 In contrast the Brussels-Austin approach views nonequilibrium systems in terms of nonlinear models whose fundamental explanatory elements are distributions; that is to say, the arrangements of the particles are the fundamental explanatory elements and not the individual particles and  trajectories.[16]  The equations governing the behavior of these distributions are generally irreversible with respect to time. In addition focusing exclusively on distribution functions opens the possibility that macroscopic nonequilibrium models are irreducibly indeterministic, an indeterminism that has nothing to do with ignorance about the system. If so, this would mean probabilities are as much an ontologically fundamental element of the macroscopic world as they are of the microscopic and are free of the interpretive difficulties found in conventional quantum mechanics. 