From a thermodynamics perspective, all natural processes are irreversible. The phenomenon of irreversibility results from the fact that if a thermodynamic system of interacting molecules is brought from one thermodynamic state to another, the configuration or arrangement of the atoms and molecules in the system will change as a result. A certain amount of "transformation energy" will be used as the molecules of the "working body" do work on each other when they change from one state to another. During this transformation, there will be a certain amount of heat energy loss or dissipation due to intermolecular friction and collisions; energy that will not be recoverable if the process is reversed.
Thermodynamics defines the statistical behaviour of large numbers of entities, whose exact behavior is given by more specific laws. Since the fundamental laws of physics are all time-reversible, it can be argued that the irreversibility of thermodynamics must be statistical in nature, that is, that it must be merely highly unlikely, but not impossible, that a system will lower in entropy.
It may, moreover, happen that instead of a descending transmission of heat accompanying, in the one and the same process, the ascending transmission, another permanent change may occur which has the peculiarity of not being reversible without either becoming replaced by a new permanent change of a similar kind, or producing a descending transmission of heat.
Forecasting and the irreversibility in the context of MA (q) models. (Special Issue: World Economic Outlook for the 1990s)
Apr 01, 1991; The modern literature on nonlinear dynamics has introduced economists to many new ways of thinking about data and many new...