Hawking modes and the optimal disperser : Holographic lessons from the observer's causal-patch unitarity

TL;DR

This paper investigates the origin of the thermal spectrum of Hawking radiation from an observer-centric, holographic perspective, revealing how geometric dispersion and quantum environment interactions influence unitarity in black hole evaporation.

Contribution

It introduces a novel holographic scheme for gravitational open quantum systems that explains the Planckian spectrum without requiring an optimal disperser, extending holography beyond AdS/CFT.

Findings

Hawking modes acquire Planckian spectrum through geometric dispersion.

Holographic quantum environment prevents the strict thermodynamic limit.

Observer-centric formulation supports unitarity in black hole evaporation.

Abstract

Based on an observer-centric methodology, we pinpoint the basic origin of the spectral Planckianity of the asymptotic Hawking modes in the conventional treatments of the evaporating horizons. By considering an observer who analyzes a causal horizon in a generic spacetime, we first clarify how the asymptotic Planckian spectrum is imposed on the exponentially redshifted Hawking modes through a geometric dispersion mechanism developed by a semiclassical environment which is composed by all the modes that build up the curvature of the causal patch of the asymptotic observer. We also discuss the actual microscopic phenomenon of the Hawking evaporation of generic causal horizons. Our quantum description is based on a novel holographic scheme of gravitational open quantum systems in which the degrees of freedom that build up the curvature of the observer's causal patch interact with the radiated Hawking modes, initially as environmental quanta, and after a crossover time, as quantum defects. Planckian dispersion of the modes would only be developed in the strict thermodynamic limit of this quantum environment, called optimal disperser, which is nevertheless avoided holographically. Finally, we outline and characterize how our microscopic formulation of the observer-centric holography, beyond the AdS/CFT examples and for generic causal patches, does realize the information-theoretic processing of unitarity.