If dark matter does not exist as a physical particle, physicists must rethink how gravity operates at massive scales. The most prominent alternative is Modified Newtonian Dynamics, or MOND. Instead of adding invisible mass to account for high orbital speeds, MOND changes the laws of motion. It suggests that when gravitational acceleration drops below a specific, tiny threshold, the force decays more slowly than Newton predicted. This mathematical tweak allows stars at the edges of galaxies to move fast without flying off into space.
Other theorists look toward gravity itself. Tensor-vector-scalar gravity (TeVeS) attempts to make these modifications fit within the broader context of general relativity. Some models even suggest gravity might leak into extra dimensions, weakening its grip over vast distances. These frameworks attempt to explain why galaxies look the way they do using only the visible matter we can actually see.
Each theory faces its own hurdles. While MOND predicts galactic rotation speeds quite well, it struggles to explain the cosmic microwave background or the behavior of massive galaxy clusters. We are still searching for a single equation that works from the smallest particles to the largest cosmic filaments.
