LIGHT AND THE QUANTUM 129 



same instant no corpuscle of light can reach 

 that spot. As we meditate upon this mysterious 

 phenomenon there constantly recurs to us the 

 scarcely credible thought that in some way an 

 atom in the source can foretell before it emits 

 its corpuscle of light whether one or both of 

 the mirrors are going to be uncovered. Ridicu- 

 lous as it may sound, this is essentially the 

 theory that I am going to offer. 



It is generally assumed that a radiating body 

 emits energy quite regardless of any near or 

 distant objects which may ultimately absorb it. 

 In other words, it is said to radiate "into 

 space." I shall make the contrary assumption 

 that an atom never emits light except to an- 

 other atom, and in this process of exchange the 

 two atoms play quite coordinate roles, so that 

 one can no longer be regarded as an active 

 agent and the other as an accidental and pas- 

 sive recipient. 



I do not wish to minimize the conflict between 

 this view and that of common sense. The light 

 from a distant star is absorbed by a molecule of 

 chlorophyl which has recently been produced in 

 a living plant. We say that the light from the 

 star was on its way toward us a thousand years 

 ago. What rapport can there be between the 



