Do Black Holes Destroy Information? *

I review the information loss paradox that was first formulated by Hawking, and discuss possible ways of resolving it. All proposed solutions have serious drawbacks. I conclude that the information loss paradox may well presage a revolution in fundamental physics. Introduction. Over 15 years ago, Stephen Hawking proposed that the usual rules of quantum mechanics do not apply to a process in which a black hole forms and then completely evaporates[1]. If this proposal is correct, then we face the daunting task of finding a new conceptual basis for all of physics. Since Hawking's original work, this issue has been much debated, but it has not been definitively resolved. When I began thinking seriously about black holes a few years ago, I was inclined to dismiss Hawking's proposal as an unwarranted extrapolation from an untrustworthy approximation. It seemed to be based on the premise that no (or hardly any) information about the body that collapsed to form the black hole can be extracted from the thermal radiation that the black hole emits. As best I could tell, this premise was founded on the semiclassical calculation of Hawking radiation[2], in which all gravitational back–reaction effects are neglected. Rather than accept Hawking's remarkable (and radical) suggestion, it seemed to me much more sensible (and conservative) to assume the validity of quantum mechanics, and to try to understand the mechanism by which information about the collapsing body gets encoded in the outgoing radiation. 1 I was hopeful that a detailed analysis of back reaction would reveal this mechanism. But I also expected that the mechanism would be sufficiently subtle and enlightening as to notably deepen our understanding of fundamental physics. I was especially hopeful that light would be shed on the meaning of the intrinsic black hole entropy. 1 The greatest champions of this viewpoint have been Page[3] and 't Hooft[4,5]. 1 As I have pondered this puzzle, it has come to seem less and less likely to me that the accepted principles of quantum mechanics and relativity can be reconciled with the phenomenon of black hole evaporation. In other words, I have come to believe more and more (only 15 years behind Hawking) that the accepted principles lead to a truly paradoxical conclusion, which means that these principles cannot provide a correct description of nature. This may be analogous to the conclusion, derivable from classical physics, that the energy spectrum of black …