At all events, it was for the dynamical reasons outlined above, and for these alone, that Newton was driven to absolute space. So far as science is concerned, this is the only aspect of Newton’s discoveries that is of interest. Newton, however, after he had established the existence if absolute space scientifically, proceeded to weld it in with his theological ideas, identifying it with the existence of the Divine Being. This was, of course, his privilege, but these further speculations were extra-scientific and were placed on a par with his writings on the horned beast of Babylon or the bottomless pit of the Apocalypse.
We may be quite certain that had absolute space been based on considerations of a purely philosophical, theological or theosophical character, it would never have survived the criticisms of subsequent scientists, some philosophical schools would have championed it, others have attacked it, but scientists without exception would have rejected it as possessing no empirical or rational foundation. That Newton’s great authority was insufficient to ensure the acceptance of his ideas is seen when we consider the fate of his corpuscular theory of light or of his relief in the impossibility of constructing an achromatic lens. But in the case of absolute space, we find that precisely because it was based on the facts of experience, it survived till quite recently, when, under the attacks of Einstein, it began to crumble. Even so, however, we must remember that it was only thanks to the very recent discovery of new facts, unknown to Newton, that Einstein was able to overthrow the absolute doctrine, and, furthermore, as we shall see, the cornerstone of Newton’s mechanics, the absolute nature of rotation, is far from having been destroyed even to-day.
As Weyl puts it when discussing the dynamical facts of motion: “It is just these facts that, since the time of Newton, have forced us to attribute an absolute meaning, not to translation, but to rotation.” Again, in the following passage, Euler expresses the same opinion, amplifying it by stating that the metaphysical nature of space and time is irrelevant to Newton’s stand. We read:
“We do not assert that such an absolute space exists.”
And again elsewhere:
“What is the essence of space and time is not important, but what is important is whether they are required for the statement of the law of inertia. If this law can only be fully and clearly explained by introducing the ideas of absolute space and absolute time, then the necessity for these ideas may be taken as proved.”
Euler’s very clear statement brings out the pragmatic and anti-metaphysical attitude towards reality which is characteristic of scientific thought. From a failure to understand the significance of scientific hypotheses, the philosophers of the idealistic school felt it their duty to do away with absolute space. Had their attacks been limited to Newton’s theological expressions of opinion, there would have been no reason to criticise their arguments, for all theological opinions can be either defended or attacked. But their failure to grasp the deeper scientific reasons that drove Newton to absolute space, led them to the erroneous belief that mechanical phenomena might be accounted for equally well under the hypothesis of the relativity of space and motion. As a matter of fact, they should have realised that the scientific hypothesis of absolute space is quite independent of our philosophical preference for realism or idealism. In classical science space was absolute in the scientific sense for idealists and realists alike. Indeed, many of Newton’s scientific successors viewed nature in an idealistic way; yet they never saw fit to refute Newton’s absolute space and motion on this score.
And now let us consider one of the typical objections that have beer presented against Newton’s absolute space. It is claimed that if, as Newton tells us, space is to be perfectly homogeneous and of infinite extent, it follows that position in space, hence motion through space must be meaningless, since there would be no means of distinguishing one position from another. Now an argument of this sort is fair enough so long as we consider purely amorphous mathematical space; it ceases to present the same force when we consider a space, such as Newton’s which is assumed to possess a rigid structure. To prove this point, lei us assume that space, though homogeneous, is bounded by a sphere In this case, the homogeneity of space would not interfere (according to the critic) with the reality of motion, for we could always refer motion to the boundary.
Suppose, then, that the boundary were to be removed to infinity: would motion through space gradually lose all meaning? It appears quite unnecessary to adopt any such view. There is no reason why a local effect should not be developed by the passage of matter through a rigid homogeneous space, regardless of whether the boundary be at a finite distance or at infinity. To put it in a very crude way, there is no reason why the individual points of absolute space should not realise the presence or absence, hence the passage, of lumps of matter; and so the boundary would have no rôle to play.
Where motion would appear meaningless would be if we assumed matter to be continuous (not atomic) and considered a material rod of infinite length gliding along the straight line it defined. In this case (from the standpoint of the points of space) the motion of the rod might escape detection. In the general case, however, where lumps of matter, hence discontinuity (regardless of the molecular hypothesis), are concerned, there appears to be no reason to reject absolute motion through empty space on the ground that motion through a homogeneous and infinite medium would be logically meaningless. Furthermore, how the critic, having convinced himself that motion must be relative, proposes to account for the physical fact that of two flywheels in relative rotation, one will burst and the other remain unaffected, baffles the understanding. Either we must assume, with Mach, that the material universe exerts a definite causal influence on a body in rotation relative to it, or else we must accept Newton’s absolute space.