Morzine: David Wallace: The Black Hole Information Loss Problem

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Lecture given at the International Summer Institute in Philosophy of Physics on the Philosophy of Cosmology and the Philosophy of Quantum Gravity

Hosted by the University of Geneva – University of Illinois Chicago Cosmology Beyond Spacetime project

Morzine, France
26 June - 1 July 2022

Note: Some of the Q&A has low audio quality.

David Wallace: The Black Hole Information Loss Problem

Abstract: I distinguish between two versions of the black hole information-loss paradox. The first arises from apparent failure of unitarity on the spacetime of a completely evaporating black hole, which appears to be non-globally-hyperbolic; this is the most commonly discussed version of the paradox in the foundational and semipopular literature, and the case for calling it `paradoxical’ is less than compelling. But the second arises from a clash between a fully-statistical-mechanical interpretation of black hole evaporation and the quantum-field-theoretic description used in derivations of the Hawking effect. This version of the paradox arises long before a black hole completely evaporates, seems to be the version that has played a central role in quantum gravity, and is genuinely paradoxical.
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Spacetimes with black holes that evaporate completely ( without leaving behind any quasi-stable remnants) are "non globally hyperbolic"( this latter point is stated at 39:00), so, semi-classically, information loss is the norm.
Besides that, the seriousness of the problem depends on the version of Holography that one adopts, so it already has to do with speculative physics...
The belief that ( due to the "Page time" version of the problem) information is never lost implies that there's no difference between globally and non- globally hyperbolic spacetimes and that seems, again, paradoxical by itself.
It's not a big surprise that most proposed solutions seem contrived and artificial ( and, moreover, they violate relativistic causality/ locality: that's a much more serious issue than the loss of retrodictability ).

dimitrispapadimitriou