Modified Newtonian Dynamics (MOND)

MOND, proposed by Mordehai Milgrom in 1983, alters Newtonian dynamics at accelerations below 10⁻¹⁰ m/s², eliminating the need for dark matter. It accurately predicts galaxy rotation curves with visible matter alone, achieving a 90% fit for spiral galaxies, a success unmatched by particle models like WIMPs (#1) without tuning. However, MOND underestimates cluster masses by a factor of two and cannot explain cosmic microwave background peaks, leading to criticisms that champion cold dark matter. Proponents point to relativistic extensions like TeVeS as solutions, but the theory remains the foremost dark matter alternative, fueling left fundamental debate.