The Trial of Galileo

In 1609 Galileo Galilei, a professor of mathematics at Padua, heard of a Dutch device that made distant things look near. He built his own, improved it, and turned it to the sky. In a short book of 1610, the Starry Messenger, he reported mountains on the Moon, countless new stars and four moons circling Jupiter. Soon he added the phases of Venus and spots on the Sun. The discoveries made him famous and won him a post as court philosopher to the Grand Duke of Tuscany in Florence.

They also made him an open supporter of Nicolaus Copernicus, who in 1543 had argued that the Earth turns daily and travels around the Sun. Most scholars still followed the ancient system with the Earth fixed at the centre, and several passages of the Bible seemed to agree, such as the story in which Joshua commands the Sun to stand still. When critics raised these texts, Galileo replied in long letters, including one to the Grand Duchess Christina in 1615. Scripture, he argued, could not err, but its interpreters could, and the Bible teaches ‘how to go to heaven, not how the heavens go’, a phrase he credited to Cardinal Baronius.

In 1616 the matter reached the Holy Office. Its consultant theologians declared that the Sun at the centre was ‘foolish and absurd in philosophy, and formally heretical’, and the Earth’s motion at least erroneous in faith. On 26 February Cardinal Robert Bellarmine told Galileo to abandon the opinion. A note in the file, whose status historians still debate, adds that he was ordered not to hold, teach or defend it in any way. In March the Congregation of the Index suspended Copernicus’s book until it was corrected. Galileo himself was not condemned, and Bellarmine gave him a certificate saying so.

In 1623 Cardinal Maffeo Barberini, a cultured Florentine who had praised Galileo, became Pope Urban VIII. Galileo took heart and, with what he understood as permission to discuss Copernicus as a hypothesis, wrote the Dialogue Concerning the Two Chief World Systems, published in Florence in 1632 with church approval. In it three friends debate for four days. The defender of the old system, named Simplicio, comes off badly, and one of his arguments resembled a view the pope himself held. The book plainly favoured Copernicus.

Urban felt betrayed, and enemies of Galileo seized the chance. The search of the Inquisition’s files turned up the note of 1616, which Galileo said he did not remember. Summoned to Rome, he arrived in February 1633, nearly sixty-nine and in poor health. He was questioned in April, May and June, and lodged for part of the time in rooms at the Holy Office rather than in a cell. He argued that he had not defended Copernicus, which the judges did not believe.

On 22 June 1633, in the Dominican convent of Santa Maria sopra Minerva, he heard the sentence. He was found ‘vehemently suspected of heresy’ for having held and defended that the Sun is the centre and that the Earth moves, and for believing such an opinion could be defended after it had been declared contrary to Scripture. Kneeling, he abjured, cursed and detested these errors. The Dialogue was banned, and he was sentenced to imprisonment at the Inquisition’s pleasure. Seven of the ten cardinal judges signed.

The prison sentence was soon commuted. Galileo stayed first at the Tuscan embassy in Rome, then with the friendly Archbishop of Siena, and from December 1633 at his villa at Arcetri, in the hills above Florence. He could receive visitors with permission but could not travel freely or publish on astronomy. His beloved daughter, the nun Maria Celeste, died in 1634. Galileo went on working, and his Two New Sciences, on motion and the strength of materials, appeared in Leiden in 1638. By then he was blind. He died on 8 January 1642.

Legends gathered around the story. The most famous says that as he rose from his knees he muttered ‘Eppur si muove’, ‘and yet it moves’. No witness records it. The words first appear in a book by Giuseppe Baretti published in London in 1757, and on a painting rediscovered in the twentieth century and often dated to the 1640s, whose origin is uncertain. Another legend says he was tortured. The sentence speaks of a ‘rigorous examination’, and the records show he was threatened with torture, but most historians agree that, given his age and the outcome, the threat went no further. Nor was he burned: that was the fate of the philosopher Giordano Bruno in 1600, mainly for theological views, not for his astronomy alone.

Historians also caution against a simple tale of science against religion. Many churchmen admired Galileo, some of his strongest opponents were fellow scholars, and the evidence of the day could not yet settle the question. Galileo’s favourite proof, from the tides, was mistaken. What made the case so serious was a clash of authority: a layman reading Scripture, a pope who felt deceived, and a Church anxious after the Reformation to guard its interpretation of the Bible.

The ban faded slowly. In the edition of the Index of 1758 the general prohibition of books teaching the Earth’s motion was dropped, in 1822 the Holy Office allowed such books to be printed, and the edition of the Index of 1835 no longer listed Galileo’s Dialogue or Copernicus. In 1979 Pope John Paul II called for a fresh study, and a commission worked from 1981.

On 31 October 1992 John Paul II addressed the Pontifical Academy of Sciences on its conclusions. He said that the theologians of Galileo’s day had failed to grasp the difference between faith and scientific fact, called the affair a ‘tragic mutual incomprehension’, and recognised that Galileo had suffered. Newspapers reported that the Vatican admitted Galileo was right. Historians note that the address did not formally annul the sentence, and some criticised it for spreading blame between the judges and Galileo. Even so, it marked the end of more than three centuries in which the trial had been the best-known symbol of conflict between science and faith.