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I Does this variant of MOND exist?

  1. May 28, 2017 #1
    MOND theories are not very popular, but they don't seem to be going away. As I understand the original one, acceleration is a function of the amount of acceleration which would be predicted by Newton's Law. I saw a proposal recently (not yet published, hence I cannot give a reference) which makes the acceleration a function rather of the mass-energy density at each point. My question is not whether this can hold water, but whether this has been tried before.
  2. jcsd
  3. May 28, 2017 #2

    Vanadium 50

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    Without a reference, what is there to discuss?
  4. May 28, 2017 #3
    MOND as a regime of quantum gravity
    Lee Smolin
    (Submitted on 3 Apr 2017)
    We propose that there is a regime of quantum gravity phenomena, for the case that the cosmological constant is small and positive, which concerns phenomena at temperatures below the deSitter temperature, or length scales larger than the horizon. We observe that the standard form of the equivalence principle does not apply in this regime; we consider instead that a weakened form of the equivalence principle might hold in which the ratio of gravitational to inertial mass is a function of environmental and global parameters. We consider possible principles to determine that function. These lead to behaviour that, in the limit of hbar to zero and the speed of light is taken to infinity, reproduces the modifications of Newtonian dynamics first proposed by Milgrom. Thus MOND is elucidated as coding the physics of a novel regime of quantum gravity phenomena.
    We propose also an effective description of this regime in terms of a bi-metric theory, valid in the approximation where the metric is static. This predicts a new effect, which modifies gravity for radial motions.
    Comments: LaTex 22 pages, one figure
    Subjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics of Galaxies (astro-ph.GA); High Energy Physics - Theory (hep-th)
    Cite as: arXiv:1704.00780 [gr-qc]
  5. May 28, 2017 #4
    Many thanks, kodama! Super! Smolin's article is definitely the sort of reference I needed. :smile:

    Vanadium 50: your criticism is valid, so I could modify my question as follows: most MOND theories base the variation on gravity as a function of velocity or acceleration; Smolin (see reference) varies this by investigating a divergence from the equivalence principle of inertial and gravitational mass. A more amateurish attempt to do something less subtle, basing it on mass-energy density, is given by http://www.allanstime.com/UnifiedFieldTheory/gravity.htm. I have also seen an attempt (not to be published) to make the gravitational attraction in an infinitesimal region proportional to -(∇ρ)/ρ, where ρ is the local density of mass energy in that region. I am interested in more serious attempts to wean MOND-type theories away from dependence on acceleration (which makes them look like theory-made-to-fit-data) and based on something like mass-energy density [so that the solution of the flat rotation curves of galaxies comes out as a consequence, similar to the emergence of desirable qualities from Prof. Verlinde's theory based on string theory (https://arxiv.org/abs/1001.0785, https://arxiv.org/abs/1611.02269 ) and, more recently, https://arxiv.org/abs/1612.03034 ]. So, any further references would be appreciated.
    Last edited: May 29, 2017
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