Negative entropy and non-equilibrium Euclidean shell

Abstract: The Gibbons-Hawking-York (GHY) approach is traditionally developed for a Euclidean path integral derivation of black hole entropy. In this work, we extend this approach to a static model of thin shell fixed outside a black hole. We compute the Euclidean action shift from a static thin shell outside the black hole, and find exact agreement with Casini's version of Bekenstein bound. We find a negative entropy deficit corresponding precisely to the apparent horizon area perturbation, which provides a holographic interpretation in terms of extremal surfaces. Therefore, we develop a Euclidean framework in which gravity emerges from a negative entropy gradient. This setup allows us to treat the configuration as a near-equilibrium steady state (NESS). Thus, we introduce Onsager reciprocity and a linear-response relation to clarify the entropic force conjecture. A dissipating external force is necessary in this setup and it generates a Hawking temperature gradient which encoding information responsible for entropy gradient. This confirms that the gravitational potential plays the role of an informational and ordering agent, rather than just driven by chaotic and disordering.