Macroscopic superpositions and black hole unitarity

TL;DR

This paper explores how macroscopic superpositions in black hole states can reconcile unitarity with the experience of infalling observers, addressing the information paradox and firewall debates.

Contribution

It introduces a framework where black hole formation and evaporation are superpositions of macroscopically distinct spacetimes, reconciling unitarity with subjective experiences of observers.

Findings

Black hole states can be superpositions of different macroscopic configurations.

Observers falling into black holes can have different experiences on different branches.

The superposition approach helps resolve the black hole information paradox.

Abstract

We discuss the black hole information problem, including the recent claim that unitarity requires a horizon firewall, emphasizing the role of decoherence and macroscopic superpositions. We consider the formation and evaporation of a large black hole as a quantum amplitude, and note that during intermediate stages (e.g., after the Page time), the amplitude is a superposition of macroscopically distinct (and decohered) spacetimes, with the black hole itself in different positions on different branches. Small but semiclassical observers (who are themselves part of the quantum amplitude) that fall into the hole on one branch will miss it entirely on other branches and instead reach future infinity. This observation can reconcile the subjective experience of an infalling observer with unitarity. We also discuss implications for the nice slice formulation of the information problem, and to complementarity.