Maxwell’s Demons in Channelled Metabolism: Paradoxes and their Resolution

Abstract

The second law of thermodynamics demands, among other things, that in an isolated system heat does not flow from a compartment at low to a compartment at high temperature. Maxwell (1871) pointed out that a “being” that could deal with individual molecules, when positioned at a trap door between two compartments at different temperatures, might open the door whenever a molecule with much higher than average kinetic energy would approach from the cold compartment, and whenever a kinetically “cold” molecule would approach from the “hot” compartment (see also Brush, 1976). Consequently, such a “Maxwell’s demon” would cause heat to flow from the cold to the hot compartment and violate the second law. For quite some time, the validity of the second law of thermodynamics seemed to depend on the absence of Maxwellian demons from the systems under consideration. Also, it was deemed plausible that the special property long sought for living systems, was nothing but the presence of Maxwellian demons within than. Whilst Maxwell already argued that beings, other than supernatural, would lack the knowledge about the positions and velocities of the molecules, Szilard (1929), Demers (1945) and Brillouin (1956) have since resolved this paradox: the demon would require a continuous influx of information, which should be counted as a kind of work-input and would violate the required isolation of the system. In fact, the collection of this information would always cost more than could be obtained by having the displaced heat drive an engine. Thus, the second law of thermodynamics does apply to all physical chemical systems, living and inanimate alike. Whenever an apparent (or, even, potentially real) violation of the second law of thermodynamics arises, one may indicate this by invoking a Maxwellian demon.