Not Even Wrong

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.

Mathematician David Goss wrote to tell me about the latest issue of the journal Current Science, which contains quite a few articles on Einstein’s legacy, including an interesting one on Einstein and the search for unification by physicist David Gross. Perhaps I’m being a bit churlish, but surely I’m not the only person who is at least a bit happy that 2005 is over and done with, so that attention can begin to be paid to some other topic than that of Einstein. He was a true giant, but I bet he’d be pretty tired of the hoopla by now.

Gross discusses Einstein’s goal of finding simple universal laws from which all physics can be deduced, and tells about how this inspired him at the age of thirteen to decide to become a theoretical physicist. He tells about Einstein’s failed attempts to find particle-like solutions to the non-linear equations of GR, unified in various ways with electromagnetism, and notes that in the early 80s, with Malcolm Perry, he found magnetic monopole solutions that were a bit like what Einstein was looking for.

Getting to topics of current interest, Gross talks about “The discovery of supersymmetry, which we all hope and some expect in a few years from now at the Large Hadron Collider…” I don’t think I’m the only one hoping not for this, but for something more interesting. I’d also be curious whether Gross puts himself among those who “expect” to see this at the LHC. There’s the usual string theory propaganda, including the incorrect claim that string theory provides “a consistent and finite quantum theory of gravity” (no, the sum of the perturbation series is not finite, and Gross is one who often says we don’t know what the theory even is). Gross also as usual stresses that he thinks we need to give up on space and time, but doesn’t know what will replace them. He concludes that Einstein was wrong to refuse to accept quantum mechanics and to ignore nuclear and particle physics, but that he was right to try and unify gravity with the other forces, saying “this we know today is the central issue in fundamental physics”, something I don’t really agree with (I’d go for understanding electroweak symmetry breaking).

This issue of the journal also contains interesting articles by Michael Atiyah on Einstein and Geometry, and by Abhay Ashtekar on The winding road to quantum gravity. There’s also a completely uncritical piece of string theory propaganda by Ashoke Sen entitled String theory and Einstein’s dream that could easily have been written ten years ago.

For more uncritical promotional material on string theory, here are two things from UC Davis. They have something there called the “High Energy Frontier Theory Initiative (HEFTI)”, and on their website you can read a report written by an external committee for the Dean at Davis promoting the idea of hiring more string/brane theorists of the phenomenological sort. The report is a few years old, but shows exactly what the consensus thinking of just about the entire high energy theory community has been for the past few years about what is the hot area to hire in. They promote the idea that particle theory is doing extremely well, so much so that

The last period of comparable experimental and theoretical ferment occurred in the early 1970s, swiftly culminating in the development of the Standard Model of particle physics.

and that the “pace of new developments is accelerating” in both theory and experiment.

Also from UC Davis is a new paper entitled Space and time from translation symmetry by Albert Schwarz. It starts off by claiming “In some sense string theory today is in very good shape”, but seems to be empty of content.

Finally, there’s a new paper out tonight reviewing the status of the string theory Landscape. It looks like landscapeologists are now ready to abandon even the idea that the number of phenomenologically viable vacua is finite, and the last part of the paper contains some impressive contortions about why this isn’t necessarily a bad thing. They also seem to have given up on Douglas’s idea of making predictions by counting vacua. They’re still counting the vacua, but now the reason given is not to make predictions, but to see if there are enough to be sure that one of them will reproduce the standard model.

The February issue of Discover Magazine contains an interview of me by writer Susan Kruglinski. I haven’t seen the magazine itself, and it’s not yet on the newsstands here, but a friend who subscribes was kind enough to send me a copy of the article. There’s a picture of me sitting underneath the blackboard outside my office taken by a photographer. The day he came I had a migraine headache, so was looking rather grim, not my usual cheery self.

For many years C. J. Mozzochi has been taking photographs of mathematicians, primarily at mathematics conferences and lectures in Princeton or in the New York City area. With help from Mark Goresky, he now has a web-site where you can view and download many of his photographs. The site will be periodically updated with additional photographs.

Follow-Ups to two recent postings:

Michael Duff has written a letter to New Scientist complaining about their recent editorial Physics’ greatest endeavour is grinding to a halt. Duff begins by claiming:

History has shown that rapid confirmation by experiment is a poor guide to the eventual value of a physical theory

but backs this up in a rather bizarre way. You might think he would list some physical theories whose experimental confirmation took awhile, instead he lists various theoretical ideas that have been around for a long time, still haven’t been experimentally confirmed, although lots of people are still working on them. Evidently for Duff the value of a physical theory is how many people are working on it (he also points out that about 500 people go to Strings 200X), not whether there is any experimental evidence for it. The examples he gives range from cases where there is zero experimental evidence, and probably never will be any (extra dimensions, supersymmetry) to ones that it is very plausible we will soon see evidence of (Higgs boson, gravitational waves) to ones that arguably we already have some evidence for (cosmological constant).

He notes that gravitational waves were predicted in 1916 and have yet to be confirmed, that string theory is more ambitious than GR so it should take longer to confirm, and that one should only really start counting in 1995, when M-theory came along. So I guess his prediction is that by 2074, we still won’t yet be anywhere near confirming string theory. Like many string theorists, he make highly tendentious claims about the relation of the standard model to experiment, writing:

decades [were] required to knock the standard model into a shape that could be confirmed by experiment

I assume he’s not talking about the QCD part of the standard model, which was born in 1973, already making verifiable predictions, and within ten years had accumulated a huge amount of evidence in its favor. The electroweak theory was first written down by Weinberg and Salam in 1967, and by ten years later the evidence for it was overwhelming. I suppose you could try and argue that the history of attempts to put together the standard model go back to Glashow in 1960 or Yang-Mills in 1954. Even using 1954, it was 19 years later that the full standard model was in place with a lot of experimental evidence already there and more pouring in. And that period would quite likely have been shorter if most of the theory community hadn’t given up on QFT and been working on the bootstrap, dual models or string theory during that time. In the case of string theory, taking Veneziano in 1968 as a starting point, nearly 4 decades later there is not a glimmer of a piece of experimental evidence for string theory. Comparing the history of the standard model to the history of string theory is just absurd.

On another recent topic, the New York Times finally today carried an obituary for Raoul Bott.

An assortment of interesting things I’ve run across recently:

There’s something called Multiversal Journeys that seems to organize lecture series on theoretical physics, with a special interest in the multiverse (at least to the extent of using it as an inspiration for the organization’s name).

UC Davis particle physicist John Terning has a weblog. Also a new graduate-level text book on supersymmetric field theories, entitled Modern Supersymmetry: Dynamics and Duality, soon to be published by Oxford.

Ever since 2001, the physicists in Paris have been running a Seminaire Poincare, modeled after the mathematicians famous Seminaire Bourbaki. The latest Seminaire Poincare was on the topic of Quantum Decoherence, and texts from the older meetings are available.

Harvard philosopher Hilary Putnam has an updated version of his 1965 article “A Philosopher Looks at Quantum Mechanics” in the latest issue of the British Journal for the Philosophy of Science. It is entitled A Philosopher Looks at Quantum Mechanics (Again). Part of my misspent youth involved taking several philosophy courses as an undergraduate at Harvard, including ones from Quine and Putnam.

In November, Joe Lykken gave a particle physics seminar at Princeton entitled Is particle physics ready for the LHC? His talk explains some of the challenges particle physics will face at the LHC. The next-to-last slide is a none too subtle dig at the lack of any particle phenomenology going on at my alma mater. It is entitled “is Princeton ready for the LHC?”, and lists the titles of the particle theory seminars going on at Princeton during the period before his talk.

The International Committe for Future Accelerators (ICFA) has a new web-site.

The Tevatron has recently achieved new luminosity records, both for peak luminosity and integrated luminosity over a week. You can follow the status of the Tevatron here.

A beautiful new paper by Greg Landweber and Megumi Harada has just appeared. It is entitled A comparison of abelian and non-abelian symplectic quotients and uses equivariant K-theory methods to get the relation between the K-theories of the symplectic quotients M//G and M//T, here T is the maximal torus of a compact Lie group G.

Update: One more. Slate today is advertising Meaning of Life TV, where various people, including some physicists, do things like promote the idea that the anthropic principle shows religion has a lot to do with science. This site has been around for a while, but just now has affiliated with Slate. Looking at it I thought “funny, this is the only thing like this trying to inject religion into science that doesn’t seem to be a Templeton Foundation project.” Then I saw the About Us link.

There’s an article in this week’s Nature by Geoff Brumfiel entitled Outrageous Fortune about the anthropic Landscape debate. The particle physicists quoted are ones whose views are well-known: Susskind, Weinberg, Polchinski, Arkani-Hamed and Maldacena all line up in favor of the anthropic Landscape (with a caveat from Maldacena: “I really hope we have a better idea in the future”). Lisa Randall thinks accepting it is premature, that a better understanding of string theory will get rid of the Landscape, saying “You really need to explore alternatives before taking such radical leaps of faith.” All in all, Brumfiel finds “… in the overlapping circles of cosmology and string theory, the concept of a landscape of universes is becoming the dominant view.”

The only physicist quoted who recognizes that the Landscape is pseudo-science is David Gross. “It’s impossible to disprove” he says, and notes that because we can’t falsify the idea it’s not science. He sees the origin of this nonsense in string theorist’s inability to predict anything despite huge efforts over more than 20 years: “‘People in string theory are very frustrated, as am I, by our inability to be more predictive after all these years,’ he says. But that’s no excuse for using such ‘bizarre science’, he warns. ‘It is a dangerous business.'”

I continue to find it shocking that the many journalists who have been writing stories like this don’t seem to be able to locate any leading particle theorist other than Gross willing to publicly say that this is just not science.

For more about this controversy, take a look at the talks by Nima Arkani-Hamed given today at the Jerusalem Winter School on the topic of “The Landscape and the LHC”. The first of these was nearly an hour and a half of general anthropic landscape philosophy without any real content. It was repeatedly interrupted by challenges from a couple people in the audience, I think David Gross and Nati Seiberg. Unfortunately one couldn’t really hear the questions they were asking, just Arkani-Hamed’s responses. I only had time today to look at the beginning part of the second talk, which was about the idea of split supersymmetry.

Update: One of the more unusual aspects of this story is that, while much of the particle theory establishment is giving in to irrationality, Lubos Motl is here the voice of reason. I completely agree with his recent comments on this article. For some discussion of the relation of this to the Intelligent Design debate, see remarks by David Heddle and by Jonathan Witt of the Discovery Institute.