Paradox Is Illuminating the Black Hole
Gabriel Lynch: The paradox arises from two facts. One is that quantum systems evolve in a “unitary” manner, which is to say that given the quantum state of a system at one time, the quantum state at other times can be uniquely determined. Information about the state is said to be preserved. The second is that black holes evaporate, and according to general relativity they take with them the information of what fell in. To an observer in spacetime after the black hole has evaporated the information available about the initial quantum system is incomplete. They can no longer determine the initial state, and it seems as though quantum information has been destroyed. In grappling with this paradox, researchers have begun to find their footing. Searching for a resolution, physicists have noticed connections between quantum theory and the geometry intrinsic to gravity that offer to alleviate the paradox by offering a duality between quantum mechanics and geometry.