Not Even Wrong

I’ve been traveling in Italy for the past ten days, and gave talks in Rome and Pisa, on the topic “Is String Theory Testable?”. The slides from my talks are here (I’ll fix a few minor things about them in a few days when I’m back in New York, including adding credits to where some of the graphics were stolen from). It seemed to me that the talks went well, with fairly large audiences and good questions. In Pisa string theorist Massimo Porrati was there and made some extensive and quite reasonable comments afterwards, and this led to a bit of a discussion with some others in the audience.

I don’t think the points I was making in the talk were particularly controversial. It was an attempt to explain without too much editorializing the state of the effort to connect the idea of string-based unification of gravity and particle physics with the real world. This is something that has not worked out as people had hoped and I think it is important to acknowledge this and examine the reasons for it. In one part of the talk I go over a list of the many public claims made in recent years for some sort of “experimental tests” of string theory and explain what the problems with these are.

My conclusion, as you’d expect, is that string theory is not testable in any conventional scientific use of the term. The fundamental problem is that simple versions of the string theory unification idea, the ones often sold as “beautiful”, disagree with experiment for some basic reasons. Getting around these problems requires working with much more complicated versions, which have become so complicated that the framework becomes untestable as it can be made to agree with virtually anything one is likely to experimentally measure. This is a classic failure mode of a speculative framework: the rigid initial version doesn’t agree with experiment, making it less rigid to avoid this kills off its predictivity.

Some string theorists refuse to acknowledge that this is what has happened and that this has been a failure. Most I think just take the point of view that the structures uncovered are so rich that they are worth continuing to investigate despite this failure, especially given the lack of successful alternative ideas about unification of particle physics and gravity. Here we get into a very different kind of argument.

It was very interesting to talk to the particle physicists in Rome and Pisa. They are facing many of the same issues as elsewhere about what sort of research directions to support, with string theory often being pursued as an almost separate subject from the rest of particle theory, leading to conflict over resources and sometimes heated debates between them and the rest of the particle physics community. Many people were curious about how things were different in the US than in Europe, but I’m afraid I couldn’t enlighten them a great deal, mainly because I just don’t know as much about the European situation, although I’ve started to learn more about this on the trip. Several wondered if the phenomenon of theorists going to the press to make overhyped claims about string theory was an American phenomenon. I hadn’t really noticed this, but it does seem to be true. While the hype starts in the US, it does travel to Europe, with the US very influential in this aspect of culture as in many others. In the latest issue of the main Italian magazine about science, there’s an article explaining how certain US theorists have finally figured out how to test string theory with the new LHC…

John Horgan keeps moving his blogging activities to different locations, the latest one is here.

For a truly sad and distressing story about what has happened to Billy Cottrell (who was mentioned snarkily by me long ago here), see this LA Weekly article and a Clifford Johnson posting. The abuse of people going on in this country associated with labeling them “terrorists” is just appalling and deeply shameful.

More from Steinn Sigurdsson on Yarn Theory.

Cern Courier reports on the recent Axion workshop at Princeton and the 2006 Quark Matter conference in Shanghai.

Lee Smolin’s book is out in the UK, here’s a review from the Financial Times.

The latest London Mathematical Society newsletter has a review of Not Even Wrong.

David Ben-Zvi was here last week and gave a wonderful colloquium talk on Langlands duality, loop spaces and representations of real groups. Much of was somewhat general philosophy about a new way of thinking about these topics, and this was quite compelling, although I need to find a sizable chunk of time to sit down and really understand what he is doing. If I can do this, maybe I’ll then take a stab at trying to explain this here. He did convince me that one needs to think not only about stacks, but derived stacks. There’s a long foundational document about this by Jacob Lurie (see here), something more readable from Bertrand Toen.

This semester Edward Frenkel is running a seminar on Topics in the geometric Langlands program. The slides of a talk by Ben Webster that are there are wonderful. One problem with this field has always been how unreadable much of the material about is. People like Webster and Ben-Zvi are starting to do a great job of explaining what is going on in a form that others have some chance of following.

Later this month the IAS will have a conference related to this topic, next year a whole program.

I’ll be travelling most of the next week and a half or so, so blogging will be light to non-existent. Behave.

There’s a short memoir out this evening on the arXiv by Peter Freund about the algebraist Irving Kaplansky, universally known as “Kap”, who died last year at the age of 89. Freund worked with Kaplansky at Chicago during the mid-seventies on the classification of Lie superalgebras, and comments about the relations between math and physics at that time. He also claims that Kaplansky told him with assurance that Hopf algebras couldn’t possibly be of relevance to physics, and that Andre Weil was the greatest living mathematician, since he called all the courses he taught “mathematics”, and lived up to this title. Freund also tells a well-known story about a talk by Weil at Chicago that he heard about first-hand from Kaplansky.

Freund’s piece is based on his talk at the recent memorial event held for Kaplansky in Berkeley at MSRI. His student Hyman Bass has a wonderful presentation describing Kaplansky’s life and work.

I have my own personal recollections of Kap since he was director of MSRI the year that I was a postdoc there (1988-9), a year during which I unfortunately had only a few short conversations with him. The conversation with him I remember best was our first, which occurred on the phone. In early 1988 I was working part-time teaching Calculus at Tufts and had applied for several full-time mathematics jobs for the next year, not at all sure that there was any chance this would work out, since my Ph.D. and first postdoc had been in physics. When the call came from Kap offering me a job at MSRI for the next year I was elated, partly because Berkeley is one of my favorite places to live as well as being an excellent place to work in both mathematics and physics. During our conversation Kap told me a bit about his work on and continued interest in supersymmetry. I didn’t really have the heart to tell him that because my own inclinations are so geometric, I’d always found supersymmetry and superalgebras a tantalizing but very frustrating subject.

Many string theorists seem to have decided to react to the criticisms of string theory that have recently been getting a lot of attention by going to the press with claims to have experimental tests of string theory that can be performed in the very near future.

The latest of these claims has nothing at all to do with the aspect of string theory that has come under criticism, its failure as a unified theory of gravity and particle physics, but instead involves the conjectural use of string theory as an approximation method in QCD. The main problem with this idea so far is that it involves not QCD but a related theory (N=4 supersymmetric Yang-Mills), and it is very unclear exactly what the relation is between the calculation and the real world. For some earlier comments about this, see here. John Baez also has a summary, and the Backreaction blog of Sabine Hossenfelder and Stefan Scherer has a very extensive explanation here.

Last week the AIP Physics News site carried a story entitled String Theory Explains RHIC Jet Suppression, which dealt with recent work by Hong Liu, Krishna Rajagopal and Urs Wiedemann concerning the jet quenching parameter, which describes how charmed quarks move through a quark-gluon plasma. In the AIP story, Rajagopal claims that their calculation “agrees closely with the experimentally observed value”, and that other related calculations “make a specific testable prediction using string theory.” This story was picked up by Scientific American, which has a story by JR Minkel. According to Scientific American, “trying to fit the QCD-like theory to reality makes the results only semi-precise, Rajagopal says,” alluding to the problem of doing the calculation in the wrong theory. Maldacena is quoted about this as follows:

It’s like saying you are trying to study water, but instead you are studying alcohol… We certainly know it’s not the correct theory, but maybe it behaves in the same way.

Theorist Ulrich Heinz is even more skeptical:

Even if any of the numbers worked out by accident, I don’t think it would validate the approach… If they predict the color of an apple, and somebody looks at a pear and finds it has the same color, would you say that the prediction was correct?

Other recent claims by Shiu et al. and Distler et al. to be able to make predictions using the string theory approach to unifying physics are covered in the latest issue of Plus magazine, in a story entitled Stringent Tests. According to this story

It seems that string theory, so far the strongest contender for a physical “theory of everything”, may soon be put to the test for the first time. Two separate teams of physicists have just published work describing how to compare the theory’s predictions with reality….

Neither of the two new tests will be capable of verifying string theory once and for all. If the results concur with its predictions, then this is just some further evidence for its correctness, not absolute proof. But the tests’ ability to falsify string theory, or at least certain aspects of it, means that a philosophical barrier has been overcome.

On a somewhat related note, I’ll soon be traveling to Italy, giving talks in Rome and Pisa on the topic of “Is String Theory Testable?”.

The March issue of Physics Today is now available. It contains a piece by Steven Weinberg based on a banquet talk he gave to a group of postdocs. He describes his own memories of his time as a postdoc, writing that “Many of us were worried about how difficult it seemed to make progress in the state that physics was in then.” This was the heyday of S-matrix theory and he comments:

Some people thought that the path to understanding the strong interactions led through the study of the analytic structure of scattering amplitudes as functions of several kinematic variables. That approach really depressed me because I knew that I could never understand the theory of more than one complex variable. So I was pretty worried about how I could do research working in this mess.

He describes envying the previous generation of 10-15 years before his time, that of Feynman, Schwinger, Dyson, and Tomonaga, thinking that all they had had to do was sort out QED, and speculates that they in turn had envied the generation before them since quantum mechanics was even easier. I can see that he’s trying to provide encouragement, ending with

So the moral of my tale is not to despair at the formidable difficulties that you face in getting started in today’s research… You’ll have a hard time, but you’ll do OK.

Postdocs in high energy physics these days do need some encouragement, but I also think they need some recognition from their elders that they’re facing a different situation than that faced by earlier generations. Coming into a field that has not seen significant progress in about 30 years is a different experience than what Weinberg or previous generations of particle physicists had to deal with. High energy physics is now facing some very serious problems, of a different nature than those of the past, and I think these deserve to be mentioned.

In the same issue, Weinberg makes another appearance, in an exchange of letters with Friedrich Hehl about the torsion tensor in GR. Hehl takes him to task for his comments in a previous letter that torsion is “just a tensor”, pointing out that it can be thought of as a translation component of the curvature. Weinberg responds that he still doesn’t see the point of this:

Sorry, I still don’t get it. Is there any physical principle, such as a principle of invariance, that would require the Christoffel symbol to be accompanied by some specific additional tensor? Or that would forbid it? And if there is such a principle, does it have any other testable consequences?

Actually, Weinberg is rather well-known for taking the point of view that GR is just about tensors, and that their geometrical interpretation is pretty irrelevant, so it’s not surprising that he doesn’t see a point to Hehl’s comment. In his well-known and influential book on GR, he explicitly tries to avoid using geometrical motivation, seeing this as historically important, but not fundamental. To him it is certain physical principles, like the principle of equivalence, that are fundamental, not geometry. There’s a famous passage at the beginning of the book that goes:

However, I believe that the geometrical approach has driven a wedge between general relativity and the theory of elementary particles. As long as it could be hoped, as Einstein did hope, that matter would eventually be understood in geometrical terms, it made sense to give Riemannian geometry a primary role in describing the theory of gravitation. But now the passage of time has taught us not to expect that the strong, weak and electromagnetic interactions can be understood in geometrical terms, and too great and emphasis on geometry can only obscure the deep connections between gravitation and the rest of physics.

This was written in 1972, just a few years before geometry really became influential in particle physics, first through the geometry of gauge fields, later through geometry of extra dimensions and string theory. I recall seeing a Usenet discussion of whether Weinberg had ever “retracted” these statements about particle physics and geometry. Here’s an extract from something written by Paul Ginsparg, who claims:

back to big steve w., when he wrote the gravitation book he was presumably just trying to get his own personal handle on it all by replacing any geometrical intuition with mechanial manipulation of tensor indices. but by the early 80’s he had effectively renounced this viewpoint in his work on kaluza-klein theories (i was there, and discussed all the harmonic analysis with him, so this isn’t conjecture…), one can look up his research papers from that period to see the change in viewpoint.

There’s an article in this week’s Science magazine by Adrian Cho entitled Dreams Collide With Reality for International Experiment. It’s about DOE Undersecretary Orbach’s warning to HEPAP (mentioned here) that current plans were too optimistic about the time-scale for the ILC, leaving a potentially dangerously long period with few US HEP experiments in progress.

Some physicists who had proposals for experiments (BTeV and RSVP) that were canceled in favor of going ahead full steam with the ILC were not amused:

Meanwhile, Orbach’s call for a program of smaller projects evoked jeers from researchers whose experiments had been cut. “This is really stupid and very frustrating because we had a program,” says Sheldon Stone, a physicist at Syracuse University in New York who worked on an experiment called BTeV that would have run at the Tevatron collider at Fermilab.

While experimentalists are worrying about the short-term, string theorists seem to be taking the long view. In his talk on String Theory: Progress and Problems at the recent conference celebrating the centennial of Yukawa and Tomonaga, John Schwarz ends with the conclusion

Even if progress continues to be made at the current rapid pace, I do not expect the subject to be completely understood by the time of the Yukawa-Tomonaga bicentennial.

I don’t find his claims about a current rapid pace of progress very convincing, and the idea of the entire next century of theoretical particle physics being dominated by the kind of unsuccessful more and more complicated string theory constructions we’ve seen for the last 25 years doesn’t seem like something to look forward to.

Turning from the difficulties of the future, Howard Georgi gave a wonderful talk on The Future of Grand Unification at the same conference, which was actually mainly about the past, largely devoted to telling the story of how he and Glashow came up with the first GUT models. He emphasizes the kinds of manipulations of representations of Lie algebras that he and Glashow were masters of and used to construct many different kinds of models. There’s also an advertisement for his wonderful book on the subject, the text for his course where I first many years ago encountered this subject. This semester I’m teaching my own course on the same material, from a rather different point of view, emphasizing geometry. It remains one of the most beautiful and central parts of modern mathematics as well as physics.

There’s a new issue of Symmetry magazine out. It is a bimonthly magazine about particle physics put out by SLAC and Fermilab, and often has interesting and informative articles. But, even though I generally read the whole thing when it comes out, I’ve always had a feeling that, somehow, there was something missing. This latest issue kind of explains why.

In a very well-done article about the BaBar experiment and B-physics, John Ellis is quoted, explaining the origin of the name “penguin diagram” as follows:

That summer, there was a student at CERN, Melissa Franklin, who is now an experimentalist at Harvard. One evening, she, I, and Serge went to a pub, and she and I started a game of darts. We made a bet that if I lost I had to put the word penguin into my next paper. She actually left the darts game before the end, and was replaced by Serge, who beat me. Nevertheless, I felt obligated to carry out the conditions of the bet.

For some time, it was not clear to me how to get the word into this b quark paper that we were writing at the time…. Later…I had a sudden flash that the famous diagrams look like penguins. So we put the name into our paper, and the rest, as they say, is history.

If you look up the original source of this, you find a bit more of an explanation of where that “sudden flash” came from. Here’s the full second paragraph:

For some time, it was not clear to me how to get the word into this b quark paper that we were writing at the time. Then, one evening, after working at CERN, I stopped on my way back to my apartment to visit some friends living in Meyrin where I smoked some illegal substance. Later, when I got back to my apartment and continued working on our paper, I had a sudden flash that the famous diagrams look like penguins. So we put the name into our paper, and the rest, as they say, is history.

Lots of other articles worth reading in the magazine, including one by an undergraduate at Humboldt State in California about taking a science course that explained how physical reality is stranger than any fiction, ending with the anthropic principle and the theory of evolutionary cosmology. The course is called Cosmos, and you can check out its web-site. Maybe I’m wrong, but I get the impression that John Ellis is not the only physicist out there who may have at one time or other sampled the agricultural products of Humboldt County…

The Princeton Physics department colloquium on “New Neutrino Oscillation Results from the MiniBooNE Experiment” scheduled for this Thursday has been canceled. I wonder what is going on with that. Have they not opened the box yet on their result, or did they do so and have a problem with what they found? Other talks about MiniBooNE results are still scheduled for March 14th in Manchester and March 17th in Montreal (the abstract of this last one is ambiguous about whether there will be results “MiniBooNE’s oscillation path and what may lie beyond, will be presented”) [Ooops, that last one was 2006, thanks Marco]. The MiniBooNE colloquium has been replaced by a Nikita Nekrasov talk on “The Mathematics of String Theory”. Not sure if I’ll make a trip down to Princeton that day; Nekrasov’s talks are usually worth hearing, but I’d prefer to hear a more technical talk about his recent work, which is quite interesting.

John Baez’s latest “This Week’s Finds” is largely about the controversy over string theory and my book and Lee Smolin’s. As usual, John’s take is quite level-headed. Faced with people who claim that string theory is “the only game in town”, John advocates leaving town, striking out and looking for another place to live and work, maybe even starting a new one. Some comments about this at his blog.

On Friday at Fermilab Michael Chanowitz gave a talk on Precision Electroweak Data and the Direct Limit on the Higgs Mass. He updates previous work on these fits, including recent CDF and D0 values for the top and W masses. The new, presumably better, top quark mass values from CDF and D0 are lower than those of a couple years ago, with recent CDF results about 170 GeV. The main interest in these fits is that they give you a predicted value of the Higgs mass, although not a very accurate one. The lower top mass drives down the predicted Higgs mass, to the point where it is starting to get in trouble with the fact that LEP showed it had to be heavier than 114 GeV at 95% confidence level. The fits to all data give a most likely value for the Higgs mass of 85 GeV, with only an 18% probability of it being over 114 GeV.

Chanowitz devotes a lot of attention to the one measured value that deviates the most (3 standard deviations) from that predicted by the other data: the forward-backward asymmetry in b-quark production at the Z-pole. If you throw this out from the fit, on the grounds that it is less reliable than the other data since it doesn’t match the SM as well, your Higgs mass really goes down, to a most likely value of 48 GeV, with only a 2% chance of it being above 114 GeV. Hard to know what to make of this, evidently it’s hard to come up with a model that would explain the anomalous forward-backward asymmetry while not ruining the rest of the fit. Maybe this is a first indication that the SM is not the full story….

Update: This just in, from Michael Nielsen. Seems like this is the month for Fields Medalists to become bloggers. First Alain Connes, now it’s Terry Tao. Will Grisha Perelman be next?

Update: Well, not Grisha Perelman, but today the latest mathematician blogger is David Goss. Goss is a specialist in the mathematics of function fields over finite fields, and his first post includes comments about how ideas have entered this very different field from physics, as well as remarks about the work of Bost and Connes that expresses zeta-functions in term of partition functions of statistical mechanical systems.

Update: A couple more. The talks at the recent AAAS session on A New Frontier in Particle Physics are available (some in a weird format I’ve never seen before which works on Internet Explorer, not Mozilla [now fixed, just a powerpoint slideshow]). Also some remarks by DOE’s Raymond Orbach at the HEPAP meeting where he seems to be raising an important question: even if the ILC is built, it may not be ready until the mid-2020s or later, and the Tevatron and SLAC B-factory will be closing down relatively soon, so “I would like to re-engage HEPAP in discussion of the the future of particle physics. If the ILC were not to turn on until the middle or end of the 2020s, what are the right investment choices to ensure the vitality and continuity of the field during the next two to three decades and to maximize the potential for major discovery during that period?”

Update: Fermilab director Pier Oddone discusses the Orbach letter and the need for planning for the possibility of a long wait for the ILC in today’s Director’s Corner at Fermilab Today:

I am requesting a steering group composed of members of our laboratory and the community under the leadership of Deputy Director Kim to produce a detailed plan for positioning the field and Fermilab in the next two decades for a robust program of discovery based on accelerators. I am asking for such a plan by August 1st.

Over at Dynamics of Cats, Steinn Sigurdsson has a posting on Yarn Theory, to some extent a review of Lee Smolin’s The Trouble With Physics. Steinn is an astrophysicist, but started out life as a string theorist before getting disillusioned with the subject. His account of his early career is well worth reading, doing a good job of capturing the atmosphere around 1990 at Caltech, a major center of string theory research. He was working on orbifold heterotic string compactifications, discouraged by how many there were. Not much has changed…

His general point of view on string theory is that it has led to the discovery of a family of unified theories, but that it is missing some basic principle that would tell us which is the true theory and why. He is sympathetic to Smolin’s criticisms of the dysfunctional way theoretical research is being pursued, focusing efforts on one very speculative idea and making it unlikely that people who chose to try and work on others will be able to make careers for themselves:

… a lot of people will not only not believe that this is a real problem, they will make sure nobody else believes you either. Someone out there quite likely is already on the right track to the true theory, but their odds of survival in the current academic system are not wonderful. We may just have to wait a generation or two for a good approach to be rediscovered, which is a shame, cause some of us want to know! Now!!

It is the same market flaw that gives us beautiful flawless large red apples in supermarkets – with no taste. To get the old intense flavour varieties that everyone loves when they taste, we would have to choose small bruised discoloured apples when we shop, and leave the flawless big red apples with no taste in the bins. But collectively we do not, and the market responds. All for the fear of being the one department head consumer to go home with an occasional rotten apple. The real shame is that the big red shiny tasteless apples are rotten just as often, they just look so good sitting there, waxed and sprayed, in the bin. ‘Course if you only get to buy one apple every three years you learn to be very conservative in your choice; don’t want a rotten or even tart apple this decade.

I think Steinn gets to the rotten core of the problem here. There are very good reasons for conservatism in deciding what kinds of research to encourage, but with the very difficult situation that particle physics now finds itself in, the standard mechanisms for making these decisions have led to a seriously problematic situation. There are various things one could imagine doing to help get out of this, but even getting started on a discussion of them first requires that the powers-that-be in the field acknowledge the existence of a problem, and that has yet to really happen.

On a completely different subject, there’s a new preprint by Michael McGuigan which manages to cite both Not Even Wrong (the book), and a Lubos Motl blog entry. The citation of my book seems unnecessary, surely there are other sources critical of string-based unification that have priority. The article is about the “see-saw” mechanism for getting the right magnitude of the cosmological constant, and it is for this that Lubos’s blog gets a citation. This does seem to be a more promising idea about the CC than many. I for one think it will be a wonderful development if the field of particle theory turns around, stops promoting pseudo-science justified by the Weinberg anthropic CC “prediction”, and heads instead in a more promising direction, all based on an entry in Lubos’s blog…

Alain Connes is now a blogger, contributing to the new Noncommutative Geometry blog. There will be a conference in his honor next month in Paris.

Today and tomorrow there’s a HEPAP meeting going on in Washington, with some of the presentations available here. Excluding the SLAC linac, which is getting moved around in the budget, the DOE HEP FY208 budget request is for $782 million, a very healthy more than 16% increase over FY2006. There’s also an HEP demography study being discussed, which somehow involves “tagging” and “tracking” HEP physicists, and they seem to be having trouble with the tagging. Not clear what sort of analysis will be performed on the data once all HEP physicist tracks have been reconstructed.

Next month on the 28th there will be a debate on the topic of

Does string theory merge general relativity and quantum mechanics to explain the origin of time, space, and the universe? Or is it extraordinarily complex mathematics that has nothing to do with physics, and so explains nothing?

between Lawrence Krauss and Brian Greene at the Smithsonian Natural History Museum in Washington. I recall attending a similar debate at the Museum of Natural History almost exactly six years ago here in New York, also featuring Krauss and Greene. Some things seem destined to never change…