I am thus asking the reader to accept information loss in black holes—and the consequent violation of unitarity—as not only plausible, but a necessary reality, in the situations under consideration. We must re-examine Boltzmann’s definition of entropy in the context of black-hole evaporation. What does ‘information loss’ at the singularity actually mean? A better way of describing this is as a loss of degrees of freedom, so that some of the parameters describing the phase space have disappeared, and the phase space has actually become smaller than it was before.
