Past and Present

Has Science Replaced Religion?

Galileo recanted his claims about the movement of heavenly bodies when challenged by the Church (left); but physicists persisted in their research, leading eventually to the development of modern particle accelerators like the one located in this lab in Grenoble, France (right). Few would say, however, that science has replaced religion in the modern world.

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Moreover, it took centuries for European thinkers to process the New World’s implications for different fields of study, and the links between the voyages of discovery and breakthroughs in science were largely indirect. The discoveries made the most immediate impact in the field of natural history, which was vastly enriched by travelers’ detailed accounts of the flora and fauna of the Americas. Finding new lands and cultures in Africa and Asia and the revelation of the Americas, a world unknown to the ancients and unmentioned in the Bible, also laid bare gaps in Europeans’ inherited body of knowledge. In this sense, the exploration of the New World dealt a blow to the authority of the ancients.

In sum, the late medieval recovery of ancient texts long thought to have been lost, the expansion of print culture and reading, the turmoil in the church and the fierce wars and political maneuvering that followed the Reformation, and the discovery of a new world across the oceans to explore and exploit all shook the authority of older ways of thinking. What we call the scientific revolution was part of the intellectual excitement that surrounded these challenges, and, in retrospect, the scientific revolution enhanced and confirmed the importance of these other developments.

THE COPERNICAN REVOLUTION

Medieval cosmologists, like their ancient counterparts and their successors during the scientific revolution, wrestled with the contradictions between ancient texts and the evidence of their own observations. Their view of an earth-centered universe was particularly influenced by the teachings of Aristotle (384-322 b. c.e.), especially as they

Were systematized by Ptolemy of Alexandria (100-178 c. e.). In fact, Ptolemy’s vision of an earth-centered universe contradicted an earlier proposal by Aristarchus of Samos (310-230 b. c.e.), who had deduced that the earth and other planets revolve around the sun. Like the ancient Greeks, Ptolemy’s medieval followers used astronomical observations to support their theory, but the persuasiveness of the model for medieval scholars also derived from the ways that it fit with their Christian beliefs (see Chapter 4). According to Ptolemy, the heavens orbited the earth in a carefully organized hierarchy of spheres. Earth and the heavens were fundamentally different, made of different matter and subject to different laws of motion. The sun, moon, stars, and planets were formed of an unchanging (and perfect) quintessence or ether. The earth, by contrast, was composed of four elements (earth, water, fire, and air), and each of these elements had its natural place: the heavy elements (earth and water) toward the center and the lighter ones farther out. The heavens—first the planets, then the stars— traced perfect circular paths around the stationary earth. The motion of these celestial bodies was produced by a prime mover, whom Christians identified as God. The view fit Aristotelian physics, according to which objects could move only if acted on by an external force, and it fit with a belief that each fundamental element of the universe had a natural place. Moreover, the view both followed from and confirmed belief in the purposefulness of God’s universe.

By the late Middle Ages astronomers knew that this cosmology, called the “Ptolemaic system,” did not correspond exactly to what many had observed. Orbits did not conform to the Aristotelian ideal of perfect circles. Planets, Mars in particular, sometimes appeared to loop backward before continuing on their paths. Ptolemy had managed to account for these orbital irregularities, but with complicated mathematics. By the early fifteenth century, the efforts to make the observed motions of the planets fit into the model of perfect circles in a geocentric (earth-centered) cosmos had produced astronomical charts that were mazes of complexity. Finally, the Ptolemaic system proved unable to solve serious difficulties with the calendar. That practical crisis precipitated Nicolaus Copernicus’s intellectual leap forward.

By the early sixteenth century, the old Roman calendar was significantly out of alignment with the movement of the heavenly bodies. The major saints’ days, Easter, and the other holy days were sometimes weeks off where they should have been according to the stars. Catholic authorities tried to correct this problem, consulting mathematicians and astronomers all over Europe. One of these was a Polish church official and astronomer, Nicolaus Copernicus (1473-1543). Educated in Poland and northern Italy, he was a man of diverse talents. He was trained in astronomy, canon law, and medicine. He read Greek. He was well versed in ancient philosophy. He was also a careful mathematician and a devout Catholic, who did not believe that God’s universe could be as messy as the one in Ptolemy’s model. His proposed solution, based on mathematical calculations, was simple and radical: Ptolemy was mistaken; the earth was neither stationary nor at the center of the planetary system; the earth rotated on its axis and orbited with the other planets around the sun. Reordering the Ptolemaic system simplified the geometry of astronomy and made the orbits of the planets comprehensible.

Copernicus was in many ways a conservative thinker. He did not consider his work to be a break with either the Church or with the authority of ancient texts. He believed, rather, that he had restored a pure understanding

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NICOLAUS COPERNICUS. This anonymous portrait of Copernicus characteristically blends his devotion and his scientific achievements. His scholarly work (behind him in the form of an early planetarium) is driven by his faith (as he turns toward the image of Christ triumphant over death). ¦ What relationship between science and religion is evoked by this image?

Of God’s design, one that had been lost over the centuries. Still, the implications of his theory troubled him. His ideas contradicted centuries of astronomical thought, and they were hard to reconcile with the observed behavior of objects on earth. If the earth moved, why was that movement imperceptible? Copernicus calculated the distance from the Earth to the Sun to be at least 6 million miles. Even by Copernicus’s very low estimate, the earth was hurtling around the sun at the dizzying rate of many thousands of miles an hour. How did people and objects remain standing? (The earth is actually about 93 million miles from the sun, moving through space at 67,000 miles an hour and spinning on its axis at about 1,000 miles an hour!)

Copernicus was not a physicist. He tried to refine, rather than overturn, traditional Aristotelian physics, but his effort to reconcile that physics with his new model of a sun-centered universe created new problems and inconsistencies that he could not resolve. These frustrations and complications dogged Copernicus’s later years, and he hesitated to publish his findings. Just before his death, he consented to the release of his major treatise, On the Revolutions of the Heavenly Spheres (De Revolutionibus), in 1543. To fend off scandal, the Lutheran scholar who saw his manuscript through the press added an introduction to the book declaring that Copernicus’s system should be understood as an abstraction, a set of mathematical tools for doing astronomy and not a dangerous claim about the nature of heaven and earth. For decades after 1543, Copernicus’s ideas were taken in just that sense—as useful but not realistic mathematical hypotheses. In the long run, however, as one historian puts it, Copernicanism represented the first “serious and systematic” challenge to the Ptolemaic conception of the universe.

TYCHO'S OBSERVATIONS AND KEPLER'S LAWS

Within fifty years, Copernicus’s cosmology was revived and modified by two astronomers also critical of the Ptolemaic model of the universe: Tycho Brahe (TI-koh BRAH-hee, 1546-1601) and Johannes Kepler (1571-1630). Each was considered the greatest astronomer of his day. Tycho was born into the Danish nobility, but he abandoned his family’s military and political legacy to pursue his passion for astronomy. He was hotheaded as well as talented; at twenty, he lost part of his nose in a duel. Like Copernicus, he sought to correct the contradictions in traditional astronomy.

Unlike Copernicus, who was a theoretician, Tycho championed observation and believed careful study of the heavens would unlock the secrets of the universe. He first made a name for himself by observing a completely new star, a “nova,” that flared into sight in 1572. The Danish king Friedrich II, impressed by Tycho’s work, granted him the use of a small island, where he built a castle specially designed to house an observatory. For over twenty years, Tycho meticulously charted the movements of each significant object in the night sky, compiling the finest set of astronomical data in Europe.

Tycho was not a Copernican. He suggested that the planets orbited the sun and the whole system then orbited a stationary earth. This picture of cosmic order, though clumsy, seemed to fit the observed evidence better than the Ptolemaic system, and it avoided the upsetting physical and theological implications of the Copernican model. In the late 1590s, Tycho moved his work and his huge collection of data to Prague, where he became court astronomer to the Holy Roman emperor Rudolph II. In Prague, he was assisted by a young mathematician from a troubled family, Johannes Kepler. Kepler was more impressed with the Copernican model than was Tycho, and Kepler combined study of Copernicus’s work with his own interest in mysticism, astrology, and the religious power of mathematics.

Kepler believed that everything in creation, from human souls to the orbits of the planets, had been created according to mathematical laws. Understanding those laws would thus allow humans to share God’s wisdom and penetrate the inner secrets of the universe. Mathematics was God’s language. Kepler’s search for the pattern of mathematical perfection took him through musical harmonies, nested geometric shapes inside the planets’ orbits, and numerical formulas. After Tycho’s death, Kepler inherited Tycho’s position in Prague, as well as his trove of observations and calculations. That data demonstrated to Kepler that two of Copernicus’s assumptions about planetary motion simply did not match observations. Copernicus, in keeping with Aristotelian notions of perfection, had believed that planetary orbits were circular. Kepler calculated that the planets traveled in elliptical orbits around the sun; this finding became his First Law. Copernicus held that planetary motion was uniform; Kepler’s Second Law stated that the speed of the planets varied with their distance from the sun. Kepler also argued that magnetic forces between the sun and the planets kept the planets in orbital motion, an insight that paved the way for Newton’s law of universal gravitation formulated nearly eighty years later, at the end of the seventeenth century.

Each of Kepler’s works, beginning with Cosmographic Mystery in 1596 and continuing with Astronomia Nova in 1609 and The Harmonies of the World in 1619, revised and augmented Copernicus’s theory. His version of Coperni-canism fit with remarkable accuracy the best observations of the time (which were Tycho’s). Kepler’s search for rules of motion that could account for the earth’s movements in its new position was also significant. More than Copernicus, Kepler broke down the distinction between the heavens and the earth that had been at the heart of Aristotelian physics.

TYCHO BRAHE, 1662. This seventeenth-century tribute shows the master astronomer in his observatory. ¦ How much scientific knowledge does one need to understand this image? ¦ Is this image, which celebrates science and its accomplishments, itself a scientific statement? ¦ What can one learn about seventeenth-century science from such imagery?

NEW HEAVENS, NEW EARTH, AND WORLDLY POLITICS: GALILEO

Kepler had a friend deliver a copy of Cosmographic Mystery to the “mathematician named Galileus Galileus,” then teaching mathematics and astronomy at Padua, near Venice. Galileo (1564-1642) thanked Kepler in a letter that nicely illustrates the Italian’s views at the time (1597).

So far I have only perused the preface of your work, but from this I gained some notion of its intent, and I indeed congratulate myself of having an associate in the study of Truth who is a friend of Truth. . . . I adopted the teaching of Copernicus many years ago, and his point of view enables me to explain many phenomena of nature which certainly remain inexplicable according to the more current hypotheses. I have written many arguments in support of him and in refutation of the opposite view—which, however, so far I have not dared to bring into the public light. . . .

I would certainly dare to publish my reflections at once if more people like you existed; as they don’t,

I shall refrain from doing so.

Kepler replied, urging Galileo to “come forward!” Galileo did not answer.

At Padua, Galileo couldn’t teach what he believed; Ptolemaic astronomy and Aristotelian cosmology were the established curriculum. By the end of his career, however, Galileo had provided powerful evidence in support of the Copernican model and laid the foundation for a new physics. What was more, he wrote in the vernacular (Italian) as well as in Latin. Kepler may have been a “friend of Truth,” but his work was abstruse and bafflingly mathematical. (So was Copernicus’s.) By contrast, Galileo’s writings were widely translated and widely read, raising awareness of changes in natural philosophy across Europe.

Ultimately, Galileo made the case for a new relationship between religion and science, challenging in the process some of the most powerful churchmen of his day. His discoveries made him the most famous scientific figure of his time, but his work put him on a collision course with Aristotelian philosophy and the authority of the Catholic Church.