ROMANCE OR SCIENCE? — HEYL 291 



its velocity will be accelerated or retarded. All that we can say is that 

 there is a certtiiii percentage probability of any particuhir behavior, 

 and that such a prediction is always verified by the result when a 

 suiRciently large number of electrons is taken into consideration. In 

 the electronic realm there is no individual causal certainty. Instead 

 there is something which is a conscious organism we woukl call 

 caprice. Dirac even uses the term " the free will of Nature." Yet 

 as we pass from the individual to the crowd, certain laws begin to 

 appear, but they are no longer causal laws; they are only laws of 

 probability. 



There is a certain measure of experimental support for this posi- 

 tion. The evidence is rather involved, and is circumstantial and 

 cumulative rather than direct and specific, but this is not a fatal 

 objection. And there is an imposing array of authority which has 

 accepted this evidence — Bohr, Heisenberg, Dirac, Jordan, Born, 

 Eddington, Bridgman, and others. The situation has been well 

 summed up b}' De Broglie in one of his essays, from which I quote the 

 following sentences: 



Causal laws replaced by laws of probability, physical individuals well 

 localized and of well-defined movement replaced by physical individualities 

 which refuse to let themselves be simply represented and can never be more 

 than half described : such are the surprising consequences of the new theories. 

 In digging under these laws of probability, shall we succeed in refindiug 

 causal laws as we have found recently behind the statistical laws of gases the 

 causal laws of the movement of molecules? Certain arguments would lead to 

 this l)elief, but it would be indeed imprudent to assert it. 



What we have said suffices, we think, to show the importance of the change 

 in the point of view which has recently taken place in physics. Whatever may 

 be the final fate reserved for tliese new doctrines it is of infinite interest to 

 philosophers that physicists have been led, even though but for the moment, to 

 doubt the determinism of physical phenomena and to question the possibility 

 of describing them in a complete fashion within the frame of space and time. 



Perhaps it would be well now to pause, to catch our breath and see 

 where we stand, if indeed we have anything left to stand on. Well 

 may we echo the dismayed queries of Macbeth and Banquo after the 

 disappearance of tlie three weird sisters: 



The earth hath bubbles, as the water has, 



And these are of them. Whither are they vanish'd? 



Into the air; and what seem'd corporal melted 

 As breath into th(^ wind. Would they had stayed! 



Were such things here as we do speak about 

 Or have we eaten of the insane root 

 That takes the reason prisoner? 



I think that we may feel safe as to the answer to the last question. 

 The reassuring thing about all these new and strange theories is that 

 they work. By means of them we are able to cut a little more closely 



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