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The quantum relative entropy of the Schwarzschild black-hole and the area law

Published 16 Jan 2025 in gr-qc, cond-mat.stat-mech, and quant-ph | (2501.09491v3)

Abstract: The area law obeyed by the thermodynamic entropy of black holes is one of the fundamental results relating gravity to statistical mechanics. In this work we provide a derivation of the area law for the quantum relative entropy of the Schwarzschild black-hole for arbitrary Schwarzschild radius. The quantum relative entropy between the metric of the manifold and the metric induced by the geometry and the matter field has been proposed in G. Bianconi "Gravity from entropy", Phys. Rev. D (2025) as the action for entropic quantum gravity leading to modified Einstein equations. The quantum relative entropy generalizes Araki entropy and treats the metrics between zero-forms, one-forms, and two-forms as quantum operators. Although the Schwarzschild metric is not an exact solution of the modified Einstein equations of the entropic quantum gravity, it is an approximate solution valid in the low coupling, small curvature limit. Here we show that the quantum relative entropy associated to the Schwarzschild metric obeys the area law for large Schwarzschild radius. We provide a full statistical mechanics interpretation of the results.

Summary

  • The paper demonstrates that the quantum relative entropy of a Schwarzschild black hole adheres to the area law in the large radius limit.
  • The study employs an entropic quantum gravity framework that interprets the Schwarzschild metric under low coupling assumptions, accounting for non-zero Riemann tensor effects.
  • Its findings bridge quantum information theory and gravitational physics, guiding future experimental and theoretical research in quantum gravity.

Quantum Relative Entropy of Schwarzschild Black Holes and the Area Law

The paper at hand explores the intricate relationship between quantum information theory and gravitational systems, specifically focusing on the quantum relative entropy of the Schwarzschild black hole. This research provides a novel derivation of the area law applicable to the quantum relative entropy associated with the Schwarzschild black hole. The approach taken involves interpreting the Schwarzschild metric not as an exact solution to the modified Einstein equations of entropic quantum gravity, but as a viable solution under assumptions corresponding to low coupling limits.

Overview of the Schwarzschild Metric and the Entropic Quantum Gravity Action

The central theme revolves around the quantum relative entropy, which measures the "distance" between two quantum operators—here taken as the metric of a manifold and the metric induced by its geometric configurations and matter fields. This entropy is proposed as a modified action in the entropic quantum gravity framework, distinguishing itself from the Einstein-Hilbert action by incorporating dependencies on the Riemann tensor. Within this framework, the Schwarzschild metric, despite not being an exact solution due to its non-zero Riemann tensor, provides a critical test of entropic gravitational theories due to the non-trivial character of its geometry.

Methodology and Results

The paper calculates the quantum relative entropy of the Schwarzschild metric, revealing compliance with the area law in scenarios of large Schwarzschild radius. This finding is significant since the area law typically associates the entropy of black holes with the surface area of their event horizons—a proposition foundational to both holographic principles and theories of quantum gravity.

The mathematical development presented shows that for a Schwarzschild black hole, the quantum relative entropy is non-zero when considered under assumptions of modified gravity. As the Schwarzschild radius approaches large values, calculations reveal linearity with respect to the area, affirming the area proportionality typical of black hole entropies. Deviations from this law are observed for smaller radii, indicating influences of coupling factors not present in classical thermodynamic considerations. Such results impart theoretical insights into the statistical mechanics underpinning gravitational entropy.

Implications and Future Research

The implications of this research are multilayered, impacting both theoretical constructs of quantum gravity and potential experimental validations. The derivation of an area law from an entropic perspective can influence investigations into analog gravity systems and efforts to empirically test quantum gravitational effects. This is particularly pertinent as empirical techniques improve through developments in gravitational wave detection and quantum information science.

The findings of this paper suggest directions for future research centered around solving modified Einstein equations specific to black hole configurations within the entropic quantum gravity paradigm. Additionally, exploration into the second quantization of the theory could yield a more profound understanding of how quantum information properties manifest in higher-dimensional gravitational systems.

In conclusion, this paper enriches the discourse surrounding quantum gravity by providing a statistical mechanics perspective through the lens of quantum relative entropy, reinforcing its potential role as a bridge between quantum information theory and gravitational physics. Future theoretical and experimental pursuits may further elucidate the viability and implications of entropic approaches to understanding the fundamentals of our universe.

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