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Anisotropic speed of light?

  1. Dec 13, 2006 #1

    Wallace

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    Anisotropic speed of light??

    I hope this paper is appropriate to discuss here, as it demonstrates some interesting, if highly controversial, results. http://xxx.lanl.gov/abs/astro-ph/0608223

    If you are interested in learning about relativity, avoid this thread, if you are an expert I'd love you thoughts on this work.

    Mods, if this is going to cloud the water here then lock away, but I'd be interested to see if anyone can spot any glaring errors in the analysis. As I see it this is an apparently valid experimental result. Intuitively I would think that if the effect they find is real then it would have been seen before, but then again I can't think of any direct tests published recently that have measured this to the precision that these guys report.

    On the one hand cranks annoy me as much as anyone, on the other hand it erks me slightly that these kind of papers are generally ignored by the mainstream. I'm not implying this is due to some kind of conspiracy, rather I think people are too busy to bother, but I'd like to see some more attention paid to refuting these kind of claims that get submitted to astro-ph.

    I would expect this paper does contain errors that invalidate the result, but I lack the skill to find any.
     
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  3. Dec 14, 2006 #2

    Aether

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    Fig. 3 of the paper shows that what they are actually measuring is the time-averaged quantization error of their A/D converter, and Figs. 3-7 show that they are basing their analysis on only four day's worth of "data".
    Mansouri & Sexl (their Ref. 1) describe several real experiments that constrain [tex]\alpha=-0.500 \pm 0.021[/tex] or better...compare that to the results reported in this paper of [tex]\alpha=-0.4106 \pm 0.0225[/tex].
     
    Last edited: Dec 14, 2006
  4. Dec 14, 2006 #3

    Ich

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    It's even worse. They did not measure anything at all as long as their apparatus was fixed. They obtain a=-0.41 only when they rotate it, and then carefully neglect any systematical errors the rotation might induce.
    Some people here (including Aether) still know that they claimed a few moths ago to have measured a=0 with essentially the same apparatus - and essentially the same confidence in their results.
     
  5. Dec 20, 2006 #4

    paw

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    I'm not sure I see any glaring errors unless you count the precision itself as a glaring error. The problems I see are related to the precision.

    The authors restrict their search to two narrow 17deg windows around the passage of Leo across the local horizon. They claim the apparatus is only sensitive enough to detect anisotropies in these narrow windows. This in itself suggests the apparatus is inadequate and any separation of a signal from noise is problematic.

    In fig 9 the error bars don't indicate a good fit to their model. Further they don't give the CL. Is it 1, 2, 3 or more sigma? I suspect the CL is 1 sigma as the only CL they report is quoted from COBE data. This suggests to me they are reporting results at a similar CL.

    While I don't claim any particular expertise in this area I do have considerable experience interperting data and the associated error and in my opinion the authors don't prove conclusively that this signal dependance on the Earth's movement is anything more than noise. I would respectfully suggest they need a more sensitive instrument and data over serveral 24hr periods with a better overall fit at a higher confidence level before republishing.
     
  6. Dec 20, 2006 #5

    Aether

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    Good points Ich and paw.
    Signals with a 24hr period are most likely due to thermal drift, so terrestrial experiments that try to constrain the Mansouri-Sexl parameters are often repeated many times over the course of one or more years in an attempt to detect a clear sidereal signature (e.g., a signal having a frequency of 366.25 cycles per year as opposed to 365.25 cycles per year).
     
  7. Dec 21, 2006 #6

    paw

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    I agree, but it does seem they are claiming to have detected anisotropies in c due to the Earths rotation. That's why I suggested several 24hr periods.

    The sidereal signature should be much easier to detect. Unfortunately, there's probably no thermal drift that could be interperted as a variation in c.:biggrin:

    You have to admit, a clearly positive result would definately have an impact on physics and cosmology. Personally, though, I don't think we'll ever see that. I think any clear anisotropy would have been detected by now.
     
  8. Dec 21, 2006 #7

    Aether

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    Yes, but this isn't a credible paper at all. Wallace said
    When papers like this are submitted to a journal, then they will either get quietly shot down or they will get published. Perhaps the authors of papers that never get published should be expected to either withdraw the paper from arxiv.org, or at least to post the referee's criticism in an addendum to the paper?
    We do know that the first-order anisotropy reported in the paper under discussion here has been ruled out by other experiments, but we do not really know what future experiments might find at ever-higher levels of precision.
     
    Last edited: Dec 21, 2006
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