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Black hole singularity is a surface not a point

Andrew J. S. Hamilton*

Tyler McMaken†

  • Department of Mathematics and Physics, University of Mary, 7500 University Drive, Bismarck, North Dakota 58504, USA

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Phys. Rev. D 114, 024088 – Published 30 July, 2026

DOI: https://doi.org/10.1103/1pvt-3pn5

Abstract

It is widely repeated in the popular literature and elsewhere that the singularity at the center of a black hole is a point. It is not true. Two observers who free fall into a spherical black hole along two different angular trajectories at the same time t do not encounter each other at the central singularity; rather, they lose causal contact with each other already well away from the singularity. Counterintuitively, in general relativity two points can be spatially close yet causally distant. The singularity is a surface not a point. The story for rotating black holes is more complicated, but the same conclusion holds. For a rotating black hole, the singular surface almost certainly resides at its inner horizon, where even the tiniest classical or quantum perturbations ignite the exponential mass inflation instability, precipitating collapse to a spacelike singular surface. There are implications for quantum gravity. We argue that, whatever the ultimate theory of quantum gravity may be, the quantum states of a black hole probably reside at its effectively two-dimensional singular surface, which coevolves unitarily with, and in thermodynamic equilibrium with, the hot atmosphere of trapped Hawking radiation that the black hole generates within its event horizon.

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Phys. Rev. D 114, 024088– Published 30 July, 2026
  • Received 3 January 2026
  • Accepted 15 June 2026
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