Maxwell's demon

American  

[maks-welz dee-muhn] / ˈmæks wɛlz ˈdi mən /

noun

1. a hypothetical creature that can separate faster-moving molecules from slower-moving ones without expending energy, used in a thought experiment concerning the second law of thermodynamics.

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Maxwell's demon Scientific  

/ măks′wĕlz′,-wəlz /

1. 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.

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Example Sentences

Information was once thought to be immaterial, “but Maxwell's demon shows that it can have objective physical consequences”, says quantum physicist Arnau Riera, at the Institute of Photonic Sciences in Barcelona, Spain.

From Nature • Oct. 31, 2017

Gleick ranges over the scientific landscape in a looping itinerary that takes the reader from Maxwell’s demon to Godel’s theorem, from black holes to selfish genes.

From New York Times • Mar. 18, 2011