File:Maxwell's_demon.svg · Wikimedia Commons · See Wikimedia Commons
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Encyclopedic overview
Schematic figure of Maxwell's demon thought experiment
Maxwell's demon is a thought experiment that appears to disprove the second law of thermodynamics. It was proposed by the physicist James Clerk Maxwell in 1867. In his first letter, Maxwell referred to the entity as a "finite being" or a "being who can play a game of skill with the molecules". Lord Kelvin would later call it a "demon".
Excerpted from Wikipedia’s “Maxwell's demon” article, available under the CC BY-SA 4.0 licence.