The Clockwork Universe: Isaac Newton, the Royal Society, and the Birth of the Modern World - Edward Dolnick (2011)
Part I. Chaos
Chapter 16. All in Pieces
Galileo, Newton, and their fellow revolutionaries immediately turned their backs on yet another cherished idea. This time they banished common sense. Long acquaintance with the world had always been hailed as the surest safeguard against delusion. The new scientists rejected it as a trap. “It is not only the heavens that are not as they seem to be, and not only motion,” Descartes argued, in a modern historian’s paraphrase. “The whole universe is not as it seems to be. We see about us a world of qualities and of life. They are all mere appearances.”
It was a Polish cleric and astronomer named Nicolaus Copernicus who had struck the first and hardest blow against common sense. Despite the evidence, plain to every child, that we live on solid ground and that the sun travels around us, Copernicus argued that everyone has it all wrong. The Earth travels around the sun, and it spins like a top as it travels. And no one feels a thing.
This was ludicrous, as everyone who heard about the newfangled theory delighted in pointing out. For one thing, the notion of a sun-centered universe contradicted scripture. Had not Joshua ordered the sun (rather than the Earth) to stand still in the sky? This was a huge hurdle. In the 1630s, nearly a century after Copernicus’s death, Galileo would face the threat of torture and then die under house arrest for arguing in favor of a sun-centered universe.
(Isaac Newton was born in the year that Galileo died. That was coincidence, but in hindsight it seemed to presage England’s rise to scientific preeminence and Italy’s long drift to mediocrity. What was not coincidence was that seventeenth-century England welcomed science, on the grounds that science supported religion, and thrived; and seventeenth-century Italy feared science, on the grounds that science undermined religion, and decayed.)
Copernicus himself had hesitated for decades before publishing his only scientific work, On the Revolutions of the Celestial Spheres, perhaps because he knew it would stir religious fury as well as scientific opposition. Legend has it that he was handed the first copy of his masterpiece on his deathbed, on May 24, 1543, although by that point he may have been too weak to recognize it.
Religion aside, the scientific objections were enormous. If Copernicus was right, the Earth was speeding along a gigantic racetrack at tens of thousands of miles an hour, and none of the passengers suffered so much as a mussed hair. The fastest that any traveler had ever moved was roughly twenty miles an hour, on horseback.
These arguments came from the most esteemed scholars, not from yokels. They knew, on both scientific and philosophical grounds, that the Earth does not move. (Aristotle had argued that the Earth rests in place because it occupies its natural home, the center of the universe, just as an ordinary object on the ground stays in its place unless something comes along and dislodges it.) Scholars pointed to countless observations that all led to the same conclusion. We can be sure the Earth stands still, one eminent philosopher explained, “for at the slightest jar of the Earth, we would see cities and fortresses, towns and mountains thrown down.”
But we don’t see cities toppled, the skeptics noted, nor do we see any other evidence that we live on a hurtling platform. If we’re racing along, why can we pour a drink into a glass without worrying that the glass will have moved hundreds of yards out of range by the time the drink reaches it? If we climb to the roof and drop a coin, why does it land directly below where we let it go and not miles away?
But Copernicus’s new doctrine inspired fear as well as ridicule and confusion, because it led almost at once to questions that transcended science. If the Earth was only one planet among many, were those other worlds inhabited, too? By what sort of creatures? Had Christ died for their sins? Did they have their own Adam and Eve, and what did that say about evil and original sin? “Worst of all,” in the words of the historian of science Thomas Kuhn, “if the universe is infinite, as many of the later Copernicans thought, where can God’s Throne be located? In an infinite universe, how is man to find God or God man?”
Copernicus could not disarm such fears by pointing to new discoveries or new observations. He never looked through a telescope—Galileo would be one of the first to turn telescopes to the heavens, some seven decades after Copernicus’s death—and in any case telescopes could not show the Earth moving but only provided evidence that let one deduce its motion.
On the contrary, everything that Copernicus could see and feel spoke in favor of the old theories and against his own. “Sense pleads for Ptolemy,” said Henry More, a colleague of Newton at Cambridge and a distinguished English philosopher. But common sense lost out. The old, Earth-centered theory that Ptolemy had devised was a mathematical jumble, and that marked it for death. The old system worked perfectly well, but it was a hodgepodge.
The great challenge to pre-Copernican astronomy had to do with sorting out the motions of the planets, which do not trace a simple course through the sky but at some point interrupt their journey and loop back in the direction they’ve just come from. (The stars present no such mystery. Each night Greek astronomers watched them rotating smoothly through the sky, turning in a circle with the North Star at its center. Each constellation moved around the center, like a group of horses on a merry-go-round, but the stars within a constellation never rearranged themselves.)
The path of Saturn as seen from Earth, as depicted by Ptolemy in 132-33 A.D. From March through June, Saturn appears to reverse course.
Accounting for the planets’ strange course changes would have been enough to give classical astronomers fits. Making the challenge all the harder, classical doctrine decreed that planets must travel in circular orbits (since planets are heavenly objects and circles are the only perfect shape). But circular orbits didn’t fit the data. The solution was a complicated mathematical dodge in which the planets traveled not in circles but in the next best thing—in circles attached to circles, like revolving seats on a Ferris wheel, or even in circles attached to circles attached to circles.
Copernicus tossed out the whole complicated system. The planets weren’t really moving sometimes in one direction and sometimes in the other, he argued, but simply orbiting the sun. The reason those orbits look so complicated is that we’re watching from the Earth, a moving platform that is itself circling the sun. When we pass other planets (or they pass us), it looks as if they’ve changed course. If we could look down on the solar system from a vantage point above the sun, all the mystery would vanish.
This new system was conceptually tidier than the old one, but it didn’t yield new or better predictions. For any practical question—predicting the timing of eclipses and other happenings in the solar system—the old system was fully as accurate as the new. No wonder Copernicus kept his ideas to himself for so long. And yet think of the astonishing leap this wary thinker finally nerved himself to make. With no other rationale but replacing a cumbersome theory with one that was mathematically more elegant, he dared to set the Earth in motion.
A few intellectuals might have been won over by a revolutionary argument with nothing in its favor but aesthetics. Most people wanted more. How did the new theory deal with the most basic questions? “If the moon, the planets and comets were of the same nature as bodies on earth,” wrote Arthur Koestler, “then they too must have ‘weight’; but what exactly does ‘the weight’ of a planet mean, what does it press against or where does it tend to fall? And if the reason why a stone falls to Earth is not the Earth’s position in the center of the universe, then just why does the stone fall?”
Copernicus did not have answers, nor did he have anything to say about what keeps the planets in their orbits or what holds the stars in place. The Greeks had provided such answers, and the answers had stood for millennia. (Each planet occupied a spot on an immense, transparent sphere. The spheres were nested, one inside the other, and centered on the Earth. The stars occupied the biggest, most distant sphere of all. As the spheres turned, they carried the planets and the stars with them.)
No one could yet answer the new questions about the stars and planets. No one knew why objects on Earth obey one set of laws and bodies in the heavens another. No one even knew where to look for answers. John Donne, poet and cleric, spoke for many of his perplexed, frustrated contemporaries. “The Sun is lost, and th’ earth, and no man’s wit / Can well direct him where to look for it,” he lamented, in a poem written a year after Galileo first looked through his telescope.
“The new Philosophy calls all in doubt,” Donne wrote in another verse. “ ’Tis all in pieces, all coherence gone.”