The two faces of Hawking radiation

TL;DR

The paper proposes that near a black hole horizon, an observer can detect a divergent quasi-thermal spectrum of ingoing modes, revealing a duality between near-horizon and distant perceptions of Hawking radiation.

Contribution

It introduces the concept of horizon-infinity duality and shows that ingoing modes can have divergent thermal spectra near the horizon at the semiclassical level.

Findings

Ingoing modes exhibit a divergent quasi-thermal spectrum near the horizon.

A horizon-infinity duality relates near-horizon and asymptotic observer perceptions.

The effect occurs at the semiclassical level, independent of firewall hypotheses.

Abstract

What happens when Alice falls into a black hole? In spite of recent challenges by Almheiri et al. -- the ""firewall" hypothesis -- the consensus on this question tends to remain "nothing special". Here I argue that something rather special can happen near the horizon, already at the semiclassical level: besides the standard Hawking outgoing modes, Alice can records a quasi-thermal spectrum of ingoing modes, whose temperature and intensity diverges as Alice's Killing energy $E$ goes to zero. I suggest that this effect can be thought of in terms a "horizon-infinity duality", which relates the perception of near-horizon and asymptotic geodesic observers -- the two faces of Hawking radiation.