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B Does gravity self interact with itself

  1. Sep 11, 2017 #1

    wolram

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    I would have thought that this would have been tested before but this paper suggests that it is a new theory.

    arXiv:1709.02481 [pdf, other]
    A possible explanation for dark matter and dark energy consistent with the Standard Model of particle physics and General Relativity
    A. Deur
    Comments: 6 pages, 2 figures
    Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

    Numerical calculations have shown that the increase of binding energy in massive systems due to gravity's self-interaction can account for galaxy and cluster dynamics without dark matter. Such approach is consistent with General Relativity and the Standard Model of particle physics. The increased binding implies an effective weakening of gravity outside the bound system. In this article, this suppression is modeled in the Universe's evolution equations and its consequence for dark energy is explored. Observations are well reproduced without need for dark energy. The cosmic coincidence appears naturally and the problem of having a de Sitter Universe as the final state of the Universe is eliminated.
     
  2. jcsd
  3. Sep 11, 2017 #2

    bapowell

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    The section on comparison with observations seems pretty weak. For the CMB, only the location of the 1st acoustic peak is considered, but really the full temperature power spectrum should be fit under this new model. In particular, the Sachs-Wolfe plateau at low-l is sensitive to dark energy densities and should be determined with the new model.
     
  4. Sep 11, 2017 #3

    wolram

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    Thank you bapowell.
     
  5. Sep 11, 2017 #4

    kimbyd

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    Nit: also, it's worth bearing in mind that the plateau itself has pretty low statistical power, due to the large inherent error bars are low-##\ell##. My understanding is that the statistics only become convincing if you correlate this plateau with nearby large-scale-structure.
     
  6. Sep 11, 2017 #5

    PeterDonis

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    I'm highly skeptical of this claim. The mass of a system, as seen from far away, which corresponds to the "strength of gravity" it causes, does not change if you rearrange its internal components, but it seems like the paper is claiming the opposite.

    It does not look like this paper has been published in a peer-reviewed journal, and I'm not sure I would trust it as a source.
     
  7. Sep 11, 2017 #6

    PAllen

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    For what it's worth, this paper references two others by the same author for its major results. These papers have been published in peer reviewed journals:

    https://arxiv.org/abs/0901.4005

    https://arxiv.org/abs/1611.05515

    The methods are not at all conventional classical GR methods. None of these papers seem to have generated any buzz in the GR or cosmology communities (esp. no cites other than self cites). However, I express no opinion on the merits unless I spend some time studying these.
     
  8. Sep 11, 2017 #7
    @Janus helped me understand problems with the idea of "galactic binding energy" in another thread.

    Edit:
    My understanding from the paper is they aren't claiming the mass changes, but rather the gravitational effect on external objects is decreased/suppressed due to "the trapping of gravity's field":

    This mechanism and the trapping of the field with ensuing suppression of the force at large scale are well-known phenomena in QCD, the other self-interacting force that has a strong regime.​
     
    Last edited: Sep 11, 2017
  9. Sep 11, 2017 #8

    PeterDonis

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    That doesn't make me any less skeptical. The implied analogy with QCD doesn't look valid to me. The QCD force gets suppressed at large distance scales (the technical term is "asymptotically free") because it's an SU(3) non-Abelian gauge theory with 8 spin-1 gauge bosons, whose renormalization group flow leads to a coupling constant that decreases at higher energies. The obvious way to build a QFT for gravity leads to a spin-2 theory with only one gauge boson, whose structure doesn't look at all the same (the gauge group is basically the group of diffeomorphisms, which isn't even compact), and is not renormalizable to begin with.
     
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