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I Gravitational acceleration and the baryon distribution

  1. Sep 25, 2016 #1
    <<Mentor note: Moved from this thread>>

    I read this article

    http://thedaily.case.edu/rotating-g...cisely-determines-gravitational-acceleration/

    It claims that the rotation of galaxies can be explained without a need for dark matter. I not an educated physicist, so I have a hard time judging if this is right or even relevant to this tread.

    The have tried to find a PDF on arxiv to support the article. Guess it must be this one...

    https://arxiv.org/abs/1609.05917

    If this means the end of dark matter, this discussion seems irrelevant, but then again I really don't know :-)

    If this post is not relevant, feel free to delete it :-)
     
    Last edited by a moderator: Sep 25, 2016
  2. jcsd
  3. Sep 25, 2016 #2

    Orodruin

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    After going through the paper, it certainly does not mean the end of dark matter. What the paper says is that they can accurately predict the rotation curve from the distribution of the visible matter, not that this prediction is based on standard gravity. The authors state this quite clearly in the abstract.

    What it would mean in the dark matter paradigm is that the distribution of baryons would be correlated with the distribution of dark matter. To me this does not sound too far fetched. Of course, alternative theories like modified gravity could also reproduce this.

    It should be noted that rotational curves are not theonly observation currently associated with dark matter.
     
  4. Sep 25, 2016 #3
    Thank you for clarifying this for me. :-)
     
  5. Sep 25, 2016 #4
    Gravitational acceleration and the baryon distribution
    Sorry, my age takes its toll and this headline reminds me of the EMP (Einstein's Mach Principle),
    which in general says that all masses in the universe are dependent on each other and are the
    reason for inertia - recently partially confirmed by the sophisticated experiments "Gravity Probe"
    (http://www.nasa.gov/mission_pages/gpb/ ), which verified the effects
    of Thirring-Lense (frame dragging) and the geodetic precession, e.g. here:
    "Gravity Probe B: Final Results of a Space Experiment to Test General Relativity
    C. W. F. Everitt et al., Phys. Rev. Lett. 106, 221101 – Published 31 May 2011"
    and here:
    https://einstein.stanford.edu/RESOURCES/KACST.html
    So, if these tiny effects, measured in the orbit of the earth, applicated to the majestic rotating
    masses of any galaxy, would, I'm convinced* of, result in a satisfying solution of the
    "Dark Matter" conundrum without the need of speculative assumptions of unknown particles
    (*sorry, I did not yet tried to do some estimate calculations by myself, but may be someone else
    will do it with a prospect of a participitation of a Nobel Prize :biggrin: together with C. W. F. Everitt).
    What a pity that the EMP was abandoned so quite early, still in the 1930s by Einstein himself, due
    to the overwhelming persuavive power of the redshift interpretation as an expansion of nearly all
    of the controlling astronomers at that time. May be not the introduction of the cosmological
    constant λ was Einstein's "biggest blunder" but the drop of the EMP and with it his very own
    stationary and closed universe, finite, but without limits.
     
  6. Oct 6, 2016 #5
    Yes, I also read the paper, and tried to start a separate thread about it in the cosmology forum that mods redirected to here. I appreciate the comment from @Orodruin above because as (yet another) lay person I don't trust my own reading of such things for sharing. But in this case my reading was similar: the data show that the distribution of the "missing" (non-baryonic, "dark") mass is uncannily similar to the distribution of the ordinary matter (stars and gas).

    I think this result is quite unexpected. Here are a few informal ways of stating that: first, you know those pop science illustrations showing the gauzy halo of dark matter around the normal matter of a galaxy? You won't be seeing those anymore - ruled out by this data. Second, this data is equivalent to saying that on a galactic scale, every atom of ordinary matter is behaving exactly as if it has too much mass. Or equivalently, on a galactic scale, the law of gravitation is different, but in way that is not the same as MOND or MOG or other prior efforts, and that is not seen at smaller scales like the solar system nor at much larger scales like the matter distribution of the entire observable universe.

    Finally, as @Orodruin points out, there are many reasons for belief in dark matter. The question is whether behavior of the dark matter described in this paper turns out to be consistent with the requirements of the other places that dark matter has been "plugged in" to either existing physical theory or new hypotheses. The head-scratching required to answer this question will take some time so the answer presumably isn't known yet. But it will be fascinating to watch the consequences.
     
  7. Oct 6, 2016 #6

    Chronos

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    It does not explain CMB data favoring DM so far as I can see.
     
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