1 82 THE QUANTUM THEORY 



Hamiltonian dynamics, prepares us for the discovery 

 that a particular lump of it can have a special import- 

 ance. And yet a lump of standard size 6-55. io~ 27 erg- 

 seconds is continually turning up experimentally. It is 

 all very well to say that we must think of action as 

 atomic and regard this lump as the atom of action. We 

 cannot do it. We have been trying hard for the last 

 ten years. Our present picture of the world shows 

 action in a form quite incompatible with this kind of 

 atomic structure, and the picture will have to be redrawn. 

 There must in fact be a radical change in the funda- 

 mental conceptions on which our scheme of physics is 

 founded; the problem is to discover the particular 

 change required. Since 1925 new ideas have been 

 brought into the subject which seem to make the dead- 

 lock less complete, and give us an inkling of the nature 

 of the revolution that must come; but there has been 

 no general solution of the difficulty. The new ideas will 

 be the subject of the next chapter. Here it seems best 

 to limit ourselves to the standpoint of 1925, except at 

 the very end of the chapter, where we prepare for the 

 transition. 



The Atom of Action. Remembering that action has two 

 ingredients, namely, energy and time, we must look about 

 in Nature for a definite quantity of energy with which 

 there is associated some definite period of time. That is 

 the way in which without artificial section a particular 

 lump of action can be separated from the rest of the action 

 which fills the universe. For example, the energy of consti- 

 tution of an electron is a definite and known quantity; it 

 is an aggregation of energy which occurs naturally in all 

 parts of the universe. But there is no particular duration 

 of time associated with it that we are aware of, and so it 



