80 THE ANATOMY OF SCIENCE 



ings of a clock. The statement that OA, OB 

 and OC are of equal length is equivalent to the 

 statement that if the whole figure represents an 

 ordinary space-time map, and if OA, OB, OC 

 are the space-time paths of three clocks, all of 

 which struck eight at the point O, then if the 

 first strikes nine at A, the second will strike 

 nine at B, and the third at C. 



Let us pause for a moment to consider the 

 effect upon our concept of time of identifying 

 kinematics with a geometry. In a geometry it 

 would be ridiculous to find a certain theorem 

 true regarding a geometrical figure, but false 

 if the figure is turned upside down. There can 

 be no such dissymmetry between up and down. 

 So in a pure kinematics there can be no dis- 

 symmetry between past and future. Indeed, if 

 we consider the solar system and the events in 

 space and time that we call eclipses, we know if 

 astronomical measurements are made over a 

 period of years we can calculate the eclipses of 

 one thousand years hence; but we can also cal- 

 culate the eclipses of one thousand years ago, 

 and with precisely the same accuracy. On the 

 other hand, in daily life we recognize a remark- 

 able dissymmetry between past and future ; wit- 



