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re: THERMODYNAMICS AND THE SUSTAINABILITY OF FOOD PRODUCTION



The recent posting by Jay Hanson about entropy and sustainability contains a 
mistake in the physics. He says that when a water table is lowered its 
entropy increases because more energy will be required to pump water to the 
surface.

Entropy sometimes is realted to how much energy is required to do something, 
but not always. It applies only to thermodynamic (i.e., statistical) 
processes, such as heat transfer, a change in temperature, mixing of 
dissimilar substances, or a chemical reaction. Merely raising or lowering the 
height of something does not change its entropy. The reason that more energy 
is required to lift water from a deeper water table is simply that you are 
working against gravity over a greater change in height (same reason it takes 
twice as much work to climb two flights of stairs as one); it has nothing to 
do with thermodynamics or entropy.

William Lockeretz
Tufts University
Medford, MA