PROBABILITY AND ENTROPY 157 



tion of steady flow such as a miUer experiences 

 as his wheel is turned by the constant current 

 of a mountain stream. He does not ask where 

 the water comes from. Nor do we yet know the 

 source of this cosmic energy. 



Is this the whole basis of our idea of one-way 

 time.? We have observed that the notion of a 

 flow of time in one direction seems to be derived 

 partly from the unidirectional sequence in our 

 own consciousness, and partly from the extreme 

 dissymmetry between past and future in the 

 world about us. When we see a boat upon a calm 

 sea we know the direction of its motion by the 

 wake that it leaves behind. So our own thoughts 

 leave a wake of memories, and here and there we 

 seem to see glimpses of a similar phenomenon 

 among other living creatures. Again, when we 

 meditate upon those cataclysmic events which 

 make it so difficult to think of time turned back- 

 ward in its flight, we realize that not all, it is 

 true, but certainly the most striking examples 

 are furnished by the sudden demolition of 

 highly complex structures slowly built up by 

 man or by other living things. All this leads us 

 to wonder whether in the world of animate 

 nature there may not be phenomena which 



