196 Henry Quastler 



22. P. D. Klein: Efficiency of information transmission by biochemical co-factors. This 

 volume. 



23. R. Carnap and Y. Bar-Hillel: Tech. Rep. Res. Lab. Electr., Mass. Inst. Tech., no. 247 

 (1952). 



DISCUSSION 



A. Rapoport: It is admirable of biologists to look 'up to' physicists and mathematicians, 

 but it is somewhat embarrassing to physicists and mathematicians to be looked upon with 

 such confidence as a source of methodological gifts which can be immediately applied in 

 biological investigations. It is noteworthy that the greatest discoveries of the physicists are 

 stated in 'pessimistic' terms. They are statements about what cannot be done. For example 

 the First Law of Thermodynamics is essentially a definitive demolition of an age-old dream. 

 The law says in effect that the perpetual motion machine cannot be constructed. But it also 

 holds out a hope of a machine that will keep on working provided only that a large supply of 

 heat is available — the so-called perpetual motion machine of the second kind. The Second 

 Law of Thermodynamics puts an end to that dream. It says that such a machine cannot be 

 constructed either and prophesies the 'heat death' of the Universe. Maxwell introduced 

 his demon in the hopeful conjecture that the intervention of an intelligence might restore the 

 order lost by the continual increase of entropy. Szilard in his now classical paper showed 

 that this too is an illusion, that the demon must pay for the restored order by becoming 

 'disordered' (a biologist would say 'denatured') himself. 



Yet it would be a mistake to consider these discoveries as admissions of defeat only. 

 Each has brought a broadened understanding; the First Law of Thermodynamics by revealing 

 heat as a source of energy ; the Second Law by revealing the role of entropy. Szilard's 

 investigation rests on quantum-theoretical principles and so provides an important juncture 

 between thermodynamics, information theory, and quantum theory. It appears, therefore, 

 that the grand discoveries of physics have a sobering effect. I think the principles of information 

 iheory are of a similar kind. Typically they are statements of hmitations. Their constructive 

 side is in defining the framework in which the search for new knowledge or for new means of 

 prediction and control must be confined. 



