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The bones in our throat (Weinberg)

  1. Oct 8, 2004 #1


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    "The bones in our throat" (Weinberg)


    Steven Weinberg gave an interesting talk about the current situation in particle physics yesterday (7 October) called Where Do We Stand?

    Audio is available----as well as slides and video. Around minute 18 into the audio he starts talking about the cosmological constant and dark energy. Uses the image of a bone stuck in the throat.

    the whole 25th Anniv. of Kavli Institute Santa Barbara ("The Future of Physics") is overwhelmingly dominated by Particle Physics perspective but, given that reservation, looks like it will have some fascinating talks.

    Peter Woit's comment is at
    Last edited: Oct 8, 2004
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  3. Oct 11, 2004 #2


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    Michael Peskin at KITP25

    Michael Peskin was part of the panel right after the two opening talks---those given by Steven Weinberg and Frank Wilczek.

    Peskin gave a 6 minute talk which was in stark contrast to Weinberg's perspective. In fact Peskin pointed out the diametric opposition and expressed regret that Weinberg had already left. I found Peskin's talk to be among the most interesting at the conference.

    this is Peskin's homepage at the Stanford-SLAC Theory Group

    this has the audio of the 4 panel-members, including Peskin,
    each limited to 6 minutes

    For half a dozen years Peskin has written the annual Spires review of what's hot in physics. Here is what he says about this on his homepage
    ---exerpt Peskin homepage---
    Top-cited papers in high-energy physics

    Annually, the SLAC SPIRES bibliographic database announces the 40 most highly cited papers of the previous year in high-energy physics. For the past few years, I have written a review of the developments in physics of which these papers were a part:

    2003 Edition: Cosmology; Neutrinos; Extra Space Dimensions; String Theory
    2002 Edition: Neutrinos; Cosmology; Extra Space Dimensions; String Theory
    2001 Edition: String Theory; Extra Space Dimensions; Cosmology; Muon g-2; Neutrinos
    2000 Edition: M-Theory; Non-Commutative Field Theory; Extra Space Dimensions; Cosmology; Neutrinos
    1999 Edition: Strings and Branes; Neutrinos; Extra Space Dimensions; CP Violation
    1998 Edition: Strings and Branes; Neutrinos
    1997 Edition: M Theory; Experimental Developments; Supersymmetry Phenomenology
    ---end quote---

    Here are some pictures of Peskin, a cross between Gerard Depardieu and Groucho Marx:
  4. Oct 11, 2004 #3


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    "The bones in our throat" (Weinberg) .
    An interesting talk, particularly his thoughts on the anthropic principle, the CC, and
  5. Oct 12, 2004 #4


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    I like Weinberg, we gave him a honoris causa doctorate from Salamanca. But when reading his books, or some other writtings, it seems clear that he has always believed QFT to be an effective theory, an aproximation to something else. For a long time, this something else has been hoped to be strings theory.
    Last edited: Oct 12, 2004
  6. Oct 12, 2004 #5


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    Alejandro I have listened to a lot of the KITP25 talks----especially David Gross and Gerard 't Hooft (and of course Weinberg too! he's great)
    and I keep hearing the idea of "physics without time" and suggestions of a new quantum mechanics.

    I was just looking at Rovelli's book and he has a section called "physics without time"-----it looks like David Gross and Carlo Rovelli are both having their attention caught by this idea.

    Also Rovelli on page 268 uses the phrase "a general relativistic quantum physics" in this insight which I will quote in a moment. But just think about the concept itself.
    General Relativity does not have time-translation symmetry. And although a special relativistic quantum physics should have unitary time-evolution, I suspect that a general relativistic quantum physics should not have a unitary time-evolution operator. Please tell me if you disagree!

    I suspect that when they say "without time" the practical meaning of this is that there should not be a unitary time-evolution operator.

    I have a feeling that there is a ferment going on about what it should look like: a general relativistic quantum physics. (Loop Gravity must only be a small part of this ferment!)

    Anyway here is the quote I mentioned from rovelli's book:
    "Holding on to the idea of the necessity of a unitary time evolution...is an anchorage to a notion that is inappropriate to describe general relativistic quantum physics."

    this is the idea that I am also getting from some of the high level "future of..." talks at KITP25. Please tell me if you think I am mistaking their drift.
    Last edited: Oct 12, 2004
  7. Oct 12, 2004 #6


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    Julien Barbour should be named between the people wondering about timeless physics. In some sense time was forced into physics by Newton, via the angular momentum, and then generalised to the concept of Hamiltonian evolution, Liuville etc. But nobody can be sure about if it is a fundamental concept.

    I can not decide about the question of unitary evolution. Tomita-Takesaki results strongly point the need of an one-parameter group, and I believe to remember that it s an unitary evolution. I like microscopic reversibility.
  8. Oct 12, 2004 #7


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    strange as it seems Rovelli allows for a one-parameter group but it is not time. look at his book section 3.2.6 called "Evolution Parameters" in chapter 3, which is called Relativistic Mechanics

    there seem to be some subtle things about Relativistic (general of course) Mechanics---two quite different parameters which, by unfortunate historical accident, are both called "t".

    See page 90 of the 31December draft, right after equation 3.126

    Maybe I am being too pedantic :smile: and you know about this already
    but it is a philosophical snag that seems to have collected some confusion around it
  9. Oct 12, 2004 #8


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    I will check Rovelli's tomorrow.

    Let me add another philosophical point: if time is defined old-way from preservation of angular momentum, some significance should come from the fact that angular momentum is quantised. Actually, multiples of hbar.

    (people forgots very frequently that "spin 1/2" actually means "spin h/2"... so for instance classical fermions do not exist.)
  10. Oct 19, 2004 #9
    Arivero said:
    it seems clear that he (steven weinberg) has always believed QFT to be an effective theory, an aproximation to something else.

    In sci.physics.research Alfred Einstead has said:

    " it is fundamentally impossible to formulate QFT
    (in its present form) in a quantum theory of gravity, which ipso
    facto, also means that a quantum theory of gravity cannot be a QFT."

    Perhaps this is the kind of reasoning weinberg has used.
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