ar X iv : g r - qc / 9 80 60 12 v 1 3 J un 1 99 8 YITP - 98 - 35 Black holes , brick walls and the Boulware state

The brick-wall model seeks to explain the Bekenstein-Hawking entropy as a wall-contribution to the thermal energy of ambient quantum fields raised to the Hawking temperature. Reservations have been expressed concerning the self-consistency of this model. For example, it predicts large thermal energy densities near the wall, producing a substantial mass-correction and, presumably , a large gravitational back-reaction. We reexamine this model and conclude that these reservations are unfounded once the ground state—the Boulware state—is correctly identified. We argue that the brick-wall model and the Gibbons-Hawking instanton (which ascribes a topological origin to the Bekenstein-Hawking entropy) are mutually exclusive, alternative descriptions (complementary in the sense of Bohr) of the same physics.