The Gravity of Belief

When religion affects science.

Image: Copernicus. Pinterest.com

Science and religion appear to operate independently, but the story of the development of our understanding of gravitation shows that there is an invisible pull that invariably attracts them. 

Gravity is so deeply embedded in our conceptualization of the universe that a scientific worldview without it seems absurd. But the existence of gravitation is far from obvious because there are two seemingly unrelated sets of observable phenomena it explains—objects near us fall straight down to the ground, and heavenly bodies rise and set in the sky night after night forever. 

If an object moves, Aristotle reasoned, then there is something in the body that wants to be in a different place. What an object wants would be a function of its chemical composition, so earthly matter that moves in a straight line and orbiting entities in space must be made of different substances. So, we need physics to explain the terrestrial objects’ motions and astronomy for the rest. Different types of motion meant different explanations, which thereby require different sciences.

Rejecting this was the point of Isaac Newton’s infamous apple story. During a pandemic, Newton was sent home to the farm from Cambridge. They didn’t have Zoom, so he sat alone under an apple tree looking at the moon, wondering what keeps it in its orbit around the Earth when an apple fell to the ground in front of him. At that moment, he claimed, he realized that the reasons for these different motions were the same, there was a single cause for both, and the idea of gravity was born.

Except, of course, that it wasn’t.

Descartes’ Catholic Vortices

Image: Descartes, mentalfloss.com

A unified theory explaining both celestial orbits and terrestrial falling was offered by the French polymath René Descartes who was both a committed Catholic and a devotee of the new science. As Galileo found out a generation earlier, it was a difficult combination. The Church, following Thomas Aquinas, had deemed Aristotle’s theories its official doctrine. The Earth is fixed at the center of the universe, and everything else orbits it…period.

Using his telescope, Galileo discovered the phases of Venus and the moons of Jupiter, demonstrating that this could not be correct. The sun-centered explanation of Copernicus had to be right. Still, the Pope’s theologians argued that if the earth was moving, there would be a constant wind in one direction, and the trajectory of falling objects would slant—but neither is true. So, with papal authority, it was asserted that the earth does not move. Galileo was arrested and twice convicted for saying otherwise.

Science says the earth orbits the sun, and religion says the Earth does not move: seemingly mutually exclusive claims. Descartes cleverly showed how both could be simultaneously true.

The Church requires that the earth does not move, but what does it mean to move? A thing moves when it is at one place at one time and at a different place at a different time. To be at a different place is to be surrounded by different space. But what if something brought its space with it?

If we think of space itself as a substance, then we need to understand its behavior. Descartes proclaimed that space is a weightless liquid that flows, and the effect of mass on it is to create vortices in space. An object close to the center of a whirlpool of water gets sucked straight into it, whereas an object floating far away from the center of the whirlpool would get caught in the circular current of the eddy and thereby would orbit the center. The notion of a vortex thereby would explain the straight line motion of objects close to the Earth, but the orbits of the moon around the Earth and the Earth around the sun.

But because the Earth created one vortex and the sun created another, the Earth could keep its space around it, and that entire complex of space and Earth would be pulled around the sun. Since the earth was forever bathed in the same space, it does not move—motion, again, is to be surrounded by different parts of space at different times—and yet still orbits the sun. Descartes’ vortex theory of gravitation posits a single external force to explain both terrestrial straight-line motion and astronomical orbits. And more interestingly, does so in a way that fits Descartes’ theology.

Newton’s Hand of God

Image: Newton, vanguardngr.com

Newton studied the writings of Descartes. He understood Cartesian vortex theory and Descartes’ Catholicism and rejected both. Political tensions during Newton’s time were linked to the Catholic/Protestant divide. Newton was a vocal anti-Catholic, so rejecting both the theories of Aristotle and Descartes was as much a religious as a scientific statement.

Johannes Kepler had shown that astronomical objects’ orbits were elliptical, and replacing Descartes’ vortex with an invisible force of attraction required a mathematical account of the force. The strongest mathematical tools at the time were those of analytic geometry, which Descartes had developed, but they were not enough, so Newton was forced to create stronger ones. 

That necessitated his development of what he called “fluxions” and what we now call calculus. With his infinitesimal calculus, he gave humanity his law of universal gravitation that, coupled with his laws of motion, explained everything from orbits to the tides to the shape of the earth to the falling of apples.

But what explained gravity? The vortex theory showed why things moved—they were caught in a vortex of space and pulled around. But what is making the apple fall? What is keeping the moon in its orbit? When Cartesians challenged Newton, his response was “hypotheses non fingo,” I frame no hypotheses. It is just how it works; he was saying, do not ask me about the underlying mechanism.

But this was not an answer in good faith. Newton did think he knew the source of gravitation, and it involved his faith. Newton heard that a regional Anglican priest was citing his law of gravitation as evidence for the existence of God, and Newton wrote to him to express his agreement with the sentiment. The priest’s argument was a version of the argument from design where Newton’s picture was so elegant that it necessitated a Divine Creator. Newton concurred…almost.

Descartes’ vortex picture allowed space itself to move the objects in it. Only physical causes were needed to explain physical events. This came to be known as Descartes’ “mechanical philosophy,” and Newton decried its elimination of God from the active workings of the world. Descartes’ being Catholic was bad enough, but his theory supported deism—the view that God created and then abandoned the universe—and so was doubly flawed.

In his letter, Newton reflected on the priest’s correct claim that the source of gravitation had to be internal to the attracted objects or external in the form of some agent causing the force. He demands not to be among those who advocate an internal force. While he does not explicitly name the external agent, it would have to be something whose reach extends across the universe and would be strong enough to move the heaviest objects. Gravity, he contended, was the working of God’s hand. Newton believed that gravitation was universally accessible evidence of the Divine presence.

Unlike Catholicism, in which only the Pope has a direct connection to God and the Church exists as a structure to mediate that relationship with the rest of humanity, by seeing God as acting gravitationally on the universe, Newton asserted that all could see, and indeed physically feel, the pull of God. This democratizing of the Divine is very Protestant in flavor. Descartes’ gravitational theory, on the other hand, was explicitly designed to mesh Copernicanism with the position of the Pope, which had ensnared Galileo a generation earlier. Newton’s theory of gravitation is thus as Protestant as Descartes’ is Catholic.

Einstein’s Cosmic Mollusk

Image: Einstein, symmetrymagazine.org

Newton’s theory was the most successful scientific view in human history, reigning supreme for 300 years until Albert Einstein formulated his general theory of relativity in 1916. Having replaced Newton’s laws of motion with his special theory of relativity in 1905, he took aim at gravitation to finish the job and offer an explanation for the one thing Newton could not explain—the orbit of Mercury. 

The ellipse of Mercury’s orbit did not close on itself but advanced slightly, causing the path of the innermost planet around the sun to trace out a cosmic daisy-like one would make with the old toy Spirograph. Einstein labored for the better part of a decade to account for this, and what emerged was a completely different sort of picture.

Space was no longer “fixed and immovable,” as Newton thought, an inert piece of three-dimensional graph paper underlying reality. Instead, it was more like Descartes’ picture, a substance that affected and was affected by the stuff in it. But instead of the Cartesian fluid filled with vortices, Einstein pictured his space as a mollusk, a squishy irregular oyster where you could move its pearl around by pushing into it at different points. The Einstein Field Equations connect the universe’s mass and energy distribution with the underlying space’s curvature. Mass tells space how to curve, and the curvature of space tells mass how to move. And it tells it exactly and necessarily. For Einstein, that was essential.

When a rabbi wrote to Einstein to ask if he believed in God, Einstein replied that he believed in the God of Spinoza. Baruch Spinoza was an apostate Jew who aroused the ire of both the rabbis and Christian clergy of 17th century Amsterdam for his pantheism, arguing not only is God is the universe itself, not a distinct entity from it, but also that the universe—and therefore God—is governed by the laws of logic. 

Logic, according to Spinoza, is stronger than the will of God, meaning that the course of the universe is completely predetermined. Logic commands God. Spinoza’s great work The Ethics is written as an homage to Euclid’s magnum opus, The Elements, starting with axioms and deductively deriving theorems, but where Euclid focuses on geometry, Spinoza applies the form to reasoning about God.

Connecting God to geometry, geometry to the universe, and the universe to God also connects Spinoza to Einstein. Einstein professed what he called his “cosmic religion.” For Einstein, there is no personal God, that is, no God apart from the universe itself. What there is are immutable laws that govern the behavior of everything. Those laws are deterministic. Given the state of the universe at any one instant in time, the laws determine exactly how it will be at every other time. And it all happens in terms of the geometry of the universe. The curvature of spacetime determines the motions of everything in it.

Einstein has complete faith in the existence of these immutable deterministic laws, although he does not ask where they came from. Like his beloved Spinoza, for Einstein, they are the logic of the universe, an intrinsic feature of the world, not to be separated as the will of an external agent. Not only is Einstein’s gravitational equation different from Newton’s, but they also diverge in this theological sense. Newton did see the laws of nature as the design of an intelligent Creator and saw physicists as reading the mind of God, whereas Einstein saw the laws as the thing-in-itself.

The determinism that Einstein thought to be required in this Spinozan worldview would, of course, be the heart of his objections to quantum mechanics, the theory that would lead us to our current conundrum in physics, where we have two fundamental theories that are mutually exclusive. The hope to find a theory of everything that is capable of uniting general relativity with the quantum world, that is, a theory of quantum gravitation, is the project awaiting the next genius on the level of Descartes, Newton, and Einstein.

Given that for Einstein, as with Descartes and Newton, the account of gravitation is interwoven with their theological commitments since there appears to be an irresistible force attracting science and religion in this matter, maybe the next theory will require not just a new physical insight, but a metaphysical one as well.