  We propose a novel approach to intrinsic decoherence without adding new
assumptions to standard quantum mechanics. We generalize the Liouville equation
just by requiring the dynamical semigroup property of time evolution and
dropping the unitarity requirement. With no approximations and statistical
assumptions we find a generalized Liouville equation which depends on two
characteristic time t1 and t2 and reduces to the usual equation in the limit t1
= t2 -> 0. However, for t1 and t2 arbitrarily small but finite, our equation
can be written as a finite difference equation which predicts state reduction
to the diagonal form in the energy representation. The rate of decoherence
becomes faster at the macroscopic limit as the energy scale of the system
increases. In our approach the evolution time appears, a posteriori, as a
statistical variable with a Poisson-gamma function probability distribution as
if time evolution would take place randomly at average intervals t2 each
evolution having a time width t1. This view point is supported by the
derivation of a generalized Tam Mandelstam inequality. The relation with
previous work by Milburn, with laser and micromaser theory and many
experimental testable examples are described.
