Space and Time in Classical Mechanics
Section Three
Einstein briefly touches on the problem of space and time in classical mechanics. How should we make sense of the notions of space and time in classical mechanics? Here, Einstein clearly has the notions of "absolute space" and of "absolute time" in his mind.
... we entirely shun the vague word "space", of which we must honestly acknowledge, we cannot form the slightest conception, and we replace it by "motion relative to a practically rigid body of reference."
... With the aid of this example it is clearly seen that there is no such thing as an independently existing trajectory ..., but only a trajectory relative to a particular body of reference. ...
These data must be supplemented by such a definition of time that, in virtue of this definition, these time-values can be regarded essentially as magnitudes ... capable of observation. (pp. 10-11)
Einstein's argument may look quite attractive. But the matter is not as simple as this. Is the similar argument applicable to circular motions, as Newton pointed out a long time ago? Moreover, the stone's motion in our example is a motion within a gravitational field (or an accelerated motion); thus "space" and "time" may not be so easily removable.
See my Commentary on Newton's Scholium.
Last modified, April 18, 2002. (c) Soshichi Uchii
suchii@bun.kyoto-u.ac.jp
