The Scientific Revolution

Although the Catholic and Protestant churches encouraged the study of science and many prominent scientists were themselves clerics, the search for a secular, scientific method of determining the laws of nature undermined traditional accounts of natural phenomena. Christian doctrine had incorporated the scientific teachings of ancient philosophers, especially Ptolemy and Aristotle; now these came into question. A revolution in astronomy contested the Ptolemaic view, endorsed by the Catholic church, which held that the sun revolved around the earth. Startling breakthroughs took place in medicine, too. Supporters of these new developments argued for the scientific method, which combined experimental observation and mathematical deduction. The use of the scientific method culminated in the astounding breakthroughs of Isaac Newton at the end of the seventeenth century. Newton’s ability to explain the motion of the planets, as well as everyday objects on earth, gave science enormous new prestige.

The traditional account of the movement of the heavens derived from the second-century Greek astronomer Ptolemy, who put the earth at the center of the cosmos. Above the earth were fixed the moon, the stars, and the planets in concentric crystalline spheres; beyond these fixed spheres dwelt God and the angels. In this view, the sun revolved around the earth, the heavens were perfect and unchanging, and the earth was “corrupted.” Ptolemy insisted that the planets revolved in circular orbits (because circles were more “perfect” than other figures). To account for the actual elliptical paths that could be observed and calculated, he posited orbits within orbits, or epicycles.

In 1543, the Polish clergyman Nicolaus Copernicus (1473–1543) began the revolution in astronomy by publishing his treatise On the Revolution of the Celestial Spheres. Copernicus attacked the Ptolemaic account, arguing that the earth and other planets revolved around the sun, a view known as heliocentrism (a sun-centered universe). He discovered that by placing the sun instead of the earth at the center of the system of spheres, he could eliminate many epicycles from the calculations and thus simplify the mathematics. Copernicus died soon after publishing his theories, but when the Italian monk Giordano Bruno (1548–1600) taught heliocentrism, the Catholic Inquisition (set up to seek out heretics) arrested him and burned him at the stake.

Copernicus’s views began to attract widespread attention in the early 1600s. When the Danish astronomer Tycho Brahe (1546–1601) observed a new star in 1572 and a comet in 1577, the traditional view that the universe was unchanging came into question. Brahe still rejected heliocentrism, but the assistant he employed when he moved to Prague in 1599, Johannes Kepler (1571–1630), was won over to the Copernican view. Kepler developed three laws of planetary motion, published between 1609 and 1619, that provided mathematical backing for heliocentrism and directly challenged the claim long held, even by Copernicus, that planetary motion was circular. Kepler’s first law stated that the orbits of the planets are ellipses, with the sun always at one focus of the ellipse.

The Italian astronomer Galileo Galilei (1564–1642) provided more evidence to support the heliocentric view and also challenged the doctrine that the heavens were perfect and unchanging. After learning in 1609 that two Dutch astronomers had built a telescope, Galileo built a better one and observed the earth’s moon, four satellites of Jupiter, the phases of Venus (a cycle of changing physical appearances), and sunspots. The moon, the planets, and the sun were no more perfect than the earth, he insisted, and the shadows he could see on the moon could only be the product of hills and valleys like those on earth. Galileo portrayed the earth as a moving part of a larger system, only one of many planets revolving around the sun, not as the fixed center of a single, closed universe.

In 1616, the Catholic church forbade Galileo to teach that the earth moves; then, in 1633, it accused him of not obeying the earlier order. Forced to appear before the Inquisition, he agreed to publicly recant his assertion about the movement of the earth to save himself from torture and death. Afterward, Galileo lived under house arrest and could publish his work only in the Dutch Republic, which had become a haven for scientists and thinkers who challenged conventional ideas. (See “Document 15.2: Sentence Pronounced against Galileo.”)

In the same year that Copernicus challenged the traditional account in astronomy (1543), the Flemish scientist Andreas Vesalius (1514–1564) did the same for anatomy. Until then, medical knowledge in Europe was based on the writings of the second-century Greek physician Galen, Ptolemy’s contemporary. Drawing on public dissections (which had been condemned by the Catholic church since 1300) he performed himself, Vesalius refuted Galen’s work in his illustrated anatomical text, On the Construction of the Human Body. The English physician William Harvey (1578–1657) used dissection to examine the circulation of blood within the body, demonstrating how the heart worked as a pump. The heart and its valves were “a piece of machinery,” Harvey insisted, and they obeyed mechanical laws. Nature, he said, could be understood by experiment and rational deduction, not by following traditional authorities.

In the 1630s, the European intellectual elite began to accept the new scientific views. Ancient learning, the churches and their theologians, and long-standing popular beliefs all seemed to be undercut by the scientific method. Two men were chiefly responsible for spreading the reputation of the scientific method in the first half of the seventeenth century: the English Protestant politician Sir Francis Bacon (1561–1626) and the French Catholic mathematician and philosopher René Descartes (1596–1650). They represented the two essential halves of the scientific method: inductive reasoning through observation and experimental research, and deductive reasoning from self-evident principles.

In The Advancement of Learning (1605), Bacon attacked reliance on ancient writers and optimistically predicted that the scientific method would lead to social progress. The minds of the medieval scholars, he said, had been “shut up in the cells of a few authors (chiefly Aristotle, their dictator) as their persons were shut up in the cells of monasteries and colleges,” and they could therefore produce only “cobwebs of learning” that were “of no substance or profit.” Knowledge, in Bacon’s view, must be empirically based (that is, gained by observation and experiment).

Although Descartes agreed with Bacon’s denunciation of traditional learning, he was concerned that the attack on tradition might only replace the dogmatism of the churches with the skepticism of Montaigne—that nothing at all was certain. Descartes aimed to establish the new science on more secure philosophical foundations, those of mathematics and logic. In his Discourse on Method (1637), he argued that mathematical and mechanical principles provided the key to understanding all of nature, including the actions of people and states. All prior assumptions must be repudiated in favor of one elementary principle: “I think, therefore I am.” Everything else could—and should—be doubted, but even doubt showed the certain existence of someone thinking. Descartes insisted that human reason could not only unravel the secrets of nature but also prove the existence of God. Although he hoped to secure the authority of both church and state, his reliance on human reason rather than faith irritated authorities, and his books were banned in many places. He moved to the Dutch Republic to work in peace. Scientific research, like economic growth, became centered in the northern, Protestant countries, where it was less constrained by church control than in the Catholic south.

The power of the new scientific method was dramatically confirmed in the grand synthesis of the laws of motion developed by the English natural philosopher Isaac Newton (1642–1727). Born five years after the publication of Descartes’s Discourse on Method and educated at Cambridge University, where he later became a professor, Newton brought his most significant mathematical and mechanical discoveries together in his masterwork, Principia Mathematica (1687). In it, he developed his law of universal gravitation, which explained both movement on earth and the motion of the planets. His law held that every body in the universe exerts over every other body an attractive force directly proportional to the product of their masses and inversely proportional to the square of the distance between them. This law of universal gravitation explained Kepler’s elliptical planetary orbits just as it accounted for the way an apple fell to the ground.

Newtonian physics combined mass, inertia, force, velocity, and acceleration—all key concepts in modern science—and made them quantifiable. Once set in motion, in Newton’s view, the universe operated like a masterpiece made possible by the ingenuity of God. Newton saw no conflict between faith and science. He believed that by demonstrating that the physical universe followed rational principles, natural philosophers could prove the existence of God and so liberate humans from doubt and the fear of chaos. Even while laying the foundation for modern physics, optics, and mechanics, Newton spent long hours trying to calculate the date of the beginning of the world and its end with the second coming of Jesus. Others, less devout than Newton, envisioned a clockwork universe that had no need for God’s continuing intervention.