The evolution of scientific thought from Newton to Einstein

by A. D'Abro

A second argument presented by More has no greater merit. A simplified form of it would be as follows: Two trains pass each other, moving in opposite directions. If motion were relative, we could maintain that, as referred to the first train, a telegraph pole was speeding north, while, as referred to the second train, it was moving south. As the pole cannot be moving north and south all at the same time, relative motion cannot exist, and the pole must therefore be at rest in absolute space; whence More concludes that space must be absolute.

It is scarcely necessary to state that Newton’s arguments were of a totally different calibre, and even to-day it appears extremely difficult to refute them in their entirety. Newton was one of the earliest exponents of the scientific method. As he tells us himself:

“For the best and safest method of philosophising seems to be, first, diligently to investigate the properties of things and establish them by experiments, and then later seek hypotheses to explain them.... For hypotheses ought to be fitted merely to explain the properties of things and not attempt to predetermine them except so far as they can be an aid to experiments.”

These statements of Newton appear perfectly clear and merely reflect the spirit of scientific procedure. It has been held, however, by numerous philosophers who have written on the “metaphysics of science” that Newton departed from his avowed empirical method when he formulated his theory of absolute space and time. It is scarcely credible that any one at all conversant with mechanics could ever maintain an opinion of this sort, but as it appears to be widespread in certain quarters, it may be of interest to examine its claims.

We may state that the question is one of the utmost importance; for were it established that Newton’s absolute motion did not appear to be imposed by the dynamical facts of mechanics, it would be impossible to understand the philosophical significance of Einstein’s cylindrical universe.

Let us then return to Newton’s exposition. He starts out in the Principia by expressing his belief in absolute immovable space everywhere the same, and in absolute time. These statements are followed by a description of the experiment of the rotating bucket of water and others of a kindred nature. According to the critic, Newton evidently intended absolute space and time to be taken in the light of necessary presuppositions. But apart from the fact that in the order written the statements on absolute space and time precede any reference to experiment, there appears to be no basis for any such belief. Here we must remember that Newton was a scientist writing for the benefit of fellow scientists; and it is a method commonly followed by mathematicians to state a proposition and then show why the statement must be accepted as correct. Although the statement of the proposition precedes the proof, no one would be misled into believing that we were asked to accept the proposition in the light of a philosophical presupposition which might lead to controversy, and then regard the demonstration as an argument of secondary importance. And it is the same with absolute space and time. Just as Euclid follows up his statement of a geometrical proposition by a proper demonstration, so does Newton proceed to demonstrate the existence of absolute space by showing that absolute rotation is revealed by a number of experiments (by the experiment of the rotating bucket of water, among others). Had manifestations of absolute motion been unknown to Newton, had absolute motion eluded experiment, there never would have been any reason for him to postulate its existence in physics; and as a result its direct consequences, namely, absolute space and time, would have been reduced to meaningless hypotheses and no longer to necessary conclusions.

As a matter of fact, Newton mentions explicitly two methods of presentation which may be adhered to. Thus, we read in his Opticks:

“By this way of analysis we may proceed from compounds to ingredients, and from motions to the forces producing them; and in general from effects to causes, and from particular causes to more general ones, till the argument end in the most general. This is the method of analysis: and the synthesis consists in assuming the causes discovered, and established as principles, and by them explaining the phenomena proceeding from them, and proving the explanations.”[147]

As an illustration of the two methods, we may consider the case of the law of gravitation. Either we may say: The planets have been found to describe conics round the sun, with certain definite motions, and in order to account for these motions we must assume the existence of a solar attraction; or else we may say: The law of gravitation is such and such, and the proof of it is that the planets describe conics round the sun. From the standpoint of neatness of presentation, the deductive method is preferable, but from the standpoint of the chronological order of discovery, the first method describes the situation.

Let us not, then, waste any more time in dwelling on these perfectly obvious points which Newton explains time and again in answer to the criticisms of his contemporaries. The important point to decide lies elsewhere. Is it true that, as Newton imagined, the dynamical facts of motion, established empirically and illustrated in the experiment of the rotating bucket render absolute motion, hence absolute space, inevitable? Here we may be permitted to point out that a question of this sort must be left for scientists, trained in the school of rigorous thinking, to decide. It is indeed obvious that critics, like Berkeley and Kant, who possessed such hazy ideas of mechanics as to confuse velocity and acceleration, momentum and force, were too poorly equipped to express any opinions of value.[148] Turning, then, to the verdict of subsequent scientists, men of the calibre of Euler, Laplace and Poincaré, we find the conclusion unanimous. Absolute space is recognised by all as the simplest physical hypothesis that will account for the observed mechanical facts. To that extent it corresponds to reality. Even Einstein, to whom the downfall of the Newtonian position is due, recognises that with the facts at Newton’s disposal, his solution was the only one that could be defended.