PROBABILITY AND ENTROPY 145 



his illuminating essays. The one part, which we 

 may call one-way time, is that unidirectional 

 sequence which we find in our own consciousness 

 and memory, and also in the world of appar- 

 ently irreversible phenomena. The other part, 

 which we may call two-way time, is one in which 

 future and past are symmetrical. It is purely 

 and simply one of the dimensions in the space- 

 time manifold of kinematics. 



This distinction, however, means that for one 

 kind of physics, mechanics, we must use one of 

 these concepts, and for another branch of phys- 

 ics, thermodynamics, we must use the other. I 

 propose to show that for all physical science 

 only one time-concept is necessary, namely, the 

 symmetrical or two-way time. But before doing 

 so let us proceed a little further with the dis- 

 cussion of the second law of thermodynamics. 



Do you believe in miracles.'^ Let us consider 

 a box with a one-gram weight resting on its 

 floor. Let us place this box in a bath maintained 

 at an extremely constant temperature, we will 

 say 65° F., and let the whole be protected by the 

 most perfect mechanism that we can think of to 

 shield it from external jars. Let us, in other 

 words, shut it off from all external influences, 

 lea\dng only a small hole through which we may 



