xiv INTRODUCTION 



that ultimately a reader will identify some symbol, say 

 BREAD, with one of the conceptions of familiar life. But 

 it is mischievous to attempt such identifications prema- 

 turely, before the letters are strung into words and 

 the words into sentences. The symbol A is not the 

 counterpart of anything in familiar life. To the child 

 the letter A would seem horribly abstract; so we give 

 him a familiar conception along with it. "A was an 

 Archer who shot at a frog." This tides over his imme- 

 diate difficulty; but he cannot make serious progress with 

 word-building so long as Archers, Butchers, Captains, 

 dance round the letters. The letters are abstract, and 

 sooner or later he has to realise it. In physics we have 

 outgrown archer and apple-pie definitions of the funda- 

 mental symbols. To a request to explain what an electron 

 really is supposed to be we can only answer, "It is part 

 of the A B c of physics". 



The external world of physics has thus become a world 

 of shadows. In removing our illusions we have removed 

 the substance, for indeed we have seen that substance is 

 one of the greatest of our illusions. Later perhaps 

 we may inquire whether in our zeal to cut out all that is 

 unreal we may not have used the knife too ruthlessly. 

 Perhaps, indeed, reality is a child which cannot survive 

 without its nurse illusion. But if so, that is of little con- 

 cern to the scientist, who has good and sufficient reasons 

 for pursuing his investigations in the world of shadows 

 and is content to leave to the philosopher the determina- 

 tion of its exact status in regard to reality. In the world 

 of physics we watch a shadowgraph performance of 

 the drama of familiar life. The shadow of my 

 elbow rests on the shadow table as the shadow ink 

 flows over the shadow paper. It is all symbolic, and 

 as a symbol the physicist leaves it. Then comes the 



