The two faces of Hawking radiation

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.