4 ms·
With respect to the Bullet Cluster (which is often mentioned as a counterexample to MOND): discussion of why that does not rule out MOND: https://web.archive.o
by Beldin 6y ago
With respect to the Bullet Cluster (which is often mentioned as a counterexample to MOND): discussion of why that does not rule out MOND:
https://web.archive.org/web/20160721044735/http://www.astro.umd.edu/~ssm/mond/moti_bullet.html https://web.archive.org/web/20160721044735/http://www.astro....
- pdonis 6y agoHis argument is basically "well, we still need some dark matter with MOND, just not as much". That seems like a weak argument.
- dogma1138 6y agoNot exactly if you need a little as in just enough to be explained by “missing” baryonic matter and other DM candidate that fit the standard model it’s not a weak argument on its own.
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- narag 6y agoWasn't it estimated to be 90%?
- btilly 6y agoNot as weak as you think. When we go looking for sources of dark matter, we have lots of options of things that aren't lit up. For example looking at the distribution of the sizes of the stars, we expect there to be a lot of giant gas balls that weren't quite big enough to start fusion. We don't see them, but we've got good reasons to believe that they are there and can even make a good guess as to how much of them there are. However when we try to make estimates for each kind of dark matter that we think of, we come up a lot short of the amount of dark matter which is required to explain the gravitational dynamics of galaxies. This is when we are getting into the territory of imagining new kinds of particles that physics hasn't yet discovered. Therefore the debate isn't about whether dark matter exists - it obviously does. It is about whether exotic forms of dark matter need to exist.
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- pdonis 6y ago> when we try to make estimates for each kind of dark matter that we think of, we come up a lot short of the amount of dark matter which is required to explain the gravitational dynamics of galaxies The dynamics of galaxies are not the only place where non-baryonic dark matter is needed. Our understanding of baryogenesis in the early universe places limits on how much total baryonic matter there can be in the universe. But the expansion history of the universe requires much more matter than that (about 5 times as much IIRC).