On occasion of Galileo's conflict with the Inquisition the issue of absolutism versus relativity became clear as far as the general problems of the truth of science and of the truth of speculation and religious symbolization are concerned. These general problems were formidable. Nevertheless, they might have been cleared up quickly, and they were cleared up in principle by Leibniz.
The obstacle to a rapid advancement toward a theory of relativity in physics arose from the internal problems of the new science. This obstacle was present already in Galileo's theory of motion, but it became fully visible only with Newton's formulation of the general law of gravitation and the consequent elaboration of a general theory of physics in the Principia Mathematica. Newton found it necessary to assume the existence of absolute space and of absolute motion. . . . For it may be that there is no body really at rest, to which the places and motion of others may be referred. . . . Newton envisages absolute space as an absolute order of places; this order of places is a primary system to which motion ultimately can be referred. Only translations [i.e.,extractions by the mind] out of those places are truly absolute motions. Since, however, these absolute places cannot be observed by the senses, the question arises as to what purpose we should assume their existence? This delicate question Newton covers by his vague reference to the philosophical disquisitions that make such deeds necessary.
Embarking on such philosophical disquisition, Newton finds that rest and motion, absolute and relative, can be distinguished by their properties, causes, and effects. It is a property of rest, that bodies really at rest do rest in respect to one another. This definition of rest holds good in spite of the fact that such absolutely resting bodies, if they exist at all, may be found only in the region of the fixed stars, or even beyond that region, whereas absolute rest cannot be determined from the positions of bodies in our region.
While empirical observation does not show any bodies at absolute rest, Newton nevertheless introduces this concept. Here we have tracked down the first serious reason that would induce a physicist to make the assumption of absolute space: he needs the assumption for the purpose of defining rest. And he needs this concept in order to maintain the first law of motion that every body continues in its state of rest, or of uniform motion in a [straight] line, unless it is compelled to change that state by forces impressed upon it. Without the assumption of absolute space no meaning can be given to the notion of absolute rest, and absolute rest seemed to Newton, as it did to Galileo, a fundamental experience that could not be dispensed with in the formulation of the first law of motion.
[While the theoretically indicated course would have been to drop the concepts of absolute time and space, Newton refused to do so, for he believed, following the Cambridge Platonist Henry Moore, that the concept of absolute space protected the notion of God as the divine substance that manifests its own infinity in the double infinity of absolute space and time, thereby refuting Descartes's identification of extension and matter that would have materialized space.]
. . . . The intellectuals who absorbed the Newtonian system, in particular after its popularization through Voltaire, were satisfied with Newton's recognition of absolute space and could dispense with his religious motivation. The system of the Principia was complete with the first edition; the Scholium Generale [Newton's commentary] of the second edition added nothing to empirical physics. Here was a system of the world, legitimated by the genius of the man whose name at this time carried more authority in the intellectual world than anybody else's. And this system showed the world as consisting of nothing but matter obeying a uniform law. The theory of absolute space sealed this system ontologically against God, and by virtue of this character, the Newtonian system became socially effective. The well-intentioned theory of absolute space had resulted in precisely the disorder it had intended to avert.
. . . .The Scholium Generale had announced the precept hypotheses non fingo: whatever is not deduced from the phenomena is to be called an hypothesis; and hypotheses, whether metaphysical or physical, whether of occult qualities or mechanical, have no place in experimental philosophy. The assumption of absolute space was a glaring contradiction to this declaration; certainly this fundamental hypothesis was not deduced from the phenomena. We shall not be surprised, therefore, when now we turn to Berkeley and his criticism of Newton's theory, to find some pungent remarks concerning the boundaries between physics and metaphysics.