Maxwell's demon

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Maxwell's demon is a thought experiment created by the Scottish physicist James Clerk Maxwell to "show that the Second Law of Thermodynamics has only a statistical certainty." The thought experiment demonstrates Maxwell's point by describing how to violate the Second Law. In the experiment, an imaginary container is divided into two parts by an insulated wall, with a door that can be opened and closed by what came to be called "Maxwell's Demon". The hypothetical demon opens the door to allow only the "hot" molecules of gas to flow through to a favored side of the chamber, causing that side to spontaneously heat up while the other side cools down.

Contents

Origin and history of the idea

When Maxwell introduced the concept, in his letters to colleagues, and in his book, Theory of Heat, he described it as a "finite being."

The thought experiment first appeared in a letter Maxwell wrote to Peter Guthrie Tait on 11 December 1867. It appeared again in a letter to John William Strutt in 1870, before it was presented to the public in Maxwell's 1871 book on thermodynamics titled Theory of Heat.[1]

William Thompson (Lord Kelvin) was the first to use the word "demon" for Maxwell's concept, in the journal Nature in 1874, and implied that he intended the mediating, rather than malevolent, context of the word.[2][3]

Original thought experiment

The second law of thermodynamics ensures (through statistical probability) that two bodies of different temperature, when brought into contact with each other and isolated from the rest of the Universe, will evolve to a thermodynamic equilibrium in which both bodies have approximately the same temperature. The second law is also expressed as the assertion that in an isolated system, entropy never decreases.

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