LHC Update

Posted on June 11, 2010 by woit

See here for a new status report on the state of beam commissioning at the LHC. About two weeks ago a peak luminosity of about 2 x 1029cm-2s-1 was reached, using beams with 13 bunches, but each bunch relatively low intensity. Since that time, efforts have been directed at increasing the bunch intensity towards nominal values. During this process, there has been little new physics data gathered, although the plan has been to interleave physics runs on weekends with beam commissioning during the week.

On Wednesday, this plan was changed, with the focus now completely devoted to commissioning beams with nominal bunch intensity. The hope is to have collisions of high intensity bunches in two weeks or so and then provide a 4 week period of stable running for physics during August, at luminosities an order of magnitude higher than now available. The limiting factor will be the stored energy in the beam, which is approaching Tevatron levels. To go higher will require much more testing of the beam protection systems.

This week in Hamburg there was a conference people have been waiting a long time for, Physics at the LHC 2010, the first conference devoted to the presentation of LHC experimental results. So far the results are based on very low luminosities, so are only able to check that the machine is working and rediscover various well-known features of the Standard Model. As the luminosity increases, it will start to become possible to observe or rule out various exotic particles at masses not reachable by the Tevatron, as long as the cross-sections are high.

Mostly such things are unmotivated and not expected to turn up, but one story to watch is that of supersymmetry, as the LHC becomes capable of observing strongly-interacting superpartners at masses beyond the Tevatron’s reach. The MSSM includes a huge number of unknown extra parameters, so the masses of these things are unknown. Given one motivation for supersymmetry, that it is supposed to stabilize the electroweak scale, one would expect superpartners to readily show up at the new mass ranges being investigated by the LHC. The problem with this is that it’s hard to understand why they haven’t already been seen at the Tevatron, or indirectly in other experiments through the effects of higher-order processes. Taking current non-observations into account, even if one has faith that superpartners exist at masses the LHC can probe, it doesn’t seem likely that the earliest LHC data will be able to see them (for more specific analysis along these lines, see for instance this talk).

I’m quite dubious that the LHC will ever see superpartners, but many prominent theorists claim that this is likely to happen. It would be interesting to pin them down on what LHC luminosity is needed to see what they are expecting to see.

Update: A particularly noteworthy talk is that of Mike Lamont, where he gives estimates of the progression of integrated luminosity this year. They’re significantly more pessimistic than similar estimates from early this year, with about 50 inverse pb this year instead of 200, but still on track for 1000 inverse pb by late 2011.

Posted in Experimental HEP News | 3 Comments

Not In Our Lifetimes

Posted on June 9, 2010 by woit

A report from one of last Saturday’s events at the World Science Festival has string theorists Brian Greene and Shamit Kachru admitting that they’d be surprised to see experimental evidence for string theory in their lifetimes:

John Hockenberry, the panel’s moderator, asked Greene if he thought experimental evidence would come during his lifetime.

“I’d be surprised,” said Greene.

“And in your lifetime?” Hockenberry asked Kachru.

“…I’d be surprised,” conceded the young physicist reluctantly.

For more reports about the same panel discussion, see here and here.

Posted in Uncategorized | 26 Comments

Through the Wormhole with Morgan Freeman

Posted on June 9, 2010 by woit

The Science Channel is starting up yet another show on physics tonight, with Michio Kaku’s Sci-Fi Science and Into the Universe with Steven Hawking being joined by Through the Wormhole with Morgan Freeman. The topics being covered by Freeman are the usual ones: Black Holes, Aliens, Is Time Travel Possible? What Happened Before the Big Bang? etc.

The series unfortunately first starts out by bringing religion into it, with an episode called Is There a Creator?

Did our Universe just come into being by random chance, or was it created by a God who nurtures and sustains all life?

I gather that the episode begins with speculative physics elements that include Alan Guth on the multiverse and Garrett Lisi on E8 unification, but then moves on to speculative God stuff, with a neurophysiologist followed by the “maybe we’re just a simulation” business. The New York Times today has a depressing review, by a writer who wants more of the God part and less physics:

…this opening installment, which is supposed to be about whether there’s a Creator, almost immediately degenerates into theoretical yakking by scientists about unified theories of this and missing particles of that.

Especially with recent news coverage of that particle accelerator near Geneva, it seems as if we’d been hearing about this type of physics for a long time, and the discussion never does go anywhere or have much practical relevance. Anybody got a particle big enough to plug that busted oil pipe in the Gulf of Mexico?

Anyway, after about half an hour, Mr. Freeman’s show does get intermittently interesting because it turns itself more directly to the Creator question. (Questions are pivotal to this series; future episodes include “How Did We Get Here?” and “Are We Alone?”) Doesn’t answer it, of course, but does check in on an assortment of scientists who have an assortment of theories.

One thinks our idea of God is a kind of neuropsychological tic and plunks a ridiculous-looking contraption he calls a God helmet on research subjects’ heads to try to prove it. Another suggests that we’re nothing but a computer simulation created by our own descendants. If this program can stay away from same-old science and work this territory — theories that sound a little bit crackpotish, a little bit geniusy — it might set itself apart in an increasingly crowded genre.

Update: Chad Orzel weighs in here.

Posted in Uncategorized | 32 Comments

Prerequisites

Posted on June 9, 2010 by woit

The Abstruse Goose recently provided an excellent summary of how to go about learning string theory. It starts with “String Theory for Dummies”, here. Tommaso Dorigo’s latest say of the week is somehow relevant.

Posted in Uncategorized | 5 Comments

Where Do They Go?

Posted on June 6, 2010 by woit

HEPAP has had a Demographics Committee since about 1999, charged with gathering data on what happens to young people in the US who enter the field of High Energy Physics (both theory and experiment). The latest report from the committee is here, but it contains more questions than answers. The data gathered show that only 10-20% of HEP graduate students end up with permanent tenured positions at HEP institutions, and the other 80-90% in some sense “leave” the field.

The committee seems to have had very little success at finding out what happens to the “leavers”, perhaps because its data-gathering method is based on questionnaires filled out by one person at each institution. Very typically, once someone “leaves” academia for a different career track, within a few years their ex-colleagues no longer know where they are or what they are doing. On the other hand, in the age of Google and Facebook, tracking people down has become rather easy, so it’s unclear why an effort hasn’t been made to do this, if not for everyone in the database, than at least for a randomly chosen statistically significant sample.

I’d certainly be curious to see some real data, but based on my personal experience I’d guess that the 80-90% number sounds right, with “leavers” going into a wide variety of different careers. The financial industry may be the most popular, but I also know many who have gone into the computer or telecommunications industries, as well as other fields in academia.

By this count, I and others who have ended up in mathematics departments count among the “leavers”. I’m very happy with how my own rather unusual career path has worked out, but have generally advised others that it relied too much on good luck for anyone else to try and emulate it. A few days ago I heard from someone at the Perimeter Institute who told me about a new “hybrid research/IT position” that they are trying to fill. The job listing is here, with a detailed description of what they are looking for here. They seem to be a looking for a candidate with both a research Ph.D. and IT experience, which is a somewhat unusual combination. A Ph.D. with little IT experience but the right skills (quick learner with patience, common sense, enjoys working with technology and helping others with their technical problems) who is interested in the position might want to try and convince them that most of the IT skills get picked up on the job anyway…

Posted in Uncategorized | 11 Comments

Quick Links

Posted on June 3, 2010 by woit
  • Several blogs have now pointed out the wonderful snarXiv site, which automatically produces random plausible-sounding hep-th entries. It’s something along the same lines as the famous Postmodernism Generator. For entertainment, you can try playing snarXiv vs. arXiv.
  • HEPAP is meeting in Washington today, presentations here
  • At Fermilab, the User’s Meeting continues today, talks here.
  • Last week was Brookhaven Forum 2010, talks available here.
  • Talks by Michaels Atiyah and Green at the Young Researchers in Mathematics 2010 meeting are available here. Atiyah reminisces about his early career and offers a lot of helpful career advice for young mathematicians. For the future, he’s betting that topology and symmetry will remain crucial themes in mathematics, with solitons continuing to be interesting since they live in the intersection. Green gives a very standard promotional talk on string theory. For some reason he explains to the young mathematicians the story of the string theory anthropic landscape explanation for the CC, then remarks that he personally finds it to be a cop-out.
  • The Edge web-site has a wonderful discussion with my Columbia colleague Emanuel Derman, covering his early career in particle physics, his days as a Quant, and thoughts about the current state of the finance business.
  • From Fabien Besnard, the news that Vladimir Arnold died today in Paris.
    • Posted in Uncategorized | 15 Comments

    More Quantum Information Theory From String Theory

    Posted on May 27, 2010 by woit

    Claims made recently in the CERN Courier that string theory can be applied to Quantum Information Theory (see here) are being followed up with a new paper entitled Four-qubit entanglement from string theory which appears to claim that, despite what some might think, string theory is falsifiable since it makes experimentally testable predictions about Quantum Information Theory:

    Falsifiable predictions in the fields of high-energy physics or cosmology are hard to come by, especially for ambitious attempts, such as string/M-theory, to accommodate all the fundamental interactions. In the field of quantum information theory, however, previous work has shown that the stringy black hole/qubit correspondence can reproduce well-known results in the classification of two and three qubit entanglement. In this paper this correspondence has been taken one step further to predict new results in the less well-understood case of four-qubit entanglement that can in principle be tested in the laboratory.

    Previous papers along these lines about the three-qubit case involved some algebra that I referred to as “remarkably obscure”, a comment that “was like waving a red flag in front of a bull” as far as John Baez was concerned, leading him to some expository comments about the subject in his latest This Week’s Finds in Mathematical Physics. About the string theory claims he comments:

    Unfortunately, Duff gets a bit carried away. For example, he says that string theory “predicts” the various ways that three qubits can be entangled. Someone who didn’t know physics might jump to the conclusion that this is a prediction whose confirmation lends credence to string theory as a description of the fundamental constituents of nature. It’s not!

    Unlike the three-qubit papers, this latest one sticks to mathematics that is not particularly obscure. The mathematics invoked is the quite beautiful subject of the classification of nilpotent orbits in a Lie algebra. I’ve been trying to learn more about some related topics in recent months, having to do with the role of nilpotent orbits in representation theory. Part of this story involves what are now known as “finite W-algebras”, and these have a BRST definition. I’ve been curious about the relation of this to the BRST/Dirac Cohomology relationship I’ve been working on.

    The mathematical problem at issue here is that of classifying SL(2,C)4 orbits on the four-fold tensor product of C2. For an exposition of this problem aimed at mathematicians, see these lecture notes by Nolan Wallach. In the new paper, the authors claim that the Kostant-Sekiguchi theorem implies that this classification is the same as that of orbits of SO(4,C) on its Lie algebra, and this latter classification also classifies certain sorts of black holes in supergravity, but I haven’t checked the details of this. It’s a complete mystery to me why the use of the Kostant-Sekiguchi theorem to relate the straight-forward mathematics used in QIT to a black hole classification problem is going to somehow turn string theory into falsifiable, experimentally testable science.

    Posted in This Week's Hype | 9 Comments

    Short Items

    Posted on May 25, 2010 by woit
  • Beam intensity at the LHC continues to increase with successful collision this morning of beams containing 13 bunches of protons, producing an initial luminosity of about 1.5 x 1029cm-2s-1. This is about a factor of 1000 below the goal for later this year, 2000 below typical luminosities at the Tevatron. The current plan is for proton-proton collisions this year until November 1, then a shift for a while to heavy ions. Integrated luminosity is about 10 nb-1, see a graph here.
  • Last week this result (also see here) from DZero got a lot of attention in the press, including a front page story in the New York Times. The claim is of observation of a CP-violating effect not predicted by the Standard Model, with a significance of 2-3.2 sigma, depending on exactly what numbers you look at. If I had to bet, I’d bet that this, like lots of other purported violations of the SM over the last 35 years, will ultimately disappear. Unfortunately, it seems that CDF is unlikely to be able to confirm or disconfirm this. For blog postings from people who actually know something about this, see here and here.
  • There’s an interesting interview with Shing-Tung Yau at Discover. This fall he has a new book coming out: The Shape of Inner Space.
  • My colleague Brian Greene is keeping very busy, with the World Science Festival here in New York next week, and filming a four-part NOVA series based on is book Fabric of the Cosmos.
  • If I weren’t planning a trip to South America to see another eclipse in July, I’d probably be trying to find an excuse to go to Paris that month, and ICHEP 2010 might do the trick. Now, it seems even physics conferences have blogs.
  • Herbert Neuberger has a very nice survey here, based on a colloquium talk, of our understanding of non-perturbative QCD.
  • Frank Quinn has a long essay here which has quite a few interesting things to say about mathematics, mathematics research, mathematics education, and relations to physics. Quinn is a topologist who has interacted with physicists since the late 80s, in the context of topological quantum field theory. I learned about this from a posting at the n-Category Cafe, where some illustrious commenters have an interesting exchange about TQFT.
  • For a long time now, particle theory has been divided up between phenomenology and string theory, with formal QFT an increasingly marginalized subject. At the same time, more and more mathematicians have been studying QFT long enough to become quite expert at it. In the future it seems conceivable that this will ultimately lead to new discoveries about QFT coming out of math, not physics departments. For an indication of how things are going, take a look at the recent MSRI workshop in honor of Alan Weinstein. Videos of some of the talks are supposed to be available at some point. I’m most looking forward to seeing what Graeme Segal has to say about Geometric aspects of the positivity of energy in quantum field theory, and curious to know what Reshetikhin had to say about Hamiltonian structure of gauge theories (it appears that video of that talk will not be available). Next week Reshetikhin is teaching a master-class on gauge theories in Amsterdam (web-site here), and he taught a course on QFT there last fall

    • Updates:

  • See Resonaances for some news that makes the DZero supposed SM violation look less likely. Some support for the claim came from earlier data showing similar SM violation in another channel, but the latest from CDF is that, with more data, this has gone away.
  • Latest from the LHC is that on Tuesday morning a peak luminosity of about 2 x 1029cm-2s-1 was reached. Integrated luminosity is now about 16 nb-1.
  • Nature has an interview with Brian Greene about the new orchestral work from Philip Glass inspired by his recent children’s book.

    • Update: A more skeptical report on the DZero result from Adrian Cho at Science Magazine is here.

    Posted in Uncategorized | 16 Comments

    Applying String Theory to Quantum Information Theory

    Posted on May 10, 2010 by woit

    There’s a remarkable article by Mike Duff in this month’s CERN Courier, arguing the case that string theory does too have important applications: in Quantum Information Theory. The claim seems to be that since the same algebraic structures appear in black-hole entropy calculations in string theory and in the analysis of certain cases of the entanglement of qubits, this provides an application of string theory to Quantum Information theory. There’s some remarkably obscure algebra involved, from exceptional structures such as E7, the octonions and the Fano plane to Cayley’s nineteenth century work on hyperdeterminants. Besides the very complicated mathematics and physics, what I don’t understand about this is the claim that if the same classical algebraic structure gets used to do a calculation in string theory and in subject A, it means that string theory is being applied to subject A.

    While the mathematical physics story Duff tells may be of some interest (to learn more about it, there are review articles here and here), unfortunately he can’t resist the temptation to shanghai it into service in the string wars. He gives a less-than-honest description of the problem with string theory:

    The partial nature of our understanding of string/M-theory has so far prevented any kind of smoking-gun experimental test.

    The problem with string/M-theory is not that it is missing a “smoking-gun experimental test”, it is that it is missing any kind of experimental test whatsoever, which is rather different. He defends the failure of string theorists to come up with any experimental test after more than 25 years of work by thousands of physicists writing tens of thousands of papers with a comparison of the situation to that of the time lag between the 1935 Einstein-Podolsky-Rosen paper and J.S. Bell’s work 29 years later. One obvious difference is that, before Bell, hardly anyone tried to come up with such a proposal, unlike the case of string theory, where the issue has been the central one in the field since 1984.

    Under the heading “Further Reading”, one is referred to Duff’s 2007 debate with Smolin, which I posted about here, based on second-hand reports from those in attendance. Until now I don’t think I’d seen the transcript of the debate, which is available here. I notice that Duff sums up his argument as follows:

    The trouble with physics ladies and gentleman is that Lee Smolin and Peter Woit having lost their case in the court of science, are now trying desperately to win it in the court of public opinion. Thank you.

    It seems to me that Duff, having lost his case in the court of his physicist peers, where string theory unification is widely seen as a failure and young string theorists are just about unemployable, is now trying desperately to win it with tendentious argumentation in the court of popular opinion (well, at least in the pages of the CERN Courier…).

    Update: Lubos seems to mostly agree with me about this:

    So the role of the qubits, or the arguments of the hyperdeterminants, are “physically” completely different.
    …

    A superficial similarity of one aspect is very far from a full-fledged mathematical equivalence.

    Update: John Baez’s latest TWF has an explanation of some of the mathematics involved here.

    Posted in This Week's Hype | 38 Comments

    LHC Update: Bing Bang Machine Could Confirm or Disprove String Theory

    Posted on May 5, 2010 by woit

    Today’s CERN LHCC meeting had a wide-range of reports about how the machine is doing (1 nb-1 now, 10 nb-1 over the next 5 weeks), what the experiments are seeing (charm, Ws), and what physics might be possible with the 2010-11 run (limits on some supersymmetric and other more exotic scenarios).

    Reuters this evening reports on the meeting, headlined with the typical delusional nonsense about string theory and the LHC which we’re in for several years of {“Could confirm or disprove string theory”).

    Update: This story has made it to various media outlets, including one that has it as Collider on Track With Bing Bang Research. Title of posting edited appropriately.

    Posted in Experimental HEP News, This Week's Hype | 16 Comments