MOND vs GR

I’ve written a number of posts about the observational evidence behind dark matter. In yesterday’s io9, Alasdair Wilkins wrote a provocative story about an interesting paper by University of Maryland Astronomer Stacy McGaugh. The paper is a study of 47 gas rich galaxies, in which the rotation curves and gas masses are estimated. Stacy shows the relationship between rotational velocity and baryonic (ordinary) mass is exactly what a simple MOND calculation (without dark matter) would predict:
  M_bpropto V_f^4
and, he argues, standard general relativity using dark matter, fits quite badly.

Alasdair cited my previous article, and I was delighted to get an email from Stacy this morning arguing the merits of MOND. He is quite persuasive, but ultimately I am not convinced.

If you’d like to see the complete debate, check this out.

-Dave

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2 Responses to MOND vs GR

  1. Richard Moody Jr. says:

    A major problem with MOND is that if the universe has “only” matter to work with you more or less have to abandon the SCM because there is inadequate time (13.7 billion years) to form the massive walls and voids. Using known velocities of galaxies it is estimated some of the walls and voids are 100+ billion years old.

    Here is a simple fix that can explain several problems with both the MOND and dark matter models.

    What if dark matter repels matter? This means you have a push rather than a pull. This has several benefits,

    1) The walls and voids still form in the correct time frame,

    2) As dark matter is expelled the galaxies are only impacted by matter and MOND takes over,

    3) Experiments on earth will show no evidence of dark matter and/or severly attenuated numbers of hits,

    4) It obviates the need for dark energy because it predicts an accelerating universe. Dark matter here explains both dark matter and “dark energy”.

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