Black Hole - Open Questions - Information Loss Paradox

Information Loss Paradox

Because a black hole has only a few internal parameters, most of the information about the matter that went into forming the black hole is lost. It does not matter if it is formed from television sets or chairs, in the end the black hole only remembers the total mass, charge, and angular momentum. As long as black holes were thought to persist forever this information loss is not that problematic, as the information can be thought of as existing inside the black hole, unaccessible from the outside. However, black holes slowly evaporate by emitting Hawking radiation. This radiation does not appear to carry any detailed information about the stuff that formed the black hole, meaning that this information appears to be gone forever.

For a long time, the question whether information is truly lost in black holes (the black hole information paradox) has divided the theoretical physics community (see Thorne–Hawking–Preskill bet). In quantum mechanics, loss of information corresponds to the violation of vital property called unitarity, which has to do with the conservation of probability. It has been argued that loss of unitarity would also imply violation of conservation of energy. Over recent years evidence has been building that indeed information and unitarity are preserved in a full quantum gravitational treatment of the problem.