Not Even Wrong

I’d been wondering what’s up with Witten and his ongoing work on geometric Langlands. He has been giving talks about this since last summer, and in the past has always quickly produced a paper (often a quite long one) once he has some new result like this that he’s publicly talking about. It had surprised me that it was taking him unusually long to get this written up, but now comes news from Anton Kapustin (via Lubos) that Witten is working on a document 3-400 pages long. This length would certainly explain why it is taking longer than usual, and surely the end result will be something quite interesting. The Kapustin rumor also claims that whatever this 300-400 page thing is that Witten is working on, it’s not a paper. Mysterious… The obvious guess is that it will actually be a book.

The German weekly Die Zeit has an article this week by Max Rauner about string theory, the Landscape, and the controversy over whether this is science or not. My German is rather shaky, but as far as I can tell it’s an intelligent summary of the controversy, emphasizing Susskind and his new book, and quoting many of the usual suspects. The same issue also has an interview with philosopher of science Martin Carrier about the question of whether or not string theory is a science.

Update: Eli Rabett has put up a translation of the article into English on his blog.

There’s an extended version of the interview of me by Susan Kruglinski in the February issue of Discover magazine that is now available, for free, on-line.

Before anybody starts yelling about AdS/CFT or topological strings when they read the headline “No one has a plausible idea about how string theory can explain anything”, I’ll just point out that, yes, it’s certainly plausible that some day string theory will explain something about QCD, and it already has explained some things in mathematics. The headline is a summary of some things I say in the interview, and in context it should have been clear I was talking about the use of string theory to predict anything not already predicted by the standard model.

Update: Harvard string theorist Lubos Motl has posted his commentary on the Discover article. If you read the comment section there, keep in mind that he is deleting comments from anyone who disagrees with him. I encourage anyone new to the current controversy over string theory to read what I have to say, read what Lubos has to say, and carefully look into the scientific issues involved to make your own judgement about what is going on here.

Lawrence Krauss and Leonard Susskind have a letter to the editor in this week’s New York Times Sunday Book Review, complaining about John Horgan’s NYT Book Review essay Einstein Has Left the Building of a couple weeks back. For some discussion of an earlier Susskind-Horgan exchange about another NYT piece of Horgan’s, see here and here.

Krauss and Susskind write that “Horgan evidently sees the two of us as being on opposite sides of an imagined controversy”, but that “the fact is that there is little of substance that we disagree about.” They accuse Horgan of thinking “that reconciling quantum mechanics with Einstein’s theory of gravity is a frivolous pursuit”, whereas “both of us feel that reconciling the conflict between gravity and quantum mechanics is one of the deepest problems in modern physics.” They comment about extra dimensions:

As for Horgan’s bête noire of physics — higher dimensions, or what he refers to as “hyperspace theories” — he writes: “But pursuers of this ‘theory of everything’ have wandered into fantasy realms of higher dimensions with little or no empirical connection to our reality.” That both of the present writers recognize that additional degrees of freedom of one sort or another are needed to characterize the physics of elementary particles may come as a surprise to Horgan. What the two of us may disagree about is what may be the likely physical and mathematical basis of this fact. But we both recognize that the mathematical spaces that we already deal with in describing the quantum theory of matter are in a certain sense more mathematically exotic than simple possible extra physical dimensions.

It seems to me that Krauss and Susskind are creating a straw man to attack here, not really dealing with Horgan’s actual criticisms, the full text of which was:

Especially as represented by best sellers like “A Brief History of Time,” by Stephen Hawking, and “The Elegant Universe,” by Brian Greene, physics has also become increasingly esoteric, if not downright escapist. Many of physics’ best and brightest are obsessed with fulfilling a task that occupied Einstein’s latter years: finding a “unified theory” that fuses quantum physics and general relativity, which are as incompatible, conceptually and mathematically, as plaid and polka dots. But pursuers of this “theory of everything” have wandered into fantasy realms of higher dimensions with little or no empirical connection to our reality. In his new book “Hiding in the Mirror: The Mysterious Allure of Extra Dimensions, from Plato to String Theory and Beyond,” the physicist Lawrence Krauss frets that his colleagues’ belief in hyperspace theories in spite of the lack of evidence will encourage the insidious notion that science “is merely another kind of religion.”

I don’t see Horgan here criticizing the attempt to quantize gravity as “frivolous”. His criticism of physicists as having “wandered into fantasy realms of higher dimensions with little or no empirical connection to our reality”, is a justifiable one that deserves to be seriously addressed. Krauss and Susskind’s comment that Horgan would be surprised that both of them think that new degrees of freedom will be needed to characterize elementary particle physics doesn’t seem to have any basis in fact. Horgan isn’t making broad claims that physicists shouldn’t look for new degrees of freedom, he is very specifically referring to the use of extra space-time dimensions.

Krauss and Susskind at least implicitly take Horgan to task for referrring to such extra dimensions as “hyperspace”. He may well have picked this up from Michio Kaku who wrote a book with this title. By the way, tonight Kaku will be appearing on the Art Bell “Coast to Coast” radio program, a program which is mostly concerned with UFOs and the like. If Krauss and Susskind want an example of the kind of theoretical physics research that Horgan is bothered by, they could check out this radio program.

Theorist Richard Szabo has had part of an evening he spent last week at the bar in a Bloomsbury hotel memorialized in today’s Observer Magazine.

An interesting paper appeared on the arXiv yesterday, by Hermann Nicolai and Kasper Peeters, entitled Loop and spin foam quantum gravity: a brief guide for beginners. It includes some of the same material as an earlier paper Loop quantum gravity: an outside view that they wrote with Marija Zamaklar.

Nicolai and Peters (as well as Zamaklar) are string theorists, and given the extremely heated controversy of the last few years between the LQG and string theory communities over who has the most promising approach to quantum gravity, one wonders how even-handed their discussion is likely to be. They identify various technical problems with the different approaches to finding a non-perturbative theory of quantum gravity that are often referred to as “LQG”. I’m not an all an expert in this subject, so I have no idea whether they have got these right, and whether the problems they identify are as serious as they seem to claim. Their main point, which they make repeatedly, is that

.. the need to fix infinitely many couplings in the perturbative approach, and the appearance of infinitely many ambiguities in non-perturbative approaches are really just different sides of the same coin. In other words, non-perturbative approaches, even if they do not `see’ any UV divergences, cannot be relieved of the duty to explain in detail how the above divergences `disappear’, be it through cancellations or some other mechanism.

What they are claiming seems to be that LQG still has not dealt with the problems raised by the non-renormalizability of quantum GR. They don’t explicitly make the claim that string theory has dealt with these problems, but the structure of their argument is such as to imply that this is the case, or that at least string theory is a more promising way of doing so. Their one explicit reference to string theory doesn’t really inspire confidence in me that they are being even-handed:

The abundance of `consistent’ Hamiltonians and spin foam models … is sometimes compared to the vacuum degeneracy problem of string theory, but the latter concerns different solutions of the same theory, as there is no dispute as to what (perturbative) string theory is. However, the concomitant lack of predictivity is obviously a problem for both approaches.

While they are being very hard on LQG for difficulties coming from not being able to show that certain specific constructions have certain specific properties, they are happy to state as incontrovertible fact something about string theory which is not exactly mathematically rigorous (the formulation of string theory requires picking a background, causing problems with the idea that all backgrounds come from the “same” theory, and let’s not even get into the problems at more than two loops).

The article is listed as a contribution to “An assessment of current paradigms in theoretical physics”, and I’m curious what that is. Does it contain an equally tough-minded evaluation of the problems of string theory?

It should be emphasized again that I’m no expert on this. I’m curious to hear from experts what they think of this article. Well-informed comments about this are welcome, anti-string or anti-LQG rants will be deleted.

Update:

There’s a new expository article about spin-foams by Perez out this evening.

There’s a review of Susskind’s book The Cosmic Landscape in this Sunday’s New York Times book review section. The reviewer does a reasonably good job of laying out what the Landscape controversy is about, characterizing Susskind’s attitude as “braggadocio” with “an air of smugness”, and noting that “He allows remarkably little doubt about string theory considering that it has, as yet, not a whit of observational support.”

This week’s Village Voice has a profile of Susskind.

Update: More about this over at Uncertain Principles.

Federal funding for high energy physics in the US has been declining significantly in recent years. The recently completed FY 2006 budget has a 2.7% cut for high energy physics in the DOE budget, which provides the bulk of US funding for high energy physics research. The NSF also provides some support, but its budget for the mathematical and physical sciences is up only 1.5%, significantly below inflation (I don’t know what the number is for high energy physics at the NSF by itself).

Over at Cosmic Variance, Joanne Hewett has commented on how depressing and discouraging the budget situation is, describing discussions amongst those charged to plan for the future as “downright scary at times.” One of the worst immediate effects of the 2006 budget had been that the Brookhaven heavy ion collider RHIC would only have been funded for 12 weeks of operation instead of the planned 20 due to higher electric power costs.

Today Brookhaven made a remarkable announcement about this. A group led by ex-mathematician Jim Simons, head of the hedge fund Renaissance Technologies (for more about him and his hedge fund, see here and here) has come up with a contribution of the $13 million needed to run RHIC for the full 20 weeks. The group contributing this money includes other partners at Renaissance, which is based on Long Island, not very far from Brookhaven.

I’m sure the significance of this new source of funding for high energy physics will be debated in the community in coming days. My initial reaction is that while it’s wonderful that the worst immediate effect of the budget cuts for 2006 has been avoided due to the generosity of Simons and others, this doesn’t materially change the long-term problems.

There’s more about this at Entropy Bound, the blog of Peter Steinberg, who works on an experiment at RHIC.

Update: More comments about this are from Joanne Hewett at Cosmic Variance and Chad Orzel at Uncertain Principles.

Update: More about Simons from New York Newsday.

Over the last couple years there has been a large amount of hype about cosmic strings, including press releases from Santa Barbara, and a story in New Scientist about The First Evidence for String Theory?.

The Santa Barbara press release from June 2004 concerned a paper by Polchinski and others about potentially observable fundamental strings of cosmic size. It stated that “LIGO… could provide support for string theory within two years.” There are five months left for this prediction to work out.

The New Scientist story was about an astronomical object optimistically given the name “CSL-1” (for Capodimonte-Sternberg-Lens candidate), that supposedly might be a galaxy lensed by a cosmic string, causing it to appear doubled. Of course the much less exotic and much more likely possibility was always that it was just two similar looking neighboring galaxies. Recently the Hubble space telescope was used to take a closer look at CSL-1, and as reported here and here the Hubble image clearly shows that it’s not a cosmic string, just two nearby galaxies.