Sunday, June 26, 2005

Weird Science: Maxwell’s Demon

We all have our inner demons, don’t we? Well one of the greatest physicists of the 19th century, James C. Maxwell (1831 - 1879) certainly came up with a doozy of one in 1871.

He theorized that a creature (know today as Maxwell’s Demon) could, in principle, open and close a tiny door between two volumes of gases. This demon could then concentrate the slower moving molecules in one area and faster moving molecules in another area by doing so. And yes, drugs were readily available in 1871, but to Maxwell’s credit, I believe he dreamt this one up without their aid.

If this creature could exist, then Maxwell was able to break the second law of thermodynamics. I bet he was pretty hyped up about it at the time. The second law basically says that heat does not naturally flow from a colder body to a hotter one. Anybody sharing a bed with a thermonuclear spouse, knows all about that. . . .

So, in order for heat to flow from a colder body to a warmer body work must be expended. If Maxwell’s creature did its job of channeling molecules, usable energy in the system would increase and the second law the second law of thermodynamics is broken. The demon could direct a flow of kinetic energy, and this energy (excess from the system of two gases) could power a perpetual motion machine. Ta Da!

Now the silly thing about all this is, it wasn’t until around 1950 (yeah, post Einstein) that Maxwell’s Demon was discounted as rubbish by the French physicist Leon Brillouin. He demonstrated that the decrease in entropy (entropy: a measure of the amount of energy unavailable for work during a natural process) would be offset and exceeded by the increase in entropy of the Demon’s actions in activating the door. The second law is not violated but holds true.

I’m pretty sure Brillouin had access to drugs too, or at least copious quantities of wine. And all this goes to show me is that we humans are always looking to get something for nothing. But the truth is, entropy has us all by the short and curlies - demons, physicists and thermonuclear spouses aside.

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