At the moment there are no better alternatives that satisfy all the observations. If you try to replace General Relativity with something like Modified Newtonia

At the moment there are no better alternatives that satisfy all the observations. If you try to replace General Relativity with something like Modified Newtonian Dynamics (MOND) [1], then you can get good fits to galaxy rotation curves. However, there are many sources of astronomical/cosmological data that will not bend to alternative gravity models, e.g the precise fluctuations of the cosmic microwave background put stringent bound on the matter components of the Universe. [1] https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#Outstanding_problems_for_MOND https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#Ou...