[sfifs]

The phrase "Dark Matter" literally means we don't know and therefore until something testable is postulated and tested (to be fair i believe some candidates have fallen by the wayside over the years as measurement has improved), it's principally equivalent to plugging in a giant X and giving it properties not unlike Fermi's famous elephant curve fitting comment.

[mr_mitm]

Just FYI I have a PhD in cosmology, so no need to explain to me what "Dark Matter" does or doesn't mean, but thanks anyway. It sounds like you saw that video by Angela Collier about how Dark Matter is a set of observations, and while I think it's a good video, it's a bit disingenuous to pretend that working scientists put theories of dark matter and theories of modified gravity in the same category. I know Collier literally says that MOND is a DM theory, but I respectfully disagree, as this does not reflect the reality of the language researchers use. Even if you didn't see that video, my point still stands.

Basically, our equation isn't working, and roughly speaking the equation has gravity on the left hand side and matter content on the right hand side. Matter tells spacetime how to curve and spacetime tells matter how to move, is the old motto. Because the equation isn't working, we have two options: modifying the left hand side or modifying the right hand side (or both). In my perception, researchers refer to the first option as theories of modified gravity, and the other option as theories of dark matter.

Putting both options into one category is over simplifying the situation and isn't helpful.

[andrewflnr]

She's done some interesting stuff, but I really hate that Collier video. It seems to have badly muddied the water.

[tekla]

Hey I'm sure a bunch of Youtube videos from Collier and Sabine makes you an expert in the field of physics because they make you feel smart.

[flqn]

"Just FYI I have a PhD in cosmology" is the credentials for the poster being an expert.