Chapter III 



TIME 



Astronomer Royal's Time. I have sometimes thought it 

 would be very entertaining to hear a discussion between 

 the Astronomer Royal and, let us say, Prof. Bergson on 

 the nature of time. Prof. Bergson's authority on the 

 subject is well known; and I may remind you that the 

 Astronomer Royal is entrusted with the duty of finding 

 out time for our everyday use, so presumably he has 

 some idea of what he has to find. I must date the 

 discussion some twenty years back, before the spread of 

 Einstein's ideas brought about a rapprochement. There 

 would then probably have been a keen disagreement, 

 and I rather think that the philosopher would have had 

 the best of the verbal argument. After showing that 

 the Astronomer Royal's idea of time was quite non- 

 sensical, Prof. Bergson would probably end the dis- 

 cussion by looking at his watch and rushing off to catch 

 a train which was starting by the Astronomer Royal's 

 time. 



Whatever may be time de ]ure } the Astronomer 

 Royal's time is time de facto. His time permeates every 

 corner of physics. It stands in no need of logical de- 

 fence; it is in the much stronger position of a vested 

 interest. It has been woven into the structure of the 

 classical physical scheme. "Time" in physics means 

 Astronomer Royal's time. You may be aware that it is 

 revealed to us in Einstein's theory that time and space 

 are mixed up in a rather strange way. This is a great 

 stumbling-block to the beginner. He is inclined to say, 

 "That is impossible. I feel it in my bones that time and 



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