Too Much Good Stuff

Posted on June 30, 2007 by woit

I’ve been finding recently that an increasing serious problems with blogs is that there are too many good ones with material worth reading. I’ve learned quite a lot recently from many well-informed blog postings, but the sheer number of these makes it hard to find the time for other things one should be doing.

I’ll violate my usual rule of sticking to math and physics and report that my brother Steve is joining me in the family blogging business by being involved as Publisher in a new venture that just launched this week called Xconomy. Basically it’s a blog based up in Cambridge, with offices in Kendall Square, devoted to news about what they call the “exponential economy”, that part of the economy responsible for what is perhaps too optimistically described as exponential growth in certain areas. They’re focusing on events and news relevant to new technology, especially bio-technology, businesses in the Boston area. For some interesting blog postings by their CEO Bob Buderi about what it’s like to start up this sort of business, see here and here. For a nice posting about Doc Edgerton, see here.

Back to physics and math, over at Backreaction there’s an excellent posting on the GZK cutoff and high energy cosmic ray experiments, and a report from Loops 07 sent in via Blackberry by Sabine Hossenfelder.

An American Physics Student in England tells about a recent conference on Heavy Flavour Physics, giving a very nice overview of what is going on in that field.

The latest This Week’s Finds in Mathematical Physics from John Baez is out (available here, blog entry and comments here). It’s a wonderful description of the various mathematical patterns that the standard model particles fit into. Most well known is what happens in SU(5) and SO(10) GUTs, where one can fit the fermion quantum numbers into something that can equivalently be described as the spinor representation in d=10, or the exterior algebra $\Lambda ^* (\mathbf C ^5)$. John goes on to explain various possible connections to the exceptional groups, including a recent idea from Garrett Lisi about how to use E8 to get three generations.

The blog entry comments discuss two recent papers by Chamseddine and Connes about their non-commutative algebra approach to this question of mathematically characterizing the SM degrees of freedom. The papers are on the arXiv, entitled A Dress for SM the Beggar, and Why the Standard Model. Because of these papers and Witten’s recent one, John seems to be getting a bit more optimistic about physics, writing “I get the feeling that theoretical physics may not be quite so stagnant after all!”

All sorts of interesting stuff at the Secret Blogging Seminar, including yet more about Connes: a “review” by A. J. Tolland of the first quarter of the new book by Connes and Marcolli (available here), which A. J. claims has the title Noncommutative Geometry, Quantum Fields, Kitchen Sinks and Motives. Like the earlier fat book on non-commutative geometry by Connes, it’s an amazing document, ranging widely over physics and mathematics, covering ground from QFT to the Riemann hypothesis, at a level varying from expository sections on well-known subjects to more speculative research-level discussions. I’ve just started looking at it, may bring along a copy for summer vacation reading when I head up to a lake in New Hampshire tomorrow.

Other interesting things at the same blog include reports (here and here) from Ben Webster about talks by Sergei Gukov on categorification and gauge theory (about which he has a new expository paper here), as well as about an earlier talk by Gukov on Arithmetic Topology and Gauge Theory.

Also worth reading are posts from Ben Webster about centers of blocks of category O, various comment section discussions with David Ben-Zvi at both this blog and the n-category cafe, and a series of postings by David Speyer about quadratic reciprocity and geometric class field theory (I’m running out of energy to provide links…).

From Ben-Zvi (who could run a really great blog if he chose to…) there are notes from the recent conference at Northwestern on non-commutative geometry. These include an intriguing lecture by Beilinson, as well as lectures by Nadler and Ben-Zvi himself about their recent work which connects geometric Langlands with questions about more conventional representation theory using striking ideas about how to handle loop spaces. They have a recent paper about this, which has been very high on my list of things I wish I understood better ever since David gave an inspiring talk about this here a couple months ago.

Finally, one more thing definitely worth looking at in light of Witten’s new work: an expository and historical article by Jim Lepowsky about the story of the relation of vertex operator algebras and the monster group. He explains what is so remarkable about the specific vertex operator algebra that Witten is connecting to 3d gravity on AdS, including the ways in which it is conjecturally uniquely the “smallest” such structure in a specific sense.

Posted in Uncategorized | 17 Comments

Strings 2007

Posted on June 25, 2007 by woit

Strings 2007 is starting today, and already there seem to be a large number of different laptops connecting to this blog from wlan.uam.es. I’m hoping that some of their owners will write in here with news of how the conference is going. I’ll also try and add links here to any blog and press coverage of the conference that I see or hear about.

Witten’s new 83 page paper entitled Three-Dimensional Gravity Revisited appeared on the arXiv last night and presumably this is the detailed version of what he’ll be talking about in the first of tomorrow’s talks at the conference. It corresponds pretty much to what he talked about here in New York a few weeks ago, which was described here. I assume many of those laptops at the conference are being used to download and read copies of Witten’s paper. At his blog, Clifford Johnson notes that he won’t be at Strings 2007, and hopes that this will ensure that there will be an exciting breakthrough announced there, just like what happened when he decided not to attend Strings 1995.

As I write this, I see that string theorist Jacques Distler is there live-blogging. Here’s the first of his reports.

Update: Some of the slides of the talks are already on-line. The slides for Witten’s talk are available here.

Update: There’s an interesting posting here by Jacques Distler about the Witten talk, and, for those who enjoy such things, quite a rant from Lubos here, prompted by my comment that in this case Witten is investigating quantum gravity using non-perturbative QFT, not strings.

I’ve been reading Witten’s paper a bit more carefully, and it raises all sorts of interesting issues. He makes the point that even in 3d, we really don’t know exactly what “non-perturbative pure quantum gravity” is. He uses the Chern-Simons formulation of 3d gravity in terms of gauge theory to motivate his guess at the correct boundary CFT, and then once he has that he has something much more well-defined to study.

This is a bit reminiscent of the compact, non-gravitational situation. There Chern-Simons theory works fine perturbatively, but to understand the non-perturbative theory one connects it to a CFT on the boundary, in this case the Wess-Zumino model (this is the story that got Witten a Fields medal).

Update: B. Yen has set up a video-blog for Strings 2007, where there will be iTunes podcasts of the conference available.

Update: Latest report from Jacques Distler is that, since Witten’s one, which he got to write about:

there have been some very cool talks

(emphasis in the original), but he can’t tell us even which ones they were since his laptop is malfunctioning. Slides of the talks are available here. I’ve looked through them and, besides Witten’s, don’t see anything I would describe as “very cool”, but maybe that’s just me.

Update: All the talks are on-line now and I just looked through the last of them, and watched the summary talk by Gross. Lisa Randall discussed recent calculations of black-hole production at colliders, with the bottom line being that even in the unlikely event the gravity scale is within reach of the LHC, existing bounds already pretty much rule out the possibility of seeing the kind of dramatic effects from black hole production that have been widely advertised as something that might be seen at the LHC.

Gross noted that the conference was much less mathematical than last year’s, possibly because Yau was not involved in organizing it. He was most enthusiastic about describing the many talks on AdS/CFT, especially the Beisert talk which told about recent progress in getting an exact solution of N-4 SYM. Some talks referred to possible applications of AdS/CFT not just in QCD and heavy-ion physics, but in condensed matter physics (using the duality to get info about relevant CFTs). He told about Polchinski’s speculation that “maybe AdS/CFT will solve high Tc superconductivity”, but dismissed it with “sounds great, but seems unlikely to me.” He dealt with the landscape talks by flashing them by quickly, in a lower and less enthusiastic voice, noting that they made up at least a quarter of the talks at the conference. He dealt similarly with the cosmology/anthropic talks, describing Bousso’s as “an attempt to make the anthropic principle precise if not respectable.”

After the summary, he gave his own take on the state of string theory, saying that one had to be honest about the lack of falsifiable predictions and that now he had a slide headed “The Failures of String Theory”. He continues to feel that the main failure is because we “don’t know what string theory is”, that something is missing, some principle that would pick out not a “vacuum” but a “cosmology”, one perhaps using new ideas about what space and time are. He said he was not too upset by the landscape, because “we don’t know what the rules are” in string theory, so one can’t argue that string theory implies the landscape. He appeared to feel that he is losing the debate, complaining that this used to also be the opinion of his colleagues, but that they were going over to the other side because of the cosmological constant, saying that if another explanation of the CC was found 90% of the anthropicists would come back to his side. He tried to minimize the size of the CC problem, measuring it with respect to a supposed 1 TeV SSYM breaking scale and working in energy, not energy density units, so it is only too small by a factor 1016. He compared this to Dirac’s famous large number problem (which Dirac tried to solve not anthropically, but by time-varying constants, leading to a prediction that was falsified), which was finally “explained” by asymptotic freedom. His message to the anthropocists was “just because you don’t know an explanation doesn’t mean it doesn’t exist”.

Finally he mentioned that Strings 08 will be at CERN, Strings 09 in Rome, and no one has yet agreed to host Strings 10. He argued that the series of Strings conferences “must go on”, because they are “like the canary in the coal mine”, and if they stop that would be a very bad sign for string theory.

I’m curious to know what those in attendance thought of this; it wasn’t exactly a rousingly optimistic portrayal of the state of the subject…

Update: There’s an article in El Pais about the conference and about the state of string theory. My Spanish isn’t perfect, but as far as I can tell the piece was pretty much pure unadulterated hype, of the sort that it is one goal of the Strings XX bashes to generate.

Update: Jacques Distler finally got his computer fixed, and posted about one example of what he considered a “very cool talk” with exciting new ideas. Unfortunately, it seems the ideas are not that new, since a commenter wrote in to his blog to point to papers from four and a half years ago that do pretty much the same thing.

Posted in Strings 2XXX | 80 Comments

Assorted News

Posted on June 22, 2007 by woit

Yesterday Sean Carroll and I appeared on the BBC Radio 4 program The Material World, in a segment on String theory – knot good enough?, about the controversy over string theory. The segment started with a piece from the play Humble Boy by Charlotte Jones, in which the main character is working on string theory. I don’t think anything either of us said was particularly controversial or would be in any way surprising to a regular reader of either of our blogs. The same program had a segment on the multiverse three weeks ago.

Some more titles of talks at next week’s Strings 07 have appeared. Witten’s talk is entitled “Three-Dimensional Gravity Revisited” and presumably will be about the new ideas described here. So, at least one talk there will be about a non-string theory approach to quantum gravity more along the lines of the LQG program. The schedule doesn’t seem to include any discussion session like the one at Strings 05 where the audience voted against the anthropic landscape.

A competing conference to Strings 07, Loops 07 will be taking place at the same time next week, but in Mexico, not Madrid. It’s much smaller, with less than a third as many participants. There will be one plenary talk on string theory, Moshe Roszali speaking on “Background Independence in String Theory”.

As the hunt for the Higgs is heating up at Fermilab, and CERN has officially announced the delay of LHC startup until next May, there’s a group of filmmakers who may be well-positioned if something exciting is found at the Tevatron. For the last few years 137 Films has been making a film to be called The Atom Smashers, following scientists working at FNAL. Filmmaker Clayton Brown is keeping a blog about this.

Yet another bogus “possible [experimental] signature for string theory”. Even Lubos doesn’t seem to believe this one, so I’ll just quote his argument:

My personal guess based on our work on the weak gravity conjecture is that the black hole bound is also satisfied in string theory for localized macroscopic objects, up to small corrections. This belief of mine is supported by the observation that Gimon & Hořava don’t have any explicit solution for their “superspinar”.

Christina Sormani tells me she has created a Wikipedia article on the proof of the Poincare conjecture, see here. For the latest on Perelman, see here.

Posted in Uncategorized | 54 Comments

The Triple-Scoop

Posted on June 15, 2007 by woit

Experimenters at the Tevatron have released data showing the existence of a new baryon, built out of a down, strange and bottom quark, and having a mass of 5.774 +/- .019 GeV. It has been given the name “Ξb“. The FNAL press release is referring to this as a “triple-scoop” baryon, since it contains one quark from each of the three generations. Tommaso Dorigo has a new posting about this.

Postings on this blog tend to involve a certain amount of discussion of bad behavior by theorists, so I guess I should point out here that this story comes with some accusations of less than good behavior by experimentalists in the way this was announced. The press release is all about the announcement of this discovery by the D0 experiment, and about their paper, which was submitted to the arXiv Tuesday night. It turns out though that D0’s competition, CDF, also has had the same result for a while, and it had already been “blessed” but not officially announced. So CDF was “scooped” at the last moment for the “triple-scoop”, and I imagine there are dark accusations going around about how D0 might have found out about this and rushed out the paper and press release. Supposedly there is an informal one-week notification period that the two experiments normally observe to keep this kind of thing from happening. Anyway, looks like they’re trying to fix it up a bit: the FNAL web-site contains a “special announcement” of back-to-back seminars about this, D0 at 1pm, which will “immediately be followed” by a CDF seminar. The D0 seminar is called

First observation of a new b-baryon, Ξb

whereas the CDF seminar is entitled

Observation of a new b-baryon, Ξb

Posted in Uncategorized | 15 Comments

Random Collection of Stuff

Posted on June 14, 2007 by woit

Pretty much everybody in the math community seems to be getting a blog. Many of the new bloggers are quite good research mathematicians (including even some Fields Medalists). Two very new ones are:

Secret Blogging Seminar: Named after a “Secret Russian Seminar” at Berkeley, a group blog of several ex- and current Berkeley math graduate students (Ben Webster, A.J. Tolland, Scott Morrison, Noah Snyder and David Speyer)

Math Life: The blog of UT Austin’s number theorist Fernando Rodriguez Villegas

A few things I learned from the Secret Blogging Seminar postings and following associated links:

The Microsoft Research group at UCSB working on “topological quantum computation” is now known as Station Q, and has a web-site.

Googling “Secret Russian Seminar” led to the web-site of Scott Carnahan, a student of Richard Borcherds who will be a postdoc at MIT this fall. Carnahan has some interesting sets of notes there, including notes from Borcherds’ 2004 course on QFT. Back in 2001, Borcherds had taught an earlier version of this course, and notes taken by Alex Barnard are available. According to Carnahan, Borcherds began the 2004 course with the comment:

Some of you might remember I gave a class a few years ago on the standard model. It ran into a few technical problems, the main one being the fact that I didn’t know what I was talking about. I’ve learned a thing or two since then, and I’m going to try again.

I’ve finally been making some progress in understanding some mathematics associated to BRST; if this keeps making sense I hope to get something written about it this summer. I recently noticed that the pretty much incoherent Wikipedia entry on the BRST formalism, has been joined by another incoherent one on BRST quantization. Both entries contain the warning at the top “This article or section may be confusing or unclear for some readers”, which is an understatement.

A new issue of Symmetry Magazine is out, and it contains a report on the recent string theory debate in Washington between Brian Greene and Lawrence Krauss. An editorial noted how amazing it is that this sort of thing drew 600 people willing to pay $25. There’s lots of interest out there in fundamental physics in general, and this controversy in particular.

Can’t remember where I saw this earlier today, but there’s a famous quotation I hadn’t heard before from economist John Kenneth Galbraith which seems to apply well to the current situation in string theory:

Faced with the choice between changing one’s mind and proving there is no need to do so, almost everyone gets busy on the proof.

Update: One more. Adrian Cho at Science Magazine has an article about the debate going on over how long to run the Tevatron. The chair of the P5 panel is saying that they will recommend running through 2009, but that “It would take some unusual circumstances to justify running beyond 2009.” But, if the LHC takes longer to get working correctly than planned (there’s a history of this with new accelerators), and Tommaso’s Dorigo’s rumors of sightings of a Higgs at the Tevatron ever start to firm up, it’s going to be hard to justify starting to tear the machine down…

Update: Yet one more about math blogging. Lieven le Bruyn has changed his blog from NeverEndingBooks to Moonshine Math (also known as NeverEndingBooks, v. 2). He begins with a wonderful blog posting about the j-function which explains one of my favorite remarkable facts about numbers:

$$e^{\pi\sqrt{163}}=262537412640768743.99999999999925\ldots$$

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US Particle Physics Planning

Posted on June 11, 2007 by woit

Last week both SLAC and Fermilab hosted “Users Meetings”, providing a forum to discuss the current status and future plans of the two laboratories. The SLAC agenda is here, and talks from previous years are available here, with this year’s perhaps available later.

The Fermilab meeting was also celebrating the 40th anniversary of its first Users Meeting, which was held back in 1967 at a time when Fermilab was under construction, with plans for a 200 GeV fixed-target machine underway, led by director Robert Wilson. This year’s talks are available here. The status of the Tevatron is described in Roger Dixon’s talk. Already the machine has delivered nearly 3 fb-1 of luminosity to the two experiments there, half of this over the last year. They are projecting to have 6-7 fb-1 by the end of FY 2009 (a bit more than two years from now). The current plan calls for operation of the Tevatron only until the end of FY 2009, and a year or so ago there was even some discussion of shutting it down before then. With the machine operating well, a healthy US HEP budget, the LHC startup now not until 2008, and some cautious optimism that that the Tevatron might be able to accumulate enough data to see the Higgs under some scenarios, it looks like no one is about to shut the Tevatron down early, rather the question will be how much extra time to give it. There seems little point to shutting it down as long as the LHC is not producing results that make it obsolete, and no one knows yet how long that is going to take. While those running Fermilab would like to know what they will be doing several years in advance so that they can plan and budget, it may be difficult to do this since no one knows what will happen with the LHC.

Fermilab is in the middle of a long-range planning exercise, with a Steering Group meeting trying to put together a plan by August 1. They have many of their materials available on-line. Some of the discussion revolves around the question of the ILC, with talks showing that in principle it would be possible to start construction of the ILC in 2012 and have it built by 2019, but few people believe that things will happen this fast. Whether building the machine makes sense will depend on what is seen at the LHC. Other scenarios are under discussion, for example see here. Other than the LHC, the main things one could conceive of building at Fermilab would be a more intense proton beam (proton driver), or accelerating muons to provide a “neutrino factory” and perhaps ultimately a muon collider.

While US HEP has a difficult task ahead to figure out what to do after the Tevatron shuts down and the energy frontier moves to CERN, at least the budget situation is looking a lot better than it was a few years ago. At the Users Meeting, there was a presentation by the DOE’s Robin Staffin showing budget figures that included a 6.8% increase planned for FY2008, after a 5.9% increase from FY2006 to FY2007. For some reason the federal government seems to have decided to put significantly more money into fundamental physics research, and HEP is benefiting from this. For more about the general situation with the Federal science research budget, see this recent talk by John Marburger, the director of Office of Science and Technology Policy.

For the budget situation in mathematics, see this report in the latest Notices of the AMS about the NSF budget numbers. After flat budget numbers for the past couple years, there was a 3.3% increase for mathematics research in FY2007, and the proposal for FY2008 has a 8.5% increase. Math is cheap compared to HEP, with the NSF spending on math (which is the bulk of federal math research funding) only about a quarter the size of the HEP budget. The AMS Notices article also computes numbers for what fraction of the NSF budget goes to different fields, noting that in FY2004 18.3% was for math, 20.9% for physics, while the FY2008 proposal goes 17.8% to math, 23.6% to physics.

Update: Also at SLAC, this week the DOE is there to review the lab. Presentations prepared for the DOE are on-line. Michael Peskin gave a presentation about the work of the theory group. He highlighted (besides hopes about the LHC) the work of SLAC’s Lance Dixon on computing perturbative QCD amplitudes, including its relation to N=4 supersymmetric Yang-Mills and to the conjectural finiteness of N=8 supergravity.

Posted in Uncategorized | 23 Comments

Dispute Chez Les Physiciens

Posted on June 7, 2007 by woit

Yesterday evening there was a public debate about string theory held in Paris, between Lee Smolin and Thibault Damour. So far, accounts of the debate have appeared in Le Monde and at Fabien Besnard’s blog Mathephysique.

The Le Monde article is not very informative, but indicates that Damour defended string theory against charges that it was not testable by claiming that it predicted “possible classes of experimentally testable phenomena” at the LHC. Besnard gives a more detailed account, describing how Damour answered these charges of lack of testability with: “Lee, a subtle thinker, surely doesn’t believe himself the naive Popperian position he is defending”. He also evidently claimed that string theory was testable because it would be confirmed if a violation of the equivalence principle was found (he really should talk to Lubos, see here). Remarkably, he also claimed that observation of the kind of DSR dispersion relations that Smolin thinks LQG leads to would not be a problem for string theory, since one could also get them out of string theory (here I think he needs to talk to both Lubos and Jacques Distler).

Update: I hear that the event was recorded, and audio should be available by the end of the week at the web-site linked to above.

Posted in Uncategorized | 60 Comments

Imposter String Theorist at Stanford

Posted on June 6, 2007 by woit

In recent years many people in the particle theory community have been wondering what’s going on with the Stanford theory group, as it has become dominated by work on things like the anthropic landscape. It turns out that, for a while now, there was someone there who even they were wondering about. Her name is Elizabeth Okazaki, and evidently for the last four years she has

attended graduate physics seminars, used the offices reserved for doctoral and post-doctoral physics students and — for all intents and purposes made the Varian Physics Lab her home

this despite the fact that she has no formal affiliation with the university. Some press stories about this are available from The Stanford Daily (more here) and the San Francisco Chronicle.

According to the Stanford paper, students interviewed said that Okazaki:

claimed to be a visiting scholar in the humanities, looking to provide an interdisciplinary perspective on string theory. On several instances, she has said that she was working with Physics Prof. Leonard Susskind, one of the world’s most respected string theorists.

but

Susskind told The Daily that Okazaki was not officially associated with him or his lab in any way.

“As far as I know, she has no official connection with anyone in the physics department,” Susskind said. “In fact, as far as I can tell, she has a very limited knowledge of physics itself.”

The story in The Stanford Daily on-line has a long associated comment thread, containing (besides a lot of nonsense) some comments from people in the Stanford physics department that provide more insight into the situation.

The San Francisco Chronicle article quotes Stanford graduate student Surjeet Rajendran about the situation as follows:

A university has a lot of weird people… Some of the faculty are weird, some of the grad students are weird. So you don’t really know who’s who. And you feel rather, I guess, rude asking them, ‘What the hell are you doing?’

For another perspective on this, see Scott Aaronson’s posting on The Groupies of Science, where he makes the point that “Science Needs More Groupies, Not Less”, and argues that:

When we discover a stowaway on the great Ship of Science, why throw her overboard when we could make her swab the decks?

Posted in Uncategorized | 41 Comments

All Landscape, All the Time

Posted on June 5, 2007 by woit

There seems to be a peculiar trend going on in the particle theory community. Just about all theorists I talk to, correspond with, argue with on blogs, etc. claim to be quite unhappy with the Landscape, and insist that most of their colleagues share this view. On the other hand, all evidence is that Landscape research is becoming increasingly influential at the highest levels of the string theory community. The most prominent yearly string theory conference, Strings 07, will soon be taking place in Madrid, and titles of many of the talks there have just been announced. The largest contingent of speakers is from Stanford, and it appears likely that landscape studies will be the most popular topic at the conference, with various aspects of AdS/CFT running a close second. Just counting the number of times “Landscape” appears in the title of a talk, so far there are 4 such talks out of 31 with announced titles. Last year at Strings 06, out of about 50 talks, 2 had “Landscape” in the title. Naively extrapolating this eternally inflationary trend to the future, pretty much all Strings 1X talks should be about the Landscape…

Another indication of where the field is going is the yearly TASI summer school aimed at training graduate students in particle theory. This year the topic is “String Universe”, and several of the lecture series are about the Landscape, with two having “Landscape” in the title. Videos of the talks are being made available now, even as the summer school is going on. I learned about this from Clifford Johnson, who writes that the talk he most wanted to look at and recommends to everyone is Raphael Bousso’s on “Cosmology and the Landscape”.

Harvard’s Lubos Motl traditionally has been a landscape skeptic, but in recent months he has been writing more and more positive things about this subject. His latest posting advertises a new paper by Raby and Wingertner calculating statistics on (an extremely small piece of) the heterotic landscape.

Update: Lubos has written a posting entitled Landscape 2007 in response to this one. His point of view seems to be that although he doesn’t like the Landscape, he doesn’t have a workable vacuum selection principle, and as time goes on and no such principle is found, this makes the Landscape more and more likely to be correct. He doesn’t seem to even consider the possibility that the existence of the Landscape and the lack of a vacuum selection principle means that string-based 10/11d unification is just a failed idea. I suspect his point of view may be widely shared among string theorists, explaining the simultaneous unhappiness with the Landscape and its increasingly widespread adoption as a research program.

Posted in Uncategorized | 87 Comments

Endless Universe

Posted on June 2, 2007 by woit

There’s a new popular book about cosmology now out on bookstore shelves, Endless Universe by Paul Steinhardt and Neil Turok. The authors are the inventors of a competing model to inflationary cosmology, variously called “ekpyrotic” or “cyclic” cosmology. They describe coming up with the same idea simultaneously during a lecture at Cambridge on M-theory by Burt Ovrut back in 1999. Ovrut was describing his work on the Horava-Witten scenario, which involves two parallel branes (we live on one of them), and during the lecture both Steinhardt and Turok started wondering about whether one could explain the big bang as a collision of branes. They went up to discuss this with him after the talk, and continued the discussion on a train ride to London that evening to see a performance of the play Copenhagen. This train ride was a central part of a 2002 BBC TV program Parallel Universes and a recent play Strings by Carole Bugge that I saw performed here in New York late last year.

The book is very much an advertisement for cyclic cosmology, and devotes a lot of space to doing something which is rarely done, explaining the problems with inflationary cosmology. Steinhardt has worked extensively on coming up with viable inflationary models, and a large part of the book explains the story of this research. Perhaps the most interesting aspect of the book is the story that Steinhardt and Turok each tell about their careers and how they ended up working together on this alternative to inflation. The problems with inflation are described in the context of promoting their cyclic model of branes colliding, moving apart and then back together in a repeating pattern. They heavily sell the idea that a cyclic model with no beginning of time is conceptually much preferable to a standard inflationary model in which the universe emerges at a given time. Reading this made clear to me why, at the recent String Cosmology meeting here in New York, Turok was so persistently questioning one speaker about whether everything he was doing didn’t just depend on an unmotivated choice of initial conditions.

Steinhardt and Turok do a pretty good job of demolishing the inflationary multiverse and the associated Anthropic Landscape philosophy that has become so popular in recent years. They correctly describe the main problem with the inflationary multiverse as the lack of any way to test the idea, even in principle, making it not really a scientific idea at all. As for the testability of their own theory, they devote an entire chapter to the question of contrasting its predictions for the CMB with those of inflation. They claim that both cyclic and inflationary cosmology make the same predictions for the WMAP results (implicitly criticizing the commonly made argument that WMAP provided strong support for inflation). The one possible test that they point to that could distinguish the inflation and cyclic scenarios is the expected more sensitive measurement in coming years of a possible B-mode polarization signal due to gravity waves in the CMB. They claim that inflation predicts a significant amount of B-mode polarization, whereas the cyclic model doesn’t. Unfortunately, from what I can tell by looking at the recent literature on “string cosmology” (e.g. here), various inflationary scenarios can give a wide range of amounts of such polarization, with stringy models like “brane inflation” and “modular inflation” leading to essentially none, just like in the cyclic case. So, I guess the cyclic model is in principle falsifiable, if next generation CMB experiments turn up measurable B-mode polarization. But if this doesn’t happen, I don’t see how one is ever, even in principle, going to distinguish experimentally between the cyclic and inflationary scenarios, which will make this whole area of research highly problematic.

On the whole the book seems to me to be too much of an advertisement for a very speculative idea, and I don’t think the public needs more of this in this kind of format. I didn’t notice anything in the book about what the case against cyclic cosmology might be, so anyone who wants to find out the other side would have to go on a search of the scientific literature, something most members of the public might not be able to do. Most strikingly, since the cyclic model is based on brane ideas motivated by string theory, the book contains endless hype about string theory, without so much as a word about its problems. One would have to read extremely carefully to realize that there is not a shred of experimental evidence for string theory. As for recent public debates about the problems of string theory, the authors just pretend they don’t exist. They give a long list of recent popular books in this area, such as those of Susskind and Vilenkin promoting the Landscape, but somehow neglect to include the two such books that have taken a critical point of view on string theory.

Associated with publication of the book, it looks like there will be various stories in the media promoting the cyclic vs. inflationary debate, trying to make it into a modern version of the old steady-state vs. Big Bang controversy. On the Edge web-site there’s a recent piece by Turok, which gives a good explanation of his current research and point of view. From NPR, there’s a very recent radio show about the cyclic model, entitled Forget the Big Bang Theory, where “renegade physicist” Turok’s model is described as “fighting words in the halls of science.”

Posted in Book Reviews | 29 Comments