Date: Wed, 28 Jan 1998 17:36:28 -0500 From: ghio@temp0200.myriad.ml.org (Matthew Ghio) Subject: Re: Interesting Chemical Reaction

Here's something to ponder:

Consider two objects initially at the same temperature. One is at the focus of a hemispherical mirror. An elliptical mirror with both objects at its foci encloses the remaining space.

Because of the spherical mirror, the first object reabsorbs most of its heat lost by radiation, but most of the second object's radiated heat is reflected upon the first. Hence the first object becomes warmer relative to the second.

The entropy here appears to decrease, but according to thermodynamics that is impossible. Can anyone explain how it is that the total entropy would not decrease?

Perpetual motion machines built on violations of thermodynamics involving hemispherical and ellipsoidal mirrors have been around for years. They don't work. The objects do not change temperature. Trace a ray from each object. In every direction, it hits an object which is at exactly the same temperature as it is. It may be itself, or it may be the other object. But in each case, the temperature is the same in all directions. The "sky" is the same temperature as the object, so it does not change temperature.