Isaac Newton (4 page)

The Civil War had ended and so had the Protectorate of Oliver Cromwell, dead from malaria, buried and then exhumed so his head could be stuck on a pole atop Westminster Hall. During the rebellion Puritan reformers had
gained control of Cambridge and purged the colleges of many Royalist scholars. Now, with the restoration of Charles II to the crown, Puritans were purged, Cromwell was hanged in effigy, and the university’s records from the Protectorate years were burned. This riverside town was a place of ferment, fifty miles from London, a hundredth its size, a crossroads for information and commerce. Each year between harvest and plowing, tradesmen gathered for Stourbridge Fair, England’s largest: a giant market for wool and hops, metal-ware and glass-ware, silk and stationery, books, toys, and musical instruments—a bedlam of languages and apparel, and “an Abstract of all sorts of mankind,” as a pamphleteer described it.
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Newton, scrupulous with his limited funds, bought books there and, one year, a glass prism—a toy, imprecisely ground, flawed with air bubbles. Often enough, the complex human traffic had another consequence: Cambridge suffered visitations of plague.

The curriculum had grown stagnant. It followed the scholastic tradition laid down in the university’s medieval beginnings: the study of texts from disintegrated Mediterranean cultures, preserved in Christian and Islamic sanctuaries through a thousand years of European upheaval. The single authority in all the realms of secular knowledge was Aristotle—doctor’s son, student of Plato, and collector of books. Logic, ethics, and rhetoric were all his, and so—to the extent they were studied at all—were cosmology and mechanics. The Aristotelian canon enshrined systematization and rigor, categories and rules. It formed an edifice of reason: knowledge about knowledge. Supplemented by ancient poets and medieval divines, it was a complete education, which scarcely changed from generation to generation.
Newton began by reading closely, but not finishing, the
Organon
and the
Nicomachean Ethics
(“For the things we have to learn before we can do them, we learn by doing them”).
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He read Aristotle through a mist of changing languages, along with a body of commentary and disputation. The words crossed and overlapped. Aristotle’s was a world of substances. A substance possesses qualities and properties, which taken together amount to a
form
, depending ultimately on its essence. Properties can change; we call this
motion
. Motion is action, change, and life. It is an indispensable partner of
time
; the one could not exist without the other. If we understood the cause of motion, we would understand the cause of the world.

For Aristotle motion included pushing, pulling, carrying, and twirling; combining and separating; waxing and waning. Things in motion included a peach ripening, a fish swimming, water warming over a fire, a child growing into an adult, an apple falling from a tree.
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The heavy thing and the light thing move to their proper positions: the light thing up and the heavy thing down.
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Some motion is natural; some violent and unnatural. Both kinds revealed the connections between things. “Everything that is in motion must be moved by something,” Aristotle asserted (and proved, by knotted logic).
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A thing cannot be at once
mover
and
moved
. This simple truth implied a first mover, put in motion by no other, to break what must otherwise be an infinite loop:

Since everything that is in motion must be moved by something, let us take the case in which a thing is in locomotion and is moved by something that is itself in motion,… and that by something else, and so on continually: then the series cannot go on to infinity, but there must be some first mover.

To the Christian fathers, this first mover could only be God. It was a testament to how far pure reason could take a philosopher; and to how involuted and self-referential a chain of reasoning could become, with nothing to feed on but itself.

This all-embracing sense of motion left little place for quantity, measurement, and number. If objects in motion could include a piece of bronze becoming a statue,
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then philosophers were not ready to make fine distinctions, like the distinction between velocity and acceleration. Indeed, the Greeks had a principled resistance to mathematicizing our corruptible, flawed, sublunary world. Geometry belonged to the celestial sphere; it might relate music and the stars, but projectiles of rock or metal were inappropriate objects for mathematical treatment. So technology, advancing, exposed Aristotelian mechanics as quaint and impotent. Gunners understood that a cannonball, once in flight, was no longer moved by anything but a ghostly memory of the explosion inside the iron barrel; and they were learning, roughly, to compute the trajectories of their projectiles. Pendulums, in clockwork, however crude, demanded a mathematical view of motion. And in turn the clockwork made measurement possible—first hours, then minutes. Of an object falling from a tower or rolling down an inclined plane, people could begin to ask: what is the distance? what is the time?

What, therefore, is the velocity? And how does the velocity, itself, change?

Nor was Aristotle’s cosmology faring well outside Cambridge’s gates. It was harmonious and immutable: crystalline spheres round the earth, solid and invisible, carrying the celestial orbs within them. Ptolemy had perfected his universe and then, for hundreds of years, Christian astronomers embraced and extended it, reconciled it with biblical scripture, and added a heaven of heavens, deep and pure, perhaps infinite, the home of God and angels, beyond the sphere of fixed stars. But as stargazers made increasingly detailed notations, they catalogued planetary motions too irregular for concentric spheres. They saw freaks and impurities, such as comets glowing and vanishing. By the 1660s
—new news every day
—readers of esoterica knew well enough that the earth was a planet and that the planets orbited the sun. Newton’s notes began to include measurements of the apparent magnitude of stars.

Although the library of Trinity College had more than three thousand books, students could enter only in the company of a fellow. Still, Newton found his way to new ideas and polemics: from the French philosopher René Descartes, and the Italian astronomer Galileo Galilei, who had died in the year of Newton’s birth. Descartes proposed a geometrical and mechanical philosophy. He imagined a universe filled throughout with invisible substance, forming great vortices that sweep the planets and stars forward. Galileo, meanwhile, applied geometrical thinking to the problem of motion. Both men defied Aristotle explicitly—Galileo by claiming that all bodies are made of the same stuff, which is heavy, and therefore fall at the same rate.

Not the same
speed
, however. After long gestation, Galileo created a concept of uniform acceleration. He considered motion as a state rather than a process. Without
ever using a word such as
inertia
, he nonetheless conceived that bodies have a tendency to remain in motion or to remain motionless. The next step demanded experiment and measure. He measured time with a water-clock. He rolled balls down ramps and concluded, wrongly, that their speed varied in proportion to the distance they rolled. Later, trying to understand free fall, he reached the modern definition, correctly assimilating units of distance, units of speed, and units of time. Newton began to absorb this, at second or third hand; Galileo had written mostly in Italian, a language few in England could read.
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In Newton’s second year, having filled the beginning and end of his notebook with Aristotle, he started a new section deep inside:
Questiones quædam philosophicæ
—some philosophical questions. He set authority aside. Later he came back to this page and inscribed an epigraph borrowed from Aristotle’s justification for dissenting from his teacher. Aristotle had said, “Plato is my friend, but truth my greater friend.” Newton inserted Aristotle’s name in sequence:
Amicus Plato amicus Aristoteles magis amica veritas
.
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He made a new beginning. He set down his knowledge of the world, organized under elemental headings, expressed as questions, based sometimes on his reading, sometimes on speculation. It showed how little was known, altogether. The choice of topics—forty-five in all—suggested a foundation for a new natural philosophy.

Of the First Matter. Of Atoms
. Could he know, by the force of logic, whether matter was continuous and infinitely divisible, or discontinuous and discrete? Were its ultimate parts
mathematical points or actual atoms? Since a mathematical point lacks body or dimension—“is but an imaginary entity”—it seemed implausible that even an infinite number of them could combine to form matter with real extension,
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even if bits of vacuum (“interspersed inanities”) separated the parts. The question of God’s role, as creator, could be dangerous territory. “Tis a contradiction to say the first matter depends on some other subject”—in parentheses he added, “except God”; then, on second thought, he crossed that out—“since that implies some former matter on which it must depend.” Reasoning led him, as it had led ancient Greeks, to atoms—not by observation or experiment, but by eliminating alternatives. Newton declared himself a corpuscularian and an atomist. “The first matter must be attoms. And that Matter may be so small as to be indiscernible.” Very small, but finite, not zero. Indiscernible, but unbreakable and indivisible. This was an unsettled conception, because Newton also saw a world of smooth change, of curves, and of flow. What about the smallest parts of time and motion? Were these continuous or discrete?

Quantity. Place
. “Extension is related to places, as time to days yeares &c.”
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He invoked God on another controversial question: Is space finite or infinite? Not the imaginary abstract space of geometers, but the real space in which we live. Infinite, surely! “To say that extension is but indefinite”—Descartes said this, in fact—“is as much to say God is but indefinitely perfect because wee cannot apprehend his whole perfection.”

Time and Eternity
. No abstract disputation here; he just sketched a wheel-shaped clock, to be driven by water or sand, and raised wholly practical questions about making
clocks with various materials, such as “metalline globular dust.” Only then did he reach
Motion
, and again, he began by looking for the root constituents, the equivalent of atoms.
Motion
led to
Celestiall Matter & Orbes
—which took Newton, encountering the early echoes of Continental thought, to Descartes. In Descartes’s universe, there could be no vacuum, for the universe was space, and space meant extension, and extension surely implied substance. Also, the world’s principles were mechanical: all action propagated through contact, one object directly pushing another, no mystical influences from afar.

In the cosmos of Descartes, matter fills all space and forms whirling vortices
.
(illustration credit 2.1)

So a vacuum could not transmit light. Light was a form of
pression
, Descartes said—imaginatively, because philosophers had barely begun to conceive of pressure as a quality that an invisible fluid, the air, could possess. But now Newton had heard of Robert Boyle’s experiments with an air-pump, and
pressure
was the word Boyle used in this new sense. Newton began again:

Whether Cartes his first element can turne about the vortex & yet drive the matter of it continually from the
[sun] to produce light, & spend most of its motion in filling up the chinks between the globuli.
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