Christian dogma was also being undermined from another direction – but so gradually and gently that at first no one paid any attention. In 1506, eleven years before Luther nailed up his theses on the church door, a quietly-spoken physician named Nicholas Copernicus became secretary and medical adviser to his uncle, the bishop of Ermland, between Prussia and Poland. Copernicus was a canon of the Church, and his hobby was astronomy. Six years later, when his uncle died of food poisoning, Copernicus had more time to devote to the stars, and he wrote a small book suggesting that the sun is the centre of the universe and that the earth is a ball that travels round it once a year. This amazing assertion contradicted everything believed by the Church throughout the Middle Ages, which accepted the complex system of Ptolemy in which the earth is the centre of the universe. To anyone who observed the heavens closely, Ptolemy’s system had enormous disadvantages, in that it had to explain why the planets travel around the earth in such strange and complicated orbits – sometimes even going backwards. Copernicus, who was a timid little man and in no way a revolutionary, saw that these contradictions vanished if he assumed that the earth goes round the sun, like all the other planets. No one was shocked by Copernicus’s ideas, even when he published On the Revolutions of the Heavenly Bodies in 1542; in fact, the pope’s right-hand man, Cardinal Schoenberg, suggested that the book ought to be published, and no one paid much attention when it appeared. Copernicus died shortly after it came out, and was soon forgotten. Half a century later, the greatest astronomer of his time, the Dane Tycho Brahe, was convinced that Copernicus was mistaken and that the earth was the centre of the universe. His reason had nothing to do with religious prejudice. He saw that if the earth moved round the sun, then it must travel millions of miles every year. In that case, the stars ought to change their positions – as a church tower changes its position when seen from a moving train. And they don’t. Tycho did not realise that the stars are so many billions of miles away that we would not notice the small changes in their position – it would be many years before someone would invent an instrument delicate enough to measure it.
Although Tycho had no magnifying telescope – they had not yet been invented – he made thousands of minute observations of the position of the planets. When he died in 1601, his young assistant Johannes Kepler, who believed in Copernicus’s theory, studied Tycho’s figures and tried to understand the laws that governed the planets. What baffled him was that Tycho’s figures showed that every planet travels at different speeds at different times. That seemed absurdly complicated. Then, one day, he succeeded in working out the shape of such an orbit, and saw that it was not at all complicated. It was a simple ellipse – a shape like an egg. He published his theory in a book called The New Astronomy in 1609. Astronomers read it with interest; no one else paid much attention.
One of these astronomers was a brilliant but self-assertive Italian named Galileo Galilei, the professor of mathematics at Padua University. In the year Kepler’s book came out, Galileo heard about a new invention that had become fashionable in Holland. Lenses had been around for about three centuries – in fact, primitive rock-crystal lenses have been found in ancient Nineveh and Carthage. Now a Dutchman had discovered that if two lenses are put into opposite ends of a cardboard tube they will magnify distant objects. Galileo quickly made himself a telescope. Then he stepped outdoors one fine night in the autumn of 1609 and looked at the moon. What he saw amazed him. Instead of a smooth surface, he saw a landscape covered with pockmarks; closer examination showed he was looking at mountains and valleys. Then he looked at the Milky Way – which to the eye looks like white gas – and saw that it was made up of millions of stars.
It was when he turned his telescope on Jupiter that he received the most exciting revelation. He saw three tiny white ‘stars’ close to the edge of the planet, and the next day, they had moved around to the other side – proving that they were not stars. Jupiter had moons, like the earth. But our moon had always been used by opponents of (Copernicus as the chief objection to his theory. If the earth went round the sun, then why should the moon go round the earth? Surely it could not be an exception to the law of nature? Now Galileo could see that our moon is not an exception – other planets have them too. In a state of great excitement, Galileo wrote a book called The Starry Messenger. It made him instantly famous, and became the seventeenth-century equivalent of a bestseller. It was like Marco Polo’s travels, a book about strange, distant regions, and everybody wanted to read it. At forty-five, Galileo suddenly found himself famous.
Galileo was, in fact, a great scientist; but his discoveries had so far not been of the kind that cause widespread interest. At the age of eighteen, he had been sitting in the cathedral at Pisa when he noticed the lamp swinging back and forth from the ceiling. He timed the swings, and observed that they always took the same time. A few years later, he went to the top of the leaning tower and dropped a heavy and a light cannon ball at the same moment; he observed that they struck the ground at the same time – disproving Aristotle’s assertion that heavy objects fall faster than light ones.
But as a human being, Galileo had serious shortcomings; from early on in his academic career, he displayed a crude self-assertion that gave much offence. And his sudden fame at forty-five acted as an intoxicant. The Academy of Science made him a member; at a banquet in his honour the new invention was christened ‘the telescope’. The pope, Paul V, gave him an audience. The Jesuits honoured him with ceremonies. For a man with Galileo’s thirst for fame, it must have been a heady experience. It made him more arrogant than ever. When scientific opponents raised objections to his theories, he treated it as a personal affront, and tried to crush them with sheer rudeness. It must be admitted, of course, that in most cases, he was right and they were wrong; but this does not excuse his bad manners. And the Church began to worry about the sheer dogmatism with which he asserted his opinions.
This was, in fact, a matter in which the Church had right on its side. Cardinal Robert Bellarmine, one of the soundest thinkers of his time, said that if Galileo thought that Copernicus was right, then it was up to him to prove it. And this was precisely what Galileo could not do. For he still lacked one essential insight: a theory of gravitation. Only gravity could explain why the planets circled around the sun as if attached to strings, and why they had reacted on one another until their orbits ceased to be circular and turned into ellipses. In fact, an English doctor named William Gilbert had stumbled on this essential clue in writing a book called On Magnets in 1600; he had suggested that the earth itself was an enormous magnet, and that this explained why things stuck to its surface as it spun round instead of flying off into space. But Galileo failed to grasp the importance of Gilbert’s idea. Instead, he wrote a book called Dialogue on the Two Chief World Systems in which he continued to insist that Copernicus was obviously correct. The new pope, Urban VIII, read it in manuscript and insisted that Galileo should stop asserting what he could not prove; he ought to present the two systems (Ptolemy and Copernicus) and leave the reader to make up his own mind.
To a man of Galileo’s headstrong temperament, this was intolerable. In a thoroughly underhand way, he had the book printed with a papal seal of approval, which he persuaded out of a good-natured but ignorant priest. It came out in 1632. And when the pope read it, he exploded with rage. It was not Galileo’s opinions that annoyed him so much as the fact that Galileo had quite openly defied him. He was as headstrong as Galileo, and he had a great deal more power. So the book was confiscated, and Galileo had to appear in front of the Inquisition. He had virtually no defence. He had promised the pope that he would teach the Copernican hypothesis as theory, not as proven fact, and he had broken his word. Galileo was forced to retract his statement that the sun was the centre of the universe, although legend adds that he muttered under his breath ‘It moves all the same’ (meaning the earth). Then he was allowed to go free. Historians of science like to assert that the episode reveals the bigotry of the Church and the honesty of the man of science. In fact, the Church emerges from the trial of Galileo with considerable credit; it was the scientist who was entirely to blame.