Dark Matters
This post will be about the main points of evidence for the existence of dark matter. To evaluate whether a competing theory to dark matter is plausible, it's important to know what the actual arguments in favor of dark matter are in more detail than just "dark matter is the stuff you have to add to get galactic rotation curves to work out". A competitor has to address the strongest arguments in favor of the existence of dark matter, not just the weaker fare like galactic rotation curves. So, when reading some hot new arxiv paper about dark matter or the lack thereof, it is fairly useful to know the top five lines of evidential support for dark matter (in my own personal estimation, others may differ). This lets you at least check whether the result is directly addressing the major cruxes that the case for dark matter rests upon, or just picking off one particular piece of evidence and sweeping the rest under the rug, even if you lack the full technical ability to evaluate the claimed result. This post will be saving the best for last, so if you're not going to read the whole thing, skip down to sections 4 and 5. Also, what exactly is meant when the term "dark matter" is used in this post? Anything with mass (so it's affected by gravity and gravitationally influences other things) which does not interact via the electromagnetic force. Electrons, protons, nuclei, and atoms emphatically do not count. Black holes, neutrinos, WIMPS (weakly interacting massive particles), and axions would count under this definition. The last two are theoretical, the first two are very much established. Of course, it would be a massive cop-out to go "neutrinos exist, therefore dark matter does", so "dark matter" will be used with a followup connotation of "and whatever the heck is (we don't know yet), there must be 5x more of it in the universe than matter made of atoms or atom parts, no way around that whatsoever" Point 1: Galactic Rotation Curves The story begins with galaxy r
