ABSTRACT
Outside a black hole, or in a constant accelerating frame, one deals with space-time manifolds that possess horizons. It is well-known that observers bounded within such a manifold can detect radiation whose characteristics bear a remarkable resemblance to that from a black body. However, before discussing this, the author briefly mentions two basic points about quantum mechanics: It is well known that a pure quantum-mechanical state can carry coherent phase correlations between dynamical variables that are localized in different regions outside each other's light cones. Quite often in physics, even for a pure state it is difficult to measure all commuting variables in the system. These are usually referred to as inclusive measurements, in which only part of the final system is included in the detection. These inclusive measurements account for most of the experiments in physics.
