"But this conflicts with the laws of quantum physics, which say that such information can never be completely wiped out. "

"Black Holes and Information

Above we mentioned the Black Hole Has No Hair theorem, which states that no matter what falls into a black hole, the only properties that remain are the total mass, charge, and angular momentum of the object. Thus if, say, an encyclopedia falls into a black hole all the information in the encyclopedia is lost.

We can state this circumstance in another way using Quantum Mechanical terminology. Before it falls into a black hole the encyclopedia has in principle a single well defined wave function. This is called a pure state. After it falls into the hole, however, we have seen that the description of its mass-energy becomes a combination of the possible standing wave states that can exist with nodes on the event horizon. This is called a mixed state.

However, Quantum Mechanics provides no mechanism by which a pure state can become a mixed one. This is usually called the "Information Problem" with black holes.

Hawking, Kip Thorne and others believe that when this problem is resolved, it will turn out that the information really has been irretrievably lost. However, John Preskill and others firmly believe that a mechanism for the information to be released by the evaporating black hole must and will be found in a correct theory of quantum gravity.

Thus, in February 1997 Preskill offered a bet to Hawking and Thorne that:

"When an initial pure quantum state undergoes gravitational collapse to form a black hole, the final state at the end of black hole evaporation will always be a pure quantum state."

Hawking and Thorne accepted the bet. The wager is:

"The loser(s) will reward the winner(s) with an encyclopedia of the winner's choice, from which information can be recovered at will."

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