Black hole information paradox

The apparent conflict between black hole evaporation and quantum mechanics: Hawking radiation seems to erase information about matter that formed a black hole, although quantum evolution preserves it.

Hawking radiation: Thermal radiation predicted to emerge from black holes through quantum effects near their horizons. Its apparently thermal character makes the radiation seem unable to encode the details of infalling matter.
Quantum unitarity: The principle that closed quantum systems evolve reversibly, preserving total probability and information. The paradox arises because complete evaporation seems to violate this principle.
Jacob Bekenstein: The physicist who proposed that black holes have entropy proportional to horizon area. His entropy proposal made black hole information capacity a physical question.
Information loss: The loss of information about an initial quantum state during physical evolution. Hawking’s original conclusion accepts this outcome, contrary to standard quantum unitarity.
Black hole interior: The region of spacetime enclosed by a black hole’s event horizon. How interior information is encoded in outgoing radiation remains central to the paradox.
Hawking's calculation: Stephen Hawking’s semiclassical derivation of particle creation by black holes. The derivation predicts radiation entangled with interior partners, leading to information loss if evaporation completes.
Quantum entanglement: A quantum correlation in which the joint state of systems cannot be described as independent states. Entanglement between outgoing radiation and interior partners drives Hawking’s information-loss argument.
Stephen Hawking: The theoretical physicist whose work predicted black hole radiation and argued that evaporation loses information. His 1976 claim framed the paradox as a conflict with quantum mechanics.
Thermal radiation: Radiation whose state is characterized by a temperature and lacks detectable deviations from thermal equilibrium. Perfectly thermal Hawking radiation cannot by itself carry the detailed information required for unitary evaporation.
Quantum extremal surface: A surface that extremizes generalized entropy, combining area and quantum-field entropy. Its location determines which interior regions enter island-formula radiation entropy.

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