PRINCIPLE OF INDETERMINACY 221 



Suppose for example that we wish to know the posi- 

 tion and velocity of an electron at a given moment. 

 Theoretically it would be possible to fix the position with 

 a probable error of about 1/1000 of a millimetre and 

 the velocity with a probable error of 1 kilometre per 

 second. But an error of 1/1000 of a millimetre is large 

 compared with that of some of our space measurements; 

 is there no conceivable way of fixing the position to 

 1/10,000 of a millimetre? Certainly; but in that case it 

 will only be possible to fix the velocity with an error of 

 10 kilometres per second. 



The conditions of our exploration of the secrets of 

 Nature are such that the more we bring to light the 

 secret of position the more the secret of velocity is 

 hidden. They are like the old man and woman in the 

 weather-glass; as one comes out of one door, the other 

 retires behind the other door. When we encounter un- 

 expected obstacles in finding out something which we 

 wish to know, there are two possible courses to take. It 

 may be that the right course is to treat the obstacle 

 as a spur to further efforts; but there is a second 

 possibility — that we have been trying to find some- 

 thing which does not exist. You will remember that 

 that was how the relativity theory accounted for the 

 apparent concealment of our velocity through the 

 aether. 



When the concealment is found to be perfectly sys- 

 tematic, then we must banish the corresponding entity 

 from the physical world. There is really no option. 

 The link with our consciousness is completely broken. 

 When we cannot point to any causal effect on anything 

 that comes into our experience, the entity merely becomes 

 part of the unknown — undifferentiated from the rest of 

 the vast unknown. From time to time physical discover- 

 ies are made; and new entities, coming out of the un- 



