THE STRETCHED HORIZON AND BLACK-HOLE COMPLEMENTARITY

Three postulates asserting the validity of conventional quantum theory , semiclassical general relativity, and the statistical basis for ther modynamics are introduced as a foundation for the study of blackhole e volution. We explain how these postulates may be implemented in a ''st retched horizon'' or membrane description of the black hole, appropria te to a distant observer. The technical analysis is illustrated in the simplified context of (1 + 1)-dimensional dilaton gravity. Our postul ates imply that the dissipative properties of the stretched horizon ar ise from a course graining of microphysical degrees of freedom that th e horizon must possess. A principle of black-hole complementarity is a dvocated. The overall viewpiont is similar to that poineered by 't Hoo ft but the detailed implementation is different.