What quantum foundations teach us about black holes

by Ladina Hausmann (ETH)

Wednesday 8 Apr 2026, 10:00 → 12:00 Europe/Zurich

4/3-006 - TH Conference Room (CERN)

Black holes provide a setting to test assumptions about the interplay of quantum theory and gravity. These tests have led to several puzzles, such as the xeroxing or firewall paradox. A common feature of these puzzles is that they combine the perspectives of an infalling observer and an exterior observer, who, for fundamental reasons, have access to different systems. Experiments involving observers with fundamentally different perspectives were also considered independently in quantum information. These are the so-called Wigner's friend experiments, which do not involve gravity. Recent versions of these experiments have shown that different perspectives are difficult to combine: even mild assumptions about how they might be combined are inconsistent with quantum theory. A careful analysis of the firewall paradox reveals that it, too, relies on such assumptions. Therefore, the firewall paradox may not stem from inconsistent assumptions about quantum gravity, but from quantum theory’s limitations in consistently combining multiple observers’ perspectives.