Signaling, Entanglement, and Quantum Evolution Beyond Cauchy Horizons

TL;DR

This paper explores how quantum states entangled across black hole horizons evolve beyond evaporation, proposing experimental tests to understand potential non-unitary or nonlinear quantum evolution in extreme spacetime conditions.

Contribution

It introduces a framework for describing nonstandard quantum evolution maps in black hole contexts and suggests terrestrial experiments to probe these fundamental questions.

Findings

Quantum evolution beyond Cauchy horizons may be non-unitary or nonlinear.

Experiments can constrain possible deviations from standard quantum mechanics.

Implications for causality and information preservation in extreme spacetime regions.

Abstract

Consider a bipartite entangled system half of which falls through the event horizon of an evaporating black hole, while the other half remains coherently accessible to experiments in the exterior region. Beyond complete evaporation, the evolution of the quantum state past the Cauchy horizon cannot remain unitary, raising the questions: How can this evolution be described as a quantum map, and how is causality preserved? What are the possible effects of such nonstandard quantum evolution maps on the behavior of the entangled laboratory partner? More generally, the laws of quantum evolution under extreme conditions in remote regions (not just in evaporating black-hole interiors, but possibly near other naked singularities and regions of extreme spacetime structure) remain untested by observation, and might conceivably be non-unitary or even nonlinear, raising the same questions about the evolution of entangled states. The answers to these questions are subtle, and are linked in unexpected ways to the fundamental laws of quantum mechanics. We show that terrestrial experiments can be designed to probe and constrain exactly how the laws of quantum evolution might be altered, either by black-hole evaporation, or by other extreme processes in remote regions possibly governed by unknown physics.