24 The Scientific Revolution

Science is the method by which we understand and predict the workings of the physical world. Its rules are rigorous, its theories testable by experiment, and its laws once established immutable—unless new evidence proves them false.

Although today science and religion are regarded by non-fundamentalists as distinct activities involved in separate spheres of human experience, in the past the two came into conflict when science’s accounts of the physical world contradicted Scripture or other accepted religious authority.

In Christian Europe in the Middle Ages, the scientific achievements of the ancient Greeks were largely unknown, and little of what we would call science was undertaken. Only in the Islamic world were the writings of the Greeks preserved and built upon, and it was only from the 12th century that Latin translations of Aristotle and others began to appear in Europe. St. Thomas Aquinas worked the philosophy of Aristotle into Christian theology, while the teachings of the ancients regarding the nature of the physical universe—from the celestial sphere to the human body—came to be regarded as unchallengeable.

Copernican cosmology Although in the 3rd century BC the ancient Greek philosopher Aristarchos had concluded that the Earth rotates about its own axis and orbits the Sun, this account of a heliocentric (Sun-centered) universe had been overshadowed in the 2nd century AD by Ptolemy of Alexandria, who held that it was the Earth, not the Sun, that was at the center of the universe. The Ptolemaic system later became incorporated into Christian doctrine, in which the Earth and human life on it were the culmination of God’s creation.

“To affirm that the Sun is in very truth at the centre of the universe … is a very dangerous attitude … ”

Cardinal Roberto Bellarmino of the Roman Inquisition, April 12, 1615

The Earth-centered version was universally accepted in Europe until the Polish astronomer and mathematician Nicolaus Copernicus (1473–1543) tried to calculate the future positions of the planets, and found the mathematics much easier if he assumed that they all (Earth included) orbited the Sun. He then realized that this would account for the observed fact that the planets at certain times appeared to reverse direction and go backward relative to the Earth.

Aware that he risked criticism or worse from the church, Copernicus waited until 1543, the year of his death, before publishing On the Revolutions of the Celestial Spheres. This met with disapproval from both Catholics and Protestants. But after his death Copernicus’s theory was backed up by detailed astronomical observations. These led Johannes Kepler (1571–1630) to work out that the planets traced ellipses around the Sun, rather than circles—which received wisdom held to be the more mathematically perfect figure. Further evidence in support of the Copernican system was produced by Galileo Galilei (1564–1642), who used the telescope he made to observe sunspots (rendering the Sun less of a perfect body than hitherto supposed) and the moons of Jupiter. Copernicanism was formally condemned by the Roman Catholic Church in 1616, and in 1633 Galileo, faced with a charge of heresy for which the punishment was burning at the stake, was forced to retract his support for the heliocentric theory. He remained under house arrest for the rest of his life.

The scientific method Copernicus had been anxious to find evidence that ancient authors had proposed a heliocentric universe, and was relieved to find references to such theories in his readings of Cicero and Plutarch. But the authority of the ancients did not remain unchallenged. The European voyages of discovery of the 15th and 16th centuries did much to alter perspectives: as the Irish scientist Robert Boyle pointed out in 1690, even an ordinary seaman traveling with Columbus to the New World “was able at his return to inform men of an hundred things that they should never have learn’d by Aristotle’s philosophy or Ptolemy’s Geography.” Earlier in the same century, the English philosopher and statesman Francis Bacon had in the light of new discoveries rejected the old dogma that “the bounds of the intellectual globe should be restricted to what was known to the ancients.” Bacon went on to assert that the recent invention of gunpowder, printing and the magnetic compass demonstrated that the moderns had already superseded the ancients.

Discovering the interior world

In the Middle Ages, the ultimate authority on medicine and human anatomy was the ancient Greek physician Galen. In Galen’s day, human dissection was forbidden, and he had come to his conclusions about human anatomy by dissecting animals. When the Flemish anatomist Andreas Vesalius (1514–64) began to dissect the corpses of recently executed criminals, he found that Galen was often mistaken. The response of the traditionalists was that human anatomy must have changed since Galen’s day. Galen had had a notion of blood circulation, suggesting that blood seeped through tiny pores in the wall separating the two ventricles of the heart. Thus when the English physician and anatomist William Harvey (1578–1657) contradicted Galen when he published his account of the circulation of the blood in 1628, it caused considerable controversy. But by the time of Harvey’s death his detailed description, based on his dissections and experiments on animals, was widely accepted.

Bacon was the pioneer of the process of induction—the derivation of general theories from observations of what actually occurs in the physical world. This contrasts with deduction, in which particular conclusions are argued from general principles—without reference to observation or experiment. Deduction is only valid in science if it is based on mathematics. Galileo himself had realized this, and was the first to insist on the use of mathematical analysis in physics.

The new scientific method, based on observation and experiment, and anchored in the remorseless logic of mathematics, was triumphantly vindicated in the work of Sir Isaac Newton (1642–1727). Newton’s discovery of the three laws of motion and the law of gravitation provided a complete mechanical explanation of the universe, whose operations were shown to be as predictable as clockwork. Newtonian mechanics underscored the great technological advances that were to follow—from steam engines to space rockets—and, despite the conclusions of relativity and quantum physics, his laws still remain valid at most scales and for most practical purposes. It was Newton’s intellectual breakthrough more than any other that laid the ground for the Enlightenment of the 18th century.

the condensed idea

Our understanding of the physical world became freed from ancient authority and religious dogma