More Links, Interesting and Tedious

Posted on February 5, 2014 by woit

First some links to interesting things:

In the category of things that have gotten tedious, first there’s the ongoing hullabaloo about “firewalls” and Hawking (with the bottom line as far as I can tell just that, yes, there is an information paradox, might have something to do with the fact that we don’t understand quantum gravity…). If this interests you, you can take a look at

In the multiverse-mania category, I’m forcing myself to read the Rubenstein book I’ve mentioned, will report on this when done, in the meantime there’s

  • In the London Review of Books, David Kaiser has a review of Lee Smolin’s book from last year Time Reborn. The review is mostly about the string theory landscape case for the multiverse, a bit about Smolin’s take on it.
  • Tom Banks has a new paper out surveying the issue of Supersymmetry Breaking and the Cosmological Constant. He surveys the anthropic string theory landscape argument and concludes that

    It is therefore fair to say, that much of the standard model, and certainly the peculiar values of many of the parameters in the standard model, cannot have an anthropic explanation. In string theory, extra generations of matter correspond to more tuning of moduli, small parameters do not appear to arise without a symmetry explanation, and symmetries are rare on moduli space.

    One cannot escape the implication that, on the basis of current theoretical knowledge, the String Landscape is ruled out by experiment.

    Besides being experimentally ruled out, the whole Landscape thing doesn’t work anyway

    My personal conclusion from all of this analysis, is that the theory of CDL tunneling provides no positive support for, and lots of negative evidence against, the proposal of a String Landscape…

    When combined with the phenomenological challenges I presented in Section 2, I conclude that the String Landscape is an hypothesis of dubious validity.

    This is a subject in which solid predictions are hard to come by, but I’ll make one here: string theory partisans will just ignore this, with the “String Landscape” now an hypothesis which has achieved some sort of new extra-scientific status. It’s an ideology you sign up for to justify not giving up on string theory (or as a foundation for your multiverse-mania), and as such, arguments like those from Banks are irrelevant.

  • Also in the category of serious scientific arguments against the anthropic landscape that will just be ignored, see Sesh Nadathur who explains why Weinberg’s original argument for the CC implies one that is 103 times too big. This is part of some arguments with Shaun Hotchkiss you might want to have a look at, see other blog postings here and here.
  • Finally, Max Tegmark is on tour promoting multiverse-mania and his Level IV version of it. The latest from him is here at Scientific American, where he’s claiming that his Level IV multiverse is science because it could be falsified by finding “some physical phenomenon that has no mathematical description.” I’ve tried arguing the absurdity of this with him in the comment section, so far no luck getting anything other than a dismissal of me as “emotional”.

    I was interested to see that his perception of what has been going on for the past decade as endless popular books promoting the multiverse have appeared is that

    whenever a physicist writes a book about them [multiverse ideas], the Web erupts with claims that they are unscientific nonsense.

    Curious to know what part of “the Web” he is referring to other than my blog…

    • Posted in Multiverse Mania, Uncategorized | 44 Comments

    The Perfect Wave

    Posted on February 4, 2014 by woit

    Sometimes when I have come across claims of exotic phenomena at the far-out edge of the field of BSM physics based on branes and string theory (like time travel, or brane-world explanations of the bad OPERA result), my initial reaction has been “Are these people on drugs?” A new book out from Harvard University Press, The Perfect Wave, by theorist Heinrich Päs explains that yes, some of this particle theory activity has its intellectual roots in psychedelic drug consumption.

    The book opens with a short chapter about surfing in Hawaii, but then turns to a long chapter about LSD, the author’s experience with magic mushrooms, and the cult of Eleusis in ancient Greece. Supposedly this cult revolved around consumption of a psychedelic brew called “kykeon”, and we’re told that this was of great influence on Plato. The discovery of atoms is also attributed to a drug trip:

    Moreover, the perception of smallest details during a drug trip may have affected the atomism of Democritus, who first assumed that the world should be built up of indivisible elements.

    The next chapter goes on to discuss quantum mechanics from this point of view. Starting with Heisenberg’s claims of inspiration from Plato’s Timaeus, Päs moves on to Heisenberg’s student von Weizsäcker and his ideas about quantum mechanics and Plato’s Parmenides:

    In summary, Weizsäcker arrives at an amazing conclusion, that the notion of complementarity has its source in ancient Greece: “We find … the foundation of complementarity already foretold in Plato’s Parmenides.” We actually can recover the feel of what the ancient Greeks experienced in their mystery cults in modern twentieth-century physics!

    From there the book moves to the multiverse and Everett’s many-worlds interpretation of QM, telling us that:

    It is actually possible to recognize the multiverse — the collection of all of Everett’s parallel universes — directly as Parmenides’s primeval One: the unity of the world the ancient Greeks felt thay had lost in the charted modern world, and for whose reunification with the individualized ego they looked in the ecstasy of their mystery cults, in their Dionysian arts, or in the flush induced by psychedelic drugs.

    The main part of the book then begins with chapter four, which starts out:

    Physics is like surfing. Or like an LSD trip.

    The final chapter closes with an invocation of Nietzsche and a return to the multiverse of the many-worlds interpretation, with this now providing the Dionysian vision of science that he desired:

    For Nietzsche, science thus was the original cause for the ancient Greek’s suffering from the separation of subject and object. And for modern humanity being torn from the integral unity of nature.

    Only if science were reconciled with the Dionysian tragedy, with art and music, only if Socrates would start to make music, only then could science grant humanity with a deep metaphysical benefit, could establish a true meaning of life.

    In view of this, it is probably most amazing that science itself, with the many-worlds interpretation of quantum mechanics, leaves some room for an entire multiverse of alternative realities beyond our immediate experience — a multiverse mirroring the unity of Parmenides’s philosophy, as well as the egolessness of Aldous Huxley under the influence of psychoactive drugs, and a Dionysian creative moment bursting open all boundaries.

    In betwen the first few chapters and the last one, there’s a short 200 page book about neutrinos. This is the field of the author’s expertise, where he started out as a theory student working with the Heidelberg-Moscow double beta decay experiment. Claims from this group that they see a signal have been challenged by recent (too recent to be in the book) results from GERDA. The GERDA results are here, Heidelberg-Moscow’s response here. Neutrino physics is a complicated and fascinating subject, and one can certainly make a good argument that it’s now the part of HEP where there are things we don’t understand and promising avenues to explore using existing technologies (you don’t need TeV-scale accelerators).

    Unfortunately what most interests Päs is the far-out part of the subject, specifically ideas like using neutrinos to travel in time by hopping between branes. In the foreword to the book he does give a warning:

    Warning up front! The book deals with established scientific insights and with wild speculations… I highly recommend that the reader be alert to this difference.

    and then briefly notes which topics he will cover are extremely speculative, but then ends with an inspirational quote from Glashow:

    The wild ideas of yesterday quickly become today’s dogma.

    These warnings are quickly left behind, and it requires a careful and well-informed reader to sort through which of the material on neutrinos has some sort of relation to reality, and which is just baseless and wild speculation.

    When I bought this recently released book in the local bookstore (Book Culture, if you’re interested…), at the same time I acquired another very recently released book, which I’ll write more about here soon. The odd thing is that both of these books come from Ivy League university presses, and both end with a stirring and enthusiastic invocation of the multiverse as providing a Neitzschean answer to rationalistic Western science. There’s definitely a trend here… For the Päs book in particular, I’m rather mystified why Harvard University Press decided this was something they should publish.

    In the next to last chapter, Päs shows some awareness of why rationalistic science is so important:

    But useful application is not the point of neutrino physics. Rather it is a quest for a better basic understanding of the universe, thereby ultimately contributing to a solid foundation for the an incorruptible, rational world view. At times when intolerance, religious fanaticism, gut instincts, and irrational esotericism are flourishing, this is an effort whose importance should not be underestimated.

    I’m not sure that “irrational esotericism” is any more of a widespread problem in the culture at large now than it has ever been. If it is though, I don’t see how promoting over-the-top groundless speculation, the multiverse, and the idea (attractive as it may be) that fundamental physics should be a Dionysian activity based on psychedelic drug consumption is really going to help…

    Update: Heinrich Päs sent me the following. It addresses a few things in the review that could easily be misunderstood, providing very helpful clarifications and some of his point of view.

    Dear Peter,

    thanks for your extensive review of my book. If you allow, I would like to comment on a few points though which might be misunderstood:

    Your review may give the impression that the wild speculations in this book are not clearly identified. However, the preface you are citing identifies GUTs, supersymmetry and cosmic inflation as speculations which nevertheless represent “the present hopes… of most of the scientists working actively in these fields”, marks string theory and extra dimensions as “wilder” speculations, admits that shortcuts in extra dimensions are “speculations squared” and that time travel in extra dimensions may be considered as “speculation to the power of 1,000”. Also later on in the book I put some effort into saying clearly when I talk about textbook science and when I discuss scientific (and other) speculations, and I always motivate these speculations. For example, I mention your very own criticism of string theory as being “not even wrong” and I actually agree with you that scientific theories should make testable predictions. Of course this is one important difference of science and religion (or esotericism). However – and I hope you didn’t take that personal – I continue by arguing that it is more useful and pragmatic to try to find out whether some ideas of string theory could actually lead to testable predictions – what people like Antoniadis, Arkani-Hamed, Dvali, Dimopoulos, Randall and Sundrum have started – than to condemn it.
    And this is another important difference of science and religion: textbook theories can be questioned. Without speculation there would be no relativity and quantum mechanics, there would actually be no science at all.

    You also mention the controversial result of the Heidelberg-Moscow group and the wrong OPERA result. Let me clarify that I’m not an author or advocate of the Heidelberg-Moscow result, and that I always have emphasized that the OPERA result is most probably due to a mistake in the experiment. The results are mentioned in the book as what they are: controversial and wrong, respectively. And while the GERDA result is not in the book, the somewhat earlier result by EXO which also challenged the Heidelberg-Moscow result with a comparable sensitivity is discussed.

    Having said this, I actually like your review. It transmits the correct idea that this book takes you on the wild trip through neutrino physics, and may some of your more intellectually adventurous readers actually motivate to buy it.

    Kind regards, Heinrich

    Posted in Book Reviews, Multiverse Mania | 23 Comments

    The Perfect Theory

    Posted on February 2, 2014 by woit

    Cosmologist Pedro Ferreira has a new book about to come out, entitled The Perfect Theory. The author accurately describes the book as a “biography of general relativity”, and it’s quite a good one, of the short and breezy variety (as opposed to the detailed and exhaustive sort).

    The theory’s parentage (Einstein), conception and birth are covered, in particular the way in which mathematics played a crucial role, with Einstein getting important help on this from his friend Marcel Grossman, as well as David Hilbert, who found the right dynamical equations at the same time. This material goes by fairly quickly though compared to many other sources for this history, in order to get to the main topic: the life story of the theory so far, nearly 100 years on. After the birth of the theory, it soon started to get wide acceptance, with Eddington helping to provide both the experimental confirmation in 1919 of the theory’s distinctive prediction about deflection of light by the sun, as well as ensuing publicity.

    Some implications of GR were found immediately (e.g. the Schwarzschild solution in 1916), and the 1920s saw early work on applying the theory to cosmology (de Sitter, Friedmann, Lemaitre). By 1929 Hubble’s observations of an expanding universe had shown the way forward in this area. Ferreira goes on to follow several different strands of how the theory has developed. These include: black holes (Oppenheimer, Wheeler, singularity theorems from Penrose, Hawking, the information paradox), cosmology (Hoyle and steady state models, the CMB, Peebles and the now standard model, with dark matter and dark energy), relation to quantum theory (DeWitt, supergravity), gravitational waves (Weber, LIGO, proposals like LISA), and quite a few others. A wealth of different topics and interesting pieces of the history of the subject are covered, although none in great detail. The emphasis is on this history, along with the present state and prospects of the subject, with not much attempt to try and explain the intricacies of the physics (which would take a much longer book).

    On the hot-button issues of string theory and the multiverse, Ferreira does a good job of giving an even-handed description of the arguments. For instance, he counsels reader to pay attention to George Ellis as well as multiverse proponents.

    For more about the book, there’s a very good review by Graham Farmelo here. Oddly though, just like with his excellent biography of Dirac, which ended with a weird attempt to claim Dirac as a string theorist, here Farmelo ends by trying to enlist Ferreira and GR in the cause of string theory:

    50 years later, the mathematical aesthetic of relativity has been enhanced by the beautiful demonstrations of its veracity that Ferreira describes. These would probably have made Born ponder why he and his peers did not spend more time developing a deeper appreciation of the theory soon after Einstein first presented it. Maybe there’s a lesson here for some of today’s string-theory sceptics?

    I’ve never seen anyone else try and claim that the history of GR is analogous to the history of string theory. As Ferreira’s book explains, unlike string theory, GR is a classic example of a testable scientific theory, coming with one impressive post-diction (precession of the perihelion of Mercury) and followed up by an impressive test of a distinctive prediction (bending of light at the 1919 eclipse). As for mathematical aesthetics, GR uses beautiful mathematics (Riemannian geometry) and its dynamics is determined by the simplest possible Lagrangian density (the scalar curvature and nothing else). Whatever the equations of string theory might be, they remain unknown. Rather than a lesson for string theory sceptics, this book provides some good lessons about what a successful fundamental theory looks like, ones that string theory proponents would be well-advised to ponder.

    “The Perfect Theory” is a good title for the book, with GR remaining our best example of a beautiful, powerful fundamental physical theory, based on the deepest mathematical ideas, with almost no free parameters. Ferreira does a great job of leading readers through the story so far of this amazing theory.

    Update: For another review of the book, see Ashutosh Jogalekar at The Curious Wavefunction.

    Update    : Nature now has a podcast with an interview of Ferreira.

    Posted in Book Reviews | 21 Comments

    Quick Links

    Posted on February 1, 2014 by woit
    • I’ve always thought more philosophers of science should be weighing in on the debate over “falsifiability” and the “demarcation problem” surrounding string theory and the multiverse (i.e. are these really science?). This is a complex and tricky subject that they have a long tradition of exploring, and it would be great to have this inform some of the debate instead of the often very naive arguments that dominate the discussion. Massimo Pigliucci does a nice job here, responding to Sean Carroll’s attack on falsifiability (see here, more discussion here). Pigliucci’s posting is great, giving a concise explanation of the way philosophers of science have found to think about these issues. It does though show that much of what needs to be examined are technical scientific issues (what exactly does “string theory” say or not say? What exactly are the conceivable things one could expect to measure and compare to theoretical predictions? What exactly is the state of efforts by string theorists to make predictions: how deadly are the obstructions they have run into?). In any case, here’s Pigliucci’s conclusion:

      But at some point the fundamental physics community might want to ask itself whether it has crossed into territory that begins to look a lot more like metaphysics than physics. And this comes from someone who doesn’t think metaphysics is a dirty word…

    • This evening at ASU there will be a program on Parallel Realities: Probing Fundamental Physics, you may be able to watch it live here. With David Gross there, at least it won’t be the usual “Isn’t the Multiverse cool?”-fest that this sort of thing recently often has turned into. Yesterday on Science Friday, Krauss, Wilczek and Brian Schmidt discussed Could There be a Crisis in Physics?
    • In case you’re wondering why there’s been no discussion here of Hawking’s recent claims about black holes, the reason is that I’m in agreement with Wilczek’s wise characterization of this on the Science Friday program:

      I think the kind thing to do is to pass this over in silence.

      If you really need some Hawking material, there’s The Top 10 Science Jokes, As Told by Stephen Hawking. Warning: safe for work, but not very funny…

    • Quite a bit funnier (although some might say, also kind of tired and sad..) is this “debate” between Bousso and Rovelli at the latest FQXi conference: String theory vs. loop quantum gravity.

    Update: Video of the ASU talks can be found here. Wilczek is still sticking with SUSY, but says “no more excuses… these particles have to materialize [at the full LHC energy]”. According to Twitter, this really was a rock-star event, with the local ladies “getting dolled up” and ready “to throw our panties onstage.”

    Posted in Multiverse Mania | 17 Comments

    Scientific Bookstores, RIP

    Posted on January 29, 2014 by woit

    A few days ago I tried to stop by the Barnes and Noble store here in New York at Fifth Ave. and 18th St., just to find that it had closed earlier this month. This was the first book store I had access to as a high school student that had a serious collection of math, physics and astronomy books, and I’ve been buying such books there for about 40 years. The huge 18th St. store dates back to 1932, and by the early 1970s was the only Barnes and Noble store, at the time that the company was revived and started its huge expansion.

    With the closing of this store, there now are no longer any bookstores that I’m aware of in New York City that have a large collection of technical math and physics books. Other Barnes and Nobles like the Columbia bookstore have a smattering of such books, and the Strand has a large collection of used and remaindered books, but that’s about it (maybe a reader will tell me about a place I don’t know). At one point in a long-ago golden age there were several bookstores here devoted to scientific and technical books, including Book Scientific and the McGraw-Hill book store.

    The same phenomenon is taking place around the country. Cody’s in Berkeley is gone, and if there’s a good technical book store in the Bay area now, I don’t know about it (but haven’t spent much time there in quite a while). Among the places in the US I regularly travel, the only bookstore I can think of that still carries quite a few math and physics books is the Harvard Coop (also some at the MIT outpost). Other countries may be doing somewhat better, with several such bookstores surviving in Paris at least (Gibert Joseph and Eyrolles for instance).

    Of course the reason for this is the internet, more specifically Amazon and the online Barnes and Noble. These do have their virtues, and allow fairly quick access to a much more vast array of technical books than any physical bookstore ever could. But the loss of the experience of being able to spend an hour or so browsing through books, with the serendipity of finding something unexpected (something that Amazon’s finely tuned algorithms wouldn’t ever present to you) is a very real one.

    RIP New York technical bookstores, I must find a way to get to Paris more often…

    Posted in Uncategorized | 56 Comments

    The Principle

    Posted on January 26, 2014 by woit

    I just found out about a new film coming out this spring, which appears to exemplify exactly the dangers I was pointing to in my last posting. It’s entitled The Principle, and features physicists Michio Kaku, Lawrence Krauss and Max Tegmark, with Kate Mulgrew (aka Captain Janeway) as narrator.

    You can take a look at the trailer, this blog, or this interview to start to get some idea of what’s going on. The person behind this is Robert Sungenis, a bizarre figure with extreme religious views. He holds a Ph.D from an institution located in Vanuatu, and is an advocate of the idea of “geocentrism”, the idea that the Catholic church was right, and scientists since Galileo have got it all wrong (see his web-site Galileo Was Wrong). For another Youtube video explaining what this is all about, see here.

    As near as I can tell from all this, without having yet seen the full film, it appears that what probably happened is the following. Sungenis decided that the anthropic principle business in cosmology supported his views, so he went and got physicists like Kaku, Krauss and Tegmark to say silly things on camera, then edited this to suit his case. Maybe the trailer is misleading, and these people actually make a cogent case against Sungenis’s nonsense and for solid science, we’ll see…

    Update: For a different point of view on this, from someone worried that geocentrists will discredit the Catholic Church, see here.

    Posted in Film Reviews | 136 Comments

    I am not now and never have been a creationist

    Posted on January 26, 2014 by woit

    Max Tegmark seems to have decided that my criticism here of the emptiness of ideas in his recent book is “similar to hate-mail I’ve been receiving from a Young-Earth Creationist”. Also, the fact that I have fans at a certain Intelligent Design blog shows that I’m “against the spirit of science”. Given this, I guess I need to formally make the statement that

    I am not now and never have been a creationist.

    More specifically, everything I’ve seen about Intelligent Design indicates to me it is nonsense, and I’ve done my best to ignore those who promote such nonsense, whether they link to my blog or not. Sometimes you’ll see trackbacks on my blog coming from such links, basically because while sometimes I delete them, other days I think ignoring these people means really not wasting any time at all on them (and I’ve had my own problems with people censoring trackbacks…). On the larger issue of how to deal with evolution-deniers, one reason I live in New York is because it’s easy to ignore such people here, they’re not much of a problem. For those living in other parts of the world where they’re more of a problem, you have my sympathy and concern. I admire and congratulate people like Lawrence Krauss for their efforts to deal with the problems caused by such deniers. For most of us, I think the best tactic is to ignore them, on the grounds that not doing so will just lead to getting more attention for them and their arguments. As part of this, any comments arguing pro or con about evolution posted here will be immediately deleted.

    While I’m not joining Krauss and others in their admirable efforts, I do think there is one way I can contribute to dealing with the threat from this kind of nonsense. If physicists like Tegmark succeed in publicizing and getting accepted as legitimate mainstream science their favorite completely empty, untestable “theory”, this threatens science in a very real way. IDers like the bloggers mentioned above now can point to mainstream physics to justify their own untestable “theory”, Intelligent Design, or whatever other nonsense they find attractive because they like having a deity around. Yes, physicists need to fight pseudo-science coming from quarters like the IDers, but they at the same time need to fight pseudo-science coming from within their own community, which in the end may be even more dangerous.

    Update: It took about 5 minutes for this posting to attract dumb arguments about religion and they’re now flooding in. Sorry, comments closed.

    Posted in Uncategorized | Comments Off on I am not now and never have been a creationist

    Platonism CageMatch at MoMath

    Posted on January 25, 2014 by woit

    After spending two hours in the middle of the day hearing about unexpected uses of twistors to study particle scattering amplitudes, yesterday I went down to Manhattan’s relatively new Museum of Mathematics, which had scheduled a “Family Friday” event, featuring Edward Frenkel and Jim Holt. The event began with Frenkel giving a presentation about math, kind of an introduction to his wonderful new book Love and Math. Everyone in the audience hoped that the kids in attendance didn’t catch his comment about a typo in reference to the LHC (given Frenkel’s film experience, some had suggested that a joint event with the neighboring Museum of Sex would have been a good idea).

    Things really got exciting though when Jim Holt joined him on the stage, for a no-holds-barred discussion of Platonism and mathematics in front of a standing-room-only crowd. Holt ripped into Frenkel as engaging in “mysticism” by claiming that mathematical objects are “real” and “exist”. He quoted from Bertrand Russell, who early in life took Platonist positions, but in his old age renounced them. Frenkel countered, dismissing Russell’s later quotes as those of someone who had gone soft in the head. He went on to quote arch-Platonist Kurt Gödel, with the response from Holt a low blow: he told the story of how Gödel had died a paranoid, starving himself to death. Holt continued the attack in the same vein, telling about Georg Cantor, and his end in the loony-bin. The implication was that Platonists are not just mystics but nuts.

    Frenkel then decided to try taking the high road, invoking W.V.O. Quine and Hilary Putnam (distinguished non-nuts Harvard professors I took courses from) and their Indispensability Argument. The basic idea there is that the best choice of what “exists” is those entities that are an indispensable part of our best theory of the material world. Not sure yet whether twistors count, but if they become part of the new unified theory of gravity and the Standard Model, then they surely exist as much as anything does. Holt parried with Hartry Field’s Science Without Numbers: A Defence of Nominalism which supposedly shows you can do Newtonian physics without math. Frenkel (together with much of the rest of the audience) scoffed at this, making the obvious riposte: what about GR?

    This was finally brought to an end with a few questions from the audience, a sizable contingent of which was underage. They seemed to be having a great time, far more entertained by this sort of thing than by the usual flashy trinkets people use to try and get them interested in math (but which seem to work better on the pre-verbal baby crowd). All in all, a highly edifying experience, I hope the Frenkel/Holt show gets taken on the road.

    For a picture of the action, see here.

    Posted in Uncategorized | 28 Comments

    The Amplituhedron and Twistors

    Posted on January 25, 2014 by woit

    Yesterday Nima Arkani-Hamed was here at Columbia, giving a theory seminar on the topic of the Amplituhedron, which is a characterization of the integration region in a calculation of scattering amplitudes by integrating over regions in the so-called positive Grassmannian. This is a modest advance in mathematical physics, one that for some reason a few months ago garnered a lot of hype (see here for more about this).

    As seems to often be the case, the Arkani-Hamed talk was a bit bizarre as an event. Scheduled to start at noon, people soon settled in with the sandwiches provided by this seminar, and he started talking about 12:15. About an hour and a half into the talk, people were reminded that he doesn’t mind if they leave while he’s speaking. Two hours into the talk, soon after he said he was only a quarter of the way through his material, I had to leave in order to do some other things. I don’t know how long the talk actually went on. It’s too bad I didn’t get a chance to stay until the end, since he promised to then explain what the current state of progress on these calculations is.

    What is being calculated are scattering amplitudes in a conformally invariant theory, with the simplest example the planar limit of tree-level amplitudes of N=4 super Yang-Mills. One wants to extend these methods to loops, to higher order terms in 1/(number of colors), and to non-conformally invariant theories like ordinary Yang-Mills (at the tree level, ordinary and N=4 super YM give the same results).

    As usual, Arkani-Hamed was a clear and very engaging speaker. Also as usual though, it’s unclear why he thinks it’s a good idea to not bother trying to fit his talk into a conventional length, but just keep talking. One reason for the length was the extensive motivation section at the beginning, which had basically no connection at all to the topic of the talk. There was a lot about quantum gravity of an extremely vague sort. In a recent talk I wrote about here, he explains one reason why he does this, that he’s describing the motivation he needs to keep doing this kind of mathematical physics. I suspect another related reason is that this kind of vague argument about quantum gravity and getting rid of space-time is all the rage, so if you’re not working on the firewall paradox, you have to justify that somehow.

    Once he got beyond the motivational stuff (and a complaint about BRST: “almost anytime you hear BRST, there is something formal and complicated going on”) the talk was worthwhile and I learned a fair amount. The main thing that struck me was just how much the whole story has to do with Penrose’s twistor program. Penrose developed twistors also with a quantum gravity motivation: they provide a very different set of basic variables, with usual space-time points not the fundamental objects. Of course I was aware of some of the twistor part of the amplitudes story (see for instance here), but I was unaware of the important role played by Andrew Hodges, of Penrose’s twistor group at Oxford, in these recent developments. Hodges, besides writing a fantastic biography of Alan Turing, has worked on twistor theory for about forty years, and some of his innovations have been crucial for the recent advances on gauge theory amplitudes. One example is his “twistor diagrams”, and for more about this and how other work of his has contributed to the emerging story, see his up-to-date Twistor Diagrams website. Hodges is a wonderful story of someone who didn’t follow fashion, but stuck to pursuing something truly worthwhile, it’s great that he has now been getting attention for this, as his work has become useful for more popular research programs.

    For those who keep asking about interesting, promising ideas about fundamental physics to work on, twistors are something they definitely should look into. The recent amplitudes work is one specific application of thinking in twistor variables, but the whole question of how to do quantum field theory in twistor space seems to me to still be wide open. Twistor theory involves some wonderfully different ways of thinking about four-dimensional geometry, and these seem far more likely to play some role in future advances in the direction of unification than any of the tired ones (GUTs, SUSY, string theory) that have dominated the field for so long.

    Posted in Uncategorized | 5 Comments

    Topcites 2013

    Posted on January 25, 2014 by woit

    The people at SLAC for a long time have been compiling “Topcites” data which includes various lists of the most heavily-cited papers in HEP. From 1997-2003 Mike Peskin each year would write something about the significance of the lists. I first wrote a blog post about one of these lists nearly 10 years ago, about the 2003 list (see here). The 2013 list has just appeared, with a blog entry here, and the lists available here.

    I haven’t written much about these lists for the past few years, since there didn’t seem to be much new to say. By the 2005 list it was becoming clear that there was so little new happening in hep-th that the list was dominated by pre-2000 papers, specifically the early AdS/CFT papers, as well as papers about speculative large extra dimension scenarios. This pattern has continued to this day. If you think citations mean something, this data shows a collapse of HEP theory having taken place sometime around mid-1999. The last two theory papers that appear in the overall heavily-cited paper list are a Randall-Sundrum paper from June 1999 and Seiberg-Witten’s String theory and non-commutative geometry (which I suspect makes the cut because “non-commutative geometry” is in the title, so this gets referenced by lots people doing something with non-commutative geometry, even if it has little to do with this paper).

    The dominance of this list and of hep-th by AdS/CFT papers is hard to exaggerate, with Maldacena’s paper long ago leaving behind every other theory paper ever written, on track to hit 10,000 citations sometime later this year. Just as “string theory” has become ill-defined, now “AdS/CFT” is starting to become ill-defined, with these 10,000 papers covering a huge variety of different things. In addition there’s a great deal of hype and ideology surrounding this subject, with an ex-Harvard faculty member and now world’s most prominent string theory blogger yesterday calling for the murder of anyone caught “talking about the AdS/CFT correspondence’s not being dependent on string/M-theory”. More positively, Matt Strassler has been writing a very long series of blog posts that appear to be aimed at sooner or later getting to AdS/CFT. He’s at number 8, but I fear at least a hundred or so would be needed to cover the subject. By the way, people who like carrying on a tedious rear-guard action in the string wars by arguing about string theory and AdS/CFT should do it at another blog.

    To get more fine-grained information about what recent work is getting cited, see listings here by arXiv category. The listing here of papers cited by hep-th papers during 2013 is dominated by the old AdS/CFT papers, but more recent things that occur in the top 10 are ABJM from 2008 (3d version of AdS/CFT), a 2006 paper on entanglement entropy from AdS/CFT (now a hot topic), and a review paper on AdS/CMT.

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