Evolution and Thermodynamics 



(1941) 



The development of modern science has led to a curious divergence 

 of world-views. For the astronomers and the physicists the world is, 

 in popular words, continually "running down" to a state of dead 

 inertness when heat has been uniformly distributed through it. For 

 the biologists and sociologists, a part of the world, at any rate (and 

 for us a very important part) is undergoing a progressive development 

 in which an upward trend is seen, lower states of organisation being 

 succeeded by higher states. For the ordinary man the contradiction, 

 if such it is, is serious, because many physicists, in expounding the 

 former of these principles, the second law of thermodynamics, employ 

 the word "organisation" and say it is always decreasing. Is there a 

 real contradiction here } If so, how can it be resolved }^ 



At the outset it must be recognised that there is no question of 

 rejecting the second law of thermodynamics. It is the basis of all our 

 engineering technique which gives mankind power in controlling 

 natural processes. The only question is, what exactly does it mean.'^ 



The Meaning of the Second Law of Thermodynamics. 



In the general language which scientific workers use every day 

 we say simply that free energy, that is, energy capable of doing work, 

 is constantly decreasing, and bound energy (entropy) is correspond- 

 ingly increasing. This absolutely irreversible process accompanies 

 every natural change, whether physical or chemical. In a series of 

 linked changes, however, there may be local decreases of entropy, 

 provided that over the whole system entropy increases. The irreversi- 

 bility of the "degradation" of energ}^ has been identified by Eddington^ 

 and many other writers with the basis of our knowledge of the one- 



^ In thinking over these problems I have had the invaluable help and counsel of a 

 number of friends: Professor Bernal, Dr. R. E. D. Clark, Dr. Danielli, Professor Dingle, 

 Professor Donnan, Sir Arthur Eddington, Dr. Guggenheim, Dr. Robin Hill, Dr. 

 Neuberger, Professor Polanyi, Dr. Shih-Chang Shen, Dr. Waddington, and Mr. Lancelot 

 Whyte. Should this survey chance to fall under their eye, they will recognise points 

 which they themselves have emphasised, but the whole responsibility for the general 

 line and conclusions must necessarily be borne by me. 



^ e.g. in The Nature of the Physical World (Cambridge, 1928). 



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