226 THE NEW QUANTUM THEORY 



There is a doctrine well known to philosophers that 

 the moon ceases to exist when no one is looking at it. 

 I will not discuss the doctrine since I have not the least 

 idea what is the meaning of the word existence when 

 used in this connection. At any rate the science of as- 

 tronomy has not been based on this spasmodic kind of 

 moon. In the scientific world (which has to fulfil func- 

 tions less vague than merely existing) there is a moon 

 which appeared on the scene before the astronomer; it 

 reflects sunlight when no one sees it; it has mass when 

 no one is measuring the mass; it is distant 240,000 miles 

 from the earth when no one is surveying the distance; 

 and it will eclipse the sun in 1999 even if the human race 

 has succeeding in killing itself off before that date. The 

 moon — the scientific moon — has to play the part of a 

 continuous causal element in a world conceived to be all 

 causally interlocked. 



What should we regard as a complete description of 

 this scientific world? We must not introduce anything 

 like velocity through aether, which is meaningless since 

 it is not assigned any causal connection with our ex- 

 perience. On the other hand we cannot limit the de- 

 scription to the immediate data of our own spasmodic 

 observations. The description should include nothing 

 that is unobservable but a great deal that is actually 

 unobserved. Virtually we postulate an infinite army of 

 watchers and measurers. From moment to moment they 

 survey everything that can be surveyed and measure 

 everything that can be measured by methods which we 

 ourselves might conceivably employ. Everything they 

 measure goes down as part of the complete description 

 of the scientific world. We can, of course, introduce 

 derivative descriptions, words expressing mathematical 

 combinations of the immediate measures which may give 



