Holographic principle

Summary

The holographic principle says that quantum gravity in a region has no more degrees of freedom than fit on its boundary. The maximal entropy is a quarter of the boundary area measured in Planck units, so information has a finite density per unit area. It was proposed by Gerard 't Hooft in 1993 and developed by Leonard Susskind in 1995. Its starting point is the Bekenstein–Hawking entropy of black holes, which grows with the horizon area and not with the volume. The AdS/CFT correspondence is the best-understood realization of the principle.