Taming Maxwell's Demon; February 1999; Scientific American Magazine; by Musser; 1 Page(s)
Building a miniature machine is not as simple as scaling down the parts. For one, the inherent chaos of the microworld tends to overwhelm any concerted motion. But what if a motor could work with the disorder, rather than against it? The recent fabrication of nanometer-size wheels brings this vision even closer to fruition.
On the face of it, seeking useful power in random molecular motions seems to repeat the mistake of Maxwell's demon, a little device or hypothetical creature that tries to wring regularity out of the randomness by picking and choosing among the motions. One incarnation of the demon, devised by the late Richard Feynman, is a ratcheted gear attached to a microscopic propeller. As fluid molecules buffet the propeller, some push it clockwise, others counterclockwise-a jittering known as Brownian motion. Yet the ratchet allows, say, only clockwise motion. Voila, a perpetual-motion machine: the heat represented by molecular tumult is turned into consistent clockwise rotation without any loss. (Feynman proposed to use it to lift fleas.)