SCIENCE AND THE UNOBSERVABLE 



By H. Dingle, D. Sc., A. R. C. S. 

 Professor of Natural Philosophy, Imperial College of Science and Technology, Uni- 

 versity of London 



A new phenomenon has appeared in modern physics: namely, an 

 attempt to apply with rigor the principle that only that which is 

 observable is significant. This is not intended to be a precise state- 

 ment of the principle. It is at least vague, and perhaps inaccurate, 

 but on that very account it is the most suitable statement with which 

 to begin our discussion. For the principle itself has not yet been 

 clearly isolated from its applications. Unconsciously, progressing 

 more by instinct than by sight, physicists have allowed it to direct 

 their thoughts, but they have not succeeded in giving it clear expres- 

 sion. Consequently it is manifested here in one form and there in 

 another, appearing to some as an outstanding example of scientific 

 arrogance and even absurdity, while to others it has an authority which 

 raises it above common sense and reason alike. The resulting con- 

 troversy, as may be imagined, has been not without dust and heat, 

 some of which, I fear, must be introduced into the placid atmosphere 

 of this Institution. Let us agree at the beginning that our own 

 considerations shall be at least cool. I will try to mitigate the dust- 

 iness, and we will make an unimpassioned attempt to understand 

 the meaning of the principle and to reach a viewpoint from which its 

 validity may be justly appraised. 



Let me say at once that the principle is not new. I have no doubt 

 that the Greeks had some words for it. It is certainly to be found 

 disturbing the thoughts of Galileo, Newton, Locke, Hume, Kant, 

 Huxley, Mach, and many others; Huxley, for example, speaks of — 

 that exact verbal expression of as much as we know of the fact, and no more, 

 which constitutes a perfect scientific theory. 2 



But on very few occasions in the past has it been more than a pious 

 belief , a doctrine which it has been proper — or only slightly improper — 

 to hold, but which not only has not been allowed to influence the 

 actual prosecution of scientific or philosophical speculation, but has 

 actually been violated therein. It is Einstein who is responsible for 

 the importance which it has today — not because he has stated it 



1 A lecture delivered before the Royal Institution of Great Britain at the Weekly Evening Meeting, 

 Friday, November 26, 1937. Reprinted by permission from the pamphlet of the Royal Institution. 



2 Hume, English men of letters, p. 55, 1879. 



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