down in the infrared. Like ‘t Hooft though, who also did this kind of calculation, he wasn’t aware of the significance of asymptotic freedom in the ultraviolet for explaining the SLAC deep-inelastic scattering results.

Fabien Besnard has a new blog (in French), which is quite interesting. His latest post is a report from a Paris conference celebrating the Einstein centenary. He’s shocked by the comments of string cosmologist Thibault Damour that Popper was wrong, scientific theories don’t need to be falsifiable.

The New York Times has an article about the actress Danica McKellar and her work in mathematical physics. She was working with Lincoln Chayes while an undergraduate at UCLA. Lincoln and his then-wife Jennifer (also a mathematical physicist, now at Microsoft Research) were graduate students with me at Princeton. I have many happy memories of them and their impressive leather outfits, and our joint trips down to the punk-rock club City Gardens in Trenton.

Over at the new Cosmic Variance blog, Sean Carroll has posted a defense of string theory against what he sees as disdain, resentment and disparaging remarks from other physicists, a defense he entitles Two Cheers for String Theory. I’ve written a couple of comments over there, and maybe this will lead to an interesting discussion. But I’ll be traveling a lot of the time during the next week and a half, so my ability to participate in such a discussion, here or over there, may sometimes be limited. We’ll see what happens….

It has been almost exactly a year since Hawking gave a talk in Dublin claiming to have found a resolution of the black hole information paradox. Tonight a preprint giving some details of his argument has appeared.

I’ll leave to the quantum gravity experts the evaluation of exactly how convincing Hawking’s argument is. It is based on using the Euclidean quantum gravity framework, which Hawking refers to as “the only sane way to do quantum gravity non-perturbatively”. I’ve always been fond of the idea that you have to think about QFTs using a Euclidean signature for the background, so I wouldn’t argue with him about this point, but I assume others will.

Sean Carroll, of Preposterous Universe, has joined forces with Mark Trodden (of Orange Quark), and new bloggers SLAC particle phenomenologist JoAnne Hewett, USC string/brane theorist Clifford Johnson, and Chicago cosmologist Risa Wechsler. They’ll be collaborating on a new weblog entitled Cosmic Variance, and I’m looking forward to following what they do with it.

This may be part of a new trend of consolidation in the physics weblogging industry, following the lead of the String Coffee Table and the massive, multi-national, government-subsidized Quantum Diaries site. Will small, independent, artisanal producers like myself be able to compete with huge combines like Cosmic Variance, with their professional software and expensive ($6.95/month!) web-hosting services? Or will we be driven out of business as our profit margins are squeezed to the vanishing point? Wait a minute, I’m not making a profit at this anyway…

Actually, today I’m in Austin, Texas on personal business. I suppose I should be looking up Jacques to see if he, Lubos and I can organize an even bigger competing organization.

A colleague informs me that the latest New York Review of Books contains a letter from one of the most well-known mathematicians in the U.S.

Most of the talks at Strings 2005 about the landscape have now taken place, although there’s at least one more this afternoon by Dine. Frederik Denef gave a survey talk entitled Constructions and distributions of string vacua. One amusing thing he does is note that even in toy models with these exponentially large numbers of states, counting the number of states with vacuum energy less than some bound is computationally an NP-hard problem. He describes a wide range of constructions that people have come up with to fix the moduli, concluding that you can “throw enough ingredients together to get sufficiently complicated potential, and this will fix moduli, at least at effective field theory level”, but that these constructions are “ugly”. He then goes on to survey various results about the statistical distributions of these states, and ends by announcing a workshop in Trieste next spring on “String Vacua and the Landscape.”

The talk on Is the number of string theory vacua finite? by Michael Douglas makes Denef’s survey of distributions of vacua kind of pointless. The number of such vacua is definitely infinite, which ruins ones ability to get a probability distribution by counting vacua. Douglas hopes that by putting in a cutoff on the diameter and volume of the compactification space, as well as the size of the vacuum energy, he can make the number of vacua finite. He explains this conjecture, for which the evidence is not very compelling.

Even if he gets the finiteness he hopes for after imposing these cutoffs, the problem then is that the distributions of vacua depend strongly on the cutoff and are peaked at the cutoff value. This is what happens in examples that Kachru talked about at the conference. Douglas is reduced to arguing that “it seems a priori plausible that cosmological selection could depend on the volume of the extra dimensions”, i.e., that somehow the Big Bang would get rid of the problem that his program is predicting large compactification spaces when he wants small ones. There seems to be no reason for this other than wishful thinking. One thing is clear though now: it makes no sense to spend time computing distributions of these vacua, since this gives a result you don’t want. In this game though, it’s not like you give up on your research program when it gives results that don’t look at all like the real world.

The August issue of Discover magazine is out, with a cover story entitled “Is String Theory About to Snap?”. The editors of the magazine describe how they recently became aware of the controversy over string theory when they organized a celebration of Einstein in Aspen last summer. They quote Lawrence Krauss as telling them “String theory may be in a worse position now regarding being testable than it has been at any time in the past 20 years.” To get a response to this, they asked Michio Kaku to write something for them. They refer to him as a “cofounder of string theory”, which I suspect some people might object to. Presumably they meant to repeat what is in their profile of him, which calls him a “cofounder of string field theory.”

Kaku’s article is entitled Testing String Theory, and is a thoroughly intellectually dishonest piece of writing, designed to mislead anyone without expertise in what is at issue here. He succeeded in misleading whoever wrote the blurb for the article which goes: “No experiment has ever allowed us to test whether any of the assumptions of string theory are true. That is about to change.” No it’s not. None of the experiments Kaku mentions will “allow us to test whether any of the assumptions of string theory are true”.

As I’ve explained in detail on other occasions, the simple fact of the matter is that string theory does not make any predictions, unless one adopts a definition of the word “prediction” different than that conventional among scientists. A scientific prediction is one that tells you specifically what the results of a given experiment will be. If the results of the experiment come out differently, the theory is wrong. String theory can’t do this, since it is not a well-defined theory, but rather a research program that some people hope will one day lead to a well-defined theory capable of making predictions.

At places in the article Kaku qualifies his claims of “predictions”, for instance saying near the beginning of the article that certain experiments “could provide significant evidence that would support string theory” (note all the qualifiers in this phrase: “could”, “significant evidence”, “support”) but that “the rub is that all the new evidence, no matter how compelling, will still provide only indirect proof.” He soon abandons his qualified language and starts talking about the following topics:

1. Gravitational waves: He says of gravitational waves created in the Big Bang: “String theory predicts the frequencies of such waves”, and that this prediction will be tested by LISA. I don’t know specifically what he has in mind here, but I know of no way to use string theory to make a specific prediction of the spectrum of gravitational waves that LISA will see. The only things he mentions are inflation and epkyrotic scenarios, the first of which has nothing to do with string theory, the second very little.

2. The LHC: Kaku discusses the possibility that superpartners exist, but does note that you don’t need string theory to have these. He also discusses possible Tev-scale particle physics effects of extra dimensions, without mentioning that string theory makes no predictions at all about what these extra dimensions are like, or even what their size is. There is absolutely no reason other than wishful thinking to expect extra dimensions in string theory of a size invisible until now, but visible at LHC energies.

3. Laboratory tests of the inverse-square law: Kaku claims: “according to string theory, at small scales like a millimeter, gravity might hop across higher dimensions and perhaps into other, parallel universes”. This is a load of nonsense. String theory predicts no such thing. It may be consistent with this, purely because it is consistent with anything. He does go on to say “Perhaps the additional dimensions would show up only on smaller scales — string theory is still somewhat vague about this prediction.” “Somewhat vague”??? As far as I know string theory makes no prediction about this at all, except that most string theorists expect effects to show up below 10^-33cm, not 10^-1cm.

4. Dark matter searches: according to Kaku “Once particles of dark matter are identified in the laboratory, their properties can be analyzed and compared with the predictions of string theory.” Only problem is string theory makes no such predictions. He’s talking about neutralinos, but in string theory the neutralino mass could be absolutely anything. After discussing these string theory”predictions” about dark matter, he goes on to speculate that maybe there is no dark matter anyway, just “huge clumps of shadow matter in a parallel universe, causing our galaxies to form in mirror-image locations”, then admits that such an idea is incapable of ever being experimentally tested.

After going through all this, he saves the real kicker for the end: “Some theorists, myself among them, believe that the final verdict on string theory will not come from experiments at all”. So he doesn’t even believe in any of the nonsense he has been spouting. He admits that “The principal reason predictions of string theory are not well-defined is that the theory is not finished.” So the earlier talk of “predictions” is now no longer operative. He goes on to invoke the pipe dream that someday someone will come up with a finished version of string theory that will predict precisely the standard model, neglecting to mention that there’s not the slightest evidence that this is a realistic possibility. On the contrary, all the evidence now points to the conclusion that, if string theory makes sense at all, it has an infinity of different vacuum states, and is probably a radically non-predictive theory. Impressive that Kaku could write a whole article about the prospects of string theory, and somehow neglect to mention the huge and very relevant controversy surrounding the idea of the landscape. Do you think he hasn’t heard about it?