International Encyclopedia of Systems and Cybernetics

"If a physical system is isolated from its environment, than the amount of entropy in the system can only increase toward a maximum (never decrease)" (A. RAPOPORT, 1966, p.6).

RAPOPORT adds: "Statistically this means that isolated systems tend to drift from less probable configurations to more probable ones, or, which is the same thing, from more "organized" to more "chaotic" ones" (Ibid). (Nowadays, RAPOPORT should probably write "disordered" instead of "chaotic", since this last term acquired a different meaning.

As stated by RAPOPORT, the system is here simply a portion of the physical universe, being well understood that it is isolated, i. e. not receiving inputs of any kind from – nor emitting any outputs toward its environment. This is obviously a perfectly theoretical case, of which only a perfectly abstract model can be constructed.

If this point is not duly understood, numerous apparent contradictions arise, particularly in relation to living and social systems, which, of course are open systems, able to maintain and even to increase their internal organization thanks to organized matter, energy and information inputs from their environment and to the possibility to export entropy toward that same environment.

Even if both situations are a consequence of the 2d Law, there is a clear-cut opposition between the abstract concept of entropic degradation of order in isolated systems and the more realistic model of self-organization through a higher production of entropy in open systems, particularly living ones. H. and L. SABELLI emphasize both aspects and use the greek word "enantiodromy" to characterize their complementarity (1994). SABELLI even redefines the 2nd Law as "the flow of all processes towards symmetry, including as such not only the uniformity of entropy, but also the creation of complex attractors and structures".

I. PRIGOGINE considers that "The second law… provides us with a universal law of macroscopic evolution, since the quantity of entropy appertaining to the system and its environment can only increase in the course of time" (1978, p.11) He has however discovered and discussed the thermodynamic conditions applicable to irreversible systems, for which the 2nd law remains in check, at least for a time.