Existence of event horizons in physically relevant spacetimes

Determine whether event horizons exist in physically relevant spacetimes, particularly in scenarios where Planck-scale quantum gravity modifications near classical singularities could remove the event horizon.

Background

The paper discusses fundamental limitations of event horizons in dynamical contexts, emphasizing their teleological, global nature that requires knowledge of the entire future of spacetime. This makes event horizons impractical in numerical evolutions and conceptually problematic when global assumptions (such as the existence and completeness of future null infinity) cannot be made.

The authors note earlier arguments that quantum-gravity-induced changes in a Planck-scale neighborhood of the classical singularity could eliminate the event horizon altogether. In light of such possibilities, they explicitly highlight that it is not known whether event horizons exist in physically interesting situations, motivating the use of quasi-local horizons for black hole mechanics and thermodynamics.

References

Indeed, Hajicek pointed out already in 1987 that the EH may be completely removed by changes in the space-time geometry in a Planck scale neighborhood of the singularity that could be induced by quantum gravity effects [PhysRevD.36.1065]. Hence, one does not know whether EHs even exist in physically interesting situations [afshordi2024blackholesinside2024].

— Thermodynamics of dynamical black holes beyond perturbation theory  (2604.00170 - Ashtekar et al., 31 Mar 2026) in Section 1.1 (Limitations of BCH-type frameworks)

The classification is local and anchored. It leaves $C0$ and $C1$ extensions, uniqueness, maximality, and dynamically selected data on the attached side open. These questions involve low-regularity causal structure and characteristic evolution beyond the endpoint.

— Optimal Extension Regularity at the McVittie Event Horizon  (2608.19581 - Li, 20 Aug 2026) in Section 6, Discussion