152 ANNUAL RBPOKT SMITHSONIAN INSTITUTION, 1940 



Proud as he is of the precision of his experiments and his thinking 

 he realizes that there is, seemingly, today a place where precision 

 breaks down. He knows, from the Heisenberg principle of uncer- 

 tainty, that he can never measure both the position and the velocity 

 of an electron with exactness. What he achieves in exactness in 

 measuring position, he loses in exactness in velocity, and vice versa. 



He is careful not to jump to conclusions too quickly from this fact, 

 although physicists everywhere are studying it. Thus Bohr, for 

 example, has extended this principle to other pairs of measurements 

 and calls these paired quantities "conjugate quantities," and the rela- 

 tionship between the two "complementary." 



What may come of this we do not yet know. It is a strange fact 

 indeed that Planck's constant enters the picture at this point. The 

 product of the uncertainty in the case of two conjugate quantities is 

 never less than Planck's constant. It appears to set a natural limit 

 on the exactness of measurement in the atomic world. 



The physicist is impressed by many other problems awaiting solu- 

 tions and for these reasons, therefore, his spirit is the spirit of 

 tolerance. 



And finally we come to the tenth great cultural value of physics. 

 This value arises from the fact that the spirit of physics is the spirit 

 of humanity. 



Einstein taught us that the observer is always part of the- experi- 

 ment. There is no such thing as setting up an experiment which is a 

 closed system independent of the observer. Wliile the physicist may 

 have thought that possible in the past, nevertheless there never was 

 a time when the physicist forgot human values. 



The physicist has always been concerned for the future of man- 

 kind. The picture of the scientist as a man who shuts himself away 

 like a hermit in a cave is an unfair picture. There are, of course, 

 such individuals but they are not representative of science. 



Let Einstein, whose theories represent man's greatest flight today 

 into the world of the abstract, speak for the scientist's interest in 

 the concrete facts of life. In February 1931, while visiting in Pasa- 

 dena, he addressed the students of the California Institute of 

 Technology. 



"Why does this magnificent applied science which saves work, and 

 makes life easier, bring us so little happiness?" he said. "The simple 

 answer is: Because we have not yet learned to make sensible use of 

 it." 



"It is not enough that you should understand about applied 

 science, in order that your work may increase man's blessings," Ein- 

 stein told the students. "Concern for the man himself and his fate 

 must always form the chief interest of all technical endeavors. Nev- 

 er forget this in the midst of your diagrams and equations," 



