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Lorentz invariance verified almost to Planck scale?

  1. Oct 28, 2009 #1

    ZapperZ

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    Last edited by a moderator: Apr 24, 2017
  2. jcsd
  3. Oct 28, 2009 #2
    Everything that is based on a curved space-time.

    Vive Logunov's RTG in a flat space time!
     
  4. Oct 28, 2009 #3

    dlgoff

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    In the article...
    I am curious what these studies on the dependence of speed on polarization are/were.

    Any references?

    Thanks
     
  5. Oct 28, 2009 #4

    ZapperZ

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  6. Oct 28, 2009 #5

    marcus

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    Nice!

    Thanks for the link.
     
  7. Oct 28, 2009 #6

    marcus

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    Unfortunately none of the QG theories being currently worked on, as far as I know.
    But the result will still be helpful.
     
  8. Oct 28, 2009 #7

    MTd2

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    It also doesn't rule out varying speed of light theories whose first order correction is quadratic in the speed of light.

    This very discussion on the 31GeV photon appeared in several blogs and even here a few months ago due to a preprint that showed on the arxiv.org. I thought that preprints to Nature articles were embargoed at least until the day of their publication. :confused: So, it's weird that this article showed up in Nature.
     
  9. Oct 28, 2009 #8

    ZapperZ

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    No, that's a myth.

    Nature doesn't embargo preprints appearing, even in ArXiv. But you run the risk of some news media picking it up, and when that occurs, then the fact that it has been covered in another media will cause it to be disqualified from Nature and Science.

    See this thread:

    https://www.physicsforums.com/showthread.php?t=325116

    Zz.
     
  10. Oct 28, 2009 #9

    atyy

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    The link http://www.nature.com/authors/editorial_policies/embargo.html you gave on the other thread seems to say that it is not a problem if other media pick it up from arXiv - it's only a problem if authors discuss it with other media.

    In fact, this article was picked up by other media from arXiv before publication in Nature:
    http://motls.blogspot.com/2009/08/fermi-kills-all-lorentz-violating.html
    http://backreaction.blogspot.com/2009/08/that-photon-from-grb090510.html
    http://egregium.wordpress.com/2009/08/17/news-from-fermi-formerly-glast/[/URL]
     
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  11. Oct 28, 2009 #10

    atyy

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  12. Oct 29, 2009 #11

    ZapperZ

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    I'm rooting for condensed matter, and therefore, I have a quantum gravity theory?

    I think this deserves zero response.

    Zz.
     
  13. Oct 29, 2009 #12

    ZapperZ

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  14. Oct 29, 2009 #13
    <mood=nitpicking>I'd be interested to know which theory they are referring to
    I know there are specific models which do so, but from the onset those are working hypothesis to see what comes out, not really "postulates". The way I see it, the hypothesis is used to shortcut the time necessary to decide whether Lorentz violations are predicted to happen as breaking of the symmetry from the postulates themselves.</mood>
     
  15. Oct 31, 2009 #14

    tom.stoer

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    Some months ago I asked regarding the current status of nnon-trivial dispersion relation in LQG / SF theories. A couple of years ago these theories seemed to propose
    - non-trivial dispersion relations, related to DSR in some semiclassical limit
    - perhaps GZK violation
    - polarization effects in CBR
    These predictions depend on the semiclassical state which is still not known and therefore everything was speculative. I haven't seen any new or updated paper regarding these subjects for months (or even years), neither on arxiv nor in any journal.

    So what is the current status of these theories?

    If their predictions are negative (which would agree with the above mentioned experiment): do these theories run into the same problem as string theory, namely to make post-dictions only?
     
  16. Oct 31, 2009 #15

    marcus

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    We could start a separate thread about prospects (are there any?) for cosmological tests of Loop/Foam theory or theories.

    If you are asking a general question about loop/foam status, then in my opinion the most significant current research is aimed (not at distinguishing between several theories but) at simply getting one background independent theory with the right classical limit.

    Accordingly you see major papers aimed at either merging different lines of investigation or establishing the classical limit.
    Lewandowski reconciling loop and foam models, to form a single combined approach.
    Ashtekar and others extending loop cosmology to anisotropic cases--relaxing assumptions.
    Ashtekar trying out spin foam cosmology.
    Rovelli's group checking to see that the limits are right.


    On the other hand, in terms of raw numbers of papers, I think cosmology is the biggest area of loop/foam research growth. Many of the papers are by comparative newcomers to the field, and are groping for observable consequences.
    There are still only a comparatively small number of researchers, but that's where I see percentage growth. Judging from the recent literature, if there is any hope of detecting a loop/foam signature in the near term, it would be in the cosmic microwave background, the universe's history of expansion/structure formation, and possibly other astrophysics.

    You mentioned dispersion, energy-dependent speed of signal propagation. I think you are right that there has been substantially no interest in that for several years in the loop/foam research community as a whole. A number of people worked on it around 2005-2006 but couldn't get any clear predictions.

    You mentioned CMB polarization. I will try to hunt up some papers about that. There have been some, but i don't recall any making definite predictions.
    If someone is interested they might have a look at this guy's papers:
    http://arXiv.org/find/gr-qc/1/au:+Mielczarek_J/0/1/0/all/0/1
    He publishes in Physical Review D, Physics Letters B, General Relativity and Gravitation, JHEP. JCAP,
    and he seems to be focusing on deriving some kind of observable signs of LQC.
     
    Last edited: Oct 31, 2009
  17. Nov 1, 2009 #16

    marcus

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    The second most highly cited Loop Foam paper for this year is by Aurelien Barrau and Julien Grain and concerns the effort to derive prediction of a "cosmological footprint" in the CMB. Probably last year no one reading this thread had heard of Barrau and Grain. This indicates the rate at which new researchers are entering the field and can quickly gain recognition.

    Barrau is associate prof at Grenoble. He has some 3 papers in Loop Cosmology so far, just in this year. They represent 3 out of his 4 most recent papers.
    http://lpsc.in2p3.fr/ams/aurelien/index_eng.html
    http://arxiv.org/find/grp_physics/1/au:+Barrau_A/0/1/0/all/0/1
    Barrau has published over 50 papers and some of his earlier work was string-related.

    As far as I can see, Barrau and Grain do not give exact quantitative predictions of what the recently launched Planck spacecraft's data will show---but they make some qualitative statements. I consider this to be work in progress---that indicates where the field is going in the empirical testing department. Anyone interested can look at their "LQG footprints" paper.
    http://arxiv.org/abs/0902.0145
    Cosmological footprints of loop quantum gravity
    J. Grain, A. Barrau
    Accepted by Phys. Rev. Lett., 7 pages, 2 figures
    (Submitted on 2 Feb 2009)
    "The primordial spectrum of cosmological tensor perturbations is considered as a possible probe of quantum gravity effects. Together with string theory, loop quantum gravity is one of the most promising frameworks to study quantum effects in the early universe. We show that the associated holonomy correction should modify the potential seen by gravitational waves during the inflationary amplification. The resulting power spectrum should exhibit a characteristic tilt. This opens a new window for cosmological tests of quantum gravity."

    =================

    In post #15 I gave a link to the papers of Jakob Mielczarek. He also is working on deriving from LQG an observable-in-CMB signature. Barrau et al cite him. I think his name is pronouced MYEL-CHA-REK. He has several recent papers about this, here are two:
    http://arXiv.org/abs/0902.2490
    Tensor power spectrum with holonomy corrections in LQC
    http://arXiv.org/abs/0908.4329
    The Observational Implications of Loop Quantum Cosmology
     
    Last edited: Nov 1, 2009
  18. Nov 1, 2009 #17
    There's a relatively recent ('08) article that basically states that LQG is only able to calculate the correct classical value of black hole entropy if the first-order term in the dispersion equation (the one constrained by FERMI) vanishes exactly.

    Of course, no one knows if the classical value of black hole entropy is correct, because no one has so much as seen a black hole, let alone measure its entropy ...
     
  19. Nov 2, 2009 #18

    tom.stoer

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    thanks a lot
     
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