The reason why all mortals are so gripped by fear is that they see all sorts of things happening on the earth and in the sky with no discernible cause, and these they attribute to the will of a god. Accordingly, when we have seen that nothing can be created out of nothing, we shall then have a clearer picture of the path ahead, the problem of how things are created and occasioned without the aid of gods.5
By letting go of the immortality of the soul and accepting that all ends at death, the human mind achieves freedom of thought; the fear of “eternal punishment at death” does nothing but obscure understanding and distort our reasoning.
With immortality off the table, Lucretius then reasons his way to a series of assertions about the universe. The atoms that make up everything we see are in “ceaseless motion” and vary in size and shape. The earth was not made for man; if it had been, it would be much more hospitable than it is. Rather, the earth gave birth to both animals and human beings; it “alone created the human race.” The soul is a real thing, but like our bodies, it is made up of material particles, of atoms—in this case, atoms “most minute.” Too tiny to comprehend, they disperse into air when the body dies, and so the soul also ceases to exist.
But the most central truth of atomism, as Lucretius explains in Book II, is that all things come to an end. All natural bodies—sun, moon, sea, our own—age and decay. None are sustained or delivered by the divine. Rather, they are struck again and again by “hostile atoms” and slowly melt away. And what is true of the physical bodies within the universe is true of the universe itself: “So likewise,” he concludes, “the walls of the great world . . . shall suffer decay and fall into moldering ruins. . . . It is vain to expect that the frame of the world will last forever.”6
Like the perishing of our own bodies, the death of the universe comes without an afterlife. No god will save our souls; no god will step in to change the course of our world.
•
Lucretius was not doing science.
He made no use of Archimedes’s calculations. He had no proof of his atoms, any more than the priests he excoriated had proof of their deities. There was no way for him to test his assertions.
Yet he managed to give voice to a principle that, in the centuries to come, would become the bedrock of modern science: Explanations cannot come from outside the material world. Or, as Lucretius himself wrote,
Since there is no thing outside the whole, there is nothing that could enter the whole and produce a change.
All that there is is what there is. And in accepting the absence of what he could not believe in, Lucretius hoped to set reason free.
To read relevant excerpts from On the Nature of the Universe, visit http://susanwisebauer.com/story-of-science.
LUCRETIUS
On the Nature of the Universe (De rerum natura)
(ca. 60 BC)
Lucretius wrote in Latin verse, the scientific prose of the ancient world. A readable, relatively modern prose translation by Ronald E. Latham is available in print only from Penguin.
Lucretius, On the Nature of the Universe, trans. Ronald E. Latham, Penguin Classics, revised sub. edition (paperback, 1994, ISBN 978-0140446104).
J. S. Watson’s older, more literal translation is still readable, and available as an e-book.
Titus Lucretius Carus, On the Nature of Things, trans. John Selby Watson, Henry G. Bohn (e-book, 1851).
To make a run at the poem in a format closer to the original, try the Oxford World’s Classics edition, which retains the poetic lines of the original. The translation itself is both clear and elegant.
Lucretius, On the Nature of the Universe, trans. Ronald Melville, Oxford World’s Classics, Oxford University Press (paperback, 2009, ISBN 978-0199555147).
SIX
The Earth-Centered Universe
The most influential science book in history
In brief, all the observed order . . . would be thrown into
utter confusion if the earth were not in the middle.
—Ptolemy, Almagest, ca. AD 150
By the second century AD, astronomers and mathematicians had used Aristotelian physics, Archimedean calculations, and Lucretian principles to construct a completely erroneous model of the universe.
This universe was spherical, and it contained five types of matter: earth, water, air, and fire, plus a fifth, mysterious substance whose existence was deduced rather than seen—the ether, thought to fill the celestial realm.
Careful observation and rigorous deduction had yielded an obvious conclusion: Our planet sat at the universe’s center. After all, if you hurl a handful of dirt or toss a basinful of water into the air, it falls down; thus, earth and water were clearly seen to be “heavy matter,” meaning that they are drawn toward the center of the universe. The earth is made of heavy matter. But since the earth is obviously not falling through space (this was scientific: no one could observe this movement; therefore it did not exist), it must already be at the universe’s core.*
Fire and air do not fall. In fact, fire can even be seen to reach upward. So fire and air were classified as “light matter,” which constantly moves upward, away from the center. The stars above the earth, along with the seven independently moving celestial bodies known as the asteres planetai (wandering stars) did not seem to be drawn to the center; ergo, they were made of light matter. And since light matter moves more easily and more quickly than heavy matter, it seemed clear that the light stars were moving around the heavy earth. To assume the opposite would have been entirely counterintuitive.1
This model was confirmed by mathematical calculations. Centuries of astronomical records—some of them inherited from the stargazing Babylonians to the east, many more recorded by Greek watchers who charted the constantly moving skies from year to year and decade to decade—yielded plenty of raw data. Second-century astronomers, using the earth-centered model, could accurately calculate the future positions of both the stars and the seven wandering planets.
The mathematics involved was both complex and ingenious. To account for the movements of the planets, Greek astronomers constructed paths for them in which each planet came to a regular stop in its orbit (a “station”) and then backtracked for a predictable, calculable distance (“retrogradation”).
Living in a time when we can see into the heavens, it is hard for us to enter into the mind-set of ancient astronomers, who had no closer vantage point than their earth-bound eyes. But in all likelihood, the Greeks did not intend for their models to be taken as snapshots of the universe; they did not believe that, should they be suddenly transported into the heavens, they would actually watch Jupiter suddenly charge backward in retrograde. The mathematical patterns were just that—not realistic portrayals of the heavens, but sets of calculations that could predict where a planet or star might be, three months, or six months, or two years hence. The mathematics was a stratagem, a way of tricking the universe into revealing part of a puzzle whose true solution lay beyond their ken.
This was called “saving the phenomena”—finding geometric patterns that matched up with observational data. These calculations, constantly adjusted, did not account for every single variation in celestial movement. But they were reliable for navigators and for timekeepers, and certainly exact enough to give astronomers confidence that—with continual small adjustments demanded by new data—they were on the right path.2
In the middle of the second century BC, the great stargazer Hipparchus made use of additional strategies: he charted orbits for the moon and the planets on which they performed additional small loops (“epicycles”) while traveling along the larger circles (“deferents”). And he calculated the center of the deferents to be not the earth itself, but a point slightly offset from the theoretical core of the universe (the “eccentric”).3
Using all of these tricks, astronomers were able to accurately predict the future position of any given star or wanderer. The earth-centered universe, with the planets dancing in their complicated revolutions a
round the core, was a model that worked. And when, around AD 150, the Greek astronomer Ptolemy took on the task of assembling all of these observations and calculations into a single manual that would account for the movements of each heavenly body, Hipparchus’s model was enshrined into an unquestioned system that would last for over a millennium and shape the mind of every astronomer who gazed at the sky.
6.1 THE SCHEME OF HIPPARCHUS
6.2 THE SCHEME OF PTOLEMY
This manual, the Almagest, makes use not only of Hipparchus’s epicycles and eccentrics, but also of a new ploy. Ptolemy, unable to find the exact equations that would make planets move at the same rate all the way around their larger orbits, proposed that while the eccentric should remain the center of the deferent, the speed of planetary movement should be measured from an imaginary standing point called the equant.
The equant was self-defining—it was the place from which measurement had to be made in order to make the planet’s path along the deferent proceed at a completely uniform rate. It was, in other words, a mathematical cheat. But it was no more of a cheat than the epicycle or the eccentric, and since it gave even more accurate predictions, it, too, became part of astronomical tradition. As mathematician Christopher Linton points out, any planetary orbit, no matter how complex, can be predicted by using the equant and eccentric and by building epicycle upon epicycle—which explains why this type of calculation remained “the cornerstone of all quantitative planetary theories” until the sixteenth century.4
•
For the next fourteen hundred years, the Almagest was almost entirely unquestioned.
In the Greek-speaking empire centered at Constantinople, the Almagest was continually studied and its calculations practiced. But there were no innovations, no paradigm shifts. The earth’s position at the center of the universe remained a fundamental truth; Ptolemy’s epicycles and equants were accepted as law.
Perhaps the very effectiveness of the Almagest prevented its interrogation; when the answers come out correct (or close enough; the Byzantines were content with a fairly generous margin of error), the method doesn’t invite much scrutiny. Maybe, as H. Floris Cohen has argued, the familiarity of the tradition discouraged Byzantine thinkers from examining it too closely. But for whatever reason, Byzantine scholars did little with their scientific texts (“apart from bouts of intensive copying and some reshuffling,” as Cohen puts it). No great questions were posed and answered by the Byzantines.5
Arab astronomers did little better.
Thanks to proximity, Muslim scholars had both access to the Greek texts and the language skills to make use of them. Around 820, the Almagest was translated into Arabic; the astronomer Ahmad al-Farghani then wrote a précis of Ptolemaic astronomy, The Compendium of the Almagest, which soon became the standard Arabic text on the subject. The ninth-century astronomers Thabit ibn Qurra and Muhammad ibn Jabir al-Battani, among others, proposed refinements to account for discrepancies between Ptolemy’s predictions and their own observations. But the Islamic tradition, as a whole, was uninterested in scientific knowledge for its own sake. Problems of faith (the nature of the Koran and of the soul, the role of logic, the relationships of Platonism and Aristotelianism to revealed knowledge) ranked much higher in the work of Muslim astronomers. And so, like their counterparts in Constantinople, they left Ptolemy’s system essentially unchallenged.6
To the west of the Black Sea, European scholars were even less engaged in understanding the universe.
European education, after all, was rooted in the Roman intellectual tradition. Thanks to the dominance of the Roman Empire, Roman learning had slowly supplanted Greek education. And the Roman mind-set was a practical one. It gave priority to skills (such as rhetoric) that were useful in law and politics; much less important was the investigation of the natural world, an interesting but not particularly practical pastime. New scientific pursuits withered. And as knowledge of the Greek language faded, so did awareness of the old Greek scientific texts.7
With the failure of the Roman political machine, the duties of education were picked up, over the course of the fifth through eighth centuries, by cathedral schools—and this learning, too, had its own biases. Bishops in the West had a vested interest in making sure there were enough educated youth to qualify as future clergymen. This required learning in the traditional liberal arts: the arts of expression (the trivium, made up of grammar, logic, and rhetoric) and the arts of knowledge (the quadrivium, encompassing arithmetic, geometry, astronomy, and music). But Christian education had inherited the Roman tendency toward pragmatism, and the trivium was far more useful than the quadrivium. A clergyman needed to be able to read, speak, and convince others. Predicting the movements of the stars, not to mention mastering the complex geometric skills needed to do so, was irrelevant.
More and more, students were given a shallow, fleeting exposure to the quadrivium. Rather than grappling with the difficult calculations of the Almagest itself, they used digests and handbooks that summarized its conclusions (spherical universe, earth at the center, rotating heavens) and left out the math. It was a physics-for-poets version of astronomy that gave them no reason to question Ptolemy’s conclusions—and no reason to ask why the calculations involved were so incredibly, obfuscatingly complicated.
Over time, the handbooks and digests essentially replaced the Almagest itself. The text became rarer and rarer in the West. The educated European knew his Ptolemaic universe but knew nothing of Ptolemy. The earth-centered universe had passed into common knowledge; it was no longer a theory proposed by a single scientist that might still be disproved, but a truism authored by no one and accepted by all.
Not until the twelfth century, when the Christian kingdoms of the Spanish peninsula began to push against the Muslim dynasties to their south, did the Almagest itself reappear.
These Muslim dynasties had controlled the lower half of the peninsula for over four hundred years. They had carried with them their Arabic translations of Greek texts from the East; and so the libraries of southern Spain contained books that the European West had forgotten, and now had no access to. But by the 1130s, Muslim strength in the south had ebbed. The Christian king Alfonso the Battler, who had managed to draw the four kingdoms of the north together under a single joint crown, began to fight his way toward the Mediterranean, and his heirs followed his example.
By 1200, much of the south, including the prosperous city of Toledo and its extensive Arabic library, was in Christian hands.
The freedom to travel to Toledo opened up an entirely new set of texts for European scholars. And although most of them knew little Arabic and less Greek, a few—such as the prolific Gerard of Cremona, who single-handedly translated over seventy major works of science, mathematics, and astronomy into Latin—had the language skills to reintroduce these “lost” books to their colleagues.†
It took Western astronomers some time to begin making use of the new, highly technical manuals of astronomy, physics, and mathematics. Centuries of language-centered education had resulted in a Europe full of scholars who weren’t practiced in the complicated geometric skills needed for a true understanding of Ptolemy. The foundation of scientific learning had well and truly decayed, and rebuilding took time.
The rebuilding accelerated dramatically when, in 1453, Constantinople fell to the Ottomans. The Greek empire of Byzantium came to a final end, and scores of Greek-speaking scholars fled away from the Turks and toward the west.
They brought some of their treasured texts with them, but primarily they brought knowledge: knowledge of the language, facility with the figures, and the conviction that the Greek intellectual legacy, little developed in times of security, was now endangered and in need of preservation.
Among them was Johannes Bessarion, a high-ranking churchman, book collector, and Aristotelian expert who had fled embattled Constantinople for Italy a decade before the final conquest. Now his attempts to bring Greek learning to the West gained energy. Among his other ef
forts, he recruited a young German professor working at the University of Vienna, Georges Peurbach, to produce a new guide to the Almagest: a combined translation, abridgment, and commentary.
Peurbach was himself an accomplished Ptolemaic astronomer, author of a popular student’s manual that summarized the traditional understanding of the universe for beginners. He knew no Greek, but he accepted Bessarion’s commission and set to work on the Arabic text. He had finished the first six books when, at age thirty-eight, he grew suddenly ill. In April 1461, just before his death, he asked his student Johann Muller—a talented German mathematician, aged twenty-five—to finish the work.
Muller, better known by his Latin nickname Regiomontanus, agreed. Putting aside his own work, he spent several years finishing Peurbach’s project. The resulting book, the Epitome of the Almagest, was a readable and accurate abridgment of the Almagest that accepted its premises without question but did not hesitate to point out its errors (for example, that Ptolemy’s system was forced to distort the size of the moon). It was the best guide yet to the complexities of the Almagest, but it was not widely read for another quarter century—not until 1496, when it was finally typeset and printed on one of the cutting-edge new presses that had spread across Europe.8
By then, Regiomontanus also was dead; he had succumbed to an obscure sickness in July of 1476, a month after his fortieth birthday. (Translating the Almagest seemed to be poor for life expectancy.) But with the publication of the Epitome, both translators were hailed (posthumously) for their efforts in bringing the Almagest to a wider audience. “These two most celebrated men,” effused the mathematician Georg Tannstetter in 1515, “magnificently restored the most noble discipline of astronomy which had almost been obliterated from human memory.”9
The Story of Western Science Page 5