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IEEE Systems, Man, and Cybernetics Society, International Conference of Cybernetics and Society

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Law of Requisite Variety, W. Ross Ashby, Second Law of Thermodynamics, Entropy


Although the Law of Requisite Variety (LRV) speaks directly about entropy (of a set of disturbances to a system, and of the states and effects of a regulator), the relation of Ashby's principle to the Second Law of Thermodynamics does not appear to have been commented on, In this paper, it is shown that, when regulation is viewed as a temporal process, the LRV can be interpreted as a statement of, and, in fact, a consequence of, the Second Law. In essence, the regulator reduces the variety (entropy) of the system being regulated by a compensatory increase of variety (entropy) within itself. The total change of entropy in regulator plus system cannot, however, be negative. Yet, while the LRV is a statement of the Second Law, it is one which casts the classical interpretations of the concepts of entropy and neg-entropy in a new light. Specifically, the LRV appears as a principle opposite, or more precisely, complimentary to what might be called the "neg-entropy principle" of Schrodinger, Bertalanffy, and others, These two principles set out alternative strategies for survival for an open system. To counter the tendency of internal order to degrade, a system may ingest neg-entropy from and/or excrete entropy into its surroundings (Schrodinger, et al). Or it may reduce entropy by shifting it, as it were, to a regulator subsystem (Ashby). Entropy has both "negative" and "positive" attributes - disorder and variety, respectively; so, too, has neg-entropy, which can imply rigidity as well as order.


This is the post-print version. The final version is available from the publisher, © 1978, IEEE Systems, Man, and Cybernetics Society, International Conference of Cybernetics and Society.

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