John Preskill was on the opposite side from Stephen Hawking and Kip Thorne in the Thorne–Hawking–Preskill bet.
The 1997 wager concerned the black hole information paradox: whether information that falls into a black hole is ultimately destroyed or preserved. Hawking and Thorne argued for information loss, while Preskill argued that quantum mechanics requires information to remain recoverable in some form. The participants formalized the bet on 6 February 1997.
The prize was an encyclopedia chosen by the winning side, described as a work from which information could be retrieved at will. In 2004, Hawking announced that he conceded the bet and presented Preskill with Total Baseball, The Ultimate Baseball Encyclopedia. Hawking compared the earlier information-loss position to burning an encyclopedia, joking that he might instead have given Preskill the ashes.
The story is sometimes confused with Hawking's separate wager with Thorne about whether Cygnus X-1 was a black hole, or with a later bet involving cosmic censorship. Those were different scientific wagers.