Illusory horizons, thermodynamics, and holography inside black holes

TL;DR

This paper clarifies the distinction between true and illusory horizons of black holes, emphasizing the role of the illusory horizon in thermodynamics, holography, and information transfer inside black holes.

Contribution

It introduces a clear differentiation between true and illusory horizons, highlighting the illusory horizon's role in encoding black hole entropy and holography, and explores implications for infallers and information transfer.

Findings

The illusory horizon is the source of Hawking radiation.

Black hole entropy is proportional to the area of the illusory horizon.

Entanglement of infallers merges with the illusory horizon at the singularity.

Abstract

There is persistent and endemic confusion between the true (future) horizon and the illusory (past) horizon of a black hole. The illusory horizon is the redshifting surface of matter that fell into the black hole long ago. A person who free-falls through the horizon of a black hole falls through the true horizon, not the illusory horizon. The infaller continues to see the illusory horizon ahead of them, all the way down to the classical singularity. The illusory horizon is the source of Hawking radiation, for both outsiders and infallers. The entropy of a black hole is 1/4 of the area of the illusory horizon, for both outsiders and infallers. The illusory horizon holographically encodes states hidden behind it, for both outsiders and infallers. The endpoint of an infaller approaching the classical singularity is to merge their states with the illusory horizon. The holographic boundary of the black hole is then the union of the illusory horizon and the classical spacelike singularity. When an infaller reaches the classical singularity, any entanglement of the infaller with outsiders or other infallers is transferred to entanglement with the states of the black hole, encoded on the illusory horizon. Locality holds between an infaller and a spacelike-separated outsider or other infaller as long as their future lightcones intersect before the singularity, but breaks down when the future lightcones no longer intersect.