68 THE RUNNING-DOWN OF THE UNIVERSE 



the second law of thermodynamics — to put some sense 

 into the world. It opens up a new province of know- 

 ledge, namely, the study of organisation; and it is in con- 

 nection with organisation that a direction of time-flow 

 and a distinction between doing and undoing appears for 

 the first time. 



Time's Arrow, The great thing about time is that it goes 

 on. But this is an aspect of it which the physicist some- 

 times seems inclined to neglect. In the four-dimensional 

 world considered in the last chapter the events past and 

 future lie spread out before us as in a map. The events 

 are there in their proper spatial and temporal relation; 

 but there is no indication that they undergo what has 

 been described as "the formality of taking place", and 

 the question of their doing or undoing does not arise. 

 We see in the map the path from past to future or from 

 future to past; but there is no signboard to indicate that 

 it is a one-way street. Something must be added to 

 the geometrical conceptions comprised in Minkowski's 

 world before it becomes a complete picture of the world 

 as we know it. We may appeal to consciousness to suffuse 

 the whole — to turn existence into happening, being into 

 becoming. But first let us note that the picture as it 

 stands is entirely adequate to represent those primary 

 laws of Nature which, as we have seen, are indifferent 

 to a direction of time. Objection has sometimes been 

 felt to the relativity theory because its four-dimensional 

 picture of the world seems to overlook the directed 

 character of time. The objection is scarcely logical, for 

 the theory is in this respect no better and no worse than 

 its predecessors. The classical physicist has been using 

 without misgiving a system of laws which do not 



