Black Holes, Entropies, and Semiclassical Spacetime in Quantum Gravity

TL;DR

This paper synthesizes existing quantum gravity results to clarify black hole entropy, information transfer, and spacetime structure, emphasizing the role of coarse-graining and extending insights to cosmological contexts.

Contribution

It offers a unified interpretation of black hole entropy and information dynamics within quantum gravity, connecting semiclassical and microscopic perspectives.

Findings

Black hole entropy is linked to coarse-graining in quantum gravity.

Detailed analysis of information transfer in Hawking radiation.

Extensions of black hole concepts to de Sitter and Minkowski spaces.

Abstract

We present a coherent picture of the quantum mechanics of black holes. The picture does not require the introduction of any drastically new physical effect beyond what is already known; it arises mostly from synthesizing and (re)interpreting existing results in appropriate manners. We identify the Bekenstein-Hawking entropy as the entropy associated with coarse-graining performed to obtain semiclassical field theory from a fundamental microscopic theory of quantum gravity. This clarifies the issues around the unitary evolution, the existence of the interior spacetime, and the thermodynamic nature in black hole physics--any result in semiclassical field theory is a statement about the maximally mixed ensemble of microscopic quantum states consistent with the specified background, within the precision allowed by quantum mechanics. We present a detailed analysis of information transfer in Hawking emission and black hole mining processes, clarifying what aspects of the underlying dynamics are (not) visible in semiclassical field theory. We also discuss relations between the black hole entropy and the entanglement entropy across the horizon. We then extend our discussions to more general contexts in quantum gravity. The subjects include extensions to de Sitter and Minkowski spaces and implications for complementarity and cosmology, especially the eternally inflating multiverse.