The brick-wall model seeks to explain the Bekenstein-Hawking entropy as a wall contribution to the thermal entropy 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 re-examine 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.

• Received 5 June 1998

DOI:https://doi.org/10.1103/PhysRevD.58.104005