Dark matter is inferred from gravitational effects that cannot be explained by visible matter alone. Galaxy rotation curves, gravitational lensing, and cosmic microwave background measurements all point to additional mass.
Leading candidates include weakly interacting massive particles (WIMPs), axions, and other beyond-standard-model particles. Experiments search for rare interactions in ultra-low-background detectors.
Alternative theories modify gravity at large scales, but the dark matter model remains strongly supported by multiple independent observations.