  A semiclassical analysis shows that in the process of black hole formation
and evaporation, an initial pure state will evolve to a mixed state, i.e.,
information will be lost. One way of avoiding this conclusion without invoking
drastic modifications of the local laws of physics in a low curvature regime
would be for the information to be restored at the very end of the evaporation
process. It is normally envisioned that this would require a final burst of
particles entangled with the early time Hawking radiation. This would imply the
emission of an extremely large number of particles from an object of Planck
size and mass and would appear to be blatantly ruled out by energy
considerations. However, Hotta, Schutzhold, and Unruh have analyzed a
$(1+1)$-dimensional moving mirror analog of the Hawking process and have found
that, in this model, information is restored via entanglement of the early time
Hawking radiation with vacuum fluctuations in the spacetime region to the
future of the event where the mirror returns to inertial motion. We analyze
their model here and give a precise formulation of this entanglement by
introducing the notion of "Milne particles." We then analyze the inertial
particle and energy cost of such an entanglement of Hawking radiation with
vacuum fluctuations. We show that that, in fact, the entanglement of early time
Hawking radiation with vacuum fluctuations requires the emission of at least as
many late time inertial particles as Hawking particles. Although the energy
cost can be made small in the $(1+1)$-dimensional mirror system, this should
not be the case for the $(3+1)$-dimensional evaporating black hole system.
Thus, vacuum entanglement has the same difficulties as the more usual burst
scenarios for attempting to avoid information loss.
