Percontations

Posted on August 24, 2009 by woit

The Templeton Foundation has recently been sponsoring a series of Bloggingheads diavlogs, under the name Percontations. This week’s episode is Fiddling With the Knobs of the Universe, and it has cosmologist Anthony Aguirre and string theorist Clifford Johnson doing their best to hype string theory and the landscape. Critics are dismissed as people who believe obviously wrong things like “if it’s statistical it’s not science”.

Johnson argues that string theory landscape research is just like any other kind of science, capable of making testable statistical predictions, predictions based on generic properties of the theory (e.g. T-duality), and predictions of some parameters based upon fixing others by observation. He neglects to mention that decades of work by people trying to do such things have shown that there are very solid reasons why they don’t work. Not only have no predictions come out of this, but the reasons why have become clear.

While hyping the landscape, he acknowledges that string theory has had a problem with hype in the past. “We all bought into it to some extent” that string theory was going to give the Standard Model, and it was bad that this was promoted in the press as a polished, definitive story of how the world works. He claims to be happy that this has been backed away from in the last several years (although he never seems to have been happy about the existence of string theory critics who have raised the issue of the problems publicly).

In a recent posting, Johnson partially resolves a mystery I’d always wondered about, that of why he left Cosmic Variance. He explains that one reason was that Cosmic Variance was taking “the obnoxious route of calling someone an idiot or stupid for their religious beliefs at the outset.” Bloggingheads has recently featured Sean Carroll and Mark Trodden of Cosmic Variance also discussing cosmology and the multiverse (see here and here), but these episodes were not sponsored by Templeton.

Posted in Multiverse Mania | 35 Comments

Various and Sundry

Posted on August 20, 2009 by woit

Back from a final short summer vacation, with no further travel plans for the indefinite future. Some things I’ve recently come across that might be of interest:

  • Tommaso Dorigo has posted his contribution to a session on “Blogs, big physics and breaking news” held at last month’s World Conference of Science Journalists in London. There’s a recording of the session available here. Besides Tommaso, one speaker was Matthew Chalmers, who talked a bit about the “String Wars”, including the role of blogs in it. The last speaker was CERN’s James Gillies who discussed CERN’s efforts to do a better job of putting out information about progress on the LHC project, under some pressure from the phenomenon of others disseminating such information if they don’t…. They’ve done a much better job of this recently, putting out informative press releases almost immediately after major decisions are taken. I’m glad to hear that he finds the role of blogs to have been a positive one.

    For a recent LHC update, see these slides from a talk at the Lepton-Photon Symposium. On page 35 there’s a copy of the latest detailed schedule that I’ve seen, which one can compare to the continuing updates on progress here.

  • Also at Lepton-Photon, here’s a talk by Shamit Kachru about using AdS/CFT to build technicolor-type models of electroweak symmetry breaking that involve strongly coupled gauge theories. He and his wife Eva Silverstein will be leaving Stanford and joining the KITP in Santa Barbara this fall, see the press release here.

    For lots more about the KITP, its programs and its finances, see this presentation by David Gross to the NSF.

  • I see there’s an interesting sounding workshop at the Fields Institute this fall, but it scares me to see that it is described as a celebration of Allen Knutson’s 40th birthday. I seem to have gotten old very quickly, with conferences now devoted not only to people younger than me, but to people much younger than me that I recall meeting when they were just starting graduate school…
  • My nomination for the all-time highest quality discussion ever held in a blog comment section goes to the comments on this posting at Secret Blogging Seminar, where several of the best (relatively)-young algebraic geometers in the business discuss the foundations of the subject and how it should be taught.
  • There’s a long and well-informed article here on the multiverse, bringing together the “What the Bleep” crowd, mainstream physicists, theologians, and the logo of the Stanford Institute for Theoretical Physics (the one Kachru and Silverstein are escaping from).
  • For a selection of the latest in cutting-edge applications of new internet technology related to physics, there’s Gordon Watts with his Deeptalk, the nLab site of the n-category cafe, and the Twitter feed of Cosmic Variance.
    • Posted in Uncategorized | 9 Comments

    This Week’s Hype

    Posted on August 12, 2009 by woit

    From Softpedia this week, the news is of a Universal Theory of the Universe in the Works. According to the article,

    The theory of quantum mechanics was devised around 1920, and explains all this, but without accounting for gravity. Therefore, uniting the two ideas has since been an effort taken on by a large number of physicists. Now, an international group believes it is closer than ever to finally managing a breakthrough.

    Professors A.A. Coley, from the Dalhousie University, in Halifax, G.W. Gibbons at the University of Cambridge, in the UK, and C.N. Pope at the Texas A&M University, in the United States, led by young mathematician Sigbjørn Hervik, at the University of Stavanger, in Norway, believe that string theory is the best option physics has at bringing the two together.

    It’s hard to tell what this is based on, but the only paper I see with those authors is this one, which doesn’t really have much of anything to do with string theory.

    The source of the Softpedia article is one from Science Daily entitled A Grand Idea About the Universal Universe that tells us that:

    A mathematician in Norway and international fellow scientists have now conceived a grand idea about the universal universe. They have developed a method that may provide answers to universal problems and characterize and describe the universe….

    “The problem is that quantum mechanics does not include gravity and the theory of relativity does not include quantum mechanics”, Hervik says.

    Many attempts have been made to find a unifying theory of both. String theory is the best candidate so far, according to Hervik.

    Ultimately this all goes back to yet another university press release, this one about Hervik’s Universe.

    Posted in This Week's Hype | 15 Comments

    25 Years On…

    Posted on August 6, 2009 by woit

    Five years ago the 20th anniversary of the “First Superstring Revolution” was being celebrated, and I wrote some postings about this history (see here, here and here). This month is the quarter-century anniversary, and I haven’t seen any evidence of anyone celebrating.

    25 years later, it’s pretty clear that the anomaly cancellation discovered by Green and Schwarz doesn’t actually provide at all the kind of explanation of some aspects of the standard model that people got excited about back then. 1984 also saw the beginning of endlessly repeated and overhyped hand-waving arguments that string theory is needed to cure the perturbative ills of quantum gravity. It turns out that these arguments don’t actually work either. The latest issue of Science has an article about recent discoveries showing that N=8 supergravity amplitudes are much better behaved than expected. Zvi Bern compares the widespread belief that string theory is needed to deal with perturbative divergences to the belief that ulcers are caused by spicy food. While you could make a plausible hand-waving argument for this, it turns out that the real culprit is a bacterium, not enchiladas. According to the article:

    The work doesn’t disprove string theory, but it has string theorists backpedaling a bit in their criticism of quantum field theory. “At certain points, our understanding has been incomplete, and we may have said things that weren’t right,” says John Schwarz of the California Institute of Technology in Pasadena. “That being said, the fact is that we still need string theory.”

    Forced to concede that a quarter-century’s worth of argument about perturbative amplitudes was wrong, Schwarz tries to shift ground by claiming that the QFT problems are non-perturbative. That may very well be, but until one actually has a viable non-perturbative version of string theory, it will be hard to argue that string theory is the only way to go.

    A new review article about quantum gravity describes how things are 25 years after the revolution, with many if not most string theorists having given up hope that string theory has anything to say about unification:

    A personal anecdote might best convey the current state of affairs. Early in the spring 2007 semester my University of Florida colleague, Charles Thorn, began a seminar by announcing his belief that:

    String theory is just a technique for summing the leading terms in the 1/N expansion of QCD.

    After years of hearing more ambitious assessments this was so shocking that I checked to be sure I had understood correctly. Charles confirmed that I had; in his current view, the effort to regard superstrings as a fundamental theory of everything was a blind alley. Later that year I related Charles’ pronouncement to string theory colleagues on three continents and solicited their own opinions. About half of them agreed with him, more often the younger people.

    Update: One more, from Martha Stewart, Some Pearls of Wisdom on String Theory.

    Posted in Uncategorized | 29 Comments

    Various Items

    Posted on August 6, 2009 by woit
  • CERN just issued a press release announcing the decision about the energy for the initial LHC run: 3.5 TeV/beam.

    The procedure for the 2009 start-up will be to inject and capture beams in each direction, take collision data for a few shifts at the injection energy, and then commission the ramp to higher energy. The first high-energy data should be collected a few weeks after the first beam of 2009 is injected. The LHC will run at 3.5 TeV per beam until a significant data sample has been collected and the operations team has gained experience in running the machine. Thereafter, with the benefit of that experience, the energy will be taken towards 5 TeV per beam. At the end of 2010, the LHC will be run with lead ions for the first time. After that, the LHC will shut down and work will begin on moving the machine towards 7 TeV per beam.

  • The Lost University will be running two courses on physics, starting September 22. The more advanced one will be taught by Jeremy Davies, based on Lynne McTaggart’s book The Field:The Quest for the Secret Force of the Universe

    This book cites scientific experiments that examine the Zero Point Field, which is believed by some to be a universal energy source that connects everything.

    The other physics course will be taught by Sean Carroll, Clifford Johnson and Nick Warner. It’s entitled Introductory Physics of Time Travel and will be the prerequisite for a later course on “Advanced Physics of Time Travel”. One of the texts will be Sean Carroll’s forthcoming book.

    More about this from Clifford Johnson here.

  • The Anacapa Society, an organization aimed at promoting theoretical physics research at undergraduate institutions, has taken up permanent residence at Amherst, more here.
  • Tommaso Dorigo is trying to stir up trouble again, this time by pointing out the intriguing fact that, looking at events with just electron-positron pairs, both D0 and CDF have seen more than expected at an invariant mass around 720 GeV. Not that this is statistically significant or anything…
  • Talks from the recent FQXI conference in the Azores are available here.
  • Talks from the on-going Newton Institute workshop on Non-Abelian Fundamental Groups in Arithmetic Geometry are available here. Commentary from Jordan Ellenberg about Deligne’s talk is here. Jordan notes that:

    When I was first giving public lectures, someone gave me the hoary advice that I should quell nervousness by imagining the members of the audience in their underwear. Strange to think that, in this new broadband world, most of them actually are.

    • Posted in Uncategorized | 3 Comments

    Back

    Posted on August 5, 2009 by woit

    I’ve spent most of the last month traveling, first to Latvia and Russia, then to China, finally to Seattle. Back now, looking forward to staying in one time zone and not seeing the interior of a plane for a while.

    In China I visited Shanghai, Suzhou, Hangzhou, Yellow Mountain, Hong Kong and Macao, all of which was an amazing experience (thanks to John Baez for, among other things, urging me to search out the few remaining sections of old Shanghai). The weather unfortunately was less than ideal, with record heat in Shanghai, rain at Yellow Mountain, and clouds the day of the eclipse. Still, it was a lot of fun to be in People’s Square and see the city go dark for 6 minutes. Here’s one view from about that moment:

    After getting back to New York from China, I turned around and went out to Seattle to attend my friend Nathan Myhrvold’s surprise 50th birthday party. This was held at the new lab of his company, Intellectual Ventures, and among the organizers were Bill Gates and Lowell Wood. In attendance were many of the luminaries of the technology and culinary worlds, with Wylie Dufresne of New York’s WD-50 one of several chefs who came in to attend the party and serve amazing food to the guests. Not the sort of party I normally attend…

    Regular blogging will resume imminently. Things seem to have been rather quiet the past couple weeks anyway. The news of delays at the LHC reported here earlier has been getting more media attention. There’s a very good article about the LHC problems by Adrian Cho at Science here, and the New York Times ran a front-page story yesterday. For some reason, the Times decided that it was important to quote what prominent theorists have to say about this, including:

    “I’ve waited 15 years,” said Nima Arkani-Hamed, a leading particle theorist at the Institute for Advanced Study in Princeton. “I want it to get up running. We can’t tolerate another disaster. It has to run smoothly from now.”

    Gordon Watts has some comments about this here (including pointing out that “running smoothly from now” is probably not in the cards), and there’s also a good posting at Resonaances.

    My understanding is that the LMC (LHC Machine Committee) was meeting today to go over all that is known about the splices problem and discuss the question of what the highest energy is at which the machine can safely run in its current state. A smaller group of people, in consultation with the experiments and the director, will then have to decide either to run at that energy, or accept further delays for repairs to allow running at a higher energy. It’s not known how long that decision will take, but presumably it will come soon. If no further repairs are to be made, the current schedule has the machine ready for injection of a beam in mid-November.

    Update: It’s 3.5 TeV/beam.

    Posted in Experimental HEP News, Uncategorized | 12 Comments

    Weinberg at CERN

    Posted on July 17, 2009 by woit

    Steven Weinberg was visiting CERN recently and gave a talk entitled The Quantum Theory of Fields: Effective or Fundamental? He discussed the ups and downs of the “market price” of quantum field theory, showing a decline since a peak in 1984, followed by a conjectured increase in the future. He also described the history of his work that led to the modern point of view on the role of QFT as an effective theory.

    He ended with comments on the “asymptotic safety” approach to quantum gravity, noting that it is quite possible that string theory is not needed, that the world can just be described at a fundamental level by quantum field theory (and thus his conjecture that QFT may come back into fashion as a fundamental theory):

    I don’t want to discourage string theorists, but there’s just the possibility that maybe that isn’t the way the world is, that the world is much more like we’ve always known, that is, the Standard Model and General Relativity.

    Update: Weinberg has a new paper on the arXiv, covering much the same material as this talk.

    Posted in Uncategorized | 5 Comments

    Latest From the LHC

    Posted on July 15, 2009 by woit

    Here’s an announcement from the CERN DG Rolf Heuer sent out to CERN employees today:

    The foreseen shutdown work on the LHC is proceeding well, including the powering tests with the new quench protection system. However, during the past week vacuum leaks have been found in two “cold” sectors of the LHC. The leaks were found in sectors 8-1 and 2-3 while they were being prepared for the electrical tests on the copper stabilizers at around 80 K. In both cases the leak is at one end of the sector, where the electrical feedbox, DFBA, joins Q7, the final magnet in the sector.

    Unfortunately, the repair necessitates a partial warm-up of both sectors. This involves the end sub-sector being warmed to room temperature, while the adjacent sub-sector “floats” in temperature and the remainder of the sector is kept at 80 K. As the leak is from the helium circuit to the insulating vacuum, the repair work will have no impact on the vacuum in the beam pipe. However the intervention will have an impact on the schedule for the restart. It is now foreseen that the LHC will be closed up and ready for beam injection by mid-November.

    This is an extra two week or so slip with respect to the latest draft schedule I’d seen. In addition, the question of how to deal with defective splices remains open. Efforts now are directed towards determining what the maximum safe energy is, assuming that the cold sectors are not warmed up, with the plan to have an answer to this question by the second week of August. Part of this effort involves study of possible changes in the parameters that determine how quenches are detected and dealt with, in order to optimize the maximum safe energy.

    Update: The latest CERN Bulletin is out, with more about this.

    Posted in Experimental HEP News | 23 Comments

    BRST and Dirac Cohomology

    Posted on July 11, 2009 by woit

    For the last couple years I’ve been working on the idea of using what mathematicians call “Dirac Cohomology” to replace the standard BRST formalism for handling gauge symmetries. So far this is just in a toy model: gauge theory in 0+1 dimensions, with a finite dimensional Hilbert space. Over the last few months I’ve finally got this to the point where I think I understand completely how this should work, at least for this toy model. I talked about this last week in St. Petersburg, and have a preliminary version of a paper on the subject, which is available here. Next weekend I’m leaving for a trip to Shanghai and Hong Kong (the plan is to be in Shanghai for the July 22 total solar eclipse, which will be visible there). After I get back at the beginning of August I’ll work on the paper a bit more, hoping to have a final version done by the beginning of September, when the academic year starts.

    The paper uses quite a lot of mathematical technology, so I fear most people will find it hard to read. This fall I hope to get back to finishing the Notes on BRST I was writing up, the idea behind those was to give a more expository account of this subject. That project got bogged down when I realized there was something I was still confused about, and after getting unconfused it seemed like a good idea to get the basic ideas down on paper, since the expository project might take a while to complete.

    First of all, what this is and what it isn’t. It’s a toy quantum mechanical model, with gauge symmetry treated using some new ideas from representation theory which are related to BRST, but different. It’s not a QFT, and not a treatment of gauge symmetry in the physical case of four space-time dimensions. I’ve been thinking about how to extend this to higher dimensions, but this requires some new ideas. Next on the agenda is to try and get something that works in 1+1 dimensions, where one can exploit a lot that is known about affine lie algebras and coset models. There also appear to be interesting possible connections to geometric Langlands in that case.

    Given a quantum system with G-symmetry, the BRST method allows one to gauge a subgroup H, picking out the H-invariant subspace of the original Hilbert space using Lie algebra cohomology methods. The proposal here is to do something different, picking out a subgroup H of symmetries one wants to keep, and gauging the rest. In the special case where Lie G/Lie H is the sum of a Lie subalgebra and its conjugate, the method proposed here reduces to the standard BRST method, but it is more general.

    An algebraic version of the Dirac operator plays a role here somewhat like that of the BRST operator in the standard formalism. One difference is that the square of this operator is not zero. However, it is in the center of the algebra of operators acting on the Hilbert space, so its action on operators squares to zero. This sort of thing has been studied a bit before in the physics literature, in the context of supersymmetric quantum mechanics models, but I do believe that the interpretation here as a method for handling gauge symmetry is new.

    One thing I want to add to the paper is some comments about the relation to the physical Dirac operator. The point of view on the Dirac operator explained here that comes out of representation theory seems to me perhaps the most intriguing part of this story. Remarkably, this Dirac operator is in some sense a quantization of the Chern-Simons form. The full story of how to use this in higher dimensions remains obscure to me, but there is some hope it will bring together the physical Dirac operator, something like BRST, and something like supersymmetry in a new way.

    Posted in BRST | 16 Comments

    Various and Sundry

    Posted on July 10, 2009 by woit

    For the latest on the status of the LHC, see the July 2 talk of Steve Myers mentioned here earlier, and a July 8 talk (slides, video) that has some more recent news. The question of what to do about bad splices is still up in the air. The current plan is to make measurements at 80K during the next few weeks on the three sectors that have not been warmed up, then present options during the second week of August to the DG and the experiments. The decision to be made will be about how long to delay the start-up to fix more splices. If more splices get fixed, the machine can safely be run at higher energy. The optimistic scenario now seems to be that it will be possible to run at some energy in the range of 4-5 TeV/beam, without introducing further delays in the current draft schedule (the latest schedule has the machine ready to start circulating beams around the end of October). Gordon Watts has more detail in a recent post, including one of the relevant plots showing the energy vs splice resistance trade-off.

    Two items on the multiverse front:

  • Lenny Susskind gives new depth and meaning to the word “chutzpah” with an article in Physics World on Darwin’s Legacy. It seems that Darwin’s legacy for physics is the field of string theory anthropic landscape pseudo-science. Luckily, I don’t think creationists normally read Physics World.
  • Sean Carroll’s book “From Eternity to Here” is now scheduled to appear next January. It has a Facebook page and a mission statement:

    You can turn an egg into an omelet, but not an omelet into an egg. This is good evidence that we live in a multiverse. Any questions?

    • String theorist Oswaldo Zapata has posted the third part of his essay on the history of superstring theory, dealing with the question of the “beauty” of string theory. Basically he argues that it was only in 1999, after it started to become clear that string theory unification wasn’t working out, that a publicity campaign about the “beauty of string theory” got started:

    During the late eighties and early nineties, and motivated by the relative success of the heterotic superstrings, string theorists were submerged in intricate and endless computations trying to recover the standard model using a ‘‘top-bottom’’ approach. At that time no one was talking publicly about a beautiful construct. In fact, the theory was in an ugly impasse and mathematical consistency was the only remote trace of beauty…

    In this section we have seen that, in contrast to what is currently claimed, string theory was not always considered to be a beautiful theory. The public recognition of the beauty of the theory is recent, dating from around 1999, and it was due mainly to the convergence of two factors: a favourable context, “internal” and “external,” and an acute sense of opportunism.

    From the Publisher’s Weekly review of Graham Farmelo’s life of Dirac:

    In 1955, Dirac came up with a primitive version of string theory, which today is the rock star branch of physics.

    The opera Hypermusic Prologue: A Projective Opera in seven Planes, libretto by Lisa Randall, had its first performance last month in Paris. It will be presented again in Barcelona in November.

    FQXI seems to like to have conferences for their members at scenic volcanic locations in the mid-Atlantic. This year it’s the Azores, here’s their schedule, talks to appear here, blogging here (Sabine Hossenfelder) and here.

    Strings 2009 finally got around to putting slides from most of the talks online here. The one talk that seemed to have something new wasn’t about strings, it was Arkani-Hamed’s talk on Holography in Flat Space: Algebraic Geometry and the S-matrix, based on work to appear with Cachazo, Cheung and Kaplan. It’s based on studying the structure of amplitudes in twistor space, and the talk includes many exclamation points, and the claim that “SOME POWERFUL MATHEMATICAL STRUCTURE IS AT WORK!”. More specifically:

    Very natural and beautiful mathematical structure – intersection theory and Schubert Calculus – seems to lie at the heart of tree and loop gluon scattering amps!

    From the slides it does appear that there’s some nice mathematics at work here, I look forward to seeing the paper.

    Posted in Experimental HEP News, Multiverse Mania, Uncategorized | 18 Comments