““During the life of a black hole, it will pull in huge amounts of matter, carrying huge amounts of intrinsic information. At the end, all that's left is a lot of hot radiation-which, being random, carries no information at all-and a tiny black hole. Did the information just disappear? This is a puzzle for quantum gravity, because there is a law in quantum mechanics that says that information can never be destroyed. The quantum description of the world is supposed to be exact, and there is a result implying that when all the details are taken into account , no information can be lost. Hawking made a strong argument that a black hole that evaporates loses information. This appears to contradict quantum theory, so he called this argument the black-hole information paradox. Any putative quantum theory of gravity needs to resolve it.””
