Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Why can't dark matter simply be ripples in spacetime?

  1. May 10, 2012 #1
    Think "gravity waves", emitting from let's say a black hole.
    It's an uneducated hypothesis, but why not?
  2. jcsd
  3. May 10, 2012 #2
    Coming from where?
  4. May 10, 2012 #3


    User Avatar
    Science Advisor

    Spacetime curvature affecting the geodesics of bodies must have a source, the energy-momentum tensor; w/o such a source (which may be radiation, matter, dark matter) there is no spacetime curvature.

    Perhaps there are exceptional cases like Brill waves
  5. May 12, 2012 #4
    I'm not seeing why ripples in space time would account for the difference between luminous and gravitational mass.
  6. May 12, 2012 #5


    User Avatar
    Gold Member


    Implications of Graviton-Graviton Interaction to Dark Matter

    A. Deur
    (Submitted on 26 Jan 2009 (v1), last revised 6 May 2009 (this version, v2))
    Our present understanding of the universe requires the existence of dark matter and dark energy. We describe here a natural mechanism that could make exotic dark matter and possibly dark energy unnecessary. Graviton-graviton interactions increase the gravitational binding of matter. This increase, for large massive systems such as galaxies, may be large enough to make exotic dark matter superfluous. Within a weak field approximation we compute the effect on the rotation curves of galaxies and find the correct magnitude and distribution without need for arbitrary parameters or additional exotic particles. The Tully-Fisher relation also emerges naturally from this framework. The computations are further applied to galaxy clusters.

    Journal reference: Phys.Lett.B676:21-24,2009
    DOI: 10.1016/j.physletb.2009.04.060

    It was peer reviewed and published in a good journal. But who cares? It didn't get even 1 citation. (the paper mentioned by INSPIRE as citing it, in fact, does not cite it)
    Last edited: May 12, 2012
  7. May 13, 2012 #6
    Thanks for posting that. I tend to stick to whatever the general consensus is among physicists for most issues, but it is at least nice to know what else may be possible.
  8. May 13, 2012 #7
    Exactly. Why not?

    If you come up with an idea, and you can't come up with a set of observations that disprove that idea, then it's not a well stated hypothesis. If you want to state a hypothesis, then *you* have to come up with the "why not?"

    Now as far as gravity goes

    1) Any plausible theory of gravity has to look like general relativity in the situations where we've been able to test GR
    2) There are hundreds of papers trying to explain dark matter through modified gravity. So far no one has come up with much that is compelling
  9. May 13, 2012 #8
    The problem is that you can get it to work with galaxy rotation curves, but it's going to do bad things for nucleosynthesis and early universe and you run into some obvious problems with pulsar timing experiments. If there are graviton-graviton interactions then you ought to see "weird things" happen at strong field strengths.

    There are a ton of papers on f(R) models to explain cosmological dark matter. What f(R) models do is to say "we have no idea how gravity might be different, so we'll just put in some random gravity equation and see what happens." Instead of focusing on a particular gravity model, you try to say things in general about gravity models.

    The other thing is that the fact a paper has no citations doesn't mean it's being ignored. For example, I can spend a week thinking about the implications of this model to binary pulsar timings. If I find that it *doesn't* affect them, that would be interesting and possibly publishable. If I find that it doesn't work, then it's not publishable.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook