This Week’s Hype

Posted on April 28, 2011 by woit

This week’s hype comes from an unusual source, John Baez and his ex-student John Huerta, who have a new article in Scientific American entitled The Strangest Numbers in String Theory.

The expository article about octonions by John (Baez) that appeared in the AMS Bulletin (copy here, a web-site here) is one of the best pieces of mathematical exposition that I have ever seen. The octonions can be thought of as a system of numbers generalizing the quaternions. As with the quaternions, multiplication does not commute, and things are even worse, it’s not associative either. So, probably best not to try and think of these as “numbers”, but they do give a very remarkable exotic algebraic structure, one that explains all sorts of other exotic structures occurring in different areas of mathematics. The article beautifully explains a lot of the intricate story of how octonions connect up surprising phenomena in algebra, geometry, group theory and topology.

If you’re a mathematical physics mystic like myself, you’re susceptible to the belief that anything this mathematically deep, showing up in seemingly unrelated places, must somehow have something to do with physics. The story of octonions is closely related to the story of Clifford algebras, which are definitely a crucial part of physics, but it seems to me we’re still a long ways from truly understanding the role in physics of Clifford algebras, much less the more esoteric octonions. One thing that is fairly well understood is that the sequence of division algebras explains some of the structure of low-dimensional spin groups in Minkowski signature, through the isomorphisms:
SL(2,R)=Spin(2,1)
SL(2,C)=Spin(3,1)
SL(2,H)=Spin(5,1)
The octonion story is supposed to be the next in line, involving Spin(9,1), but made much trickier by the fact that SL(2,O) doesn’t really exist, since the octonions are non-associative.

Back in 1982, a very nice paper by Kugo and Townsend, Supersymmetry and the Division Algebras, explained some of this, ending up with some comments on the relation of octonions to d=10 super Yang-Mills and d=11 super-gravity. Baez and Huerta in 2009 wrote the very clear Division Algebras and Supersymmetry I, which explains how the existence of supersymmetry relies on algebraic identities that follow from the existence of the division algebras. Kugo-Townsend don’t mention string theory at all, and Baez-Huerta refers to superstrings just in passing, only really discussing supersymmetric QFT. There’s also Division Algebras and Supersymmetry II by Baez and Huerta from last year, with intriguing speculation about Lie n-algebras and what these might have to do with relations between octonions and 10 and 11 dimensional supergravity. For a nice expository paper about this stuff, see their An Invitation to Higher Gauge Theory.

In contrast to the tenuous or highly-speculative connections to string theory that appear in these sources, the Scientific American article engages in the all-too-familiar hype pattern. The headline argument is that octonions are important and interesting because they’re “The Strangest Numbers in String Theory”, even though they play only a minor role in the subject. It wouldn’t surprise me at all if octonions someday do end up playing an important role in a unified theory, but the rather obscure connection to the calculation of the critical dimension of the superstring that seems to be the main point of the Scientific American article isn’t a very convincing argument for such a role.

Somehow I suspect that those string theorists who were upset by Scientific American’s decision to publish speculation by Garrett Lisi about E8 and wrote in to complain, won’t be similarly upset to find this highly speculative material about the octonions appearing in the magazine.

Posted in This Week's Hype | 27 Comments

Short Items

Posted on April 27, 2011 by woit
  • Progress on increasing luminosity at the LHC has been going extremely well, with peak luminosity a few moments ago over 7×1032cm-2s-1. So far integrated luminosity is over 200 pb-1, well on the way to the extremely conservative nominal goal for the year of 1000 pb-1. By fall, with the shutdown of the Tevatron at the end of FY 2011, the LHC experiments should be in a position to start overtaking the Tevatron and seeing evidence of a standard model Higgs if it is there.
  • It’s still very early to know how Fermilab will do in the US FY2012 budget, other than that the Tevatron will definitely not be there. However, the Obama administration is supportive in its budget proposal, and this document from the Republicans running the relevant House committee is encouraging for HEP research. Democrats and Republicans seem to agree that science research is a good thing in general, and HEP research is not one of the categories that annoys Republicans and that they suggest cutting (applied research that could be done by private companies, climate science research, environmental research, ITER). One member of the committee is freshman Republican Randy Hultgren, who represents the district that includes Fermilab, and he added his own addendum to the report, emphasizing support for HEP research. Hopefully the Republicans will want to help re-elect him by getting him anything he asks for…

    With the bizarre US budgeting process of recent years though, whatever the appropriate Congressional Committee decides may turn out to be irrelevant, with last minute budget cuts appearing from mysterious sources to get things under whatever numbers end up being agreed to.

  • The New Yorker has a profile this week of David Deutsch. I still can’t figure out what his argument is that if a quantum computer works, that means there are multiple universes.
  • Lots of people are asking me what I think of ‘t Hooft’s new paper. The answer so far is just that I don’t understand it. He’s doing something unusual with how he handles conformal symmetry, and I think one needs an expert on that to weigh in.
  • Mathoverflow continues to amaze me, providing the sort of high-quality discussion that the internet was always supposed to provide, but rarely did. For example, see this recent question, which asks about the relationship between two different ways of encoding the geometry of a manifold. One way to do this is to choose a metric, the other is to choose a connection on the frame bundle. For arbitrary bundles, there’s an infinity of possible connections and they have nothing to do with the metric, but the frame bundle carries extra structure (the vierbeins, in physicist’s language). Given a metric, this extra structure can be used to pick out a unique connection (called the Levi-Civita connection), which satisfies two conditions: orthogonality and zero torsion. The question asked is about whether one can go the other way: given a connection, is there a unique metric for which it is the Levi-Civita connection?

    The answers given include one by Fields Medalist Bill Thurston, whose comments reflects his background as a topologist, another is by MSRI director Robert Bryant, whose answer is that of a geometer, one who has delved deeply into the subject, including its roots in the work of Elié Cartan. The fact of the matter is that the relationship between these two structures is not one-to-one, for reasons that are well explained. This may be of interest to physicists thinking about the quantization of gravity. In that subject, one basic question is that of which fundamental variable to pick to “quantize”, and the conventional choice is the metric, even though in non-gravitational physics, the conventional choice is the connection. Philosophically though, the gauge symmetry involved in gravity is something like local translation symmetry, and the right analogy of a Yang-Mills connection might be not a connection on the frame bundle, but something like the vierbein, but that’s a whole other story….

    • Posted in Experimental HEP News, Multiverse Mania | 31 Comments

    This Week’s Rumor

    Posted on April 21, 2011 by woit

    A commenter on the previous posting has helpfully given us the abstract of an internal ATLAS note claiming observation of a resonance at 115 GeV. It’s the sort of thing you would expect to see if there were a Higgs at that mass, but the number of events seen is about 30 times more than the standard model would predict. Best guess seems to be that this is either a hoax, or something that will disappear on further analysis. But, since spreading well-sourced rumors is more or less in the mission statement of this blog, I think I’ll promote this to its own posting. Here it is:

    Internal Note
    Report number ATL-COM-PHYS-2011-415
    Title Observation of a γγ resonance at a mass in the vicinity of 115 GeV/c2 at ATLAS and its Higgs interpretation
    Author(s) Fang, Y (-) ; Flores Castillo, L R (-) ; Wang, H (-) ; Wu, S L (University of Wisconsin-Madison)
    Imprint 21 Apr 2011. – mult. p.
    Subject category Detectors and Experimental Techniques
    Accelerator/Facility, Experiment CERN LHC ; ATLAS
    Free keywords Diphoton ; Resonance ; EWEAK ; HIGGS ; SUSY ; EXOTICS ; EGAMMA
    Abstract Motivated by the result of the Higgs boson candidates at LEP with a mass of about 115~GeV/c2, the observation given in ATLAS note ATL-COM-PHYS-2010-935 (November 18, 2010) and the publication “Production of isolated Higgs particle at the Large Hadron Collider Physics” (Letters B 683 2010 354-357), we studied the γγ invariant mass distribution over the range of 80 to 150 GeV/c2. With 37.5~pb−1 data from 2010 and 26.0~pb−1 from 2011, we observe a γγ resonance around 115~GeV/c2 with a significance of 4σ. The event rate for this resonance is about thirty times larger than the expectation from Higgs to γγ in the standard model. This channel H→γγ is of great importance because the presence of new heavy particles can enhance strongly both the Higgs production cross section and the decay branching ratio. This large enhancement over the standard model rate implies that the present result is the first definitive observation of physics beyond the standard model. Exciting new physics, including new particles, may be expected to be found in the very near future.

    See: http://cdsweb.cern.ch/record/1346326?

    Update: Jester is up late with some comments here.

    Update: Tommaso is skeptical here.

    Update: It should be made clear that, while members of ATLAS work here at Columbia, I have no connection at all to them, and they had nothing to do with this. The source of the abstract posted here anonymously as a comment is completely unknown to me. The question has been raised of whether I should allow this kind of material to be posted to this blog and I think it’s a serious one that I have mixed feelings about. On the one hand, ATLAS has legitimate reasons for keeping this kind of information private, on the other, it’s the kind of information that traditionally has sooner or later circulated outside a collaboration in one form or another. As an example, in my graduate student days back in the early 80s, I remember Carlo Rubbia telling a large group of people at the departmental tea about how his experiment had the top quark “in the bag” (actually, they didn’t…).

    I’ve generally taken the point of view that it’s not my job to stop rumors, but rather to put out accurate information about them when available to me. But blogs do raise all sorts of issues, and they’re likely to keep coming up. I’m curious to hear if my readers have any wisdom to share about them.

    Update: Via Slashdot, some more comment about this, including disclosure of another vector of information transfer out of ATLAS:

    Someone left a copy of the note on the printer in my office building. (I work on CDF at Fermilab, but there are others in the building who work on ATLAS at CERN.) The gist of the article is that they found a bump in the diphoton mass spectrum at a mass of ~115 GeV. If the Higgs exists, it is expected to produce a bump in that spectrum, and 115 GeV is a very probable value for the mass of the Higgs. (Experiments at LEP ruled out masses up to 114 GeV, but a mass as low as possible above that fits best with other measurements.)

    Now, the inconsistencies: The bump that they found is ~30 times as large as the Higgs mass peak is expected to be. However, due to field theory that I don’t want to get into here, the Higgs peak in this spectrum could be larger than expected if there exist new, heavy particles that we haven’t discovered yet. The latest published result from CDF sets a limit of about 30 times the expected rate at 115 GeV in the diphoton channel. (Yes, this means that, if you’re optimistic enough, there’s just enough wiggle room to fit a Higgs in there while accommodating both measurements.)

    The internal note is very preliminary and uses a crude background estimate; I’ll have to see a more thorough analysis before I make any judgment on it. We shouldn’t have to wait very long; I expect that after this leak, they’ll be working overtime to push out a full published result as soon as possible.

    Update: Since I don’t traffic in rumors of dubious source, you’ll have to go here to get the latest rumors from someone younger who knows about this whole Twitter kind of thingy…

    Posted in Experimental HEP News, Favorite Old Posts | 88 Comments

    This Week’s Hype

    Posted on April 18, 2011 by woit

    This week’s string theory hype is brought to you by a press release headlined Dark Matter and String Theory? from the Institut Laue-Langevin in Grenoble, and another one from the Vienna University of Technology. These have led to a BBC News report which is getting wide distribution, claiming that Neutrons could test Newton’s gravity and string theory. According to the BBC, this is going to allow a search for:

    supersymmetric particles, part of some formulations of string theory that suggest that many extra dimensions exist over tiny length scales, which would require the precision that is only now possible with the team’s approach.

    The actual physics here is described in this paper. You’ll need to find an atomic physicist to explain exactly what this is about, but the claim is that the author’s new techniques in resonance spectroscopy can potentially be applied to measuring the gravitational potential at micrometer distance scales. This hasn’t actually been done yet. As for what string theory predicts about how the gravitational potential will deviate from the Newtonian value at these distances, the story is the usual: no predictions at all one way or another. Such violations would be very interesting, but say nothing one way or another about string theory.

    Update: The folks at Slashdot have started to get a clue, stripping the nonsense about string theory from this story before posting about it here.

    Posted in This Week's Hype | 34 Comments

    No WIMPs

    Posted on April 13, 2011 by woit

    A commenter points to the long-awaited release of a preprint from the XENON100 experiment giving results from a 100-day run last year. This is the most sensitive dark matter experiment that has released data. The result: with an expected background of 1.8 +/- .6 events, they see 3 events (i.e. about what you’d expect if there’s nothing there). For a WIMP mass of 50 GeV, this allows them to exclude certain WIMP cross-sections at the level of 7.0 x 10-45cm2. This pretty conclusively kills off some other claims by dark matter experiments to have seen something, especially the CDMS result from late 2009 (see here).

    One motivation for supersymmetry has always been that it can provide a WIMP with the right properties to explain astrophysical dark matter observations. This new data rules out some (if you use the SUSY expectations plotted in the new paper), or most (if you use the expectations plotted in the CDMS paper, see here and here) of the possible parameter space where such a particle is expected, providing yet another nail in the SUSY coffin.

    Update: More details available at Resonaances and Tommaso Dorigo’s blog.

    Update: For a detailed analysis of the implications of the XENON100 result for supersymmetry models, see here.

    Posted in Experimental HEP News | 106 Comments

    Short Items

    Posted on April 12, 2011 by woit
  • For a while now the situation with this year’s budget for science in the US has been very unclear, with threats being made of huge cuts to be instituted in the middle of the fiscal year, requiring shutdowns of labs, etc. The recently negotiated budget agreement turns out to involve only relatively small cuts for both the NSF and the DOE Office of Science, more here and here. Details still have to be determined and the legislation has to be passed, but it looks like most physics and math research will escape any serious immediate cuts. The new fiscal year starts October 1, and fighting over that budget has not even begun. From the hearings already held, it looks like math and physics research has bipartisan support, but in the new environment of significant budget-cutting, focused on discretionary non-military spending, I’d guess that budget levels for the next few years will be flat at best.
  • There’s an interesting interview with Dennis Overbye of the New York Times here. He’s noticed a problem with string theory:

    One pet peeve is press releases about papers that show that string theory is about to be experimentally tested. When you read the fine print that’s never true. There was a press release that the large hadron collider was going to test string theory. It was kind of embarassing for them.

    Scientists and science journalists just take these shortcuts And I think they become enshrined as truth in the public mind.

    He also has some comments about blogs:

    Science journalism is in a very interesting, very turbulent state I think. We still have newspapers. Some newspapers still have science reporters, like the Times. I feel like the blogs have risen up to become huge force in the coverage of science. I think the readership now is very fragmented. I think a lot of people get their information from blogs, where people can be more casual or more arcane if they want to be. I think even at my newspaper there’s a difference between people who read the science times and the font page. There are a lot of these different layers of coverage going on.

  • In the category of “string theory about to be experimentally tested” nonsense that Overbye refers to, no press releases this week, but we do have a special section of Science News with an array of over-hyped stories about Cosmic Questions, with the one on string theory assuring us that:

    Even then, the LHC will be far from powerful enough to re-create the single, unified force that physicists believe existed for a fraction of a second after the Big Bang — you’d need a collider as big as the universe itself for that. But the LHC might be able to test some of the predictions made by the leading theory that joins gravity and the other forces.

  • In the category of something I just put on my list to try and find time to listen to, there’s a Science Friday program featuring a discussion about Science and Art between Cormac McCarthy, Werner Herzog and Lawrence Krauss.
  • In the category of talks I’d like to hear but can’t, Graeme Segal will be giving the Felix Klein lectures in Bonn next month, on the topic of Three Roles of Quantum Field Theory.

    • Update: Two more

  • According to a new preprint, CDF’s observed suspicious bump that made the New York Times “is a generic feature of low mass string theory”. No word yet on whether there’s going to be a press release. I guess this also means that if D0 doesn’t see the bump, that pretty much rules out low mass string theory since its generic feature is not observed, right?
  • Langlands has written a very interesting review for Mathematical Reviews of Ngo’s paper proving the fundamental lemma.
    • Posted in Uncategorized | 12 Comments

    More on Scattering Amplitudes

    Posted on April 10, 2011 by woit

    Last week was the beginning of a program at the Santa Barbara KITP entitled The Harmony of Scattering Amplitudes which will focus on topics including recent advances in computing N=4 super Yang-Mills scattering amplitudes. Talks are available on-line here. There’s a full schedule of talks in the program and related talks here. On Thursday, Nima Arkani-Hamed will give a talk on “The planar integrand of N=4 super-Yang-Mills theory”, which some wag has scheduled as lasting from 1:30pm to 5am.

    For a survey of some of these recent developments, a correspondent points me to the thesis of Arkani-Hamed’s student Jacob Bourjaily, which has just appeared online here.

    Posted in Uncategorized | 8 Comments

    Suspicious Bump

    Posted on April 6, 2011 by woit

    Last night a new preprint from CDF appeared at the arXiv, discussing a signal observed in their data, at about 3 sigma significance, that could in principle correspond to a new particle not seen or predicted before. This morning’s New York Times has an article about this here. The Times does a pretty good job of getting quotes from relevant experts and explaining the situation, which is basically “if it’s real that’s very exciting, but it probably isn’t”.

    I went to check Tommaso Dorigo’s blog only to find that he had a short posting up explaining that a more detailed one was embargoed until the public talk this afternoon at Fermilab (live stream at 1600 CDT here). This seemed rather odd since the Times had clearly been given the story a few days ago, embargoed only until last midnight. He now has a full posting up, and you should go there for a detailed and authoritative look at what this all means (most likely not much, modeling the huge background you have to subtract is hard).

    Update: For other blog postings about this well worth reading, try Michael Schmitt, Resonaances, Gordon Watts and Flip Tanedo.

    Update: Took about 21 minutes from the time of release of this data to submission of a paper explaining it.

    Posted in Experimental HEP News | 20 Comments

    2011 Templeton Prize

    Posted on April 6, 2011 by woit

    This years $1.6 million dollar Templeton Prize has been awarded to astronomer and cosmologist Sir Martin Rees. The Templeton Foundation has traditionally been largely devoted to promoting the intersection of science and religion, so one surprising aspect of this choice is that, while Rees is a very accomplished scientist, he doesn’t believe in God (although he likes the music and architecture in churches):

    In fact, Rees has no religious beliefs, but considers himself a product of Christian culture and ethics, explaining, “I grew up in the traditions of the Anglican Church and those are ‘the customs of my tribe.’ I’m privileged to be embedded in its wonderful aesthetic and musical traditions and I want to do all I can to preserve and strengthen them.”

    Rees does seem to believe in something that the Templeton people are willing to take as a replacement for belief in God: belief in the Multiverse. He has been one of the leading figures promoting the Multiverse and anthropic explanations, even before the recent string theory landscape pseudo-science made this so popular. For more about his views, see a 2003 interview In the Matrix, which leads off with:

    All these multiverse ideas lead to a remarkable synthesis between cosmology and physics…But they also lead to the extraordinary consequence that we may not be the deepest reality, we may be a simulation. The possibility that we are creations of some supreme, or super-being, blurs the boundary between physics and idealist philosophy, between the natural and the supernatural, and between the relation of mind and multiverse and the possibility that we’re in the matrix rather than the physics itself.

    Something for future Templeton candidates to keep in mind: no need now to believe in a Christian God, belief in “The Matrix” is good enough.

    Posted in Multiverse Mania | 23 Comments

    The Bogdanov Equation

    Posted on April 3, 2011 by woit

    Another book that I picked up in Paris is Lubos Motl’s L’Équation Bogdanov: Le secret de l’origine de l’Univers?. It’s a rather weird document, a mish-mash of defense of the Bogdanovs (partly by comparing their ideas favorably to loop quantum gravity), generalities about cosmology, and promotional material about string theory. Among the odd features of a book entitled “The Bogdanov Equation” is that there is no “Bogdanov Equation” in the book (or anywhere else, as far as I know). In a comment on his blog posting about the book Lubos writes

    If there is an equation written by the twins that can be shown to explain the origin of the Universe, you will read about it in the book. If there is none, you won’t find such big statements. But I can’t tell you and others the punch line here. Wink

    I don’t think it’s hard to guess which alternative is the right one…

    One of the great mysteries of the book is that of its authorship. Supposedly it was written by Lubos in English, then translated into French. I don’t doubt that large parts of it were written by him, although in a style somewhat different from his blog, and then passed through the filter of translation. Some parts of it though, especially some of the details of the endless defense of the Bogdanovs I can’t believe were written by him. For instance, pages 187-189 are taken up with a translation into French of this internet mailing list posting by “Osher Doctorow Ph.D.”, and the author is described as “Professor Osher Doctorow, mathematician at the California State University”, which appears to be misinformation of a Bogdanovian rather than Lubosian sort.

    Another commenter on the same blog posting by Lubos gives a long and detailed list of dubious things in the book and states that “To make it short, I have the impression that you are not the sole author of the book.”, asking him to clarify this issue. The response is

    Sorry but I have neither time, nor desire, not the full rights to answer ten kilobytes of such questions, some of which are well-informed observations but most of which are not.

    The book is created not only as a blog but also to satisfy a contract with the publisher. So I was okaying some proposals from the publisher. It is essentially good if you can identify these places.

    Theoretical physics in recent years has produced some very odd things, this book is one of the most bizarre.

    Posted in Book Reviews | 18 Comments