Questions About the Multiverse

Posted on July 19, 2011 by woit

The August issue of Scientific American has the multiverse on the cover, with a skeptical feature article on the topic by George F. R. Ellis, Does the Multiverse Really Exist?, which argues that heavily promoted multiverse research isn’t really testable and can’t explain much of anything. Vilenkin and Tegmark respond with The Case for Parallel Universes.

I just took a look at some of the earliest postings on this blog about the multiverse from as far back as seven years ago (e.g. here and here). Things haven’t changed at all. One might be tempted to criticize Scientific American for keeping this alive, but they just reflect the fact that this pseudo-science continues to have significant influence at the highest levels of the physics establishment. The Perimeter Institute recently ran a conference on Challenges for Early Universe Cosmology, which was dominated by multiverse mania. Unlike the case at SciAm, multiverse skepticism didn’t get prominent play at Perimeter.

Update: For those of you who just can’t get enough multiverse, the Sci-Fi film Another Earth opens Friday. Click on “Parallel Worlds” for an explanation of “the theoretical physics behind the film.”

Posted in Multiverse Mania | 29 Comments

This Week’s Leak

Posted on July 12, 2011 by woit

Everyone in the HEP community is breathlessly awaiting the release of results from the 2011 LHC run, expected to come at the EPS-HEP 2011 conference in Grenoble starting July 21. A public press conference has been announced for July 25. Presumably the new results will further tighten limits on supersymmetric particles, extra-dimensional models and other exotica, but the real excitement surrounds the question of what the news about the Higgs will be. The latest LHC data should finally allow competition on this front with the Tevatron.

Philip Gibbs at viXra log has posted here what looks like the bottom line for CMS. They are not yet able to exclude a Higgs at lower masses, including the range where the Tevatron has an exclusion region, but are able to exclude (at 95% confidence level) a SM Higgs in a higher mass region (about 275-425 GeV). This sort of result is not quite what it looks like, since precision electroweak measurements already rule out such a SM Higgs, and recall that the Higgs self-coupling increases with Higgs mass, meaning that one is entering into a region where one is not sure that perturbation theory applies. If the Higgs is not a weakly coupled field, life becomes much more complicated.

The source of the plot is variously described as “shown [July 8] at a seminar which as far as I know was public”, from “a public part of the CERN repository”, and “not yet public but was made accessible on a Fermilab site”.

ATLAS, the competition for CMS, presumably has a similar plot up its sleeve just about ready for release at EPS-HEP 2011. Once the two experiments have made public their independent results at this conference, they intend to immediately get to work producing a combined plot, with goal of releasing it at Lepton-Photon 2011, which will take place in Mumbai August 22-27.

Posted in Experimental HEP News | 11 Comments

Higher Speculations

Posted on July 8, 2011 by woit

Some commenters here a while ago made the excellent suggestion that I should take a look at a book published this spring, Helge Kragh’s Higher Speculations: Grand Theories and Failed Revolutions in Physics and Cosmology. I’ve always wondered what historians of science would make of the increasing dominance of research in fundamental physics by unsuccessful highly speculative research programs, and have also often wondered if there are any relevant historical parallels to this situation. This book does a great job of addressing those questions, and it’s pretty much unique in doing so.

Kragh spends the first half of the book on history, the second half on currently popular (of varying degrees of popularity…) topics including varying constants of nature, cyclic cosmological models, anthropics, the multiverse and string theory. He doesn’t explicitly make any attempt to evaluate how successful these current efforts are, but they are discussed in the context of previous failures and parallels are drawn. I didn’t know much about the history of “vortex theory” in nineteenth century physics, and this turns out to be possibly the best historical parallel to the story of string theory. Here’s an extract from the extensive and enlightening discussion of that bit of scientific history:

From its beginnings in 1867 to its end at about 1900, the [vortex] theory was frequently justified on methodological and aesthetic grounds rather than its ability to explain and predict physical phenomena. In an 1883 review of ether physics, Lodge described the vortex atom theory as ‘beautiful’ and ‘the simplest conception of the material universe which has yet occurred to man’. He added, just as Michelson would do twenty years later, that it was a ‘theory about which one many almost dare to say that it deserves to be true’.

The audience listening to William Hicks’ address at the 1895 meeting of the British Association for the Advancement of Science would not suspect that the vortex theory of atoms was dying. Without paying much attention to the theory’s disappointing record with regard to empirical physics, Hicks reviewed in an optimistic tone the theory of various vortex objects such as rings, spheres and sponges. He realized that relatively little progress had been made over the years in the mathematical development of the theory, and that progress was even more lacking in the theory’s contact with experiments. However, these problems he deftly turned into a defence of the theory, for the undeveloped mathematical framework meant that the theory could not be rigorously tested. Hicks was convinced that the road towards progress would be to develop still more advanced mathematical models. The vortex theory, he said ‘is at present a subject in which the mathematicians must lead the attack’.

Surely many physicists of the day would have described vortex theory as “our best hope for a unified theory”, and one wonders if any of them thought of it as a “part of 20th century physics that fell by chance into the 19th century.”

Kragh’s book does something really remarkable and valuable: it starts to put some aspects of the last 30 years of fundamental physical theory into a plausible historical context. The future of the subject remains a mystery though, but one can hope that on the vortex theory timeline we’re about to hit the analog of 1900, with successful rather than failed revolutions ahead of us.

Posted in Book Reviews | 29 Comments

Local Blogs

Posted on July 1, 2011 by woit

There are now several excellent blogs somehow related to mathematics being run by local people, including a couple new ones, so I thought it would be a good idea to mention these here:

  • Andrew Gelman of the Columbia Statistics department runs the very active Statistical Modeling, Causal Inference and Social Science blog, which features a wealth of all sorts of different topics, from technical ones about statistics, to social science applications.
  • Emanuel Derman, who started his career as an HEP theorist, was one of the early migrants to the financial industry, and now is teaching here at Columbia in the Financial Engineering program, has a new blog at Reuters. His last book was the very interesting My Life as a Quant, this fall he has a new one coming out entitled Models Behaving Badly.
  • Cathy O’Neil, a mathematician who taught here for a while before changing career path, starting with a job at the hedge fund D.E. Shaw, has recently started the wonderful Mathbabe blog.
  • I think I mentioned this already, but one of my colleagues, Johan de Jong (Cathy’s husband) also has a blog, the Stacks Project Blog. If your metric to evaluate blogs is something like “quality of information” x “degree of abstraction and technicality”, his has to be the best blog in the world.

    • If you have comments on these blogs, I encourage you to post them there rather than here. I would be interested in hearing about any other local math/physics related blogs that I’m unaware of.

    Update: Another local math/physics-related blog has made its debut today, Davide Castelvecchi’s Degrees of Freedom. It’s part of a network of new blogs being launched today by Scientific American, which is based here in New York.

    Posted in Uncategorized | 3 Comments

    Strings 2011

    Posted on June 27, 2011 by woit

    Strings 2011 started today in Uppsala, with attendance quite a bit lower than in the past (259 registered participants, versus 500 or so at some of the past such conferences). One reason for this may be the high conference cost (discussed here), another may be that excellent video of the talks is available, so why bother traveling to Uppsala?

    The opening talk was by David Gross, who tried to address the question “Where do we stand?” for string theory. He claimed the field is “extremely healthy”, “vibrant and exciting”, “making enormous progress in a variety of areas'”, with “stupendous progress” in N=4 planar SYM. At the same time, he acknowledged that it was “very sobering” that string theory was 43 years old.

    In the past, Strings XXXX conferences often featured a call for progress towards making predictions that could be tested at the LHC. With LHC data now coming in, Gross acknowledged that this had been a failure: there are no string theory LHC predictions. He put a positive spin on this by noting that the lack of any BSM signal at the LHC so far is not a worry for string theory, since string theory can’t be tested at the LHC. As for the lack of any supersymmetry signal so far, he says that “I personally am not yet worried”, while acknowledging that some people are becoming pessimistic. While no SUSY is not a worry for string theory, he feels that “it would be awfully nice for string theory if SUSY appeared”. Supposedly he has made bets on SUSY at the LHC, but he gave no indication of when he would start to worry (or pay off the bets) if SUSY continues to not be there.

    The main area of progress he sees is the usual gauge-gravity duality that has dominated the field for years, together with progress on N=4 SYM amplitudes. He sees Verlinde’s “Entropic Gravity” as an “exciting development I find enormously interesting”. Evidently later this week Verlinde will discuss his latest ideas about this which supposedly include an explanation of dark energy and dark matter.

    Gross went over quickly the questions about string theory he first raised in a similar talk 26 years ago, which mostly remain unanswered, including the basic one of “What is String Theory?”. The additional questions raised by attempts to understand the emergence of spacetime in a deSitter background were one factor that inspired him to end with the quote that:

    The most important product of knowledge is ignorance.

    To which he added “After 43 years of string theory , it would be nice to have some answers.”

    Surprisingly, not a word from Gross about anthropics or the multiverse. I assume he’s still an opponent, but perhaps feels that there’s no point in beating a dying horse. Susskind isn’t there and oddly, the only multiverse-related talks are from the two speakers brought in to do public lectures (Brian Greene and Andrei Linde, Hawking’s health has kept him from a planned appearance). So the multiverse is a huge part of the public profile of the conference, but pretty well suppressed at the scientific sections. Also pretty well suppressed is “string phenomenology”, or any attempt to use string theory to do unification. Out of 35 or so talks I see only a couple related to this, which is still the main advertised goal of string theory.

    I’m looking forward to the talks of Witten, Gaiotto and Gukov, which I hope will provide a gentle introduction to their intriguing recent long papers on the arXiv. To the extent I find time to watch talks this week and have any comments about them, I’ll try and add updates to this posting.

    Update: After looking at most of the talks online, the most remarkable thing about Strings 2011 is how little there is about string theory. One of the speakers, Chris Hull, started off his talk with the comment:

    At lunch today one of the organizers was observing that my talk was unusual in being one of the few talks actually about string theory. It would be interesting to speculate on what that might mean about the state of the field, but it would be invidious to do so here.

    One of the main themes of the conference so far has been study of mathematically interesting supersymmetric QFTs in 3,4,5 and 6 dimensions, often obtained from a specific class of 6d theories, which themselves remain poorly understood (what is known about them was reviewed by Greg Moore). Witten gave an overview of his work relating Khovanov homology and QFT, which involves a chain of various 6d, 5d, 4d, 3d and 2d QFTs. Nati Seiberg reviewed the technology used for constructing these theories on various special backgrounds, noting that this was all about “rigid” SUSY theories, with supergravity and string theory making no appearance.

    Update: The videos of the talks are now all up. I took a look at the Verlinde talk, and the ideas he is putting forward still strike me as pretty much empty of any significant content. In Jeff Harvey’s summary of the conference, he notes that many people have remarked that there hasn’t been much string theory at the conference. About the landscape, his comment is that “personally I think it’s unlikely to be possible to do science this way.” He describes the situation of string theory unification as like the Monty Python parrot “No, he’s not dead, he’s resting.” while expressing some hope that a miracle will occur at the LHC or in the study of string vacua, reviving the parrot.

    That the summary speaker at the main conference for a field would compare the state of the main public motivation for the field as similar to that of the parrot in the Monty Python sketch is pretty remarkable. In the sketch, the whole joke is the parrot’s seller’s unwillingness, no matter what, to admit that what he was selling was a dead parrot. It’s a good analogy, but surprising that Harvey would use it.

    Posted in Strings 2XXX | 33 Comments

    Bad Boys of Physics

    Posted on June 22, 2011 by woit

    Scientific American is running a Bad Boy of Physics story (also see here) in the July issue, about Lenny Susskind. Here’s the “nut graph”:

    Physicists seeking to understand the deepest levels of reality now work within a framework largely of Susskind’s making. But a funny thing has happened along the way. Susskind now wonders whether physicists can understand reality.

    In the interview, Susskind explains that he was a bad boy as a youth, but “just so much better than anybody else, including the professor.” In recent years he has been the most prominent promoter of the string theory multiverse, and now claims that this pseudo-science convincingly dominates the field (SciAm seems to agree…), with the situation just like in the early days of QCD:

    A large fraction of the physics community has abandoned trying to explain our world as unique, as mathematically the only possible world. Right now the multiverse is the only game in town. Not everybody is working on it, but there is no coherent, sharp argument against it.

    In 1974 I had an interesting experience about how scientific consensus forms. People were working on the as yet untested theory of hadrons [subatomic particles such as protons and neutrons], which is called quantum chromodynamics, or QCD. At a physics conference I asked, “You people, I want to know your belief about the probability that QCD is the right theory of hadrons.” I took a poll. Nobody gave it more than 5 percent. Then I asked, “What are you working on?” QCD, QCD, QCD. They were all working on QCD. The consensus was formed, but for some odd reason, people wanted to show their skeptical side. They wanted to be hard-nosed. There’s an element of the same thing around the multiverse idea. A lot of physicists don’t want to simply fess up and say, “Look, we don’t know any other alternative.”

    Susskind had a distinguished career as a theorist for many years, and has managed to do quite well with his multiverse campaign for quite a while now. There has been a lot of coverage of this story on this blog, for some high points, see here, here, here and here.

    In other news, the media has been full of stories about another physicist who has been a bad boy, David Flory. He started his career as an HEP theorist back in the late 1960s, as a student at Yeshiva University, and collaborator there with Susskind. Like a huge number of other people, he got his permanent academic job in 1969, and has been at Fairleigh Dickinson University ever since.

    Posted in Multiverse Mania | 44 Comments

    Quick Links

    Posted on June 17, 2011 by woit
  • The House committee responsible for the DOE budget has passed a FY2012 appropriations bill, details here. Total funding for DOE Science is down .9% from FY2011 at $4.8 billion. HEP gets a .2 percent increase, Biological and Environmental Research is whacked %10.6, with the committee opposed to climate and atmospheric research being funded by DOE. The language about DUSEL argues against it becoming a DOE lab, but money is made available to keep options open. There is support for Fermilab’s Project X (the “intensity frontier”), but a warning that it may not be possible to continue funding both the “intensity frontier” and the LHC (the “energy frontier”).

    Fermilab this week announced a program to offer a “voluntary separation program” under which they hope 100 employees will voluntarily leave. They’re clearly trying to better position the lab for tight budgetary conditions ahead.

  • Over in the Czech Republic, Lubos Motl is hanging out with President Vaclav Klaus and is one of the contributors to his 70th birthday Festschrift. Lubos may have a career ahead in Czech politics, too bad he left the US just before the Tea Party movement got going. He would have fit in quite well with them, but I guess at least in the Czech Republic, he can legally become President some day.
  • From Physics World, it seems that Lawrence Krauss will be joining with 13 other very prominent academics to teach at New College for the Humanities, a new private university in London. The new university has caused quite a stir in Britain, since it’s unlike anything else there. Tuition will be set at US private college levels, $29,000/year, twice what other British universities charge. The business plan is not public, but Wikipedia says 10 million pounds in funding for the first two years is coming from private investors, with the 14 senior academics getting a 1/3 equity stake in the venture. It’s unclear how much teaching they’ll each be doing, since most will retain their current positions elsewhere and just give anything from one to 20 lectures per year.
  • The LHC is doing quite well, with over an inverse femtobarn delivered to the experiments already. For the latest, take a look at the slides of the talks here. At the KITP, there was a very interesting talk by Tim Nelson. He addresses the question of whether the LHC detectors, once their searches aimed at standard speculative ideas such as supersymmetry and extra dimensions turn up empty, can be reconfigured to look for other sorts of exotic possibilities, ones that the current triggers are not sensitive to.
  • There’s an article here about filmmaker Errol Morris, whose new film “Tabloid” is coming out later this year. I saw it a few months ago at a showing in New York, and highly recommend it. It’s one of the most surprising and amazing documentaries I’ve ever seen. Real life is much stranger than fiction. In the article, Morris describes his early career, which included having Thomas Kuhn throw an ashtray at him and have him kicked out of the graduate program in philosophy at Princeton. He moved on to Berkeley, where he hung out with Dan Friedan:

    “I felt that he had destroyed my life,” said Morris. It left him reeling for years to come: He still remembers sitting in a coffee shop at Berkeley with Daniel Friedan, a fellow Princeton exile and the son of feminist icon Betty, and commiserating over the frustrating time they’d had out East.

    “I’m talking about all these problems that I had with Kuhn, which was a constant refrain, and he’s telling me about all the problems he’d had in the physics department,” Morris recalls. “He said, you know, ‘They just could not appreciate me. I had discovered a new kind of physics!’ And I thought, ‘Oh, no. This looks bad. This looks very, very, very bad. This is not going to turn out well. We’re both going to the nuthouse.’ ”

    Of course, they didn’t. Friedan would go on to win a Macarthur Fellowship, and be recognized for his pioneering work on string theory. Morris, meanwhile, left academia behind once and for all to make a movie about a pet cemetery, called “Gates of Heaven,” which became a cult classic, and which Roger Ebert described as one of the 10 greatest films ever made.

  • There’s a conference going on this week and next at the ETH in Zurich on quantum gravity, with slides appearing here. My long held belief about quantum gravity is that it’s a problematic subject unless some way can be found to connect it to unification with the rest of physics, and thus some sort of testability or good reason to believe one is on the right track. Matthias Blau promotes string theory by arguing that it should be judged:

    not by, say, its failure to (so far?) provide specific predictions for BSM physics, or disgust with some of the hype and overblown claims regarding string theory (I may share your feelings . . . )

    Among other things, he explains some of the problems with M-theory, then notes that Tom Banks has a highly mystifying recent proposal about this:

    For very recent proposal for how to deal with (some of) these issues, see T. Banks, Fuzzy Geometry via the Spinor Bundle, with Applications to Holographic Space-time and Matrix Theory, arXiv:1106.1179 (and then please explain it to me . . . )

    His talk, together with the recent preprint Is string theory a theory of quantum gravity?, provides a good understanding of what the problems are facing attempts to use string theory to quantize gravity, from the point of view of a string-enthusiast.

    For the latest from the LQG camp, see Carlo Rovelli’s talk here.

    • Posted in Uncategorized | 19 Comments

    This Week’s Hype

    Posted on June 15, 2011 by woit

    Last month’s Quark Matter 2011 conference was a venue for discussion of new results from the first heavy-ion run at LHC energies last fall. I’ve looked a bit at the slides of the talks, but this is an area far from my expertise. One thing I’ve been wondering about is whether the heavily-promoted application of AdS/CFT to studying heavy-ion physics could possibly be tested at the LHC. Does AdS/CFT make any distinctive predictions about how things will change as one goes from RHIC energies to LHC energies, and have these been checked? Looking at the slides, there seem to be all sorts of interesting things being learned about heavy-ion physics, but little mention of AdS/CFT modeling of such phenomena. Perhaps an expert can help by pointing to pre-LHC predictions, and explaining whether they’ve been tested already, or may be in the future.

    Symmetry Breaking magazine today does cover Quark Matter 11, with String theory may hold answers about quark gluon plasma, which appears to mostly contain the same hype about string theory and heavy ion physics that has been current for the last half-dozen years now:

    Now, scientists have begun to see striking similarities between the properties of the early universe and a theory that aims to unite gravity with quantum mechanics, a long-standing goal for physicists.

    Unfortunately there’s nothing in the article about any LHC test of these ideas. The closest we get to that is this from Krishna Rajogopal (his talk is here):

    “String theory is like a gift to us,” Rajagopal said. “We’re challenged with understanding the quark-gluon plasma as a liquid, and while string theory doesn’t give us precision, it can help us get a feel for the shape of the subject.”

    So, I gather that AdS/CFT makes no precise, testable predictions, with the best case to be made for it that “it can help us get a feel for the shape of the subject”, whatever that means. A question for experts: if “String theory may hold answers about quark-gluon plasma”, what are the questions for which string theory is giving answers, and what does the LHC data have to say about these questions?

    Update: David Mateos has posted a write-up of his Quark Matter 2011 talk here. In it, he explains what the problems are with using AdS/CFT to say anything about QCD. In terms of the question of LHC predictions, he gives an example: the dispersion relation of heavy quarkonium mesons moving through the quark-gluon plasma. Unfortunately, this doesn’t look like much of a prediction:

    I emphasize that whether one obtains a visible peak, simply a statistical enhancement or an unobservable effect depends sensitively on many parameters related to the in-medium J/Psi physics. The latter is not sufficiently well understood to make a precise prediction, so all one should take away from figure 3(right) is that there could be an observable effect for some values of the parameters within the acceptable range.

    Posted in This Week's Hype | 41 Comments

    How the Hippies Saved Physics

    Posted on June 13, 2011 by woit

    A review that I wrote of David Kaiser’s How the Hippies Saved Physics is now available at American Scientist. A quick summary is that I think it’s a marvelous book, telling in well-researched and entertaining fashion a story I’ve always wanted to know more about. I’m not convinced though by the main argument of the title, that this group of people “saved physics”, rescuing it from an oppressive “shut up and calculate” ideology by showing the way towards the importance of Bell’s theorem and helping start the field of quantum information theory. Perhaps the author though is just emulating his subjects, known for their playful outlandishness.

    There are quite a few interesting things I learned from the book that didn’t make it into the review. One example is the story of Werner (of EST fame) Erhard’s theoretical physics conferences of the late 70s and early 80s, organized in collaboration with Sydney Coleman and Roman Jackiw. Among the factors that brought these events to an end was the advent of string theory: it was felt that no string theory conference without Witten attending would be taken seriously, and by then Witten wanted nothing to do with EST and its founder (although he had attended, with the likes of Feynman and Weinberg, the earliest conference in the series back in 1977).

    If you find this subject at all interesting, I highly recommend the book.

    For another take on the same subject, from one of its main participants, Jack Sarfatti’s memoir Star Gate is available for free these days in a pre-publication version here.

    I’m afraid that my own description of where the physicists described in Kaiser’s book ended up would not be the field of quantum information theory, but the much larger swamp of dubious claims about quantum physics that is still very influential. For example, this week at the AAAS meeting in San Diego there’s a session on Quantum Retrocausation, see this listing from the World of Parapsychology.

    Update: I should also mention that Chad Orzel discusses the book here and here.

    Posted in Book Reviews | 37 Comments

    $6.5 Million for Entropic Gravity

    Posted on June 12, 2011 by woit

    One of this year’s Spinoza Prizes goes to Erik Verlinde. It comes with 2.5 million euros to fund the prize-winner’s research. Last fall Verlinde received a 2 million euro ERC Advanced Grant to fund his research program, so that’s a total this past year of 4.5 million euros, or about $6.5 million.

    Verlinde’s current research focuses on ideas about “emergent gravity” (see here and here). According to Wikipedia his work explains the observed value of the cosmological constant.

    I’ve no idea how Verlinde will spend the money, but it looks like emergent gravity research will be extremely well financed. $6.5 million I’d estimate corresponds to about 100 postdoc-years. In a couple weeks Verlinde will unveil his latest work at Strings 2011. Since that’s among the most expensive conferences around (see here), perhaps he could chip in to fund it. I’d estimate he should be able to single-handedly fund Strings 20XX through at least 2050.

    Posted in Uncategorized | 19 Comments