Entropy and Area

Abstract

The ground state density matrix for a massless free field is traced over the degrees of freedom residing inside an imaginary sphere; the resulting entropy is shown to be proportional to the area (and not the volume) of the sphere. Possible connections with the physics of black holes are discussed.

Comments: 10 pages, in Plain TeX with one figure included, LBL-33754. (Revised version adds an important reference and corrects minor typos.)