  We construct an infinite family of microstates for black holes in Minkowski
spacetime which have effective semiclassical descriptions in terms of
collapsing dust shells in the black hole interior. Quantum mechanical wormholes
cause these states to have exponentially small, but universal, overlaps. We
show that these overlaps imply that the microstates span a Hilbert space of log
dimension equal to the event horizon area divided by four times the Newton
constant, explaining the statistical origin of the Bekenstein-Hawking entropy.
