vol 3: Development
5 Cybernetics page 2:
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... to restore theology to the mainstream of science
Entropy
On the whole, entropy never decreases (and almost always increases) in any physical process. This important discovery of nineteenth century thermodynamics has undergone an important transformation on its way into the age of information.
After confused beginnings, physicists realised that there are two important quantitites related to heat, energy and entropy. Energy is conserved in adiabatic systems, that is sub-systems of the world that allow no energy in from or out to their environment. Entropy is conserved in reversible processes.
Sadi Carnot invented the classical reversible process, the Carnot cycle, which takes in energy and entropy at a high temperature, outputs some of the energy and all of the entropy at a lower temperature, and outputs the remainder of the energy as mechanical work, that is energy with zero entropy.
Engineers who design heat engines are interested in the efficiency of their machines, that is what proportion of the energy n the fuel is converted into mechanical energy at the machine output. Carnot, using his idealised cycle, was able to show that the maximum efficiency of such a machine depended only on temperatures. If T1 is the heat input temperature and T2 the heat output temperature, the theoretical maximum efficiency of the Carnot cycle it (T2 - T1)/T2. Such a machine can only work at 100% efficiency if its heat output temperature is absolute zero!
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