Brownian ratchet

English Etymology In reference to Brownian motion. Noun en physics An apparent perpetual motion machine, the subject of a thought experiment, that would consist of a tiny paddle wheel and a ratchet, and might seem to be able to extract useful work from random fluctuations (heat) in a system at thermal equilibrium, in violation of the second law of thermodynamics. en Feynman-Smoluchowski ratchet See also en Maxwell's demon en eponyms