5 - Motion and change of distance

Summary

Introduction

Sometimes things move; sometimes they stay in the same place. These are old, simple and primitive thoughts. Even so, they pervade the most subtle and sophisticated modern physical theories. I will discuss the impact of relativity theory on these old simple ideas. I hope to highlight some simple, basic presuppositions in classical thinking about rest and motion that have turned out false and which are still widely thought to be obvious. I have to say a little about coordinate systems for spacetimes or frames of reference corresponding to them. But I look at them only to draw some lessons that might be applied to the older, simpler ideas. I try to give a rational reconstruction of our simplest ideas of rest and motion; so I offer speculation rather than proof. Though I am guessing, I hope the guess is educated enough to shed some light and hold some interest.

I shall begin with John Locke, an author whose thought has much influenced C. B. Martin. Martin taught me to admire Locke and his virtues of realism, or rather, perhaps, of ontic seriousness. If this paper succeeds it will have something of those virtues and reflect Charlie Martin's benign influence, as so much of the writing of his students does. Neither Locke nor Martin has an extensive theory of motion, but Locke has such sensible things to say about it, even though what he said has turned out false. And there was no way Locke could have foreseen this.