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A deviation from General Relativity on cosmic scales

  1. Oct 26, 2009 #1

    A deviation from General Relativity?


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  2. jcsd
  3. Oct 26, 2009 #2
    Some discussion of this over on http://blogs.discovermagazine.com/cosmicvariance/2009/10/12/a-new-challenge-to-einstein/" [Broken] (Sean Carroll).
    Last edited by a moderator: May 4, 2017
  4. Oct 26, 2009 #3


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    I know she revised her initial estimate of confidence from something like 99.99% to what it stands right now at 98%. It will be interesting to see if she cleans things up once again, which is my suspicion.
  5. Oct 27, 2009 #4


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    The result is interesting, and it may be pertinent to mention the value eta = 1/3, comes naturally from the 2002 version of Self Creation Cosmology.

    i.e. when the Robertson parameters alpha = 1 and gamma = 1/3.

    http://arxiv.org/abs/gr-qc/0302088 (eq. 60).

    It would seem though that is not the case for z < 1.

  6. Oct 27, 2009 #5


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    Yes, the strangest part of this result, if one was to accept it at face value, is that it implies that the law of gravity itself changes over time, in a rather significant way. Given that the COSMOS team have indicated the photometric redshift calibrations for high redshift are probably a bit dodgy (they are being improved with a follow up spectroscopic survey z-COSMOS) I'd be very wary of giving too much weight to this result yet, since the signal of the deviation only occurs at the very highest redshifts, were the photometric errors will be greatest.

    The z-COSMOS team have stated that they are doing a similiar analysis using the updated redshifts, so when that is published the picture should become clearer.
  7. Oct 27, 2009 #6


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    Wouldn't the observational error estimates take care of that?
  8. Oct 27, 2009 #7


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    In principle, but error estimation is astronomy/cosmology is often quite tricky. It's those pesky unknown unknowns that are the killer. Quite often you will see results presented with a statistical error but no systematic error, because it is simply unknown. For instance, Hubble's original 'Hubbles constant' was orders of magnitude away from the current best value, yet the 'error' on the value in the original publication was much smaller than this difference, because Hubble didn't realise (not that he could have!) that he had an enormous systematic error lurking in the Cephied period-luminosity calibration.

    In this particular case, the COSMOS team have stated that there are problems with the high-z photo-z's originally published in terms of an un-moddelled systematic. Photo-z's are a bit of a nightmare, the term 'catastrophic error' is a technical term in that field. The z-COSMOS follow up survey will significantly reduce this systematic.
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