We investigate the quantum evolution of large black holes that nucleate
spontaneously in de Sitter space. By numerical computation in the s-wave and
one-loop approximations, we verify claims that such black holes can initially
"anti-evaporate" instead of shrink. We show, however, that this is a transitory
effect. It is followed by an evaporating phase, which we are able to trace
until the black holes are small enough to be treated as Schwarzschild. Under
generic perturbations, the nucleated geometry is shown to decay into a ring of
de Sitter regions connected by evaporating black holes. This confirms that de
Sitter space is globally unstable and fragments into disconnected daughter
universes.Comment: 10 pages, 8 figures, to appear in PR