3 ms·
Strictly speaking we don't, but we have reasons to believe that on a galactic scale it doesn't. There was that famous example a few years back where we had obs
by saalweachter 9y ago
Strictly speaking we don't, but we have reasons to believe that on a galactic scale it doesn't. There was that famous example a few years back where we had observed two galaxies hitting each other, and it "looked" like the regular ol' matter (eg, interstellar gas clouds) in each galaxy had "hit" each other and stopped while the dark matter in each had passed through the other galaxy unimpeded.
Which would seem to indicate that either dark matter is sparse and heavy (and just doesn't hit things very often) or diffuse and not-very-interacting with other matter.
- EGreg 9y agoI am not convinced. What can possibly be said about two galaxies "hitting" each other if we observe only a sliver of time? Secondly, the stopping would happen because of gravity, and that would affect dark matter too.
- saalweachter 9y agoGas clouds also interact electromagnetically: https://en.wikipedia.org/wiki/Bullet_Cluster https://en.wikipedia.org/wiki/Bullet_Cluster
- sls 9y agoYou shouldn't be convinced by one sentence saying that a conclusion was reached a few years back. But you also have no basis for confidence in the negation of that conclusion on the basis of that almost total lack of data or theory. You can't honestly believe that teams of people with physics Ph.D.s just didn't address these questions - how do we infer from observational data, what do we infer from that data - so go read the paper.