Bekenstein-Hawking entropy

Bekenstein-Hawking entropy is the entropy assigned to a black hole by the formula S = A/4Gℏ, where A is the area of the event horizon, G is Newton's gravitational constant, and ℏ is the reduced Planck constant. Proposed by Jacob Bekenstein in 1972 and validated by Stephen Hawking's 1974 discovery of Hawking radiation, this formula states that a black hole's information content is proportional to the area of its boundary, not the volume of its interior. This was the first concrete evidence for the holographic principle, suggesting that the fundamental degrees of freedom of spacetime may reside on boundaries rather than in bulk volumes. The formula remains one of the most profound clues to the nature of quantum gravity.