J. ROBERT OPPENHEIMER 



versible step, to a world infinite in both space and time, in 

 which the earth as one part of an immense machine followed 

 the laws of Kepler and of Newton, a modest planet circling the 

 sun. 



At many other times new knowledge has given us a dif- 

 ferent view of ourselves, has changed the words and the ideas 

 in terms of which we think and talk to one another, has altered, 

 as Butterfield likes to say, "our thinking caps." It is barely a 

 century ago that this happened in our understanding of man's 

 relation to other forms of life; many of us can remember the 

 hostility and suspicion with which the theory of evolution was 

 still greeted in the earlier years of this century. In this country, 

 indeed, the appointments to the presidency of some old, great 

 private universities, made at mid-twentieth century, seem to 

 me to attest a lingering but substantial doubt as to our need 

 for new knowledge. 



Those of us who have lived through the great discoveries 

 in atomic mechanics which culminated three decades ago in 

 the quantum theory, have long believed that these, too, had 

 powerful and deep lessons for man's understanding of his own 

 situation, not in this case about his habitat, nor his relations to 

 other forms of life, but about the nature, power, and limits of 

 his knowledge. There has been some dispute about the episte- 

 mological interpretation of quantum theory, but very little. In 

 part this may be because the experience it describes is remote 

 from common life, and thus abstract. But a deeper reason is not 

 hard to find. Old beliefs do not afford the basis for spirited re- 

 sistance to the new, when they are no longer held with firmness 

 and in common understanding. It is fifty years since William 

 James wrote: 



The point I now urge you to observe particularly is the part 

 played bv the older truths. . . . Their influence is absolutely 

 controlling. Loyalty to them is the first principle — in most cases it 



