  Eugenio Bianchi and Matteo Smerlak have found a relationship between the
Hawking radiation energy and von Neumann entropy in a conformal field emitted
by a semiclassical two-dimensional black hole. We compare this relationship
with what might be expected for unitary evolution of a quantum black hole in
four and higher dimensions. If one neglects the expected increase in the
radiation entropy over the decrease in the black hole Bekenstein-Hawking A/4
entropy that arises from the scattering of the radiation by the barrier near
the black hole, the relation works very well, except near the peak of the
radiation von Neumann entropy and near the final evaporation. These
discrepancies are calculated and discussed as tiny differences between a
semiclassical treatment and a quantum gravity treatment.
