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

    This Week’s Hype

    Posted on July 7, 2009 by woit

    A Leiden University press release headlined Physical Reality of String Theory Demonstrated is being picked up and used to generate news stories in the media.

    It starts off:

    String theory has come under fire in recent years. Promises have been made that have not been lived up to. Leiden theoretical physicists have now for the first time used string theory to describe a physical phenomenon.

    which follows the usual dishonest and misleading template for attempts to deal with string theory’s failure as a unified theory. The idea is to put out a press release announcing that string theory has finally lived up to its promise and shown its critics to be wrong, because of evidence it may work as an approximation method for some strongly coupled condensed matter or nuclear physics model. The fact that this has nothing to do with string theory’s continuing utter failure as a fundamental theory is carefully not mentioned, ensuring that non-expert readers of the press release will be misled.

    A common excuse for this is that it is being done by journalists, with the scientists involved having no responsibility for the misleading material. In a news media story, conceivably this could be the case, but a university press release is something different. University researchers have both the right and the responsibility to ask for the retraction of a university press release that mis-characterizes their work. When they don’t do this, they make themselves responsible for actively misleading the public about this subject.

    Posted in This Week's Hype | 25 Comments

    LHC Status

    Posted on July 1, 2009 by woit

    If you want to keep up with the latest news on the LHC status, tomorrow at 3pm Geneva time there will be a webcast of a talk by Steve Myers. The abstract reads:

    The status of the LHC will be presented. This will include the repair of sector 34, the ongoing consolidation work in the other sectors, and the progress with the new Quench Protection System. The results of recent resistance measurements of the copper stabilizers will be presented.
    The plans for powering the LHC and the tunnel access restrictions will also be discussed. Finally the planning for the start-up and the programme for future operational consolidation work will be detailed.

    One crucial piece of news will be what was learned from the resistance measurements in the sector that was just warmed up, and whether warming up of the other sectors will be required.

    I’ll miss this since I’ll be on a plane.

    Posted in Uncategorized | 11 Comments

    Conferences

    Posted on June 29, 2009 by woit

    In a couple days I’ll be leaving for a week-long trip to Riga and St. Petersburg. I’ll be in St. Petersburg from July 5-8, and will give a talk on BRST and Dirac Cohomology at a conference there. I’m finishing up a draft of a paper on the subject now, will try and write about it here after I get back from the conference.

    The Strings 2009 information blackout continues. Still no talks or blogging on-line, although a new twit has made it out, summarizing the conference:

    more effort being put into contact w experiment•hope for LHC•fundamental issues need more attention•much optimism

    although that could have functioned as a summary of pretty much every Strings XXXX conference held during the past 20 years.

    Even if no information about the Strings 2009 talks ever gets out, many of the same speakers are speaking at uncountably many other strings conferences scheduled before and after the big one, conferences that are likely to have web-sites that make the talks available. Here are some of them:

    Florence

    Warsaw

    Saclay

    Porto

    Lisbon

    Benasque

    Frascati

    Potsdam

    Wroclaw (Robert Helling will be blogging)

    Crete

    Santa Barbara

    For less technical and more audio-visual enlightenment, you might want to check out the following:

    A CBC podcast interview with Lee Smolin.

    A Bloggingheads diavlog with Sean Carroll and Mark Trodden.

    Posted in Uncategorized | 16 Comments

    Strings 2009 Out of Juice?

    Posted on June 23, 2009 by woit

    I had a suspicion that Strings 2009 wasn’t going to be scientifically very active, since not much has been going on in that field recently, but I still found it surprising how little news from the conference was making its way out to the internet. The conference is nearly half over, no evidence of any activity has appeared on the conference web-site, and until now I couldn’t find anything at all on the internet discussing what is going on there.

    However, something did just turn up. Over at the Bad Astronomy and Universe Today Forum, under the topic heading “Off-Topic Babbling”, there have been two communications from Terry Giblin. In the first, written on Sunday, Terry writes that he’s on the road to Rome for the conference, and since it looks like he’ll be late, he’d like someone from the stage or audience to call him on Skype so he can ask the opening speaker (David Gross) a “strings question on quantum tunneling and singularities.”

    That doesn’t seem to have worked out. In his latest communication, he says that he finally did make it to Rome, where he reports:

    It would appear that I have not missed much over the past two days, yesterday the internet at the conference was only working slowly.

    Today they had a power outage, so the conference was cancelled.

    I hope I have more success tomorrow or the coming week.

    Its amazing to think you can change the outcome of a conference, without being physically present……….

    Update: A twitter from Marco Baumgartl has made it out to the internet, bringing more confirmation of problems:

    I’d loved to give you live updates from the Strings 2009 conference, but they have severe wifi problems there, can’t connect

    Update: An anonymous correspondent attending the conference reports that disorganization is a problem, and that there have been no major announcements. David Gross’s talk listed 8 fundamental problems for string theory and gave the string community a grade of A-F for progress on each problem (this sounds familiar, I vaguely recall him giving such a report card at some other talk a few years ago, I wonder if the grades have changed…)

    The atmosphere was much like in other recent years: some disillusionment in the air, but people continuing to work along similar lines. The talks were described as sketchy and mostly incomprehensible to much of the audience, with many of the younger string theorists rather bitter about the lack of much of an attempt on the part of the speakers to give clear explanations and put their work in any sort of context (the audience of 450 has widely varying backgrounds, this is not a specialist conference).

    Update: Well, the conference is over now, but still no slides of talks, or any blogging from anyone there, other than Jacques Distler’s attempt to find someone to go to dinner with a week ago. Reports I’ve gotten from the conference describe Vafa’s talk as “Good, in fact too good to be true”, and claim that Arkani-Hamed showed up two hours late for his talk, then went over time by 20 minutes.

    Update: Still nothing on the conference web-site about the talks, or on blogs. Physics World does have a report from Edwin Cartlidge, who noted that the scientific talks were appropriately held at the University of St. Thomas Aquinas, named after the great Scholastic philosopher. He also reports on the public talks held yesterday. Witten appears to have decided the best thing to do was to not talk about string theory, but instead talk about particle physics, the LHC, dark matter and supersymmetry. He left string theory to Brian Greene, who somehow convinced Cartlidge that what this is all about is “that 10500 is somewhat bigger than 10120, and that’s a measure of how much we don’t understand dark energy.”

    Greene pointed out that string theory requires an extra 6 (or 7) dimensions of space in addition to the three that we are aware of. Helpfully, these dimensions are so small that we can’t see them, but unhelpfully there are rather a lot of ways of curling these extra dimensions up – some 10500 different ways as it turns out. And we would have to study all 10500 if we want to find out whether or not string theory describes the real world.

    For Greene, all is not lost, however. He pointed out that 10500 is somewhat bigger than 10120, and that’s a measure of how much we don’t understand dark energy. In a nutshell he argued that if we happen to live in one of the few of the 10500 universes where conditions are just right for us to exist then there’s a damn good chance that we could have such an apparently statistically unlikely dark energy. For Greene, this suggests we might be on the right lines with string theory. Others may be less convinced.

    Update: The exponent problem has been fixed.

    Posted in Strings 2XXX | 33 Comments

    Gina Says

    Posted on June 23, 2009 by woit

    At the height of the string wars a couple years ago, one of the participants was a mysterious anonymous commenter going under the name “Gina”. Earlier this year Gil Kalai wrote to me to reveal that he was the person behind “Gina”, and that he had put together a book based on these blog discussions, to be entitled “‘Gina Says,’ Adventures in the Blogosphere String War”. He has now put the first part of manuscript up on his blog, the posting is here.

    Back in January he sent me a copy of what he had written, I haven’t checked to see what changes might be in the version available now. Instead of writing something about this here now, I think I’ll just include part of my e-mail to him back in January, which gave my reaction to the project then:

    Hi Gil/Gina…

    Thanks for sending me the draft of the book. I read through it quickly, amused to relive again some battles of the string wars. When people ask me if I’ll write another book, often I’ve answered that I was considering just cutting and pasting together a lot of things from my blog, other blogs, and my e-mail, all of which told a rather amazing and often amusing tale. Funny to see that you’ve done something a bit like this yourself. During this period I also remember often telling people that I felt like I was living in a comic novel.

    Actually, I’ve no intention of publishing anything about the “String Wars”, although happy if other people want to. I’m rather glad that they have died down, and I’m trying to devote my time instead to a research project I’m quite excited about (the BRST stuff I’ve started writing about on the blog).

    Some comments about issues you raise, and some added context for some of these stories:

    In my book, I tried to avoid saying much at all personally critical about string theorists and their behavior, the sort of thing that Lee Smolin did more of. I generally agree with what Lee wrote, but, in the past my personal contacts with string theorists were mostly with quite reasonable people that I didn’t think it appropriate to criticize in this way. After my experiences in the “string wars” though, I ended up feeling that Lee actually didn’t go far enough; that, individually and as a community, there are very real behavioral and ethical problems in how all too many string theorists do business. My impression is that the “string wars” brought a lot of this out into the open, and have damaged the perception of string theory among physicists and the wider community, more so than anything Lee wrote. Like Lee, what I was hoping our books would lead to would be a serious discussion of the issues involved. There was some of this, but all too much name-calling and bad behavior.

    Some context about Clifford Johnson: independently of each other, both Lee and I wrote to him when our books were in draft form, asking if he would be willing to take a look at them, and let us know if there was anything we had wrong. He just ignored my e-mail, and I gather Lee got a similar response. He appears to be a rather nice guy, and I found this response kind of odd, it was one reason for my mistaken guess that he was the Cambridge referee. I still find his behavior exceedingly strange: how can you write long blog entries denouncing books you refuse to read? He seems to have an ability to refuse to acknowledge the existence of inconvenient realities that goes beyond anything I’ve seen before.

    …

    In your fantasy of the future, you mention my book being translated into Czech. Funny, a publishing company there did buy the rights a year or so ago, and I think they will be bringing it out. Sometimes reality and fantasy are indistinguishable in this story…

    Update: There’s a posting about this over at Physics World.

    Posted in Uncategorized | 30 Comments