If the Universe contains at least one inflationary domain with a suffi
ciently large and homogeneous scalar field phi, then this domain perma
nently produces new inflationary domains of all possible types. We sho
w that under certain conditions this process of the self-reproduction
of the Universe can be described by a stationary distribution of proba
bility, which means that the fraction of the physical volume of the Un
iverse in a state with given properties (with given values of fields,
with a given density of matter, etc.) does not depend on time. This re
presents a strong deviation of inflationary cosmology from the standar
d Big Bang paradigm.