Killing horizons kill horizon degrees

TL;DR

This paper proposes that black hole entropy may originate from the transformation of observable boundary degrees of freedom into gauge degrees of freedom at the horizon, challenging the idea that microstates are localized on the horizon.

Contribution

It demonstrates through phase space analysis that entropy can result from boundary-to-horizon degree of freedom conversion in various black holes, including Schwarzschild.

Findings

Entropy arises from boundary to horizon degree transformation.

The phase space analysis applies to a broad class of black holes.

Horizon degrees of freedom may be gauge, not physical, in origin.

Abstract

Frequently it is argued that the microstates responsible for the Bekenstein-Hawking entropy should arise from some physical degrees of freedom located near or on the black hole horizon. In this Essay we elucidate that instead entropy may emerge from the conversion of physical degrees of freedom, attached to a generic boundary, into unobservable gauge degrees of freedom attached to the horizon. By constructing the reduced phase space it can be demonstrated that such a transmutation indeed takes place for a large class of black holes, including Schwarzschild.