  Hawking's prediction of black-hole evaporation depends on the application of
known physics to fantastically high energies -- well beyond the Planck scale.
Here, I show that before these extreme regimes are reached, another physical
effect will intervene: the quantum backreaction on the collapsing matter and
its effect on the geometry through which the quantum fields propagate. These
effects are estimated by a simple thought experiment. When this is done, it
appears that there are no matrix elements allowing the emission of Hawking
quanta: black holes do not radiate.
