  The information loss paradox is widely regarded as one of the biggest open
problems in theoretical physics. Several classical and quantum features must be
present to enable its formulation. First, an event horizon is needed to justify
the objective status of tracing out degrees of freedom inside the black hole.
Second, evaporation must be completed (or nearly completed) in finite time
according to a distant observer, and thus the formation of the black hole
should also occur in finite time. In spherical symmetry these requirements
constrain the possible metrics strongly enough to obtain a unique black hole
formation scenario and match their parameters with the semiclassical results.
However, the two principal generalizations of surface gravity, the quantity
that determines the Hawking temperature, do not agree with each other on the
dynamical background. Neither can correspond to the emission of nearly-thermal
radiation. We infer from this that the information loss problem cannot be
consistently posed in its standard form.
