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The
Brownian ratchet is a thought experiment about an apparent perpetual motion
machine conceived by Richard Feynman[1] in a physics lecture at the
California Institute of Technology
on May 11, 1962 as an illustration of the laws of thermodynamics. The simple machine,
consisting of a paddlewheel and a ratchet, appears to be an example of a
Maxwell's demon, able to extract useful work
from random fluctuations in a system
at thermal equilibrium. Feynman's detailed analysis showed
why it cannot actually do this.
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