The Interior of a Unitarily Evaporating Black Hole

TL;DR

This paper investigates how the interior of unitarily evaporating black holes can be described using microscopic operators, revealing differences between young and old black holes and proposing a global operator framework for the interior.

Contribution

It introduces a construction of global operators for black hole interiors that work across microstates, connecting to entanglement wedge reconstruction.

Findings

Operators act only on black hole degrees of freedom for young black holes.

Operators involve radiation degrees of freedom for old black holes.

Operators obey the correct algebra with exponentially suppressed corrections.

Abstract

We study microscopic operators describing the experience of an observer falling into the horizon of a unitarily evaporating black hole. For a young black hole, these operators can be taken to act only on the degrees of freedom in the black hole region: the soft---or stretched horizon---modes as well as the semiclassical modes in the zone region. On the other hand, for an old black hole, the operators must also involve radiation emitted earlier; the difference between the two cases comes from statistics associated with the coarse-graining performed to obtain the effective theory of the interior. We find that the operators relevant for the interior theory can be defined globally as standard linear operators throughout the microstates, which obey the correct algebra up to corrections exponentially suppressed in the ratio of excitation energy to the Hawking temperature. We conjecture that the existence of such global operators is required for the emergence of the semiclassical picture. We also elucidate relation between the present construction and entanglement wedge reconstruction of the interior.