Short Items

Posted on September 17, 2010 by woit
  • The Fermilab Physics Advisory Committee recently recommended that the Tevatron be kept running for an additional three years (until 2014). By the end of that time it should be able to accumulate a total of 20 fb-1 of data, which would give sensitivity to a standard model Higgs at the 3-sigma level over the entire interesting mass range. The cost for this would be a total of about \$150 million, which would likely have to come out of Fermilab’s $810 million/year budget. While the idea of continuing to do physics at the high-energy frontier and possibly beat the LHC to the Higgs, for less than 10% of the lab budget/year seems to be a no-brainer, director Oddone still may not be completely sold on the idea. Keeping the Tevatron going would set back some of the projects the lab has planned for its future in a post-Tevatron world. There’s also significant concern about the future federal budget situation, and how to make sure that the best possible case is made for a future of Fermilab, in an environment where people may be looking for large, expensive programs that could be cut. For more about this, see Adrian Cho’s article Higgs or Bust? in Science.

    One huge consideration in this decision is that of what will happen at the LHC. CERN is facing its own budgetary problems, and has just decided to shut down during 2012 not just the LHC (for repair of magnet interconnections), but the entire accelerator complex. Work continues this year on trying to raise the luminosity of the machine, but progress is slow. They still are an order of magnitude lower than where they want to be by the end of the year, with only a few more weeks left before the machine is shutdown as a proton-proton collider and reconfigured for a heavy-ion run. If all goes according to plan, by late 2011 the LHC would have 1 fb-1 of data, enough to compete with the Tevatron in the Higgs search. But, so far, plans like this have turned out to be overly optimistic, with things taking longer than expected.

    In today’s CERN Bulletin and Fermilab today, Oddone and CERN DG Heuer issued a joint statement downplaying the competition between their labs:

    The press makes much of the competition between CERN’s LHC and Fermilab’s Tevatron in the search for the Higgs boson. This competitive aspect is real, and probably adds spice to the scientific exploration, but for us such reporting often feels like spilling the entire pepper shaker over a fine meal.

  • CheapUniverses.com is now selling a Universe Splitter iPhone app for $1.99, complementing its other products. At $3.95, the Basic Universe:

    Using quantum physics, we split your universe into two branches, then we send you an email to inform you which branch you’re in.

    As celebrity endorser, they have Garrett Lisi explaining:

    The functioning of this app is in complete agreement with the many-worlds interpretation of quantum mechanics.

  • The author is always the last to know such things, but I’ve heard rumors that someone intends to bring out a Czech edition of Not Even Wrong.
  • High quality videos of talks from the Princeton IAS summer school on supersymmetry are available here.
  • In Langlands-related news, there’s an excellent new preprint by David Nadler about the fundamental lemma and Ngo’s proof. This is one of the most ferociously difficult topics to understand in current math research, and Nadler’s article is about the best expository piece on the subject that I’ve seen.

    This semester there’s a program on Langlands Duality in Representation Theory and Gauge Theory at Hebrew University.

    There’s a fascinating recent preprint by Kevin Buzzard and Toby Gee on The conjectural connections between automorphic representations and Galois representations. They conjecture a reciprocity sort of relation between algebraic automorphic representations and Galois representations, not just for GL(n), but for arbitrary reductive groups. This involves invoking a twist by “half the sum of the positive roots”, a phenomenon that arises in various places in representation theory, often indictating that spinors are involved (“half the sum of the positive roots” is the highest weight of the spinor representation).

    • Posted in Experimental HEP News, Langlands, Multiverse Mania, Not Even Wrong: The Book | 16 Comments

    Hawking Gives Up

    Posted on September 7, 2010 by woit

    David Gross has in the past invoked the phrase “never, never, never give up”, attributed to Churchill, to describe his view about claims that one should give up on the traditional goals of fundamental physics in favor of anthropic arguments invoking a multiverse. Steven Hawking has a new book out this week, called The Grand Design and written with Leonard Mlodinow, in which he effectively announces that he has given up:

    We seem to be at a critical point in the history of science, in which we must alter our conception of goals and of what makes a physical theory acceptable. It appears that the fundamental numbers, and even the form, of the apparent laws of nature are not demanded by logic or physical principle. The parameters are free to take on many values and the laws to take on any form that leads to a self-consistent mathematical theory, and they do take on different values and different forms in different universes.

    Thirty years ago, in his inaugural lecture as Lucasian professor, Hawking took a very different point of view. He argued that we were quite close to a final unified theory, based on N=8 supergravity, with a 50% chance of complete success by the year 2000. A few years after this, N=8 supergravity fell into disfavor when it was shown that supersymmetry was not enough to cancel possible ultraviolet divergences in the theory. There has been a recent revival of interest as new calculational methods show unexpected and still not completely understood additional cancellations that may fully eliminate ultraviolet divergences. Hawking shows no interest in this, instead signing on to the notion that “M-theory” is the theory of everything. The book doesn’t even really try to explain what “M-theory” is, we’re just told that:

    People are still trying to decipher the nature of M-theory, but that may not be possible. It could be that the physicist’s traditional expectation of a single theory of nature is untenable, and there exists no single formulation. It might be that to describe the universe, we have to employ different theories in different situations

    The book ends with the argument that

  • Our TOE must contain gravity.
  • Supersymmetry is required to have a finite theory of gravity.
  • M-theory is the most general supersymmetric theory of gravity.

    • ergo

    M-theory is the unified theory Einstein was hoping to find. The fact that we human beings – who are ourselves mere collections of fundamental particles of nature – have been able to come this close to an understanding of the laws governing us and our universe is a great triumph.

    This isn’t exactly an air-tight argument…

    The book begins in a more promising manner, with a general philosophical and historical discussion of fundamental physical theory. There’s this explanation of what makes a good physical model:

    A model is a good model if it:

    1. Is elegant
    2. Contains few arbitrary or adjustable elements
    3. Agrees with and explains all existing observations
    4. Makes detailed predictions about future observations that can disprove or falsify the model if they are not borne out.

    The fact that “M-theory” satisfies none of these criteria is not remarked upon.

    The book is short (about 100 pages of actual text, interspersed with lots of color graphics and cartoons), and contains rather little substantive science. There are no references of any kind to any other sources. The discussion of supersymmetry and M-theory is often highly misleading. For example, we are assured that

    various calculations that physicists have performed indicate that the [super]partner particles corresponding to the particles we observe ought to be a thousand times as massive as a proton, if not even heavier. That is too heavy for such particles to have been seen in any experiments to date…

    With no references, one has no idea what these “various calculations” might be. If they are calculations of masses based on the assumption that the supersymmetry and electroweak-symmetry breaking scales are similar, they typically predict masses visible at the Tevatron or LEP. I suspect that the logic is completely backwards here: what is being referred to are calculations based on the Tevatron and LEP limits that require masses in the TeV range.

    As for the fundamental problem of testability of M-theory, here’s the only thing we get:

    The theory we describe in this chapter is testable…. The amplitude is reduced for universes that are more irregular. This means that the early universe would have been almost smooth, but with small irregularities. As we’ve noted, we can observe these irregularities as small variations in the microwaves coming from different directions in the sky. They have been found to agree exactly with the general demands of inflation theory; however, more precise measurements are needed to fully differentiate the top-down theory from others, and to either support or refute it. These may well be carried out by satellites in the future.

    This looks like one of many dubious claims of “testability” of multiverse theories, which tend to founder on the measure problem and the fact that one has no idea what the underlying theory actually is. Without any details or references though, it’s hard to even know exactly what the claim is here.

    One thing that is sure to generate sales for a book of this kind is to somehow drag in religion. The book’s rather conventional claim that “God is unnecessary” for explaining physics and early universe cosmology has provided a lot of publicity for the book. I’m in favor of naturalism and leaving God out of physics as much as the next person, but if you’re the sort who wants to go to battle in the science/religion wars, why you would choose to take up such a dubious weapon as M-theory mystifies me. A British journalist contacted me about this recently and we talked about M-theory and its problems. She wanted me to comment on whether physicists doing this sort of thing are relying upon “faith” in much the same way as religious believers. I stuck to my standard refusal to get into such discussions, but, thinking about it, have to admit that the kind of pseudo-science going on here and being promoted in this book isn’t obviously any better than the faith-based explanations of how the world works favored by conventional religions.

    For some reviews of the book showing a bit of skepticism, see ones by Craig Callender, Fred Bortz, and Roger Penrose. For much more credulous reviews, see for example James Trefil (who evidently has his own multiverse book coming out). The Economist has a news story about this, which assures us that Hawking is

    a likely future recipient of the Nobel prize in physics (if, as expected, his 1974 theory that black holes emit radiation despite their notorious all-engulfing gravitational pull is confirmed by experiments at the Large Hadron Collider in CERN).

    Update: There’s a new posting at physicsworld.com by Hamish Johnston that brings up the issue of the potential damage caused by this to the cause of science funding in Britain:

    This morning there was lots of talk about science on BBC Radio 4’s Today Programme — but I think it left many British scientists cringing under their duvets.

    Hawking explained that M-theory allows the existence of a “multiverse” of different universes, each with different values of the physical constants. We exist in our universe not by the grace of God, according to Hawking, but simply because the physics in this particular universe is just right for stars, planets and humans to form.

    There is just one tiny problem with all this — there is currently little experimental evidence to back up M-theory. In other words, a leading scientist is making a sweeping public statement on the existence of God based on his faith in an unsubstantiated theory…

    Physicists need the backing of the British public to ensure that the funding cuts don’t hit them disproportionately. This could be very difficult if the public think that most physicists spend their time arguing about what unproven theories say about the existence of God.

    Update: Today’s Wall Street Journal has a quite positive review of the book by Sean Carroll.

    Update: See here for John Horgan’s take on the Hawking book:

    I’ve always thought of Stephen Hawking—whose new book The Grand Design (Bantam 2010), co-written with Leonard Mlodinow, has become an instant bestseller—less as a scientist than as a cosmic, comic performance artist, who loves goofing on his fellow physicists and the rest of us…

    Toward the end of the meeting [in Sweden, 1990], everyone piled into a bus and drove to a nearby village to hear a concert in a Lutheran church. When the scientists entered the church, it was already packed. The orchestra, a motley assortment of blond-haired youths and wizened, bald elders clutching violins, clarinets and other instruments, was seated at the front of the church. Their neighbors jammed the balconies and seats at the rear of the building.

    The scientists filed down the center aisle to pews reserved for them at the front of the church. Hawking, grinning ear to ear, led the way in his motorized wheelchair. The townspeople started to clap, tentatively at first, then passionately. These religious folk seemed to be encouraging the scientists, and especially Hawking, in their quest to solve the riddle of existence.

    Now, Hawking is telling us that unconfirmable M-theory plus the anthropic tautology represents the end of that quest. If we believe him, the joke’s on us.

    Posted in Book Reviews, Multiverse Mania | 83 Comments

    Researchers Discover How to Conduct First Test of “Untestable” String Theory

    Posted on September 1, 2010 by woit

    A couple people this morning pointed me to today’s press release from Imperial College, headlined Researchers Discover How to Conduct First Test of “Untestable” String Theory and subtitled “New study suggests researchers can now test the ‘theory of everything'”. In case you miss the headline and subtitle, and thus the point that string theory is now testable due to the efforts of Imperial College researchers, the rather short press release repeatedly drives the point home:

    The new research, led by a team from Imperial College London, describes the unexpected discovery that string theory also seems to predict the behaviour of entangled quantum particles. As this prediction can be tested in the laboratory, researchers can now test string theory…

    Using the theory to predict how entangled quantum particles behave provides the first opportunity to test string theory by experiment…

    The discovery that string theory seems to make predictions about quantum entanglement is completely unexpected, but because quantum entanglement can be measured in the lab, it does mean that at last researchers can test predictions based on string theory…

    There’s a blog posting written about the preprint of this paper when it first appeared here, in which I pointed out that the result worked out in the paper is just an example of a well-known piece of mathematics that comes down to classifying nilpotent orbits. This is based on a famous 1971 theorem of Kostant-Rallis, and Nolan Wallach worked out in detail here the specific example considered by Duff et al. in lecture notes for a 2004 summer school. The initial preprint didn’t refer to this mathematical literature, but a revised version was soon issued in which a reference to the Wallach notes was added to the bibliography. There’s no trackback to the discussion on Not Even Wrong at the arXiv listing for the paper due to the arXiv’s censorship policy, but perhaps one or more of the authors of the preprint are regular readers here…

    I have no idea how this paper is supposed to contain a “test” of string theory. The simple quantum mechanics problem at issue comes down to classifying orbits of a group action on a four-fold tensor product, exactly what Wallach worked out in detail in his notes, as an example of Kostant-Rallis. If you do an experiment based on this and it doesn’t work, you’re not going to falsify string theory (or Kostant-Rallis for that matter). By now there’s a long history of rather outrageous press releases being issued about the discovery of supposed “tests” of string theory. This one really takes the cake…

    Update: The press release is having its intended effect, generating stories headlining false claims about string theory . So far today, there’s String Theory:Testing the Untestable?, New study suggests researchers can now test the ‘theory of everything’, Scientists Say They Can Now Test String Theory and Researchers Devise the First Experimental Test of Controversial, Confusing String Theory. There’s even UK Scientists discover way to test untestable string theory, which has the test already performed:

    Scientists at the Imperial College London have managed to conduct the first string theory test, destroying previous beliefs that it was untestable….

    The discovery will please physicists, most of whom consider string theory the best available for explaining the universe.

    Unfortunately, no details on how the test turned out…

    Update: The subtitle on the press release has been changed. It used to be “New study suggests researchers can now test the ‘theory of everything'”, now it’s “New study presents unexpected discovery that string theory may predict the behaviour of entangled quantum particles.”

    Update: No press campaign for a “finally string theory is testable” claim is complete without a Slashdot story (actually, stories, here and here):

    Big news for theoretical physicists who are fed up with the inability to test String Theory…

    Update: Lisa Grossman has a story about this at Wired Science. She went to the trouble of contacting well-known string theorists for their opinion, which is unanimous that this is not a “test of string theory”:

    “Already I can imagine enemies sharpening their knives,” Duff said.

    And they are. A chorus of supporters and critics, including Nobel laureate and string theory skeptic Sheldon Glashow and string theorists John Schwarz of Caltech, James Gates of the University of Maryland, and Juan Maldacena and Edward Witten of the Institute for Advanced Study in Princeton agree that Duff’s argument is “not a way to test string theory” and has nothing to do with a theory of everything.

    I’m still trying to figure out what the supposed test of string theory is, since I can’t find such a thing in the published paper. The Wired article has a bit more explanation from Duff:

    Whether the result is some fundamental principle or some quirk of mathematics, we don’t know, but it is useful for making statements about quantum entanglement.

    As far as I can tell, we do know where their results come from, a “quirk of mathematics” known as the Kostant-Rallis theorem, applied to the invariant theory question that comes up in quantum entanglement.

    The article also contains quotes from me, saying about what you’d expect.

    Update: Science News has completely uncritical coverage of the “First Test of String Theory” claims.

    Posted in This Week's Hype | 14 Comments

    Everything is Emergent

    Posted on August 26, 2010 by woit

    During the past year Erik Verlinde has made a splash (most recently in the New York Times). with his claim that the reason we don’t understand gravity is that it is an emergent phenomenon, an “entropic force”. Now he and Peter Freund are taking this farther, with a claim that the Standard Model is also emergent. Freund has a new paper out on the arXiv entitled “Emergent Gauge Fields” with an abstract:

    Erik Verlinde’s proposal of the emergence of the gravitational force as an entropic force is extended to abelian and non-abelian gauge fields and to matter fields. This suggests a picture with no fundamental forces or forms of matter whatsoever.

    Freund thanks Verlinde, who evidently has much the same idea:

    I wish to thank Erik Verlinde for very helpful correspondence from which it is clear that he independently has also arrived at the conclusion that not only gravity, but all gauge fields should be emergent.

    He remarks that this new theoretical idea is remniscent of Geoffrey Chew’s failed “bootstrap program” of the sixties:

    It is as if assuming certain forces and forms of matter to be fundamental is tantamount (in the sense of an effective theory) to assuming that there are no fundamental forces or forms of matter whatsoever, and everything is emergent. This latter picture in which nothing is fundamental is reminiscent of Chew’s bootstrap approach [9], the original breeding ground of string theory. Could it be that after all its mathematically and physically exquisite developments, string theory has returned to its birthplace?

    It’s very unclear to me why this is supposed to be a good thing. In his Nobel prize lecture, David Gross, a student of Chew’s explains:

    I can remember the precise moment at which I was disillusioned with the bootstrap program. This was at the 1966 Rochester meeting, held at Berkeley. Francis Low, in the session following his talk, remarked that the bootstrap was less of a theory than a tautology…

    Posted in Uncategorized | 49 Comments

    This Week’s Hype

    Posted on August 25, 2010 by woit

    I’m rather busy these days with a move to a new apartment, but maybe there’s time for a quick edition of “This Week’s Hype”.

    A commenter on the previous posting points to Amanda Peet’s recent talk entitled String Theory for the Scientifically Curious. In the question and answer section, she responds to someone who asks her to comment on Phil Anderson’s claim that string theory makes no falsifiable predictions. She describes this claim as “absolutely fundamentally completely utterly wrong” and says that Anderson should “be smacked around the head” for saying it. She then goes on to a vigorous and extensive personal attack on Lee Smolin.

    Her argument that string theory really is falsifiable is that a paper by Distler and collaborators shows this and has been published. The paper she is referring to is this one, which started off as a preprint with the title Falsifying String Theory through WW scattering, but was only published after a forced change of title to “Falsifying Models of New Physics Via WW Scattering”. One reason for this is that there’s actually nothing about string theory in the paper. Evidently Peet just saw the preprint, not the published version. If you want to know more about this particular piece of hype, see blog postings here, here, and here.

    For more Amanda Peet in action, there’s a classic video from the KITP, blogged about here.

    Posted in This Week's Hype | 17 Comments

    Geometric Langlands at the KITP

    Posted on August 17, 2010 by woit

    There’s a very interesting program going on at the KITP discussing recent work of mathematical interest on 4d supersymmetric gauge theories (N=2 and N=4). These include various connections of 4d gauge theory to geometric Langlands uncovered by Witten and collaborators a few years ago, as well as last year’s conjecture by Alday-Gaiotto-Tachikawa of a relation between 4d gauge theory and 2d Liouville conformal field theory. In his introductory talk, Edward Frenkel discusses the possibility of a relationship between these ideas and the much earlier ideas about 2d conformal field theory that were inspirational at the beginnings of research on geometric Langlands (about which he has written extensively).

    Yesterday and today Witten gave two talks on some new work. The first was about the very basic problem of how you quantize a finite dimensional symplectic manifold, which he approached using the phase-space path integral. The idea was similar to that described in a 2008 paper with Gukov, where the quantum mechanical problem gets turned into a 2d topological QFT problem. The innovation here is that he does this explicitly at the level of the path integral, using the kind of techniques for complexifying the problem, using holomorphicity and choosing appropriate path integral integration contours, that he pioneered in his recent paper on Analytic Continuation of Chern-Simons Theory. The second talk applied these ideas to the case of Chern-Simons theory. The path integral there is somewhat like the phase-space sort of path integral, and he expressed it in terms of a 4d QFT. He claims to be able to thus solve a well-known problem, that of how to get a QFT that gives Khovanov homology, which is a topological invariant with Euler characteristic the Jones polynomial. Unfortunately I get lost at the end when he has to go to 5 dimensions and perform some duality transformations. I gather he’ll have a paper about this relatively soon, and I’ll try again to see exactly how this works then.

    Perhaps a collection should be taken up to buy a new camera for the KITP. The resolution of the one they have now been using for years is such that you often can’t quite read what the speaker is writing on the blackboard. Still, it’s wonderful to be able to follow along as they quickly put a lot of high-quality talks on-line.

    Posted in Langlands | 6 Comments

    Gossip

    Posted on August 17, 2010 by woit

    As the date for announcement of the 2010 Fields Medals approaches, gossip about who the winners might be has been circulating. Math Overflow is by far the best internet site for authoritative discussion between knowledgeable mathematicians, but, unlike this site, they have a “no gossip” rule, leading to the closing of discussion threads like this one.

    You can bet on who the Fields Medalists might be here. I assume there’s no bet possible for Ngo since he’s a sure thing…

    Update: It’s Ngo and Villani, also Elon Lindenstrauss and Stanislav Smirnov. For the announcement and information about the work of the prize winners, see here. Accurate rumors about this don’t seem to have started circulating until the ICM announced the winners to the press late Tuesday. This information was embargoed until today, breaking the embargo didn’t seem sporting…

    Update: Best blog by far for following this is that of Timothy Gowers, who was on the committee that picked the Fields medal winners, and promises to tell us about Cedric Villani’s outfit.

    Posted in Uncategorized | 13 Comments

    Hype or Not Hype?

    Posted on August 6, 2010 by woit

    The high point of my expertise in condensed matter physics was about thirty years ago, when I studied the subject in order to pass one of the general exams at Princeton. At the party after the test was graded, Phil Anderson came up to (after a fashion…) compliment me, noting that he was glad to see that even though I hadn’t been able to solve one of the condensed matter problems, I had known enough to realize that the calculation I was trying to do was giving a result that couldn’t be right and had written that on the test.

    Since then, my little understanding of the subject has slowly decayed over the years, so I’m in no position at all to evaluate claims made about new advances. Recently there has been a lot of interest in applications of gauge/gravity duality to certain condensed matter systems, and this week there’s a new article out in Science (not available on the arXiv itself, but based on this arxiv preprint), together with a press release from MIT. This has led to news stories headlined String Theory Explains Superconductors, and String theory and black holes show a possible path to practical superconductors. This latest story starts off:

    A leading candidate for room temperature superconductors is the copper compound cuprate, but no one knew how cuprates facilitated superconductivity…until some brave souls looked inside a black hole and broke out the string theory to explain how they work.

    So, hoping that there might be someone expert on this out there and willing to comment, what’s the verdict: hype or not hype?

    Posted in This Week's Hype | 65 Comments

    Short Items

    Posted on August 4, 2010 by woit
  • There has been some recent progress on increasing the LHC luminosity. Recent physics fills have peak luminosities around 2.5 x 1030cm-2s-1, total integrated luminosity is above 500 nb-1, with a goal of getting to 1000 nb-1=1 pb-1 this week. The current goal is to get to peak luminosity of around 1 x 1032cm-2s-1 this year, but there are only about 12 weeks left in this year’s proton run. To achieve next year’s goal of 1 fb-1 in integrated luminosity, they will need to get to peak luminosities around 2 x 1032cm-2s-1.
  • According to a new preprint entitled It’s On, with only 70 nb-1 of analyzed data ATLAS has already been able to rule out some parts of the huge parameter space of supersymmetry models, beyond that already ruled out by the Tevatron. These limits come from looking for missing transverse energy.

    A story at Ars Technica says:

    John Ellis was quite a bit more optimistic; he expects that we might be seeing new physics once we’ve obtained somewhere in the neighborhood of a trillion events, which may happen as soon as this autumn. Since the Higgs boson, the ostensible target of the LHC, is in a noisy place, in terms of the other particle decays with similar signatures, we may actually end up seeing supersymmetry first. Since the experiments are so well-tuned, it may only be a matter of hours before it’s flagged, and the rumors start to filter out.

    A trillion events is about 10 pb-1.

    If there’s no sign of supersymmetry in this year’s LHC data, how discouraging will this be for those who expect to see supersymmetry at this energy scale?

  • Besides supersymmetry, something else that experimentalists will be looking for in the initial LHC data will be a fourth generation quark. The Tevatron has been able to put limits of 300 GeV or so on the mass of such a thing, see Tommaso Dorigo’s latest posting for more about this topic.
  • Capitalist Imperialist Pig has a review of a movie with the title String Theory. It seems that this is actually a very popular movie title, used by at least two feature-length films (here and here) as well as three shorts (here, here and here). For some reason (as far as I can tell), no one has yet used Not Even Wrong as a film title.
  • Colliding Particles is a well-done on-going series of films featuring experimentalists working at the LHC. There are six of them so far, and they’re available on-line here.
  • While I was away Erik Verlinde made the New York Times with his “entropic” theory of gravity. There’s also a talk at ICHEP available here. This week he’s promoting this at SciFoo, going on at the Googleplex, see a report here:

    So far all this is just an “intuition”, Verlinde says. Now he needs to find the mathematics to prove it. Then he shrugs and says perfectly matter-of-factly that this was how Einstein started out too.

    I really don’t get this at all….

  • From David Berenstein I learned about Jonathan Rosenberg’s comic series Scenes From A Multiverse (some randomly chosen examples here and here).
  • Finally, from Gordon Watts, a wonderful tale of the tenure process.

    • Update: One more. There’s a very informative long piece by Stephen Hawking here about his scientific career.

    Update: See Resonaances for more about the “It’s On” paper.

    Posted in Uncategorized | 26 Comments

    Witten Talk and Interview

    Posted on July 27, 2010 by woit

    In conjunction with his receipt of the Newton Medal, Edward Witten gave a public talk in London (now available on-line here), and an interview (available as part of a pod-cast here).

    Witten’s talk was a rather polemical argument for string theory, in which he laid out his reasons for still feeling that string theory is on the right track. The video is in two parts, with the first part not especially interesting since it is pretty much word-for-word the standard arguments for string theory that he and others have been making since the mid-eighties. The second part has some more interesting content, including Witten’s comments on the evolution of his own personal relationship to the subject. This started in the early eighties, before the 1984 “First Superstring Revolution”, when he began studying string theory, feeling that it was an approach to unification that deserved more attention than it was getting.

    A recurring theme in his talk is that “string theory” has gone through unexpected changes in perspective over the 30 years he has been working on it, with the unspoken argument being that some new change in perspective may yet make the current deadly problems of string unification go away. He takes an ambiguous attitude towards attempts in recent years to argue for a change in perspective to the pseudo-scientific “landscape”, explaining the arguments of proponents while not signing on to them. In the podcast he says “I don’t know if this is the right picture of the universe”, in the talk it’s “to my thinking we still need more clues to have a better picture whether that is the right interpretation.”

    It’s interesting to compare Witten’s pro-string theory arguments to the somewhat similar ones of his much less mild-mannered thesis advisor David Gross (see here for a posting about a recent talk by Gross). Unlike Witten, Gross is clear where he stands on the anthropic landscape, denouncing it as pseudo-science. One other crucial difference has to do with their discussion of upcoming LHC results. Here, Gross argues strongly that the LHC will see supersymmetry, and is willing to put money on the table to back this up. Witten’s talk barely refers to the LHC, and while he argues that a point in string theory’s favor is its relation to supersymmetry, all he’s willing to say about supersymmetry or extra dimensions at the LHC is “it might happen if we’re fortunate enough.” The next interesting part of the string theory story may very well be what happens in 2013-4 when it becomes clear that supersymmetry and extra dimensions are not going to be seen at LHC energies. After paying off his debts, I wouldn’t be surprised to see Gross take this as an opportunity to back off from the idea of string theory unification. On the other hand, in his talk Witten seems to be positioning himself for carrying on as before, by now making arguments for string theory that don’t at all involve low-energy supersymmetry.

    Witten ends his talk with the argument that we still know very little about what string theory is, and this implies that it remains an excellent subject for young physicists to start to work on. I suspect he sees all too well that among physicists the tide has changed, with students turning to other subjects as jobs in string theory dry up and prospects for progress on string theory unification look increasingly dismal. He’s trying to counter this by restating the arguments that have continued to keep him interested in the subject.

    Update: Clifford Johnson has some very interesting and accurate comments on Witten and on how others react to him here.

    Posted in Uncategorized | 25 Comments