Return to the Paradoxes

Abstract

In 1930 the discussion about the irreversibility paradoxes was resumed momentarily by L. Szilard (1929) and G. Lewis (1930). Szilard revived Maxwell’s demon, the “sorting” demon described by Maxwell (1871) as a “door” that could open or shut to selectively allow only the fast molecules to pass from a gas on the left side to a gas on the right side. The gas on the right would keep getting hotter and the gas on the left, colder, in violation of the second law of thermodynamics. Szilard argued that the activity of the demon was such that if it were considered in sufficient detail, its entropy would increase by more than the decrease in the gases and there would be no violation of the second law. According to him and Lewis, irreversibility is not the kind of thing that can be defeated by hypothetical devices but rather it is something that emerges forcefully when we pass from the two-way time of physics to the one-way time of psychology, due to nothing more, perhaps, than the “loss of information” that accompanies the passage. That popularization of the “loss of information” idea, valid as it is, and yet finally inadequate in explanations to physics, has led to important cliches in discussions about irreversibility, and it did lead to the useful Information Theory (1949) developed by Weiner and Shannon.