Chapter X 



THE NEW QUANTUM THEORY 



The conflict between quantum theory and classical 

 theory becomes especially acute in the problem of the 

 propagation of light. Here in effect it becomes a con- 

 flict between the corpuscular theory of light and the 

 wave theory. 



In the early days it was often asked, How large is a 

 quantum of light? One answer is obtained by examining 

 a star image formed with the great ioo-inch reflector 

 at Mt. Wilson. The diffraction pattern shows that each 

 emission from each atom must be filling the whole mir- 

 ror. For if one atom illuminates one part only and 

 another atom another part only, we ought to get the 

 same effect by illuminating different parts of the mirror 

 by different stars (since there is no particular virtue in 

 using atoms from the same star) ; actually the diffraction 

 pattern then obtained is not the same. The quantum 

 must be large enough to cover a ioo-inch mirror. 



But if this same star-light without any artificial con- 

 centration falls on a film of potassium, electrons will 

 fly out each with the whole energy of a quantum. This 

 is not a trigger action releasing energy already stored in 

 the atom, because the amount of energy is fixed by the 

 nature of thi light, not by the nature of the atom. A 

 whole quantum of light energy must have gone into the 

 atom and blasted away the electron. The quantum 

 must be small enough to enter an atom. 



I do not think there is much doubt as to the ultimate 

 origin of this contradiction. We must not think about 

 space and time in connection with an individual quan- 



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