Confinement by Black Holes

TL;DR

This paper investigates the conditions under which an observer can escape from a black hole, using a modern definition of black holes as future outer trapping horizons, and finds that escape is generally impossible if the horizon divides spacetime into separate regions.

Contribution

It provides a rigorous analysis of observer confinement in black holes using the concept of future outer trapping horizons, clarifying conditions for escape.

Findings

Observers on a trapping horizon must enter the trapped region.

Escape from the trapped region is possible under certain conditions.

Inside a future outer trapping horizon, escape is generally impossible if the horizon separates spacetime.

Abstract

The question of whether an observer can escape from a black hole is addressed, using a recent general definition of a black hole in the form of a future outer trapping horizon. An observer on a future outer trapping horizon must enter the neighbouring trapped region. It is possible for the observer to subsequently escape from the trapped region. However, if the horizon separates the space-time into two disjoint components, inside and outside the horizon, then an observer inside a future outer trapping horizon cannot get outside, assuming the null energy condition. A similar confinement property holds for trapped, locally area-preserving cylinders, as suggested by Israel.