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arXiv · 2507.05369

Wigner's friend's black hole adventure: an argument for complementarity?

Laurens Walleghem
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Abstract

At the heart of both black hole physics and Wigner's friend scenarios lies the question of unitarity. In Wigner's friend setups, sealed-lab measurements are modeled unitarily, probing the measurement problem. In black hole physics, the unitarity problem concerns information preservation in evaporation. We extend a recent analogy between these two puzzles exposed by Hausmann and Renner [arXiv:2504.03835] by constructing new paradoxes that merge black hole physics with extensions of the Wigner's friend scenario into a unified argument. This unified construction allows us to sharpen the black hole cloning paradox, which leaves room for a theory to consistently describe the physics of black holes satisfying the assumptions of this paradox but without operational contradictions concerning quantum theory's predictions. We close this loophole, showing that no such theory exists, conditional on standard assumptions of black hole puzzles. We moreover show how the firewall argument can be used to derive a violation of no-signalling. We conclude by briefly highlighting important subtleties in assumptions commonly used in black hole puzzles, questioning the validity of these assumptions.

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Laurens Walleghem. 2025-07-07. Wigner's friend's black hole adventure: an argument for complementarity?. https://arxiv.org/abs/2507.05369

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