  We consider the set of controlled time-dependent backgrounds of general
relativity and string theory describing ``bubbles of nothing'', obtained via
double analytic continuation of black hole solutions. We analyze their quantum
stability, uncover some novel features of their dynamics, identify their causal
structure and observables, and compute their particle production spectrum. We
present a general relation between squeezed states, such as those arising in
cosmological particle creation, and nonlocal theories on the string worldsheet.
The bubble backgrounds have various aspects in common with de Sitter space,
Rindler space, and moving mirror systems, but constitute controlled solutions
of general relativity and string theory with no external forces. They provide a
useful theoretical laboratory for studying issues of observables in systems
with cosmological horizons, particle creation, and time-dependent string
perturbation theory.
