SUMMARY 35 



four dimensions. We have been confronted with some- 

 thing not contemplated in classical physics — a multi- 

 plicity of frames of space, each one as good as any 

 other. And in place of a distance, magnetic force, 

 acceleration, etc., which according to classical ideas 

 must necessarily be definite and unique, we are con- 

 fronted with different distances, etc., corresponding to 

 the different frames, with no ground for making a choice 

 between them. Our simple solution has been to give 

 up the idea that one of these is right and that the others 

 are spurious imitations, and to accept them en bloc; so 

 that distance, magnetic force, acceleration, etc., are 

 relative quantities, comparable with other relative quan- 

 tities already known to us such as direction or velocity. 

 In the main this leaves the structure of our physical 

 knowledge unaltered; only we must give up certain 

 expectations as to the behaviour of these quantities, and 

 certain tacit assumptions which were based on the belief 

 that they are absolute. In particular a law of Nature 

 which seemed simple and appropriate for absolute quan- 

 tities may be quite inapplicable to relative quantities and 

 therefore require some tinkering. Whilst the structure of 

 our physical knowledge is not much affected, the change 

 in the underlying conceptions is radical. We have trav- 

 elled far from the old standpoint which demanded 

 mechanical models of everything in Nature, seeing that 

 we do not now admit even a definite unique distance 

 between two points. The relativity of the current scheme 

 of physics invites us to search deeper and find the abso- 

 lute scheme underlying it, so that we may see the world 

 in a truer perspective. 



