The Black Hole Information Paradox

A concise survey of the black hole information paradox and its current status is given. A summary is also given of recent arguments against remnants. The assumptions underlying remnants, namely unitarity and causality, would imply that Reissner Nordstrom black holes have infinite internal states. These can be argued to lead to an unacceptable infinite production rate of such black holes in background fields. (To appear in the proceedings of the PASCOS symposium/Johns Hopkins Workshop, Baltimore, MD, March 22-25, 1995). † Email address: [email protected] Black holes exist–we have seen new experimental evidence for this claim in descriptions of Hubble telescope data at this conference. In my talk I’d like to explain to you how this simple statement gets us into a deep paradox in our understanding of nature. This paradox is pushing us to consider abandoning one of our cherished principles of energy conservation, locality and causality, or stability. It suggests that a revision of the fundamental underpinnings of physics may be necessary. To see what the problem is, consider the formation of a large black hole from a collapsing star of mass M0, as shown in fig. 1. Once it has formed, Hawking [1] has shown that, according to the basic principles of quantum field theory, it will radiate its mass away. This result can be understood by recalling that in quantum field theory the vacuum is populated by virtual pairs of particles and antiparticles. The gravitational field of the black hole can promote one member of a pair into a real outgoing particle, while the other partner falls into the black hole with a net negative energy as measured at infinity. Collapsing Star H oizon Earth Hawking radiation Fig. 1: A spacetime diagram of collapse of a star to form a black hole. Hawking radiation arises from escape of one of a pair of virtual particles, and leads to evaporation of the black hole. Also shown are examples of light cones.