Generalized Second Law of Black Hole Thermodynamics and Quantum Information Theory

TL;DR

This paper presents a quantum thought experiment supporting the generalized second law of black hole thermodynamics, linking quantum measurement, entanglement, and entropy changes in black hole physics.

Contribution

It introduces a quantum version of a gedanken experiment demonstrating the generalized second law, incorporating quantum measurement effects and entanglement.

Findings

Quantum measurement decreases outside matter entropy

Detector entropy increase compensates entropy decrease

Black hole entropy increases due to measurement work

Abstract

We propose a quantum version of a gedanken experiment which supports the generalized second law of black hole thermodynamics. A quantum measurement of particles in the region outside of the event horizon decreases the entropy of the outside matter due to the entanglement of the inside and outside particle states. This decrease is compensated, however, by the increase in the detector entropy. If the detector is conditionally dropped into the black hole depending on the experimental outcome, the decrease of the matter entropy is more than compensated by the increase of the black hole entropy via the increase of the black hole mass which is ultimately attributed to the work done by the measurement.