Maxwell's demon is a thought experiment in statistical thermodynamics that appears to violate the second law of thermodynamics by sorting fast- and slow-moving molecules between two chambers without net work, thereby making a hot body hotter and a cold body colder instead of allowing heat to flow from hot to cold. It illustrates the distinction between temperature as a macroscopic average (a macrostate) and the underlying distribution of molecular kinetic energies (microstates), showing that individual molecules can deviate from the system's average even as the aggregate obeys the law. The resolution lies in information theory and statistical mechanics: the demon must measure and record molecular states to sort them, and this measurement and information-processing generates entropy that offsets or exceeds the entropy reduction achieved by the sorting, preserving the second law when the demon is included in the total system.
Maxwell's demon is a thought experiment in statistical thermodynamics that appears to violate the second law of thermodynamics by sorting fast- and slow-moving molecules between two chambers without …