Editing AdS/CFT correspondence (section)

=== Black hole information paradox ===

{{Main|Black hole information paradox}}

In 1975, [[Stephen Hawking]] published a calculation that suggested that [[black hole]]s are not completely black but emit a dim radiation due to quantum effects near the [[event horizon]].{{sfn|ps=|Hawking|1975}} At first, Hawking's result posed a problem for theorists because it suggested that black holes destroy information. More precisely, Hawking's calculation seemed to conflict with one of the basic [[postulates of quantum mechanics]], which states that physical systems evolve in time according to the [[Schrödinger equation]]. This property is usually referred to as [[Unitarity (physics)|unitarity]] of time evolution. The apparent contradiction between Hawking's calculation and the unitarity postulate of quantum mechanics came to be known as the [[black hole information paradox]].{{refn|For an accessible introduction to the black hole information paradox, and the related scientific dispute between Hawking and Leonard Susskind, see {{harvnb|Susskind|2008}}.}}

The AdS/CFT correspondence resolves the black hole information paradox, at least to some extent, because it shows how a black hole can evolve in a manner consistent with quantum mechanics in some contexts. Indeed, one can consider black holes in the context of the AdS/CFT correspondence, and any such black hole corresponds to a configuration of particles on the boundary of anti-de&nbsp;Sitter space.{{sfn|ps=|Zwiebach|2009|p=554}} These particles obey the usual rules of quantum mechanics and in particular evolve in a unitary fashion, so the black hole must also evolve in a unitary fashion, respecting the principles of quantum mechanics.{{sfn|ps=|Maldacena|2005|p=63}} In 2005, Hawking announced that the paradox had been settled in favor of information conservation by the AdS/CFT correspondence, and he suggested a concrete mechanism by which black holes might preserve information.{{sfn|ps=|Hawking|2005}}