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simple MOND question
The Wikipedia page for MOND
https://en.wikipedia.org/wiki/Modifi...onian_dynamics seems like a good introduction to the subject. In particular, it is clear how Eq. (1) (which is the main postulate of MOND) leads to Eq. (2), which is one of the main predictions of MOND (and it is not obvious how this arises in more standard astrophysics and cosmology). So far, so good. But the equation immediately before Eq. (2), F_N = ma^2/a_0, can be rewritten as F_N = ma(a/a_0). The standard expression, of course, is F_N = ma. In the "deep MOND regime", where a is much smaller than a_0, the factor in parentheses is much less than 1. So, the force in this case is the standard force multiplied by a factor much less than 1. In other words, at low acceleration ("deep MOND regime"), the MOND force should be LESS than the standard force. However, this regime corresponds to the outskirts of galaxies, where the observed orbital velocity is much MORE than expected from the standard force law (which is why, if one assumes the standard force law, one is led to dark matter to explain the additional force). What am I missing? |
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