  Verlinde recently suggested that gravity, inertia, and even spacetime may be
emergent properties of an underlying thermodynamic theory. This vision was
motivated in part by Jacobson's 1995 surprise result that the Einstein
equations of gravity follow from the thermodynamic properties of event
horizons. Taking a first tentative step in such a program, we derive the
evaporation rate (or radiation spectrum) from black hole event horizons in a
spacetime-free manner. Our result relies on a Hilbert space description of
black hole evaporation, symmetries therein which follow from the inherent high
dimensionality of black holes, global conservation of the no-hair quantities,
and the existence of Penrose processes. Our analysis is not wedded to standard
general relativity and so should apply to extended gravity theories where we
find that the black hole area must be replaced by some other property in any
generalized area theorem.
