286 THE EVOLUTION OF SCIENTIFIC THEORIES 



Long after microcosmic determinism was relinquished in scientific 

 practice (e.g., in statistical mechanics), it was, we saw earlier, still 

 maintained as a cosmologic absolute in principle. Quantum me- 

 chanics' denial in principle of such determinism does then produce 

 uphea^ al in the sphere of cosmology. And in the sphere of science? 

 Acquiring some powerful new tools of thought, we recognize that 

 some of our older tools are not so omnipotent as we thought. Certain 

 hopes are dashed, other new hopes are created. Scientific eflFort ac- 

 quires a strong new impetus and a slightly diflFerent slant. Of the 

 changes so made in the practice of physics, what is revolutionary? 

 Weizsacker declares : 



It is the definitive difference of quantum mechanics from classical 

 physics, that it cannot even enunciate its propositions without at the 

 same time expressing the way in which they are known. 



The establishment of this fact is just as natural with respect to the 

 practice of classical physics, as it is revolutionary for the world-view 

 not only of classical physics, but of most philosophical systems. 



The growth of order. In nature, viable species produced by muta- 

 tions may ultimately go on, through further abrupt mutations, to 

 still other forms of life. One reason we term this saltatory mode of 

 development an evolution is that we find long-term sequences of 

 organisms which constitute steady progressions toward ever higher 

 levels of organized complexity. Scientific history presents us with 

 some strikingly analogous sequences of theories. We find in all re- 

 cent cases that, however narrow in scope at its first appearance, a 

 viable new theory ultimately stretches to accommodate at least as 

 much as the theory it displaces, and generally a great deal more. In 

 long-term perspective, then, we find a development of "higher" 

 dieories that, through constantly increasing correlative indices, con- 

 trive to hold firmly in order a body of scientific experience forever 

 increasing in both size and complexity. 



This progress is a fact, but how is it possible? Weizsacker points 

 the way with this comment: 



. . . everything which is true at all in the physics of Aristotle, is con- 

 tained in classical [Newtonian] physics, even if it is in part differently 

 expressed; and we should expect the corresponding situation for the 

 relation of our physics to every future one. 



