Thorne-Hawking-Preskill bet
Encyclopedia
The Thorne–Hawking–Preskill bet refers to a public bet on the outcome of the black hole information paradox
Black hole information paradox
The black hole information paradox results from the combination of quantum mechanics and general relativity. It suggests that physical information could disappear in a black hole, allowing many physical states to evolve into the same state...

 made in 1997 by physics theorists Kip Thorne
Kip Thorne
Kip Stephen Thorne is an American theoretical physicist, known for his prolific contributions in gravitation physics and astrophysics and for having trained a generation of scientists...

, Stephen Hawking
Stephen Hawking
Stephen William Hawking, CH, CBE, FRS, FRSA is an English theoretical physicist and cosmologist, whose scientific books and public appearances have made him an academic celebrity...

 and John Preskill
John Preskill
John Phillip Preskill is an American theoretical physicist and the Richard P. Feynman Professor of Theoretical Physics at the California Institute of Technology ....

.

Thorne and Hawking argued that since general relativity
General relativity
General relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics...

 made it impossible for black holes to radiate, and lose information, the mass-energy and information carried by Hawking Radiation
Hawking radiation
Hawking radiation is a thermal radiation with a black body spectrum predicted to be emitted by black holes due to quantum effects. It is named after the physicist Stephen Hawking, who provided a theoretical argument for its existence in 1974, and sometimes also after the physicist Jacob Bekenstein...

 must be "new", and must not originate from inside the black hole event horizon
Event horizon
In general relativity, an event horizon is a boundary in spacetime beyond which events cannot affect an outside observer. In layman's terms it is defined as "the point of no return" i.e. the point at which the gravitational pull becomes so great as to make escape impossible. The most common case...

. Since this contradicted the idea under quantum mechanics
Quantum mechanics
Quantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic...

 of microcausality, quantum mechanics would need to be rewritten.

Preskill argued the opposite, that since quantum mechanics suggests that the information emitted by a black hole relates to information that fell in at an earlier time, the view of black holes given by general relativity must be modified in some way.

The winner of the bet would receive an encyclopedia of the loser's choice, from which information may be accessed.

In 2004, Hawking announced that he was conceding the bet, and that he now believed that black hole horizons should fluctuate and leak information, in doing so providing Preskill with a copy of Total Baseball, The Ultimate Baseball Encyclopedia. Comparing the useless information obtainable from a black hole to "burning an encyclopedia", Hawking later joked, "I gave John an encyclopedia of baseball, but maybe I should just have given him the ashes."

Thorne, however, remained unconvinced of Hawking's proof and declined to contribute to the award. As of 2008, Hawking's argument that he has solved the paradox has not yet been accepted by the community, and a consensus has not yet been reached that Hawking has provided a strong enough argument that this is in fact what happens.

Hawking had earlier speculated that the singularity
Gravitational singularity
A gravitational singularity or spacetime singularity is a location where the quantities that are used to measure the gravitational field become infinite in a way that does not depend on the coordinate system...

 at the centre of a black hole could form a bridge to a "baby universe," a term coined by Canadian Astrophysicist Chad Bryden, into which the lost information could pass; such theories have been very popular in science fiction. But according to Hawking's new idea, presented at the 17th International Conference on General Relativity
General relativity
General relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics...

 and Gravitation
Gravitation
Gravitation, or gravity, is a natural phenomenon by which physical bodies attract with a force proportional to their mass. Gravitation is most familiar as the agent that gives weight to objects with mass and causes them to fall to the ground when dropped...

, on 21 July 2004 in Dublin, Republic of Ireland
Republic of Ireland
Ireland , described as the Republic of Ireland , is a sovereign state in Europe occupying approximately five-sixths of the island of the same name. Its capital is Dublin. Ireland, which had a population of 4.58 million in 2011, is a constitutional republic governed as a parliamentary democracy,...

, black holes eventually transmit, in a garbled form, information about all matter they swallow:
Another older bet – about the existence of black holes – was described by Hawking as an "insurance policy" of sorts. To quote from his book A Brief History of Time:
In the updated and expanded edition of A Brief History of Time, Hawking states that "Although the situation with Cygnus X-1 has not changed much since we made the bet in 1975, there is now so much other observational evidence in favour of black holes that I have conceded the bet. I paid the specified penalty, which was a one year subscription to Penthouse, to the outrage of Kip's liberated wife."
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