[rolenthedeep]

Physics only tells us that galaxies don't move the way we think they should.

There are two explanations: there is extra mass in galactic systems that we can't detect, or our understanding of gravity is more incorrect than previously thought.

When you dig in, there's a small amount of evidence that suggests there is extra mass, but also we can modify our equations of gravity to produce similar results.

Dark matter and MOND (one of the leading alternate gravity models) both have compelling cases for them, and both show exceptions that don't match observed data.

I genuinely don't understand why people push dark matter, as a solution it's way too complex for the problem it solves. It makes more sense that our model of gravity (which we know is already incomplete) is more incomplete than it does for there to be an entire class of matter that we can't detect or even construct meaningful theories about.