Chapter 9: Fundamental Physics

Section 3: Irreversibility and the Second Law of Thermodynamics

Biological systems and Maxwell's demon

Unlike most physical systems, biological systems typically seem capable of spontaneously organizing themselves. And as a result, even the original statements of the Second Law talked only about "inanimate systems". In the mid-1860s James Clerk Maxwell then suggested that a demon operating at a microscopic level could reduce the randomness of a system such as a gas by intelligently controlling the motion of molecules. For many years there was considerable confusion about Maxwell's demon. There were arguments that the demon must use a flashlight that generates entropy. And there were extensive demonstrations that actual biological systems reduce their internal entropy only at the cost of increases in the entropy of their environment. But in fact the main point is that if the evolution of the whole system is to be reversible, then the demon must store enough information to reverse its own actions, and this limits how much the demon can do, preventing it, for example, from unscrambling a large system of gas molecules.

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From Stephen Wolfram: A New Kind of Science [citation]