Not Even Wrong

I’ve been known to claim that string theory makes no experimental predictions, so this evening thought I better take a look at a preprint that just appeared entitled GUTs and Exceptional Branes in F-theory – II: Experimental Predictions. The abstract claims that to have found “a surprisingly predictive framework”.

This paper is 200 pages long, and a companion to part I, which was 121 pages. For part I, there’s a posting by Jacques Distler that explains a bit of the very complicated algebraic geometry going on. Making one’s way carefully through the entire 200 pages of the new paper looks like a very time-consuming project, so I thought I better start by identifying what the experimental predictions are. These days, one expects experimental predictions to say something about LHC physics, but I don’t see anything about that in the paper. Perhaps this is because, except for some comments in section 16, it appears that the authors are studying a model with exact supersymmetry.

Looking at the introduction and conclusion sections of the paper, the only predictions I can see are for neutrino masses, and there are two of them. Either .5 x10^{-2 +/-.5} eV or 2 x 10^{-1 +/- 1.5} eV is given for the neutrino mass, with the error bars just those due to an unknown value of one of the geometrical parameters involved. There’s no mention of which neutrino is being discussed, and as far as I can tell this is just an order of magnitude estimate of the neutrino mass scale, one which the author’s describe as “somewhat naive”, noting that “factors of 2 and π are typically beyond the level of precision which we can reliably estimate”. It’s unclear to me whether or not other mechanisms giving quite different neutrino masses would also fit into the author’s model.

Maybe I’m missing something and an expert can help me out, but I’m not seeing anything here of the sort one would normally describe as an experimental prediction. There’s certainly nothing falsifiable at all about the model, since one knows from limits on neutrino masses and measurements of oscillations that the neutrino mass scale has to very roughly be in this kind of range. Furthermore, again maybe I’m missing something, but I don’t see any way in which more detailed calculation in this framework can make it any more predictive.

Update: Lubos has a detailed posting about this, and from reading it, it doesn’t appear that the paper has experimental predictions that I missed. I do wonder what a “musculus maximus” is…

Update: For more about this, see presentations at PASCOS 08 here and here. The first describes this as “a modest step” in the direction of predictions, the second doesn’t mention predictions at all.

Most of the time the attention paid here to efforts to popularize physics is restricted to grumpy complaints about the hype surrounding string theory as well as the more general dubious phenomenon of scientists promoting things that are more science fiction than science. Today I’m in a much more positive mood, and thought I’d take the opportunity to make some unusually sunny comments for a change.

One reason for this is that I attended the opening party for my colleague Brian Greene’s World Science Festival Wednesday night at the American Museum of Natural History, and several people have told me about the enthusiastic reception the festival events have been getting. I was hoping to attend one of the events, but it was already sold out.

Things started off during the day Thursday with a World Science Summit here at Columbia featuring a speech by Mayor Bloomberg, and award of the new Kavli prizes. That evening, at the museum event, Brian, Fred Kavli and Senator Schumer all spoke, and the crowd was entertained by the choir of the Abyssinian Baptist Church.

Among the people I got a chance to talk to at the event were several string theorists. One of these was Jim Gates, who I had the pleasure of first meeting last year down in Orlando. He was there with his wife, just back from South Africa where he is involved with the African Institute for Mathematical Sciences.

Gates told me that his collection of video lectures with impressive graphics explaining quantum mechanics, general relativity and superstring theory called Superstring Theory: The DNA of Reality has been selling well, generating over a million dollars in sales, despite not being able to get it reviewed in major publications. Strong evidence of its popularity comes from the fact that if you google “The DNA of Reality” you get an impressive variety of sources for pirated versions. Evidently he has done an excellent job of reaching a wide audience with this material. From conversations with him I know that we’re in closer agreement than you would guess, sharing an interest in the mathematics behind supersymmetry and a skepticism about extra dimensions.

I have mixed feelings about the highly enthusiastic promotion of certain speculative ideas about physics involved both here and in some of the World Science Festival events, but it’s undeniable that these are reaching a lot of people and getting them excited about science. Perhaps I can convince Jim to market what could be the ideal package: his videos to get people excited and enthusiastic about the open problems in physics, and my book to give them some skepticism about the solutions now being promoted…

Update: For an article describing what happened at the World Science Festival program about unification and string theory, see here.

Since 1968 SLAC has been maintaining a database of HEP documents called SPIRES, and this has become one of the main tools used by anybody searching the HEP literature. In recent years CERN has developed a much more modern document management system known as CDS Invenio. The two projects are now being brought together into something to be called INSPIRE, which will combine the best of both, in particular making the SPIRES data available through the more modern Invenio software.

There’s a press release from DESY about this here, and an alpha version is up and running here. The current state of the project is that most of the SPIRES functionality has been reproduced, and they are working on getting a beta version ready of a complete replacement of SPIRES.

Last week at DESY a workshop was held about this, announced as an HEP Information Resource Summit, talks are available here. There were presentations from other HEP information providers, including the APS, commercial publishers and the arXiv. The arXiv presentation discussed their desire to better support blogging, and the role of the blogosphere, including the fact that Garrett Lisi’s paper was the most downloaded article on the arXiv. The current trackback system provides links to 21 discussions of the paper, but due to the Distler/arXiv policy of censoring links to this blog, one that is missing is the discussion here. More and more very worthwhile content is appearing on blogs, so the question of how to make this readily available in a useful form will become an increasingly important one.

Unfortunately, while the arXiv does a good job of bringing together mathematics and physics, there seems to be no discussion of the role of the mathematics literature in the new INSPIRE system. Besides the arXiv, the main database used by mathematicians is the excellent MathSciNet developed by the AMS.

Update: Travis Brooks of SPIRES has a posting about this here.

For the last 15 years the New York City subway has featured “Poetry in Motion”, which places extracts of poetry in subway cars. Starting next month this program will be expanded, joined by Train of Thought, which will add “short quotations in history, philosophy, literature, and science chosen by Columbia University’s Graduate School of Arts and Sciences.” I gather that my colleague Henry Pinkham, a mathematician now dean of the Graduate School, is responsible for this. Of the first two quotations to go up next month, one is dear to my heart, from Galileo:

The book of nature is written in the language of mathematics. Its symbols are triangles, circles, and other geometric figures, without which it is impossible to understand a single word; without which there is only a vain wandering through a dark labyrinth.

Last night a preprint appeared on the arXiv from beyond the grave, an undated manuscript entitled Quantum Gravity, Yesterday and Today, found without any indication of its purpose in the files of Bryce DeWitt, who passed away in 2004.

DeWitt devoted much of his career to the question of how to quantize the gravitational field, beginning back in 1948 when he was a student of Julian Schwinger. He has some interesting comments about the dramatic changes over the years in popularity of research work on GR and quantum gravity:

Most of you can have no idea how hostile the physics community was, in those days, to persons who studied general relativity. It was worse than the hostility emanating from some quarters today toward the string-theory community. In the mid fifties Sam Goudsmidt, then Editor-in-Chief of the Physical Review, let it be known that an editorial would soon appear saying that the Physical Review and Physical Review Letters would no longer accept “papers on gravitation or other fundamental theory.” That this editorial did not appear was due to the behind-the-scenes efforts of John Wheeler.

DeWitt gives some history of his important work on the quantization of gauge theories, which culminated in working out a functional integral method to handle to all orders the ghost terms that Feynman had shown to be necessary. He describes a 1955 offer from the Glenn L. Martin Aircraft Company to fund his research in hopes that it would lead to an antigravity device, one that he didn’t accept. Instead, the Air Force supported his research during the period he was unraveling the story of ghosts, support that ended in 1966 when they finally realized that gravity research was not going to lead to magical results. With the termination of his grant, he could no longer pay page charges to the Physical Review, delaying the publication of one of his papers by a year.

He also has some interesting comments about the DeWitt-Wheeler equation:

… intensive work was carried out in those years on canonical quantum gravity, culminating in an equation that bears my name along with that of John Wheeler who was the real driving force. Research on the consequences of this equation continues to this day, stimulated by work of Abhay Ashtekar, and some of it is quite elegant. But apart from some apparently important results on so-called “spin foams” I tend to regard the work as misplaced. Although WKB approximations to solutions of the equation may legitimately be used for such purposes as calculating quantum fluctuations in the early universe, and although the equation forces physicists to think about a wave function for the whole universe and to confront Everett’s manyworld view of quantum mechanics, the equation, at least in its original form, cannot serve as the definition of quantum gravity. Aside from the fact that it violates the very spirit of general relativity by singling out spacelike hypersurfaces for special treatment, it can be shown not to be derivable, except approximately, from a functional integral. For me the functional integral must be the starting point.

He ends the paper with positive comments on string theory:

In viewing string theory one is struck by how completely the tables have been turned in fifty years. Gravity was once viewed as a kind of innocuous background, certainly irrelevant to quantum field theory. Today gravity plays a central role. Its existence justifies string theory! There is a saying in English: “You can’t make a silk purse out of a sow’s ear.” In the early seventies string theory was a sow’s ear. Nobody took it seriously as a fundamental theory. Then it was discovered that strings carry massless spin-two modes. So, in the early eighties, the picture was turned upside down. String theory suddenly needed gravity, as well as a host of other things that may or may not be there. Seen from this point of view string theory is a silk purse. I shall end my talk by mentioning just two things that, from a nonspecialist’s point of view, make it look rather pretty.

The two things he has in mind are the ability of a single string diagram to sum up a lot of Feynman diagrams, and the use of orbifolds to make possible topology-changing transitions.