Newton created his mechanics as something between an anti-atheist manifest and a treat of theology. Poor Sir Isaac, he had no idea he was gifting civilization with a major contribution to a godless world.
Most of people think of space as an empty volume where things stand. Take all things out, the space would still be there.
René Descartes wasn’t most of people. For him, space was only a relation between things, with no existence whatsoever. Thus, motion is always relative, as there is no absolute space framing the world.
Moreover, Descartes believed that the universe was composed of two kinds of things, those with extension (as the matter) and those without extension (as the spirit).
He really never managed to conciliate this duality. He put quite a lot of effort to explain how a soul interacts with its body, as a kind of very thin air pumped from the pineal gland through the nerves. He was comically wrong even for the feeble standards of the physiological knowledge of his time.
But one thing Descartes got right: for him, physics was purely mechanical. He believed in an autonomous evolution of the universe following dynamical physical laws. He didn’t know these laws well, but he was sure they existed.
Many philosophers in the 17th century were not happy at all with this Cartesian view. They were afraid that this autonomous evolution would leave no place for divine interventions, magic, miracles, alchemical transformations.
Isaac Newton was among these critics. It was around 1670 when Newton, still a young fellow in Cambridge, expressed his criticism to Descartes’ physics:
“Indeed, we find no other reason for atheism than this notion of bodies having a complete, absolute and independent reality in themselves, (…)” Isaac Newton, De Gravitatione et Aequipondio Fluidorum.
Newton understood space not as a relation between things, but as a necessity for the existence of all things—God, minds, bodies—as everything that exists must exist somewhere.
For Newton, this was so self-evident that it should even be the basis to determine the properties of space:
“(…) So the quantity of existence of God is eternal in relation to duration and infinite in relation to the space in which he is present. (…) Space is eternal in duration and immutable in nature, and this because it is the emanant effect of an eternal and immutable being.” Isaac Newton, De Gravitatione et Aequipondio Fluidorum.
Cutting to the chase, Newton was saying that
- God is infinite and eternal.
- God must exist in the space.
- Therefore, the space must be infinite and eternal.
In a perfect formal syllogism, Newton believed that he had proved that space is absolute. Many years later, when he developed his mechanics, this concept of absolute space was the cornerstone on where he built his laws of motion.
The perception of Newton as a Christian knight saving the world from the atheists remained for a while. In 1738, in one of the most influential popularization books on Newton’s work, Voltaire wrote:
“It needs much for that the alleged physical principles of Descartes could thus drive the mind to the knowledge of his Creator. (…) I say that I have known many people whose Cartesianism drove them to only admit God as the immensity of things and that, in contrast, I never met any Newtonian who were not theist in the most rigorous sense.” Voltaire, Éléments de la philosophie de Newton.
To be fair, Newton wasn’t creating all this from his mind. His conception of space as a necessity for God’s existence was shared by his professors and senior fellows in Cambridge, like Henry More and Isaac Barrow. In fact, Newton’s definitions of space, body, rest and motion in de Gravitatione are almost literal copies from those in the Syntagma Philosophicum by Pierre Gasssendi.
These natural philosophers, usually referred as neoplatonics, believed in a kind of Spirit of Nature, which could explain phenomena as the gravity or the magnetism. According to More, the Spirit of Nature would be a manifestation of God’s will on matter. It isn’t arbitrary, though. It manifests always in the same way for similar situations. Thus, apart of the crap theology, such Spirit of Nature isn’t so far from what we call Laws of Physics.
Maybe what avoided that Newton drowned himself into useless theological studies as many other philosophers from his time was a health mix of mathematical skills with a tendency to experimentation, mostly expressed in his optical and alchemical studies. On this side, the experimental philosophy of Robert Boyle, with whom Newton corresponded until Boyle’s death, was a welcome influence.
Newton and the neoplatonics were fighting a war against the exclusion of God from natural philosophy. It wasn’t only about Descartes. Thinkers like Leibniz, Spinoza, Hobbes were developing systems of world where nature evolved autonomously; where the soul was understood as a physical attribute; where the Bible didn’t contain literal truths; where God was a secondary element, maybe even an illusion.
Newton had no idea of how his mechanics—thought as a proof of God’s manifestation in the world—would backfire and become during the next 300 years the main tool for this secular understanding of nature.
We could even say that Newton wrote straight with crooked lines.
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