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Diversions

Professor Hibbert's Perpetual Motion Pages

The second law violators

John Gamgee

In 1880 John Gamgee invented an engine - the zero motor - in which heat from the surroundings boiled liquid ammonia which drove a piston. Expansion then was supposed to result in spontaneous condensation, the liquid ammonia returning to a reservoir to complete the cycle. Gamgee was probably sincere, and managed to persuade the Chief Engineer of the US Navy of its potential use. This was at a time when it was not clear where the USA would find sufficient coal to fuel its growing fleet. The Secretary of State for the Navy, and even President Garfield inspected the motor. The problem is, of course, that the gas needs to be cooled below the temperature of the ambient air, to cause it to condense (in fact to -33 degrees centigrade). This would require more energy than was obtained from the piston stroke.

Maxwell's demon?

This is an invention of James Clerk Maxwell, who suggested in 1871 that a small creature who could see and handle individual molecules might be exempt from the second law. The idea is that the demon operates a trap door in a partition between two volumes containing gas. Initially the door is open and the gas is in equilibrium. The demon now starts to open and shut the door so as to allow molecules to pass from one side to the other, but not back again. In time therefore the pressure of one volume increases. This compressed gas could then be used to do work. The first law is not violated as any cooling that occurs when then gas is released can be made up from the surroundings. The explanation, proposed by C. H. Bennett following work by Szillard, Landauer and others, requires an information argument. In order to keep going the demon must forget the results of previous observations, and this adds entropy to the environment.

Biology?

The discovery of oscillating reactions such as the Belusov-Zhabotinski reaction led to speculation that such reactions might somehow breach the laws of thermodynamics. Could biological systems also breach these laws? Could life be a manifestation of a reversal of entropy? No - although these dissipating systems, as they are called, sustain periods in which the entropy of the system decreases, they are not closed. Energy is supplied from outside to drive the reactions, the entropy of the greater system (the Universe) continues to increase. Sorry!

Back to 'Perpetual Motion.'