RECYCLING UNIVERSE

If the effective cosmological constant is nonzero, our observable univ erse may enter a stage of exponential expansion. In such a case, regio ns of it may tunnel back to the false vacuum of an inflaton scalar fie ld, and inflation with a high expansion rate may resume in those regio ns. An ''ideal'' eternal observer would then witness an infinite succe ssion of cycles from false vacuum to true, and back. Within each cycle , the entire history of a hot universe would be replayed. If there wer e several minima of the inflaton potential, our ideal observer would v isit each one of these minima with a frequency which depends on the sh ape of the potential. We generalize the formalism of stochastic inflat ion to analyze the global structure of the universe when this ''recycl ing'' process is taken into account. [S0556-2821(98)02904-X].