by Adam Frank
One hundred years after his death, Enlightenment writers would canonize Newton as a hero of pure reason. But unbeknownst to them, Newton was a passionate Christian who devoted thousands of pages to biblical studies, including prophecy. Recently rediscovered documents show Newton to be a heretic, vehemently opposed to the doctrine of the Trinity at a time when such opposition carried a death sentence.21 Throughout his life, Newton thought of himself as a “high priest of nature”; as an advocate of natural theology, he thought the study of nature revealed the creative hand of God.22 His irrevocable belief in God’s all-encompassing presence provided a principle that redefined space and time in his new physics.23 Living in the midst of a culture that was building itself along newly imagined lines, Newton’s conviction for a new natural theology manifested itself in new religious and scientific visions. And from those visions, the entire cosmos would be reworked.
Isaac Newton’s most famous scientific work was his Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy), now usually known simply as the Principia. Published in 1687, the Principia established the science of classical mechanics—an all-embracing account of force, matter and motion. Newton’s mechanics would transform the very nature of scientific endeavour, establishing a set of universal laws on the basis of which all phenomena could be described (or predicted). To construct this grand edifice, however, Newton first needed a new foundation for the stage on which physics is played—he needed to invent the absolutes of space and time.
For centuries, scholars struggled to understand the relationship between four critical concepts rooting the study of physics: time, space, matter and motion. Based on the long dominance of Aristotle, most scholars were sure that time and space held no separate reality.24 For many of Newton’s contemporaries, time held meaning only relative to changes in matter. Space held meaning only relative to the arrangement of matter. A chunk of material might be here at one moment in time and then move to there a moment later. But here, there, now and later held only relative meaning. They only made sense in relation to all the other matter, the other stuff, in the cosmos. Without a separate reality other than their reference to matter, time and space were, literally, nothing.
This perspective strongly impacted cosmological thinking. Aristotle continued to exert a strong influence even in Newton’s age. According to the ancient philosophers, the universe was a plenum, a material continuum. In their view there could be no space without matter.25 In an echo of Parmenides, a truly empty space was thought to be impossible. But in their demand that space and time be dependent on matter, scholars tied themselves into knots trying to formulate precise laws of motion. After all, motion is just an object’s change in position (space) over some duration (time). If space and time did not exist without matter, how was matter supposed to move through them?
When the young Newton entered Cambridge he showed little interest in the study of Aristotle, immersing himself instead in the new perspectives of Kepler, Galileo and the French mathematician-philosopher René Descartes.26 Descartes had gained attention with his own attempts to appropriately define space, time and motion just a few decades earlier.27 Descartes’ solution to the problem sidestepped the contentious possibility of a true void by imagining space continuously filled with primordial vortices. These vortices provided a kind of background to support matter’s motion, carrying the planets through their Keplerian orbits. Though Newton would reject Descartes’ views, they served as a foil to his own innovations.
At the beginning of the Principia comes a small scholium (Latin for “comment”). In just seven pages, the scholium rebuilds time, space and motion, clearing the way for Newton’s mechanics and the new mechanical world.
FIGURE 4.2. Descartes’ cosmological physics imagined the solar system permeated by spinning vortices which carried the planets in their orbital motions.
In essence, Newton’s innovation was to make space and time separate realities. Space is a “something” distinct from matter. It exists independent of any configuration of material. Space, for Newton, had properties independent of matter that were uniform and unchanging. Space, in other words, is the same everywhere in the universe. Just as important, time is a “something” too. It is distinct from matter and matter’s changes. Time’s flow is uniform everywhere and does not depend on the activity of matter. Newton’s new perspective can be summarized as follows:28
Absolute, true and mathematical time passes equally without relation to anything external and without reference to any change in matter or the way in which it is measured (e.g., the hour, day, month or year).
Absolute, true and mathematical space is the same everywhere; its properties remain fixed without relation to changes in matter.
Absolute motion is the movement of a body from one position in absolute space to another.
Thus Newton invented an absolute space and an absolute time. Real in and of themselves, both are constant, unchanging and independent of the relationships between matter and its changes. Newton’s new vision for the space and time of physics would come to be called the “divine sensorium”.29 It was the domain of God’s perfect perception of reality, an empty stage on which the play of the cosmos and the drama of physics would be enacted.
By defining an absolute space and time, Newton had successfully created his framework for defining motion. Then, with motion pinned down, he could define mechanics—the mathematical laws linking force and motion. The rest of the Principia would go on to articulate these mathematical laws; force, mass and acceleration would be clearly linked in a grand theoretical structure. Earth and heaven were tied together under this single set of laws, which came to be called Newtonian mechanics. Most important, these laws reworked both science and culture in ways still relevant today.
In what might be considered a marriage of the visions of Parmenides and Heraclitus, change and eternity were fused. Timeless, immutable laws governed the universe and the progress and nature of change.30 By abstracting time and space from experience, Newton’s theoretical machinery became the ideal to which all future cultural innovation would be held. The spirit of his mechanics—embodied as a faith in eternal, timeless and universal law—would soon be made concrete in the realms of government and other institutions as they rapidly attempted to master the globe.
MAPPING HEAVEN: ASTRONOMY AND COSMOLOGY AFTER NEWTON
It was a dark and stormy night on October 22, 1707, when a squadron of English warships approached the English Channel.31 The twenty-one ships, commanded by Sir Cloudesley Shovell, were returning from an unsuccessful campaign against the French port of Toulon. Under a blanket of dense fog, the squadron’s navigators believed themselves to be safely passing west of the last island outposts of Brittany and into clear Channel waters, but the weather made determinations of the squadron’s east-west position difficult. The sailing masters had no way of knowing that the ships were plunging directly into the rocky outline of the Isles of Scilly. Within minutes of striking a sharp rock outcropping, the HMS Association disappeared below the waves, taking the entire eight-hundred-man crew and Admiral Shovell with it. Three other ships were lost that night, bringing the total number drowned to more than 1,200.
The Royal Navy’s disaster of 1707 could be summed up in a single word: longitude. By the eighteenth century transoceanic commerce and military operations had grown to dominate geopolitics and geoeconomics. Maps and other navigational tools of the time were of limited use, as they couldn’t provide accurate determinations of longitude—the east-west position on the map.
Knowing one’s precise position on the globe (as in the middle of the featureless ocean) requires two numbers: latitude and longitude. Latitude is the position north or south of the equator and is easily determined with a simple observation of the sun’s highest position in the sky. Longitude is another story entirely.
While latitude measurements are relative to the equator (or the poles), what special position should longitude be judged by? N
ature did not inscribe a single giant arc running from one pole to the other for humans to judge east and west. Instead, longitude must be measured against arbitrary meridians—imaginary lines circling the globe and running through both poles. If, for example, we choose Greenwich, England, to be our reference, then longitude will be measured as east or west of that prime meridian running though Greenwich. But how do we make such measurements? Longitude measurements, it turns out, are always comparisons of time that are converted into space.
Traditional measurements of longitude required knowledge of astronomy, a calculation of local time and a very special book. The book gave times when the moon reached its highest point each night in Greenwich. If a sailor needed to find his longitude, he watched the moon and recorded the time when it reached the highest point in the sky that night (using a clock set to a local time determined by the sun’s position). This was called “shooting” the moon.32 The moon’s maximum point on its nightly arc formed a kind of astronomical anchor in time. The sailor simply compared his local time measurement for the moon with the book’s listing of the time the same event occurred in Greenwich. If the moon reached its zenith at 3:00 a.m. local time that day and the book told him the same event occurred in Greenwich at midnight, then he must be three hours ahead of Greenwich time. Three hours is one-eighth of the globe away, or 45 degrees of latitude east of Greenwich. By comparing different recorded times for a simultaneous event—the moon’s highest point in the sky—comparisons of time were transformed into determinations of position (space).
But astronomical methods for determining longitude were complex and inaccurate. The stars rotated once a day and the moon moved against the fixed background of stars once a month. These celestial dance steps made astronomical determinations of longitude a time-consuming business. Worse still, typical errors in the method translated into uncertainties of tens of miles in position, more than enough to kill scores of sailors on ships in fog-bound seas.
The widespread introduction of mechanical clocks should have offered a solution. The idea was to carry a clock synchronized to Greenwich time and a clock that was regularly updated to local time via astronomical observations. Comparing the two clocks would yield a time difference easily converted into longitude. But the motion of ships, along with changes in humidity and temperature, prevented even the most accurate timepieces of the day from working well at sea. A new form of material engagement was needed.
In 1772 Captain Cook set out on his second voyage of discovery with a copy of clockmaker John Harrison’s H4 shipboard chronometer.33 Harrison had spent his life working to perfect his longitude-determining devices.34 Returning three years later, after a voyage ranging from the tropics to the Antarctic, Cook reported that the clock’s daily tally of seconds held steady. Translated into distance, its variation never exceeded eight seconds of longitude (two nautical miles at the equator).35 Cook referred to Harrison’s invention as “our faithful guide through all the vicissitudes of climates”.36 It is not known for certain whether Harrison knew of this success, but Cook’s voyage proved beyond doubt that longitude could be accurately measured using timekeeping machines alone. The last epoch of sky-based time was ending, passing the baton to an emerging new machine era. In this way the contours of the world began to sharpen in human maps and minds.
As the globe was mapped with new precision during the seventeenth and eighteenth centuries, so too was the sky. Maps of the heavens were filled out by observations from ever more powerful telescopes as humankind took its first halting steps towards an astronomically based cosmology. As with so much else in the Age of Reason, the story begins with Newton.
In the Principia Newton laid out his vision of space and time, then used them as a background to formulate a new mechanics—a science that could accurately describe the relationship between force and motion. Newton’s laws are embodied in the famous formula F = ma (a force F applied to a mass m will produce an acceleration a). But this formula leaves the actual nature of the force undetermined. It is a general expression that applies equally to all forces—a cannon’s blast, the friction of a rough surface or the pull of a mule team.
There was, however, one force Newton knew required special attention. In the Principia Newton provided a detailed description of a new agent he called gravity—an attractive force occurring naturally between any two objects. Its strength decreases with distance (specifically, the force of gravity diminishes with the square of the distance between the objects). Most important, Newton’s gravity was universal, as applicable to apples falling from trees as it was to planets orbiting the sun. By giving a specific calculable form for gravity and making it universal, Newton wiped away the long-held distinction between the sublunar and celestial realms. With a single equation Newton cast two thousand years of Aristotelian physics aside and united the heavens and Earth.
The success of Newton’s gravitation was quickly apparent to astronomers across Europe. Kepler’s famous laws of planetary motion derive as easily from Newton’s gravity law as an overripe fruit drops from a gently shaken tree. Astronomers soon seized on the universal law of gravitation, applying it to everything from planetary orbits to tides and the rotation of the moon. With Newton’s precise formulation of the gravitational force, astronomers moved from simple descriptions of what they see in the sky to the first understanding of how these motions occurred. Through Newton’s law of gravity, astronomy becomes a science of dynamics—an explanation of objects moving through space and time. The timing was fortuitous: movement was, for the first time in human history, emerging as a recognized property of the stars.
Telescope technology had been steadily improving throughout the seventeenth and eighteenth centuries, giving astronomers deeper and more resolved images of the heavens. The addition of the filar micrometer, a device that allowed precise telescopic measurements of celestial position, enhanced celestial cartography.37 Just as nautical chronometers were producing accurate maps of the Earth, the new astronomical technologies were mapping the stars with enough precision to see their precise position in space and their movement in time.
In 1718 Edmund Halley came to question the orthodoxy that the stars were fixed in their positions relative to one another as he compared his observations of stellar positions with those found in Greek catalogues. Finding numerous discrepancies, he arrived at the astonishing conclusion that some stars had moved in the 1,500 years between ancient and modern observations. By 1738 his claims were verified for the star Arcturus.38 Twenty years later, no fewer than eighty stars had been shown to exhibit so-called proper motion—movement across the sky. The term “fixed stars” became an anachronism.
These advances in astronomy renewed interest in cosmological questions. In some cases, new cosmological theorizing relied heavily on astronomical discoveries. In other cases, they remained heavily philosophical, with astronomy playing only a supporting role. Both forms of Enlightenment cosmology would play an important role in the development of the subject into our modern era.
FIGURE 4.3. The Paris Observatory at the beginning of the eighteenth century. Newton’s mechanics becomes the basis for understanding astronomical motions as astronomers begin charting the sky with ever greater accuracy.
The introduction of Newton’s law of gravitation gave cosmological thinkers a tool they could use in asking specific questions about infinity and the evolution of the cosmos. Newton, in a series of letters to the theologian Richard Bentley, saw his own work pointing to a universe of infinite spatial extent. In a finite universe, the mutual gravitational attraction of each star upon the others would lead the entire system to collapse. Thus, an infinite universe composed of infinite stars was the more attractive alternative, but Newton understood that ultimately it too would be vulnerable to gravitational collapse. While a lattice of stars stretching to infinity would balance all gravitational attractions, the configuration was unstable; if one of the stars is nudged, gravitational forces would become unbalanced, forcing the stars to move toward
s one another and eventually collapse into giant clumps. Newton wrote that this instability made it hard to imagine how the stars could be “so accurately poised one among another, as to sit still in perfect Equilibrium”.39 The problem would come to be known as the gravitational paradox, and it would haunt cosmology well into the twentieth century. With his strong religious devotion, Newton “solved” the problem by assuming that God continued to play a role in the cosmos, periodically intervening to maintain order and prevent collapse.
While many astronomers remained bothered by this infinite number of stars (for example, how was such a number to be constructed?), the idea gradually gained acceptance. But with infinite distance came a renewed discussion of infinite time. In an era when Christian orthodoxy still required a universe only six thousand years old, most scholars were still unwilling to imagine an eternal universe. Newtonian astronomer James Ferguson saw how the gravitational paradox could be used to prove that the world’s age was finite. He wrote:
For, had it [the world] existed from eternity, and been left by the Deity to be governed by combined actions of the above [Newtonian] forces . . . it had been at an end long ago. . . . But we may be certain that it will last as long as was intended by its Author, who ought no more to be found fault with for framing so perishable a world, than for making men mortal.40
