Maxwell's demon

Max·well's demon  (mkswlz, -wlz)

n.

An imaginary creature who is able to sort hot molecules from cold molecules without expending energy, thus bringing about a general decrease in entropy and violating the second law of thermodynamics.

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[After James Clerk Maxwell.]

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Maxwell's demon  (mkswlz, -wlz)

An imaginary creature who is able to sort fast-moving molecules from slow-moving molecules without adding any energy to the system. Such a creature could separate a gas into two containers, one containing hot gas and the other cold gas, bringing about a general decrease in entropy and violating the second law of thermodynamics; however, such a creature is impossible, since the act of observing the molecules to detect their speed must add energy to the system.

Thesaurus

Noun

1.

Maxwell's demon - an imaginary creature that controls a small hole in a partition that divides a chamber filled with gas into two parts and allows fast molecules to move in one direction and slow molecules to move in the other direction through the hole; this would result in one part of the container becoming warmer and the other cooler, thus decreasing entropy and violating the second law of thermodynamics