We are reviewing Alister McGrath’s new book, “A Theory of Everything (That Matters): A Brief Guide to Einstein, Relativity, and His Surprising Thoughts on God”. Chapter 2 is entitled: “The Old World: Newton’s Clockwork Universe”. McGrath starts the chapter by pointing out how even though science is the patient and scrupulous accumulation of observations, it is also a quest for understanding in which we try to discern the deeper patterns and structures of our universe; the deeper truths that underlie what we can merely observe.
If an understanding of a set of observations becomes commonly accepted for a long enough period of time, we designate that as a “theory”. To the layman, a “theory” is just a good guess, but scientists use the term to refer to hypotheses that have held up to repeated testing. A theory is what a good hypothesis aspires to be, so to speak. Theories that have gained this kind of acceptance almost are taken to be self-evident. So what happens when such a theory turns out to have been wrong? What if a new theory comes along and is shown to be far superior to what we were used to?
Let’s take the movement of the planets. In the ancient world, people noticed that some of the objects in the sky seemed to move around i.e. weren’t in the same place in the sky night after night. They were termed “wandering stars” because they were useless for navigation. That’s why they had a negative association in Jude 1:13 “They are wild waves of the sea, foaming up their shame; wandering stars, for whom blackest darkness has been reserved forever.” If you tried to navigate by them, you would be led astray, just like the ungodly people Jude is warning about will lead you astray morally and spiritually. The ancients gave them the names of certain gods: Mercury, Venus, Mars, Jupiter, and Saturn.
So what explained the movement of these “wandering stars”? In the second century, Ptolemy of Alexandria set out a way of understanding the heavenly bodies that would be accepted by most people for more than a thousand years. For Ptolemy, the sun, moon, and planets all revolved around the Earth in circular orbits at different distances. To account for the “wandering” of the planets, Ptolemy had a system of epicycles. It worked reasonably well, although there was no physical reason why a planetary body would also revolve in an epicycle. But by the time of the 16th century as increasingly more accurate measurements were made, the Polish astronomer Nicholas Copernicus published a book arguing that the sun, not the earth, stood at the center of the known universe. Copernicus’ theory was wrong in several respects – for example, he believed the planets revolved in circular orbits at uniform speeds.
Johannes Kepler corrected those errors through his close study of the planet Mars in the early 17th century. He pointed out that the Earth and other planets revolved in elliptical orbits at variable speeds. Yet Kepler couldn’t explain why this was the case. Which brings us to Isaac Newton and his proposals for classical mechanics and gravitational theory set out in his Philosophiae Naturalis Principia Mathematica, usually referred to as Newton’s Principia in 1687.
By careful observation, Newton set out a series of principles that governed the behavior of objects on Earth and then argued that these same principles applied to the motion of the moon around the Earth and the planets around the sun. This is reflected in the well-known, but probably greatly exaggerated, story of the apple falling on his head. Newton might have creatively embellished the story through retelling it over time, perhaps to conceal the fact that another British scientist – Robert Hooke – had developed a similar idea in the 1670s.
Newton argued that the mysterious and undetectable force he named gravity was the explanation for both the apple falling to the Earth and the moon orbiting around the Earth. Newton’s Law of Gravity states that the force of gravity is equal to a constant value (G) multiplied by the two masses and divided by the distance between the two masses squared. Newton had no idea what caused gravity in the first place and refused to speculate about its origins. Initially, Newton’s demonstration of the regularity of the laws of nature was seen as confirming the Christian belief in a God who had created an ordered universe and endowed humanity with the power of reason to discover those laws. But later, as McGrath says:
God now seemed to be pointless. Having constructed the universe and set it going, God is left without any significant role. God might retire or even die, but the universe would continue to function according to the laws by which God had caused it to function. Newton, perhaps unwittingly, had laid the groundwork for a self-sustaining and self-regulating universe, with no place for God.
Newton introduce the idea of space – a vast empty container that enclosed the sun, planets, and stars. This naturally raised the question of what this “space” was made of. As with gravity, Newton refused to speculate on this question. For Newton, both gravity and space were legitimate scientific inferences from an observable phenomenon to the unobservable entity that best explains it. Newton recognized that space and time were not things we observe directly, but were rather inferences from those observations.
On the question of the nature of light, Newton took the view that a beam of light consisted of a series of rapidly moving small particles or “corpuscles” (from the Latin term corpuscula, “small bodies”). Newton’s view of light dominated the physics of the 18th century, but during the 19th century, a growing body of experimental evidence suggested that light was better understood as a wave. For example, the double slit experiment was first reported by Thomas Young in 1801. His demonstration of interference by alternate bright and dark lines was taken to be clear evidence for the wave nature of light.
Many late 19th century scientists believed that physics had finally sorted out all the great questions of the day and all that remained was to achieve greater precision in some measurements of natural properties. Yet enigmas and anomalies remained. Some observations just didn’t fit neatly into the best theories of that age. One of the most significant anomalies was known as “the advance of the perihelion of Mercury”.
Like all planets, Mercury orbited the sun in an ellipse. The point at which it was closest to the sun – known as the perihelion – was discovered to move by a tiny, but observable, amount each year. Why?
The Newtonian explanation would have been Mercury was influenced by an unknown planet of roughly half the mass of Mercury positioned closer to the sun. This explanation was similar to the discovery of Neptune based on the distorted orbit of Uranus calculated by Urbain Le Verrier. In 1846, the planet Neptune was observed. The anomalous behavior of Uranus was thus resolved without abandoning or modifying Newton’s basic ideas.
Many scientists of the 19th century saw the discovery of Neptune as confirming the reliability of Newtonianism. This sparked a search for the proposed planet, which Le Verrier named Vulcan. It, of course, was never found.
On November 18, 1915, Albert Einstein reported to the Prussian Academy that the advancing perihelion of Mercury was explained precisely and persuasively by his new general theory of relativity. In general relativity, this remaining precession, or change of orientation of the orbital ellipse within its orbital plane, is explained by gravitation being mediated by the curvature of spacetime. Einstein showed that general relativity agrees closely with the observed amount of perihelion shift. This was a powerful factor motivating the adoption of general relativity.
Beginning in the next chapter, McGrath turns to consider the many new ideas developed by Einstein, beginning with the remarkable series of four articles published in 1905 that established his reputation as one of the most significant scientific thinkers of his age – despite the fact that he was working as a clerk in the patent office in the Swiss city of Bern, not as a research scientist at a leading Swiss university or scientific research institution.