 It is usual to characterize this feature by the claim that quantum evolution “preserves information”. If one begins with a system in a precisely known quantum state, then quantum theory guarantees that the details about that system will evolve in such a way that one can infer the precise state of the system at some later time, and vice versa. This quantum preservation of details implies that if we burn a chair, for example, it would in principle be possible to perform a complete set of measurements on all the outgoing radiation, the smoke, and the ashes, and reconstruct exactly what the chair looked like. If we were instead to throw the chair into a black hole, however, then orthodoxy holds that as a consequence of the No Hair Theorems (discussed in  section 3.2  above) it would be physically impossible for the details about the chair ever to escape to the outside universe. This might not be a problem if the black hole continued to exist for all time, since one could then assume the information encoded in the chair still existed behind the event horizon, preserved by the unitary evolution in that region. The existence of Hawking radiation, however, tells us that the black hole is giving off energy, and thus it will shrink down and presumably will eventually disappear altogether, along with whatever stuff had fallen past the event horizon before that. At that point, the details about the chair will be irrevocably lost; thus such evolution cannot be described by the standard laws of quantum theory. This is the Information Loss Paradox of quantum black holes (Hawking  1976).[17]  Although the paradox is usually formulated in terms of “information”, the issues is often put here as being the maintenance of correlations between different systems, as this is a physically more perspicuous notion that lies at the bottom of the paradox, and is much less problematic than the notoriously vexed and nebulous concept of “information”. 