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It's not that simple. It's not like a) Some galaxies fit predictions, b) Some do not, and we add unknown dark matter. It's that when they do not fit prediction
by darkmighty 7y ago
It's not that simple. It's not like a) Some galaxies fit predictions, b) Some do not, and we add unknown dark matter.
It's that when they do not fit predictions, there is a single parameter (the mass of dark matter) that does explain its behavior, whose model is that of a weakly interacting gas halo. So dark matter tries to fix things in a very precise way, it's not an arbitrary curve fitting exercise.
Now whether there is really weakly interacting matter out there or some other explanation is valid is still an open question afaik; but the evidence is quite strong so far.
- astrobe_ 7y ago> Now whether there is really weakly interacting matter out there Not "out there". It's supposed to be >80% of the matter of the universe. We supposedly are eating some every day.
- pdonis 7y ago> It's supposed to be >80% of the matter of the universe. We supposedly are eating some every day. It's >80% of the average density of the matter in the universe. But that's an average over all of the universe. On the scale of our planet, or of the solar system, that density is negligible--as in "30 orders of magnitude smaller than the density of the stuff you eat" negligible.