Haha, I'm no physicist, so take anything I say with a grain of salt. Also, I don't think I can address everything you wrote, so apologies for picking and choosi

Haha, I'm no physicist, so take anything I say with a grain of salt. Also, I don't think I can address everything you wrote, so apologies for picking and choosing. I'll say what I can: > the ability to collide ... is more fundamental That's exactly the funny thing—when physicists say "dark matter" they're saying matter that attracts but doesn't collide. They can only detect it indirectly. I think they normally want to agree with you that matter interacts with light and other matter. "Dark matter" would not be their first choice of explanations. > the observation of the precession of Mercury constitutes a theory of general relativity I'm going to get pedantic here and separate observation from theory, because I think it helps talk about it. Mercury was observed to precess oddly, and nobody knew why. For quite a while, the theory was that an unseen planet was doing it. So I'd phrase it only slightly differently: > the observation of the precession of Mercury constitutes evidence for a theory of general relativity I draw the distinction because it's central to the debate about dark matter. Weird gravity isn't a theory at all—it's an observation. And it's one physicists pretty much agree on—galaxies are definitely acting weird, with respect to their visible mass. One possible theory to explain it is dark matter. Another is MOND. Any of them could be true—it's kind of probabilistic. For some physicists this new observation is shifting the probabilities in favor of dark matter, but it's obviously still flawed because we can't really explain dark because we have no positive confirmation of its existence outside of gravity. We'd love to find a WIMP, for example, but we haven't.