Effective black-to-white hole bounces: The cost of surgery

TL;DR

This paper explores geometries enabling black-to-white hole transitions via a space-like shell, examining the energy conditions, quantum effects, and the implications of such models for singularity resolution and potential violations of physical laws.

Contribution

It introduces a novel analysis of black-to-white hole bounces using a space-like shell, highlighting the quantum effects and the costs of such geometric constructions.

Findings

Null energy condition is violated in these models.

Quantum gravity effects can influence regions outside the horizon.

Possible avoidance of singularities without white-hole remnants.

Abstract

We investigate possible geometries allowing transitions from a black hole to a white hole spacetime, by placing a space-like thin shell between them. Such proposals have been advanced recently to account for singularity-resolution in black-hole spacetimes. This space-like shell can be extended to be outside the event horizon and, thereby, reproduce some of the features of these proposals. On the other hand, if the space-like shell is confined fully within the horizon, then it results in a bounce near a space-like singularity inside the black hole. For both cases, the null energy condition is necessarily violated, at least effectively, due to introduction of quantum effects. If the shell, with a non-trivial negative tension, extends beyond the event horizon, then one can see effects of quantum gravity modifications even outside the horizon as a cost of such a space-like surgery. Naturally, one needs to consider whether these types of manufactured spacetimes violates any known laws of nature, allowing for reasonable assumptions. After critically comparing our results with several models in the literature, we reiterate a new way to avoid such black-hole singularities without leaving a white-hole remnant via a quantum bounce.