International Encyclopedia of Systems and Cybernetics

A total or relative impossibility to predict the future behavior of a complex system.

Most importantly, I. PRIGOGINE and I. STENGERS observe that "… the existence of chaotic systems transforms the notion of unpredictability, frees it from the idea of a contingent ignorance, that a better knowledge would surmount, and gives it an intrinsic meaning"(1992, p.81).

While singled out processes within a stable environment are generally linear or reducible to linearity, complex systems exhibit normally a chaotic behavior, which makes them more or less unpredictable, due to constant interferences between processes of different periods resulting for a multiplicity of simultaneous initial conditions.

R. JENSEN states: "Another manifestation of the unpredictability of chaotic dynamical systems is that the time-evolution is computationally irreducible… There is no faster way of finding out how a chaotic system will evolve than to watch its evolution. The dynamical system itself is its own fastest computer" (1987, p.179).

While this is true in theory, imperfect predictability is feasible: most systems have some characterized dominant periods which remain more or less observable, even if they are to some measure deformed and obscured by chaotic ripples brought about by various or even numerous other cycles of lesser weight, as well as subject to sudden and massive trend variations. In short, some patterns remain more or less visible.

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