  Black holes are an apparently unavoidable prediction of classical General
Relativity, at least if matter obeys the strong energy condition rho + 3p > 0.
However quantum vacuum fluctuations generally violate this condition, as does
the eq. of state of cosmological dark energy. When quantum effects are
considered, black holes lead to a number of thermodynamic paradoxes associated
with the Hawking temperature and assumption of black hole entropy, which are
briefly reviewed. It is argued that the largest quantum effects arise from the
conformal scalar degrees of freedom generated by the trace anomaly of the
stress-energy tensor in curved space. At event horizons these can have
macroscopically large backreaction effects on the geometry, potentially
removing the classical event horizon of black hole and cosmological spacetimes,
replacing them with a quantum phase boundary layer, where the effective value
of the gravitational vacuum energy density can change. In the effective theory
including the quantum effects of the anomaly, the cosmological term becomes a
dynamical condensate, whose value depends upon boundary conditions at the
horizon. By taking a positive value in the interior of a fully collapsed star,
the effective cosmological term removes any singularity, replacing it with a
smooth dark energy de Sitter interior. The resulting gravitational vacuum
condensate star (or gravastar) configuration resolves all black hole paradoxes,
and provides a testable alternative to black holes as the final quantum
mechanical end state of complete gravitational collapse. The observed dark
energy of our universe likewise may be a macroscopic finite size effect whose
value depends not on Planck scale or other microphysics but on the cosmological
Hubble horizon scale itself.
