  The fundamental problem of how tunneling in thermal medium is completed is
addressed, and a new time scale of order 1/friction for its termination, which
is usually much shorter than the Hubble time, is pointed out. Enhanced
non-linear resonance is responsible for this short time scale. This phenomenon
occurs when the semiclassical periodic motion in a metastable potential well
resonates with one of the environment harmonic oscillators coupled to its
motion.
