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

    First Results From XENON100

    Posted on May 4, 2010 by woit

    The XENON100 dark matter experiment now has a paper out reporting their first results, from a test run of 11 days. They claim a 90% confidence level exclusion of 50 GeV WIMPs with a spin-independent elastic cross-section above 3 x 10-44 cm2, which one can compare with the recent CDMS limit of 3.8 x 10-44 cm2 at similar mass (70 GeV). At the time of the CDMS result many seemed to believe that the two events seen were not background (see here), with Gordon Kane claiming “it is likely it is dark matter.” The New York Times has an article today, with Kane now commenting on XENON100 “if they see a signal, it will be unambiguous”, by which I presume he means that their full data will conclusively show whether the CDMS events could have been a signal. Given that they are seeing nothing at all now, at 10 times greater sensitivity later, they may very well see an ambiguous signal…

    The XENON100 result also appears to rule out claims from the DAMA and CoGeNT experiments to have seen some sort of signal. For more on this, as always in dark matter issues, Resonaances has the best coverage of the story.

    Update: Physics World reports on objections to the XENON100 claims from a CoGeNT physicist and others, see this arXiv preprint.

    Posted in Experimental HEP News | 7 Comments

    String Vacuum Project 2010

    Posted on May 3, 2010 by woit

    I’ve written before about the String Vacuum Project (back in 2006 and 2008), and there was a story about it in Nature. This week they are having an SVP 2010 Spring Meeting at the KITP, talks available here.

    A proposal to the NSF for funding of the String Vacuum Project was first made five years or so ago, but I had heard that this and later versions hadn’t been successful. In recent years perhaps the main proponent of the project has been Keith Dienes of the University of Arizona, who organized its last meeting in Tucson two years ago. Dienes started work as a program manager at NSF last fall. Maybe it’s just a coincidence, but the SVP now has funding through an NSF grant for $150K this year, with the grant paying for bi-annual meetings (of which I guess the KITP one is the first). While “the PIs are proposing a String Vacuum Project (SVP) network with eight geographic nodes”, the grant sponsor is the University of Arizona, where the co-PI for the grant is Shufang Su, a phenomenologist who doesn’t seem to have any history of working on string vacua.

    Well, at least stimulus funding is helping get the SVP off the ground…

    Update: After looking through some of the workshop talks, it’s very unclear to me what the “String Vacuum Project” actually is. At this point it appears to just be a mechanism for getting the NSF to fund three graduate students working on string phenomenology. From the talk by Michael Douglas you learn that it’s very unclear what a string vacuum even is. It appears to involve an intractable large unknown space (including e.g. “all six manifolds”), with an unknown effective potential on it, with disagreements among practicioners about whether the effective potential is a sensible thing to look at.

    Not surprisingly, the discussion session about what the project should be doing was a sad thing to watch. One of the main topics was the SVP Wiki, which people hope to improve. Maybe it’s been moved somewhere else, but the only address I know for it (here) has been down for quite a while.

    Update: More discussion showing the current level of understanding (nil) of string vacua here.

    Update: There is now a new String Vacuum Project web-site.

    Posted in Multiverse Mania | 5 Comments

    Oy vey

    Posted on April 30, 2010 by woit

    Last Friday City College held a symposium here in Manhattan celebrating physics at City College. I was able to attend just the morning session, which began with a quick rescheduling of Anton Zeilinger for David Gross, who had overslept. Gross finally did make it and gave a talk on “The Frontiers of Particle Physics”. He says he’s taking bets in favor of supersymmetry being seen at the LHC, with 50/50 odds, and expects first evidence for supersymmetry within a year or two. By the time he got to the part of his slides about string theory he was over time, so he bypassed them, flipping ahead several slides at once.

    Unfortunately I seem to have missed the real fireworks, which were at a panel discussion that afternoon. There’s a report at Scientific American, entitled Star physicists trade barbs over cosmological model. Alan Guth was there, promoting the multiverse and the anthropic explanation of the CC. Gross was having none of it:

    “In reaction to that last talk—oy vey,”…

    Gross called Guth’s concept of eternal inflation somewhat speculative, noting that if other universes do exist, they are causally disconnected from ours—”every goddamn one of them.” As such, Gross added, talk of other universes “does bear some resemblance to talking about angels.”

    Posted in Multiverse Mania | 20 Comments

    Bohmian Spat

    Posted on April 29, 2010 by woit

    Here’s a story from the boundaries of conventional physics of the sort I normally try to resist paying any attention to, but couldn’t quite help myself this time:

    Last week I noticed amongst the e-mail from Jack Sarfatti that clutters my (and many other people’s) mailbox some forwarded messages about a kerfuffle involving the withdrawal of a conference invitation to Brian Josephson. Josephson is a Nobel Prize winner but, on the other hand, he seems to think that this sort of thing makes sense. In one of the messages, I noticed that Josephson defends himself by pointing out that his talks often don’t involve paranormal phenomena, giving as example a recent Hermann Staudinger lecture in Freiburg (Staudinger was a chemistry Nobelist, also my great-uncle).

    This mini-scandal has now made it to a Times Higher Education story today, which starts off:

    An extraordinary spat has broken out after a Nobel prizewinning physicist was “uninvited” from a forthcoming conference because of his interest in the paranormal.

    Details of the conference in August for experts in quantum mechanics sounded idyllic. Participants were due to discuss “de Broglie-Bohm theory and beyond” in the Towler Institute, which is housed in a 16th-century monastery in the Tuscan Alps owned by Mike Towler, Royal Society research fellow at Cambridge University’s Cavendish Laboratory.

    Last week, any veneer of serenity was shattered. Conference organiser Antony Valentini, research associate in the Theoretical Physics Group at Imperial College London, wrote to three participants to say their invitations had been withdrawn.

    The current situation seems to be that Josephson, David Peat and Jack Sarfatti were un-invited, but now Josephson and Peat have been re-invited.

    I had never heard of the Towler Institute before, but it sounds like a beautiful place, which physicist Mike Towler has admirably made available as a site for hosting small meetings and conferences. From the information on its web-site, this looks like the kind of place I’d find it very difficult to turn down an invitation to, no matter what the conference topic.

    The conference at issue will be held at the end of the summer, and deals with what is known as “de Broglie-Bohm theory”. One can read about this many places, including this site of Mike Towler’s. The conference summary itself refers to the de Broglie-Bohm theory’s “fringe nature in modern physics”, and for more about why it is controversial see Towler’s lecture Not even wrong: Why does nobody like pilot-wave theory?.

    After spending a little time learning about it many years ago, I quickly decided that I personally didn’t like pilot-wave theory, partly because it seems to me that it throws out all the deep, amazing and experimentally verified links between modern physics and mathematics that motivate what I love about the subjects, getting nothing much in return. I don’t see a good reason to believe that research in this area is going to lead to something interesting, but those who do have every right to keep trying. As they do so, they face serious problems in distinguishing crackpot from non-crackpot efforts, as this story makes very clear. Note that I have no intention of putting any time into this problem myself, so in this case I’m adopting a uniform policy of just deleting all comments arguing for or against de Broglie-Bohm. If that’s a topic you like to argue about, do it elsewhere.

    There’s more here from Chad Orzel.

    Posted in Uncategorized | 16 Comments

    Dark Matters

    Posted on April 28, 2010 by woit

    Initial 2010 data from the Theoretical Particle Physics Jobs Rumor Mill indicates that the particle theory job market remains as trend-driven as ever. This year, it seems that if you want a tenure-track job in the US, you must be working on phenomenology. And not just any sort of phenomenology, your work has to be about dark matter. Of the seven theorists offered tenure track jobs so far, no less than 6 are phenomenologists working on dark matter. The seventh is Davide Gaiotto, who has been working with Witten and others at the IAS on mathematically quite interesting topics that use N=2 and N=4 supersymmetric gauge theory. His offer is from Stony Brook, where much of the funding comes from Jim Simons of Renaissance Technologies. Simons is putting profits from the world’s most successful hedge fund to work keeping alive the idea that the intersection of mathematics and physics is still worth pursuing, so not everyone has to become a dark matter phenomenologist.

    (By the way, the rumor mill seems to indicate that Kachru and Silverstein are leaving the KITP, heading back to Stanford. Is that right?)

    If you’re a young theorist who wants to remain in the field, you better get to work on dark matter phenomenology. I’m afraid that this blog won’t be of much help, you should carefully follow Resonaances, which has the latest news and rumors.

    Update: It seems that my point about the dominance of dark matter hiring has even more backing than I thought, since Sergei Dubovsky evidently has an offer from Stony Brook (and other places). So, that makes it seven out of eight for dark matter so far this year.

    Posted in Uncategorized | 28 Comments

    Podcasts

    Posted on April 26, 2010 by woit

    In case you’re tired of reading me going on about the same topics and instead would like to listen to me going on about such topics, there are now two new options:

  • A couple weeks ago I did a podcast with the folks at the Rationally Speaking web-site, talking to Massimo Pigliucci and Julia Galef (their podcast site is here, direct link to my segment here). In the near future they’ll be doing a different podcast on the topic of the Anthropic Principle. Pigliucci is a philosopher of science and comments on this here.
  • Last month I visited Collin College in Texas, and they have a podcast up from an interview I did there. The site is here, link to interview here.
    • Posted in Uncategorized | 4 Comments