Chapter IX 

 THE QUANTUM THEORY 



The Origin of the Trouble. Nowadays whenever en- 

 thusiasts meet together to discuss theoretical physics the 

 talk sooner or later turns in a certain direction. You 

 leave them conversing on their special problems or the 

 latest discoveries; but return after an hour and it is any 

 odds that they will have reached an all-engrossing topic 

 — the desperate state of their ignorance. This is not a 

 pose. It is not even scientific modesty, because the atti- 

 tude is often one of naive surprise that Nature should 

 have hidden her fundamental secret successfully from 

 such powerful intellects as ours. It is simply that we 

 have turned a corner in the path of progress and our 

 ignorance stands revealed before us, appalling and insist- 

 ent. There is something radically wrong with the pres- 

 ent fundamental conceptions of physics and we do not 

 see how to set it right. 



The cause of all this trouble is a little thing called h 

 which crops up continually in a wide range of experi- 

 ments. In one sense we know just what h is, because 

 there are a variety of ways of measuring it; h is 



.0000000000000000000000000065 5 erg-seconds. 



That will (rightly) suggest to you that h is something 

 very small; but the most important information is con- 

 tained in the concluding phrase erg-seconds. The erg 

 is the unit of energy and the second is the unit of time; 

 so that we learn that h is of the nature of energy multi- 

 plied by time. 



Now in practical life it does not often occur to us to 



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