Entropy and Area
arXiv:hep-th/9303048 · doi:10.1103/PhysRevLett.71.666
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.
10 pages, in Plain TeX with one figure included, LBL-33754. (Revised version adds an important reference and corrects minor typos.)