The evolution of scientific thought from Newton to Einstein

by A. D'Abro

; whereas the inhabitants of the upper disk would note that the stars appeared to be fixed. If our observers were firmly convinced of the relativity of motion, arguing that absolute motion in space was inconceivable, they might attempt to search for the cause of all these unsymmetrical phenomena in the state of relative rotation or rest of the stars.

But unless they were able to attribute a definite causal influence to this star rotation, the solution would be no solution at all. Although it now appears that they might have guessed right, yet in Newton’s time it would have been quite impossible to justify this attitude; not for philosophical reasons, but on account of the still undeveloped condition of mathematics and physics. This solution being denied them, then would be no other recourse but to appeal boldly to suprasensible absolute space and to recognise that the lower disk was rotating anti-clockwise in absolute space with an angular velocity

, whereas the upper disk and stars were at rest. Henceforth, the causal influence would be attributed to the structure of absolute space itself; and the discrepancies noted above would be accounted for with perfect mathematical precision. (This illustration is, of course, merely an alternative way of presenting Newton’s experiment of the bucket of water.)

We are again driven to the same conclusions when we consider the problem of inertia. If here, there and everywhere are one and the same thing, why do we have to expend effort to move a body from here to there?

Again, if all motion were relative, the only significant type of motion would be motion relative to a frame of comparison. But then, if, as referred to a certain frame, the path of a free body were straight, with respect to another frame it would be crooked or curved. In other words there would be no sense in discussing the body’s absolute course, since by an appropriate choice of a frame of reference, we could make it any thing we pleased. Incidentally, the law of inertia would thereby be deprived of all meaning.

Consider, then, a number of free bodies taken at random, in relative motion with respect to one another. These bodies might ignore their mutual presences entirely (assuming even they were gifted with consciousness). If, therefore, a frame of reference were selected, there would be no reason to suppose that, as referred to this frame, the motions o the various bodies should be in any wise connected. And yet the law of inertia, deduced from experiment, proves that our anticipations would be incorrect.

For if we select a certain privileged frame, an inertial or Galilean frame, all the bodies will be found to describe straight lines with constant velocities as though there existed some secret understanding among them. Is it our frame that imposes this understanding on the unintelligent bodies? Do the bodies see the frame and agree to behave in the same way with respect to it? But the frame might be millions of miles away; furthermore, it only exists as a result of our free will; and the notions of the bodies with respect to one another would obviously remain the same even were some new frame to be chosen, or several different mes to be selected simultaneously. If we refuse to agree that it is absolute space itself which directs and guides the free bodies and which is thus the cause of this wonderful pre-established harmony, where else shall we look for a regulating cause? If we give up the search we fall back into the miraculous. Shall we appeal to the stars once more? But we have said that in Newton’s day this was impossible. There appears to be but one solution, and that is absolute space.

If we summarise all these results we see that whether we like it or not, the dynamical facts of motion and the law of inertia render an escape from absolute motion and space impossible. To be sure, as Einstein tells us, Newton might just as well have called his absolute space “Ether,” or anything else. The essential point was that something acting as an absolute background appeared to be required in order to account for the undeniable reality of centrifugal force generated by certain types of motion.