SCIENCE, YESTERDAY, TODAY, TOMORROW — SWANN 233 



THE PRINCIPLE OF PKEDETERMINATION 



In tliis evaporation of some of the elements wliicli were part and 

 parcel of the intuitive thinking of a hundred years ago, there yet re- 

 mained one principle wliich man was loath to discard. This principle 

 invoked the idea that, at any rate as regards the inanimate world, that 

 which is happening now determines that which wall happen just a 

 little later. And that which happens a little later determines that 

 which will happen still a little later, and so on, ad infinitum. It is 

 the principle of predetermination. It had its most explicit exempli- 

 fication when science, through the activities of Newton and his con- 

 temporaries, described the motions of the heavenly bodies in terms 

 of the now well-known laws of astronomy. The concentration was 

 on what we call the laws of motion of the bodies. These took the 

 form of what are called the differential equations of motion. How- 

 ever, it is sufficient to say that these laws were such that, if you spec- 

 ify what exists now, they tell you what will be found just now — 

 at the next moment, that is — and so on, ad infinitum. If you asked 

 what must be expressed now, the answer, in terms of Newton's laws, 

 is to the effect that you must assign a position and velocity for each 

 one of the bodies whose motion you wish to discuss. In terms of 

 these positions and velocities, the future is determined completely 

 in terms of the present. In order that you should not derive too 

 much comfort from this statement, however, I must remark that if 

 you should specify the positions and velocities of the bodies a thou- 

 sand years hence, those laws will equally well serve to determine 

 where they are now. It is hardly polite to destroy your comfort in the 

 belief that the present determines the future by asking you to accept 

 a doctrine to the effect that the future also determines the present. I 

 once worried myself about the problem of why, if I am to understand 

 memory in terms of the present as determined by the past, I cannot 

 also remember the future, if the laws work both ways. 



The great success of the classical astronomy of Newton and the 

 discovery of the atomic nature of matter and of the fact that the atoms 

 themselves are composed of what we call particles, made it almost in- 

 evitable that man should try to understand atoms and their doings in 

 a crude way by picturing them as models of the solar system itself on 

 an enormously reduced scale ; and so, some three-quarters of a century 

 ago, there arose atomic theories based on this idea and carrying with 

 them, therefore, in principle, the laws of predetermination. Perhaps 

 I should pause for a moment to state what, in the last analysis, is indi- 

 cated by the acceptance of such a principle. The matter is illustrated 

 by the story of a man and his slave. 



It appears that there was an ancient noble whose belief in predeter- 

 mination was very firm. And the noble had a slave who stole some of 



