Quantum field theory in curved spacetime predicts thermal radiation from black hole event horizons.
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That quantum field theory in curved spacetime predicts thermal radiation from black hole event horizons is one of the most secure results of semiclassical gravity. The prediction originates in Stephen Hawking's 1974-75 calculation, which showed that gravitational collapse leads to steady thermal emission at a temperature proportional to the horizon's surface gravity, and it has since been re-derived by several independent theoretical routes that converge on the same black hole temperature, including the Euclidean path integral, quantum tunneling across the horizon, and gravitational anomaly methods. The principal technical objection has been that the original derivation traces outgoing modes back to frequencies far above the Planck scale, where the theory's validity is uncertain. This concern is answered on two fronts: alternative derivations avoid appealing to trans-Planckian frequencies, and models with modified short-distance dispersion relations still preserve the thermal spectrum at the Hawking temperature. The mode-conversion mechanism behind the prediction has also been corroborated empirically in laboratory analogues, where Hawking-like radiation has been observed at sonic horizons in systems that possess physical short-distance cutoffs. The claim concerns what the theory predicts, and on that question the physics community is essentially unanimous. Whether astrophysical black holes in fact emit this radiation is a separate question: the predicted temperature for stellar-mass black holes is far below the cosmic microwave background, and the radiation has never been observed directly from an astrophysical source.
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