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It is shown that a \({\mathbb{Z}}^2 \)-action on a Lebesgue space is intrinsically random (IR) iff it is a Kolmogorov action (K-action). As a consequence we obtain the fact that the \({\mathbb{Z}}^2 \)-action defined by the Lorentz gas is an IR-action and the \({\mathbb{Z}}^2 \)-action defined by the ideal gas is not an IR-action.

We discuss the problem of nonunitary equivalence, via positivity-preserving similarity transformations, between the unitary groups associated with deterministic dynamical evolution and semigroups associated with stochastic processes. Dynamical systems admitting such nonunitary equivalence with stochastic Markov processes are said to be intrinsically random. In a previous work, it was found that the so-called Bernoulli systems (discrete time) are intrinsically random in this sense. This result is extended here by showing that a more general class of dynamical systems---the so-called K systems and K flows---are intrinsically random. The connection of intrinsic randomness with local instability of motion is briefly discussed. We also show that Markov processes associated through nonunitary equivalence to nonisomorphic K flows are necessarily nonisomorphic.