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Comment by fecal_henge | Hacker News Reader

Lots of people seem to talk about things being a contributor to dark matter. Is the general vibe that it's made of more than one thing?

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The general vibe is that (1) "dark matter" is absolutely required to explain observed velocity distributions in the universe at every scale larger than a few thousand stars and (2) nothing we've observed so far can be it. So... sure. Maybe all these ideas are right, though probably not. But something has to be it, so we might as well keep throwing darts until something lands.

In terms of theory it's easy to believe that the dark matter is a non-interacting particle of some kind such as a WIMP, right-handed neutrino, or axion.

The trouble is picking out which one is correct with all of the alternatives.

Physics as we know it got started when Newton developed a theory of gravity that explained what happens on the Earth and in the heavens. This success was continued when people linked the results of nuclear experiments to nucleosynthesis in stars and the big bang.

Dark matter seems to be AWOL however at the scale of the solar system and smaller so that link is broken right now -- we'd like to be able to observe the dark sector with a big detector, a particle accelerator or an axion telescope but so far we can't.

I think people phrase it that way because otherwise, it would be a much bolder claim to say that your pet theory forms all dark matter, thereby negating all the other possibilities. There's generally no need to make that much of a sweeping claim, and you probably don't have enough evidence to support it. Why not be cautious?

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