I refrain from translating the rest of this lengthy argument, based upon the treacherous foundation of Aristotelian Physics. See Aristotle, Physics, vii, viii Metaphysics, xi, 7. Whoever will derive an argument for the divine existence from the mechanism of the heavens must take his principles from Newton, not from Aristotle. Besides Motion he must take account of Force and Energy, not to say of Cosmic Evolution. He must know not only the motion of impact, as when a row of ninepins knock one another down from a push given to the first, but also the motion that is set up by gravitation. Aristotle knew nothing of gravitation; and only half knew the inertia of matter declared by Newton's first law of motion. He supposed that motion, of its own nature, not only needed starting but also needed continual keeping up by some continually acting cause. He did not know that the question with a moving body is, not what there is to keep it in motion, but what there is to stop it.
It would be a mistake to represent the Aristotelian argument of the Prime Mover as referring to some primitive push, or some rotary motion started in the primitive nebula, at the first creation of matter. Matter, to Aristotle, to Plato, and to the Greeks generally, is eternal, not created. I need hardly add that between an immovable Prime Mover and a Personal God a wide gulf intervenes which Aristotle does not bridge over. See however Chapter XXIII of this Book.
The whole idea of a Prime Mover has vanished from modern physics. The whole universe, as we know it, is a congeries of sun-and-planet systems -- some of them apparently still in process of formation -- arranged possibly in the shape of a huge convex lens. These bodies act and react on each other. And besides these molar motions there are also molecular motions quite as real. The causes of these motions are innumerable forces. The study of them carries us back to consider the 'primitive collocation' of the forces of the universe, a collocation whereby they were arranged in a 'position of advantage,' so that out of their interaction has ensued this orderly world, and in it our earth, fit habitation for living things. On this 'primitive collocation,' Father Bödder writes (Natural Theology, p. 56): "Although we have nothing to say against the assumption made by astronomers, that our cosmic system resulted from the condensation and division of a primitive rotating nebula; yet we cannot admit this nebula without observing that there must have been a first arrangement of the material elements which constituted it, one which already contained the present system, or else the said system could never have resulted from it. Now this first arrangement was neither the effect of the forces of matter, nor was it essential to matter. . . . Therefore if we would explain the origin of that system without violation of reason, we are forced to say that its first beginning, nebular or otherwise, is due to an intelligent cause." To this effect he adds this quotation from Huxley (Life and Letters of Charles Darwin, II, 201, 202): "The teleological and the mechanical views of nature are not, necessarily, mutually exclusive. On the contrary, the more purely a mechanist the speculator is, the more firmly does he assume a primordial molecular arrangement of which all the phenomena of the universe are consequences, and the more completely is he thereby at the mercy of the teleologist, who can always defy him to disprove that this primordial molecular arrangement was not intended to evolve the phenomena of the universe."
Omne quod movetur ab alio movetur, I translate "Everything in motion is put and kept in motion by another": such is the sense of St Thomas and of Aristotle. The ab alio however is not in Aristotle. His words are: "Everything in motion must be put and kept in motion by something" (Phys. vii, 1); and he adds: "Everything in local motion is moved either by itself or by another" (Physics, vii, 2) Things that had souls he thought were moved by themselves, and especially the heavenly bodies, which were guided by some sort of animating soul in perpetual circular motion. St Thomas (B. III, Chap. LXXXVII, in the Latin) has his doubts as to the heavenly bodies being animated. He considers however (B. III, Chap. LXXXII) "that sublunary bodies are ruled by God through the heavenly bodies."
Taking 'movement' for 'local motion,' the argument of the Prime Mover, for a modern mind, resolves itself into the question of 'primitive collocation.' Some collocation is presupposed to every mechanical problem. 'Why this collocation rather than that?" is a question answerable only either by a regressus in infinitum (Q.E.A.) or by an invocation of Mind and Design. The argument however may, avail itself of a wider meaning of motus, namely, change; and contend that, at the back of the changes apparent everywhere, there must he some Changeless Being, author and guide of this changing universe. So presented, it is sometimes called the 'argument from contingent to necessary being.'
Of God and His Creatures: 1.13