The black hole information paradox

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The unresolved conflict between two principles that are each extremely well supported. Quantum mechanics is unitary: the state of a closed system evolves reversibly, so in principle the past is always recoverable from the present. Hawking argued in 1976 that a black hole violates this, because the radiation it emits is thermal - determined by mass, spin and charge alone - so when the hole finishes evaporating, everything that distinguished what fell in is gone. Don Page sharpened the problem in 1993 by pointing out what unitarity requires of the entanglement entropy of the radiation: it must rise, turn over at roughly the halfway point of evaporation, and fall back to zero. Hawking's calculation gives a curve that only rises. Since 2019, calculations using replica wormholes and the so-called island formula have reproduced the Page curve from within semiclassical gravity, which most workers regard as major progress. It is not a solution: the computation says the entropy behaves as unitarity demands without saying by what mechanism information escapes. Not a place on Earth.

A node is not a place. Drawing it on a map would assert something about the world that no stored fact supports.