Cycles of Time: An Extraordinary New View of the Universe

by Roger Penrose

Indeed, for many years, Hawking himself has been one of the strongest proponents of the viewpoint that information is indeed lost in black holes. Yet, at the 17th International Conference on General Relativity and Gravitation, held in Dublin in 2004, Hawking announced that he had changed his mind and, publicly forfeiting a bet that he (and Kip Thorne) had made with John Preskill, argued that he had been mistaken and that he now believed[3.52] that the information must in fact all be retrieved externally to the hole. It is certainly my personal opinion that Hawking should have stuck to his guns, and that his earlier viewpoint was far closer to the truth! However, Hawking’s revised opinion is much more in line with what might be regarded as the ‘conventional’ viewpoint among quantum field theorists. Indeed, the actual destruction of physical information is not something that appeals to most physicists, the idea that information can be destroyed in a black hole in this way being frequently referred to as the ‘black-hole information paradox’. The main reason that physicists have trouble with this information loss is that they maintain a faith that a proper quantum-gravity description of the fate of a black hole ought to be consistent with one of the fundamental principles of quantum theory known as unitary evolution, which is basically a time-symmetric[3.53] deterministic evolution of a quantum system, as governed by the fundamental Schrödinger equation. By its very nature, in...