Short Items

  • 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.

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    26 Responses to Short Items

    1. onymous says:

      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?

      In 2010 data? Not discouraging at all. In 2011 data? Fairly discouraging. In 2014 data? Enormously depressing.

    2. DB says:

      Since supersymmetry is in a permanent state of being always “just around the corner”, failure to observe it will only strengthen such convictions.

      It is a self-reinforcing cycle.

    3. Peter Woit says:

      DB,

      I think a lot of that (although not all…) has been the LHC (or SSC) being “just around the corner”, which has been the story for a long time now. So, failure to find evidence for supersymmetry at the LHC when it finally is working will significantly change the environment.

    4. DB says:

      I would say that the environment for SUSY and especially for String Theory (which is umbilically bound to SUSY) has already changed very significantly since you (and Lee Smolin) launched your crusade. Failure to find SUSY will consolidate this trend.

      But the true believers have an ace up their sleeve: split supersymmettry – it knocks the ball into the next court and keeps the faith alive. However, they won’t be able to claim its around the next corner anymore, more like around the next galaxy!

    5. Roger says:

      DB – Split SUSY still predicts new physics at TeV energies, eg a stable gluino.

    6. Pingback: How long until new physics? « viXra log

    7. DB says:

      Thanks Roger, I must have been thinking of Supersplit Supersymmetry :))

    8. SpearMarktheSecond says:

      Energy trumps luminosity easily in the beyond the SM search business… twas ever thus. But the Tevatron is the remnant of the US HEP program, so, it gets a bit more hype than is deserved.

      The light Higgs is one kinda sorta exception. Amazing the level of hype the light (<2M_W) Higgs has produced.

    9. Anonymous says:

      In the article Hawking says he was lucky not to do a PhD project in particle physics at that time, because the Cambridge school was in support of the futile S-matrix program, and his work would have been forgotten by now…

      Maybe today’s graduate students starting a project in string theory should think about Hawking’s words? (Though nobody knows for sure)

    10. ozanam says:

      here is an excerpt from a recent article by Stephen Hawking:

      “….There was an exciting period culminating in the Les Houches summer school in 1972, in which we solved most of the major problems in black hole theory.

      This was before there was any observational evidence for black holes, which shows Feynman was wrong when he said an active field has to be experimentally driven. Which is just as well for M theory [a relative of string theory that involves membranes]. ”

      Peter, comment ?

    11. Peter Woit says:

      oznam,

      The problem with the idea of unification in 10/11 dimensions using string/M-theory is not that it isn’t experimentally driven. It’s that it doesn’t work.

    12. Shantanu says:

      ozanam,
      Eventually we did find observational evidence for black holes.
      Also there were many papers on proposed observational tests of black holes by Salpeter, Zeldovich etc, which had specific predictions which were later vindicated.
      whereas in string theory its more than 30 years without a single prediction

    13. stan says:

      “The problem with the idea of unification in 10/11 dimensions using string/M-theory is not that it isn’t experimentally driven. It’s that it doesn’t work.”

      What does this even mean? String theory has many solutions, embedded in 10/11 dimensions, that look essentially like our world, and that unify the gauge and gravitational interactions into a common calculable framework. The problem is that there is too much flexibility in constructing such scenarios, and hence it is not predictive (at least so far), But I have a hard time interpreting “it doesn’t work” as anything more than a debating stance.

    14. Peter Woit says:

      stan,

      In science “not predictive” = “doesn’t work”. This is scientific methodology 101, not a “debating stance”.

      After more than a quarter-century of learning more and more reasons why string theory unification can’t ever predict anything, claiming that it’s reasonable to believe that things are going to some day turn around and string theory unification will become predictive, now that’s a debating stance…

    15. stan says:

      Peter,

      I don’t think I’m being overly pedantic by suggesting that saying”it doesn’t work” is either too vague or else misleading, if the goal is to actually impart some understanding here. There are obviously huge distinctions between theories which are a) internally logically inconsistent b) make definite and wrong predictions c) make no predictions at all (by themselves). Theories of type a) or b) either have to be discarded or modified. Theories of type c) are not necessarily wrong, but they do have to be supplemented by extra information, incorporated into some other larger theory, etc. in order to be viewed as successful scientific explanations.

      These are pretty basic distinctions, but I honestly don’t know which of these you are driving at (or maybe you just don’t care). I personally believe that string theory is correct but of type c). I think we are going to need new ideas and physical input to make progress, but that our current understanding of string theory will be incorporated into this. I guess you think I’m just an irrational, deluded, string partisan.

      The analogy with QFT is often made. It is of course nice that our world is described by a fairly simple gauge group. But it’s easy to imagine a world governed by some hideously complicated gauge group and matter representations, maybe even strongly coupled. In such a world it could take ages before QFT would make successful predictions. Would you say that “QFT doesn’t work” in this world? This is of course more or less what many people were saying in the 1960s after failing to understand the strong interactions.

    16. Peter Woit says:

      stan,

      I’ve devoted a lot of time over the years to carefully writing a book on exactly the topic of what is wrong with string theory unification (and what many people consider far too many blog postings on the same topic). If you don’t agree with or understand the argument of the book or the blog postings that’s one thing, but you seem to be pretending they don’t exist.

      The argument you make that QFT is inherently no more experimentally testable than string theory is one I’ve answered many times, despite the obvious absurdity of claiming that the most successful scientific theory we have is not distinguishable from one that predicts nothing. Sure, you can imagine a universe governed by QFTs of such complexity that conventional scientific method would be useless. That’s not the world we live in. The currently popular idea that we live in a universe governed by a string theory with solutions of such complexity that conventional scientific method is useless is logically possible, just like the idea that we live in a simulation run by aliens, but it’s not science.

      You’re welcome to believe, as many highly competent physicists do, that some new advance is going to come along and fix the problems of string theory unification. But you should first admit that, given our current understanding of the subject, the problems are deadly and this “doesn’t work”. Maybe someone will figure out how to make it work, but I don’t think the last quarter century of history is at all encouraging, so there’s a lot to be said for getting people to move on and look for something else.

    17. stan says:

      Peter,

      My interpretation of your position is that you firmly believe that the true physics lying behind the Standard Model is “simple” in some sense, and so the correct theory describing it will lead to testable predictions in short order. Since String Theory has not provided any such predictions it must be the wrong theory. That’s fine, but I doubt you can put forth a shred of evidence supporting this — it’s an aesthetic judgement. I don’t feel compelled to hurl insults at you based on this.

      What are these “deadly problems” you mention that I must admit to? As I said at the start, the problem with string theory model building is that it is too flexible, allowing for too many ways of constructing worlds that look like ours, hence not being predictive (exactly the same problem faced by all existing QFT based attempts at unification by the way). Everyone agrees additional input is needed, the disagreement is whether this means that string theory is incompatible with whatever this new input is.

    18. Peter Woit says:

      stan,

      Sure, my belief is that particle theory will continue to advance in the same way that it always has: if we find a more accurate description of nature than the Standard Model, it will be one sufficiently simple for us to analyze it and confront it with experiment in a conventional scientific manner. This isn’t just “an aesthetic judgment”, it’s more about my understanding of what it means to do science. Claiming that string theory unification involves some new way of doing science, necessitated by the complexity of its solutions, is just a cop-out and refusal to acknowledge failure.

      The fact is that string theory unification allows no reliable and predictive computations of any kind. Why this is requires a long analysis of an incredibly complicated set-up, but whatever you think the reasons for this situation are, those are the “deadly problems”. Again, you may believe someone will someday make them disappear, but right now they’re there and looking at the history of the subject gives no reasons for such optimism.

    19. stan says:

      Peter,

      We’re starting to go in circles here. Let me just note that if we somehow were able to determine that we lived in String Theory Vacuum X of the sort that people have studied, there would be lots of predictions we could make. You think this could never happen, either because string theory has nothing to do with our world, or because even if it does it is still inherently incapable of making predictions — I’m still not clear what your position on this is.

      People will jump en masse into any new line of thought that could lead to beyond the Standard Model predictions, based on string theory or otherwise. The fact that no attempt so far has been successful in this sense is seen by some as evidence that no simple answer is lying just around the corner. I personally think that expecting to find enlightenment based on greater mathematical sophistication is a poor judgement. Since you argue based on historical precedent I will do the same: I can’t think of a single example in modern physics where a testable prediction has emerged from someone pursuing a mathematically minded approach. Advances always seem to come from applying old math to deep new physical insights. It’s actually quite remarkable how unsuccessful mathematicians have been in directly advancing physics. It’s amazing that all of known physics can be understood using math no more complicated than basic differential geometry and simple group theory. I say all this to challenge the viewpoint promoted by your book and your blog (and to prove that I have read them, at least in part).

    20. CWJ says:

      stan said: “I can’t think of a single example in modern physics where a testable prediction has emerged from someone pursuing a mathematically minded approach”

      I can:

      General relativity.

      The Dirac Equation.

      There are probably scads more.

    21. jpd says:

      whats so special about ‘modern physics’
      eg fourier and newton ?

    22. stan says:

      General relativity.

      The Dirac Equation.

      Neither of these are good examples. Riemannian geometry was at least 50 years old when Einstein used it. Everything in physics obviously uses math that was new and sophisticated at one time, but I was looking for examples involving new mathematical ideas.

      Neither did Dirac use any sophisticated math. He wanted a Lorentz invariant first order wave equation, and found that he needed objects obeying anti-commutations relations. By trial and error he found that some 4 x 4 matrices did the trick. I don’t think he needed to consult with mathematicians or read math papers to do this!

    23. stan says:

      whats so special about ‘modern physics’ eg fourier and newton ?

      Up until one or two hundred years ago, there wasn’t much distinction between a mathematician and theoretical physicist. Since then things have diverged, and mathematicians have adopted a style different from physicists. I think history shows that their style has not led to advances in the search for new physical laws.

    24. Peter Woit says:

      stan,

      The problem with the argument that “if we could determine the string theory vacuum” all would be well is that we can’t determine the string theory vacuum. The reasons for this are complicated, having to do with inherent limitations on what is calculable for each possibility in the current string theory set-up, together with the huge number of possibilities.

      I have looked closely at attempts to do string theory phenomenology and to make progress on getting to something that would do what you argue for. Everything I’ve seen is ridiculously far from being useful. The fact of the matter is that string phenomenologists have had 20 years to prepare for the opening of a new energy scale at the LHC, it’s here, and they have no predictions at all. If this isn’t failure, I don’t know what is. The idea that new LHC physics is going to match some string-inspired vacuum and justify string theory is so far-fetched that even most string theorists I know dismiss it as completely implausible.

      You’re right that my own judgment about ideas worth pursuing involves trying to get inspiration from mathematics. This has worked out sometimes in the past (e.g. general relativity), but it’s true that most of the time it has not been fruitful. I’d argue that this is because historically experiments were throwing up things that disagreed with theory, and pursuing these as hints was far more likely to lead to progress than pursuing mathematical hints. The problem now is that we don’t have much in the way of such hints from experiment, so may not have any choice but to try and make progress along other, more difficult lines. In any case, I think this is a time people should be trying all sorts of different approaches, since no one has good evidence that of any particular speculative approach working out.

    25. stan says:

      Peter,

      I agree with you that it is very hard to get particle physics predictions out of string theory. Ergo, if our world is described by a complicated string theory vacuum, doing fundamental physics is going to be very difficult. The non-sequitur comes when you present this as evidence that our world is not described by such a string theory vacuum. This makes no logical sense unless you are starting from the axiom that physics should be simple, in which case the whole argument is circular.

      Actually, I hope you’re right, and I wished I shared your optimism.

    26. Bruno Galileo says:

      woit writes, “You’re right that my own judgment about ideas worth pursuing involves trying to get inspiration from mathematics. This has worked out sometimes in the past (e.g. general relativity), but it’s true that most of the time it has not been fruitful. ”

      actually, general relativity was inspired not by mathematics, but by the very *physical* reality of gravity.

      you will recall that einstein hired mathematicians to figure it out.

      to not take my word for it, but heed freeman dyson:

      In Disturbing the Universe, Freeman Dyson writes, “Dick [Feynman] fought back against my skepticism, arguing that Einstein had failed because he stopped thinking in concrete physical images and became a manipulator of equations. I had to admit that was true. The great discoveries of Einstein’s earlier years were all based on direct physical intuition. Einstein’s later unified theories failed because they were only sets of equations without physical meaning. Dick’s sum-over-histories theory was in the spirit of the young Einstein, not of the old Einstein. It was solidly rooted in physical reality.” In The Trouble With Physics, Lee Smolin writes that Bohr was not a Feynman “shut up and calculate” physicist, and from the above Dyson quote, it appears that Feynman wasn’t either. Lee writes, “Mara Beller, a historian who has studied his [Bohr’s] work in detail, points out that there was not a single calculation in his research notebooks, which were all verbal arguments and pictures.”

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