One Gravity, Many G's: Generalized Horizon Entropy and Gravitational Susceptibility
Abstract
Effective and thermodynamic derivations of gravity theory in the context of generalized entropy can give rise to multiple, and potentially varying, gravitational couplings, raising the question of which quantity should be identified with the physically measured Newton constant. Motivated by this ambiguity, we formulate the notion of gravitational susceptibility of the horizon. In spacetimes containing multiple horizons, if the entropy is a function on a multi-horizon state space, S=S(A1,A2,⋯,An), then the derivatives of the entropy with respect to individual horizon areas define the horizon gravitational response coefficients. Different horizons may possess distinct gravitational responses without requiring multiple fundamental gravitational couplings, analogous to direction-dependent response coefficients in macroscopic media. This framework naturally suggests the possibility that horizon entropies (such as the cosmological apparent horizon and a black hole horizon) can influence one another, which could explain the black hole-cosmology coupled "black hole mass growth" previously discussed in the literature.
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BibTeX
@misc{ong2026gravity,
title = {{One Gravity, Many G's: Generalized Horizon Entropy and Gravitational Susceptibility}},
author = {Yen Chin Ong},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.09192},
eprint = {2609.09192},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.09192},
}
RIS
TY - UNPB
TI - One Gravity, Many G's: Generalized Horizon Entropy and Gravitational Susceptibility
AU - Yen Chin Ong
PY - 2026
DA - 2026/09/01
PB - arXiv
DO - 10.48550/arxiv.2609.09192
UR - https://arxiv.org/abs/2609.09192
AB - Effective and thermodynamic derivations of gravity theory in the context of generalized entropy can give rise to multiple, and potentially varying, gravitational couplings, raising the question of which quantity should be identified with the physically measured Newton constant. Motivated by this ambiguity, we formulate the notion of gravitational susceptibility of the horizon. In spacetimes containing multiple horizons, if the entropy is a function on a multi-horizon state space, S=S(A_1,A_2,⋯,A_n), then the derivatives of the entropy with respect to individual horizon areas define the horizon gravitational response coefficients. Different horizons may possess distinct gravitational responses without requiring multiple fundamental gravitational couplings, analogous to direction-dependent response coefficients in macroscopic media. This framework naturally suggests the possibility that horizon entropies (such as the cosmological apparent horizon and a black hole horizon) can influence one another, which could explain the black hole-cosmology coupled "black hole mass growth" previously discussed in the literature.
ER -