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Posted on June 1, 2011 by woit
  • The big news of the past couple days has been the release of more data by CDF which continues to show a bump in the invariant mass of two jets produced with a W. Resonaances gives an excellent description of this and its possible significance. Tommaso Dorigo remains a skeptic.

    I can’t do better than the two of them on this story, but here’s my summary take on the situation:

    With the new data, this can no longer be written off as a statistical fluke. 3 sigma you can argue away as such a fluke, but not 5 sigma.

    The main reason to be skeptical though hasn’t been the statistical significance, but the possibility that this is due to bad modeling of the background. The signal is being extracted from a huge background, so a small misunderstanding of the background could be its cause. If this is the case, the new data changes nothing, you expect to continue to see the effect as more data is analyzed.

    The fact that Tommaso is a skeptic carries a lot of weight, since he works on the CDF experiment and understands the problems well. In general, experimentalists want the experiments they work on to make great discoveries, so tend to be optimists about their own results. When someone is skeptical about a result of their own experiment, that should give one pause.

    What would really make the case for new physics here more compelling would be if the result is confirmed by one of the other experiments (DO at Fermilab, CMS or ATLAS at the LHC) that should be able to see the same effect if it is there. These groups have a certain motivation to not just confirm their competition’s discovery (raising the question of why they didn’t find this first), but to convincingly shoot it down. This posting by Pauline Gagnon of ATLAS says that they see nothing in their 2010 data. One expects that D0 is hard at work and should soon release whatever they have found. ATLAS and CMS should also be hard at work looking at the much larger 2011 data samples. We’ll know soon the results, but the public comments of Dorigo and Gagnon don’t sound to me like those they would be making if they knew their experiments had preliminary confidential results confirming the CDF anomaly.

    Finally, while there are lots of theory papers out already with supposed models explaining this, none are really compelling. This is not an experimental result with an obviously attractive theoretical explanation.

  • Abstruse Goose has commentary on SUSY here.
  • In gossip of the mathematics world, it looks like Princeton (the IAS) has stolen away number theorist Richard Taylor from Harvard.
  • Video of Graeme Segal’s Felix Klein lectures this spring at Bonn on quantum field theory are now available, and well worth watching.
  • Other interesting video available is Greg Moore’s lectures on geometry, topology and QFT at Rutgers last fall.
  • For pictures from this years Physics of the Universe Summit, see here. Any info beyond the transparencies caught in the pictures seems to be private.
  • The journal Foundations of Physics will be putting out an issue on “Forty Years of String Theory”. So far articles intended for this have appeared on the arXiv from Dean Rickles, Steven Gubser, and, last night, Steven Giddings. The Giddings contribution is entitled Is string theory a theory of quantum gravity?, and provides an unusually hype-free discussion of the relevance of gauge/gravity duality to hopes to use string theory to understand quantum gravity, writing:

    While string theory addresses some problems of quantum gravity, its ability to resolve these remains unclear. Answers may require new mechanisms and constructs, whether within string theory, or in another framework.

Posted in Experimental HEP News, Uncategorized | 9 Comments

Cycles of Time

Posted on May 27, 2011 by woit

Today’s Wall Street Journal has a review I wrote of Sir Roger Penrose’s new book Cycles of Time. The review is aimed at a much wider audience than this blog, and is the product of substantial editing to get its length down and make it as readable as possible for as many people as possible, so here are some supplementary remarks.

I should make it clear that I’m not at all convinced by what Penrose is proposing. He needs the distant future of the universe to be conformally invariant, and this requires all particles to be massless. As far as we know the electron is completely stable, with unchanging mass, and this will always ruin conformal invariance. Penrose himself notes the problem. For this to be overcome, whatever our ultimate understanding is of how particles get mass must change so that these masses go to zero in the future. It’s also seems to me that the conformal anomaly of QCD will always be a problem, with quantization and the renormalization group always breaking conformal invariance and giving a mass scale, indefinitely far into the future.

The other main problem is the one shared by most “pre-big-bang” ideas: how do you ever test them? Penrose and a collaborator last year created a stir by claiming to see in the CMB patterns of the sort he argues might be expected from black hole decays late in an era before the Big Bang, but it’s not clear there’s a real prediction here, and others who have redone this analysis say they see nothing.

Attempts to get a Big Bang in our future as well as our past generally strike me as motivated by a very human desire to see in the global structure of the universe the same cyclic pattern of death and rebirth that govern human existence. To me though, deeper understanding of the universe leads to unexpected structures, fascinating precisely because of how alien they are to human concerns and experience. Just because we might find a cold, empty universe an unappealing future doesn’t mean that that’s not where things are headed.

The book is in many ways an unusual document. It includes an extensive appendix working out some of the details of the mathematics of his proposal. In some sense he has managed to get a trade publisher to put out a highly technical discussion of a speculative idea inside the covers of a popular book, instead of going the usual route of publishing this in a refereed journal. The only references I can find to other places where he has written some of this up are to chapters in this book and this one, as well as this contribution to a conference proceeding. The technical idea behind this, that the hypothesis of the vanishing of the Weyl curvature in the early universe leads to possible cosmological models that can be extended past the Big Bang singularity he attributes to this paper of K.P. Tod. There’s a nice recent exposition of this by Tod here.

So, I’m not convinced by the speculation about the far future, and for an evaluation of the ideas about extending back through the big bang singularity you’ll need someone more expert about cosmology than me. These topics are very clearly labeled in the book as speculative, without support from other physicists or any experimental evidence. The bulk of the book though is other material providing a background and context for the speculation, and it is this which I think makes it most valuable as a popular book. Penrose is a wonderful, elegant and clear writer, and he covers a lot of ground about physics beautifully here. Most remarkable are the illustrations, by far the best visual representations of a range of important ideas that I know of. Physicists and mathematicians work with lots of internal pictures in their minds representing important aspects of the concepts they are investigating, but very rarely do they have the technical skill to grasp some of the essence of these pictures and get them down on paper. Even more rarely do they make it into wide distribution in print, so I’m glad to see that happen here.

Posted in Book Reviews | 44 Comments

Cosmological Interpretations of Quantum Mechanics

Posted on May 19, 2011 by woit

It seems that there’s now a new burgeoning field bringing together multiverse studies and interpretational issues in quantum mechanics. Last year Aguirre, Tegmark and Layzer came out with with Born in an Infinite Universe: a Cosmological Interpretation of Quantum Mechanics, which claimed:

This analysis unifies the classical and quantum levels of parallel universes that have been discussed in the literature, and has implications for several issues in quantum measurement theory… the analysis suggests a “cosmological interpretation” of quantum theory in which the wave function describes the actual spatial collection of identical quantum systems, and quantum uncertainty is attributable to the observer’s inability to self-locate in this collection.

Last month there was Nomura’s Physical Theories, Eternal Inflation, and Quantum Universe where “a picture that the entire multiverse is a fluctuation in the stationary, fractal “mega-multiverse,” in which an infinite sequence of multiverse productions occurs” is invoked and:

Our framework provides a fully unified treatment of quantum measurement processes and the multiverse. We conclude that the eternally inflating multiverse and many worlds in quantum mechanics are the same.

Most recently, tonight’s arXiv listing has Bousso and Susskind’s The Multiverse Interpretation of Quantum Mechanics:

We argue that the many-worlds of quantum mechanics and the many worlds of the multiverse are the same thing, and that the multiverse is necessary to give exact operational meaning to probabilistic predictions from quantum mechanics.

I confess that I’m having trouble making sense of any of these papers. According to Bousso and Susskind, if I want to understand how quantum mechanics describes some simple, local physical system and what happens when I do measurements of it, I need to sign on to the theory of eternal inflation and the multiverse:

We will offer some principles that we believe are necessary for a consistent interpretation of quantum mechanics, and we will argue that eternal inflation is the only cosmology which satisfies those principles.

In the case of many string theory papers, one’s problems understanding their claims could often be attributed to the highly complex and sophisticated mathematical framework involved. These papers are mostly long sections of verbiage, sometimes with pictures. My inability to make sense of them must have some other source…

Update: Lubos has an explanation of the Bousso-Susskind paper: “they’re on crack”.

Update: I suppose one could have guessed that Sean Carroll would be a fan of this. In his book he argues that the way to understand the second law of thermodynamics and the arrow of time is to invoke cosmology and the multiverse, now he seems happy to do the same thing with the interpretation of quantum mechanics. The ideas seems to be that to understand some local quantum mechanical phenomenon, you need to use cosmology and think about the horizon that is part of the deSitter geometry. I don’t find this argument any more plausible than the arrow of time one.

It does seem like this is now being promoted as the hot topic in theoretical physics, with Sean and others organizing a conference partially devoted to this at Perimeter this summer.

Posted in Multiverse Mania | 64 Comments

Particle Theory Job Market 2011

Posted on May 19, 2011 by woit

By now the hiring season for tenure-track jobs is pretty much over, and for the field of particle theory some idea of the results is available at the Theoretical Particle Physics Jobs Rumor Mill. As has been usual for the last few years, most jobs are going to phenomenologists. Remarkably, it seems that no jobs at all are going to string theorists so far this year. The final number of jobs is yet to be determined, with ten people so far getting job offers. It looks like the total number of jobs in the field will remain at the low level typical of the last three years since the recession hit in 2008.

Erich Poppitz has been compiling statistics based on the Rumor Mill data, and has the results through 2010 here. Job numbers rose to a level of 20-25 jobs/year from 2000-2007, from a low level of 10 jobs/year back in the 1990s. This phenomenon is generally attributed to jobs becoming available as the generation that was tenured during the huge expansion of universities in the 1960s finally started to retire. The recession has brought those numbers down to 15 (2008), 9 (2009) and 14 (2010). In recent years (since about 2004) he counts about a fifth of the jobs as going to string theorists. If that number does go to zero this year, that would be the first time this has happened since the numbers became available, and I would guess all the way back to shortly after string theory first became popular in 1984-5.

Posted in Uncategorized | 21 Comments

Hawking and the Google Zeitgeist

Posted on May 16, 2011 by woit

Today is the first day of this year’s Google Zeitgeist gathering of high-powered world leaders and thinkers (described here, it seems that Google either doesn’t believe in having a web presence, or it’s a secret one. Anyway, my attempts to Google it have failed). One of the headline speakers is Stephen Hawking, and the Guardian reports that:

His talk will focus on M-theory, a broad mathematical framework that encompasses string theory, which is regarded by many physicists as the best hope yet of developing a theory of everything.

M-theory demands a universe with 11 dimensions, including a dimension of time and the three familiar spatial dimensions. The rest are curled up too small for us to see.

Evidence in support of M-theory might also come from the Large Hadron Collider (LHC) at Cern, the European particle physics laboratory near Geneva.

One possibility predicted by M-theory is supersymmetry, an idea that says fundamental particles have heavy – and as yet undiscovered – twins, with curious names such as selectrons and squarks.

Confirmation of supersymmetry would be a shot in the arm for M-theory and help physicists explain how each force at work in the universe arose from one super-force at the dawn of time.

They got him to respond to some questions posed in advance, and one of them has the Guardian’s Ian Sample puzzled. Hawking’s answer to “What is the value in knowing “Why are we here?'” was:

The universe is governed by science. But science tells us that we can’t solve the equations, directly in the abstract. We need to use the effective theory of Darwinian natural selection of those societies most likely to survive. We assign them higher value.

Sample’s reaction to this:

On reading it I had one of those familiar, sinking moments of realisation that my brain is so spectacularly inferior to the interviewee’s that all I can do is hold up my hands and say: “Huh?”

At best I might have an inkling of what this means, but I am by no means sure. In this situation, it might take a while to clarify the answer, but other bright minds out there might well be able to unravel it for me and anyone else who might be interested. If you can help, post your thoughts below and put me out of my misery.

To me, it feels as though he is referring to the idea that there are many possible universes and that we can use Darwinian ideas of natural selection to work out which might be most hospitable to life as we know it, and because they are habitable in some sense we value them more highly. That’s my best guess, but I have minimal confidence in it being right.

I will do my best to clarify the answer this week.

My contribution to explaining this is that I see two possibilities:

1. Hawking has signed on to Lee’s Smolin’s ideas about cosmological natural selection.

2. Hawking has realized that once you’ve decided to trade in science for pseudo-science and head down the Multiverse Mania path, there’s no longer any point in worrying about whether what you say makes sense or not, and is behaving appropriately.

Posted in Multiverse Mania | 49 Comments

The Big Bang

Posted on May 15, 2011 by woit

There’s a new film out this weekend with a particle physics theme (no string theory), called The Big Bang, starring Antonio Banderas. I figured that it’s my duty to cover this kind of popular culture use of particle physics, so went to see the film last night. It took some effort to identify the one screen in New York where it was showing, and the theater contained about 10 people at the Saturday night 8:20 show. If it’s showing in your area (only New York and LA I think) and you want to see it on a big screen, better go very soon.

I was going to write a review, and mention as many as possible of the various physics inside jokes that appear, but this has been done better here, where the film is aptly described as belonging to the genre “nerd noir”, with a “particle physics fetish” sex scene. The film features an LHC-lookalike built underground in New Mexico, designed to search for the Higgs (God Particle). The sex scene mentioned in the review pairs Banderas with a woman with a bubble chamber event and uncertainty principle tatoos. In the throes of passion she discusses Heisenberg uncertainty, entanglement, and the Standard Model.

There’s more about the film here, and Lubos has his take here. Rex Reed really didn’t like it, and it’s hard to disagree, unless you’re a great fan of particle physics camp in movies.

Presumably this will be going more or less straight to DVD in a rather short time.

Posted in Film Reviews | 13 Comments

Recent NSF Grants

Posted on May 11, 2011 by woit

In responding to a comment on the previous posting, I was curious if one could easily get some data on relative sizes of grants in mathematics and physics, so started to do a quick search on nsf.gov. Among the first few NSF grants that turned up, I noticed a couple rather odd things:

  • Award 1056580 for a postdoc in “Dark Energy, Fine-Tuning, and the Multiverse: Testing Theories in Modern Cosmology” drew my eye, since my impression was that NSF physics panels weren’t so likely to support Multiverse Mania research. Taking a look at the details of the award gave the explanation: this one is being funded not by the physics division (PHY) at NSF, but by the sociologists (SES, Division of Social and Economic Studies). So, now it seems that multiverse studies are part of sociology, which is much more appropriate than physics, and has the added advantage of opening up new funding opportunities.
  • Trying to pick a typical theory group grant, I took a look at Award 0969020, for the string theorists at UT Austin. I was pleased to see that blogging is now a selling point on NSF grants:

    Professor Distler authors a blog which discusses and elucidates many of the important research papers which appear on the daily arXiv listings, and he plans to continue his activity.

    The abstract was the usual sort of string theory promotional verbiage, beginning:

    For the past two decades, string theory has been one of the most intensely investigated areas of theoretical high-energy physics. This is true chiefly because string theory offers what is currently the most successful method of unifying gravity with the other fundamental forces (strong, weak, and electromagnetic).

    The next one I took a look at was Award 1001296 to theorists at UPenn, whose abstract sounded kind of familiar, beginning:

    For the past two decades, string theory has been one of the most intensely investigated areas of theoretical high-energy physics. This is true chiefly because string theory offers what is currently the most successful method of unifying gravity with the other fundamental forces (strong, weak, and electromagnetic).

    • Posted in Multiverse Mania | 29 Comments

    Pricey Strings

    Posted on May 11, 2011 by woit

    In recent years most of the conferences I’ve attended have been mathematics and mathematical physics ones, and I had noticed that, while modest registration fees were often a feature many years ago, these days most such conferences, especially in the US, have no registration fee at all. It seems that mathematicians tend to organize conferences at rather modest cost, and mathematics research is very well supported by the NSF, universities and private foundations. This morning I’d been idly considering the idea of taking a day-trip down to Philadelphia next month to visit friends and maybe attend a couple talks at String-Math 2011, which has a promising list of speakers, but not yet a schedule of talks. I noticed though that registration is $200, which is a bit high as a price to attend a couple talks, whatever source I might find to pay for it.

    As one moves from mathematics topics to physics ones, it seems that things get a lot pricier. You might think that string theory not working out as hoped would lead to the availability and market-value of string theory talks heading downwards, but the opposite seems to be true. The big string theory conference this summer is Strings 2011 in Uppsala, where registration will cost you 5625 Swedish Krona (about \$900) [Organizer Joe Minahan points out that this is the on-site cost for faculty, for whom the pre-May 19 price is 4375 Swedish Krona = \$700, post-May 19 5000 Swedish Krona = \$800. Costs for students are lower]. For that you get the talks, coffee, lunch and a reception. If you want to go to the conference dinner, that’s \$112 extra. The conference series is advertised as “gathering more than 500 researchers in string theory”, although in recent years, attendance at Strings 20XX conferences has been a bit lower. Last year’s was anomalous, held in March (when academics often can’t travel) in College Station, Texas (not exactly a major tourist destination), it attracted only 193 participants, despite a relatively low registration fee of only $350. For Strings 2011, they’ve got 208 people registered already. The list of speakers is here. There’s an associated program of Public Lectures which seem likely to have little to do with string theory, instead concentrating on “mind-boggling questions” about the multiverse and the Big Bang. Those at least seem to be free.

    I haven’t added up the total cost, but if you’ve got significant funds available from a grant, university research support, or private wealth, you can spend pretty much the entire summer attending not just string theory talks, but even string phenomenology talks (see a list here). There’s the String Vacuum Project meeting in Philadelphia starting May 23, from which one could head to String Phenomenology at Nordita from May 30 to June 25, then Strings 2011 in Uppsala until July 2, a workshop and conference in Spain from July 3-29, Les Houches for most of August, then String Phenomenology in Madison August 22-26 and SUSY11 at Fermilab keeping you busy until Labor Day.

    Update: The hot topic these days is not string theory, but gauge theory amplitudes, using twistors. If you can’t afford strings, the price of the twistor talks is still low: a correspondent points out to me that for a registration fee of 15 pounds, you can attend Twistors, Geometry and Physics, a meeting this summer in honor of Penrose’s 80th birthday.

    Posted in Uncategorized | 35 Comments

    This Week’s Hype

    Posted on May 8, 2011 by woit

    Philip Gibbs points to an impressive piece of string theory hype from British Channel 4 news.

    If you watch the clip, you get the latest news about string theory and the LHC: people were getting discouraged about string theory, but now some of its predictions are being confirmed by the LHC. For the extra dimensions to appear, we may have to wait a couple years for when the machine runs at design energy.

    Not clear at all where they got this nonsense from.

    Update: The source for this seems to be a story by Jonathan Leake in The Sunday Times, entitled Stand by, we may soon enter a new universe (subscription required, but a syndicated version is freely available here). The story has David Evans of Alice trying to promote his experiment with:

    The Alice experiment may soon be able to make experimental measurements which, for the first time, can be modelled using the techniques of string theory.

    Although the experimental results will not prove string theory to be correct, an accurate prediction would certainly show that the techniques work, could distinguish between different versions of the theory, and perhaps even show whether the theory is going in the right direction.

    Given this kind of quote, one can see why the writer completely mixes up string theory unification and string theory as approximate calculational method in heavy-ion physics:

    The researchers, at Cern, the European centre for particle physics near Geneva, say results from the Large Hadron Collider suggest it could offer the first experimental test for some aspects of string theory.

    Formulated in the 1960s, this theory attempts to describe how all the fundamental forces of nature, such as gravity and electromagnetism, interact with matter.

    On paper, the theory has been highly successful, resolving many mathematical problems.

    In practice, however, there is no experimental evidence to support its predictions, including the idea that there could be as many as 11 dimensions – the three physical dimensions, time and seven others as yet undiscovered.

    At Cern, there are now hopes the LHC may be able to break this impasse.

    Then, as usual, the headline writer takes things a step further:

    SCIENTISTS have devised the first experiment capable of giving insight into one of the universe’s greatest mysteries: could there be more dimensions than we know about?

    So, out-of-control promotional efforts for ALICE are at the bottom of this one.

    Posted in This Week's Hype | 21 Comments

    Not a Leak

    Posted on May 8, 2011 by woit

    ATLAS this weekend has finally released their latest analysis of the gamma-gamma invariant mass spectrum, carried out in response to claims from within their collaboration that a 4 sigma Higgs signal had been observed in this channel. The result? Nada:

    The dominant background components are measured and found to be in agreement with the Standard Model predictions, both in terms of overall yield and invariant mass distribution. No excess is observed.

    Posted in Experimental HEP News | 2 Comments