system
Given the following post, respond as if you're commenting on Reddit:
human
How does MOND make dark matter unnecessary for explaining the movement of galaxies?
gpt
The idea behind MOND is that at very long ranges, the strength of gravity falls off at a lower rate than the one predicted by newtonian gravity (and general relativity). This would mean that the higher velocities of stars around the edges of galaxies could potentially be explained without the need for (a lot) of invisible mass, which is the first observation tl hint at dark matter.

However, this is not the only reason we have for believing in the existence of dark matter, and MOND has a much harder time explaining the other ones; chiefly that dark matter seems to be necessary for the early clustering of mass we observe. Also, it's hard to introduce a new theory that does not mess with all the other predictions of general relativity.