  Quantum physics at scales large compared to the Planck scale is described in
the framework of classical space-time geometries. A criterion for selecting
these backgrounds out of quantized gravity is proposed. It leads to an
instability of the black-hole geometry, as experienced by motion across the
horizon, against emission of Hawking quanta. A phenomenological treatment of
the evaporation process perceived by external observers who do not cross the
event horizon is presented. Evaporation occurs within a topologically trivial
``achronon" geometrical background devoid of horizons and singularities
describing a collapse frozen up to decay time scales. It is ignited as in the
conventional theory from pair creation out of the vacuum of the collapsing star
of mass $M$, but after a time of order $M\ln M$ the source of thermal radiation
shifts gradually to the star itself. This allows for a unitary evolution except
possibly for exponentially small background transition amplitudes. The emerging
picture is compared with approaches of t'Hooft and Susskind and the problem of
its overall quantum consistency is evoked. (Figures available upon request)
