Hubble's law is the observation that galaxies recede from an observer at a speed roughly proportional to their distance, formulated by Edwin Hubble in 1929 from measurements of galactic redshifts, and now understood as direct evidence of the expansion of the universe. The constant of proportionality, the Hubble constant, sets the present-day expansion rate and is a central quantity in cosmology, though measurements of its precise value by different methods have historically disagreed, a discrepancy known as the Hubble tension. The law does not imply Earth occupies any special position, since the same proportional recession would be observed from any galaxy in a uniformly expanding universe.
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