The condemantion of Galileo by the Roman Catholic Church in 1633 is one of the most dramatic incidents in the long history of the relations between science and religion. Galileo claimed in his Dialogue on the Two Chief World Systems, published the year before, that the sun-centered system of Copernicus was not only a convenient mathematical device for calculating the position of the planets but that it was the physical truth. This appeared to many Christians to run counter to statements in the Bible where the sun is described as mobile and the earth as stationary.

The clash between scientific truth and biblical revelation could have been avoided if Galileo, who had no decisive proof that the earth moves, had been more cautious and if theologians, who tended to be dogmatic, had not assumed that the Bible was to be interpreted literally whenever it mentioned natural events.

Early life

Galileo Galilei was an Italian astronomer, physicist, and natural philosopher. He was born in Pisa on February 15, 1564, and died in Arcetri on January 8, 1642. Galileo studied at the University of Pisa where he became Professor of Mathematics in 1589. Three years later he moved to the University of Padua where he taught elementary astronomy, mathematics, and physics. Medical students made up the majority of his audience, and he also lectured on fortification and military engineering to young noblemen.

Copernicanism

The first indication of Galileo's commitment to the Polish astronomer Nicolaus Copernicus (1473–1543) appeared in a letter that Galileo wrote to his former colleague at Pisa, Jacopo Mazzoni, in 1597. In August of that year he received a copy of Johannes Kepler's Mysterium Cosmographicum, in which the heliocentric theory of the solar system was vindicated on mathematical and symbolic grounds. After reading the preface, Galileo wrote to Kepler (1571–1630) to voice his approval of the view that the earth is in motion, but also to express his fear of making his position known to the public at large.

Around 1602, Galileo began making experiments with falling bodies in conjunction with his study of the motion of pendulums. He first expressed the law of freely falling bodies, namely the fact that speed increases as the time squared, in 1604, but claimed to have derived it from the assumption that speed is proportional to distance (whereas, as he later realised, speed is proportional to the square root of the distance). In the autumn of 1604, the appearance of a supernova gave him the opportunity to argue that heavenly matter is not unchangeable.

In July 1609, after hearing that a Dutchman had invented a device to make distant objects appear nearer, Galileo built one himself and gave a demonstration of his telescope from the top of the Campanile of San Marco in Venice. The practical value for sighting ships at a distance impressed the Venetian authorities who confirmed Galileo's appointment for life and raised his salary from 520 to 1,000 florins, an unprecedented sum for a professor of mathematics. Galileo never quite mastered the optics of his combination of a plano-convex objective and a plano-concave eyepiece (an opera glass), but he succeeded in producing a twenty-power telescope, which he turned to the sky in 1610. What he saw is reported in the Sidereus Nuncius (The Starry messenger), which appeared in March 1610. The work was to revolutionize astronomy. The moon was revealed as covered with mountains, new stars appeared as out of nowhere, the Milky Way dissolved into a multitude of starlets and, more spectacular still, four satellites were found orbiting around Jupiter. This was particularly important since, if Jupiter was revolving around a central body with four attendant planets, it could no longer be objected that the earth could not carry the moon around the sun. Jupiter's satellites were not a decisive argument for Copernicanism, but they removed a major obstacle to having it seriously entertained by astronomers.

The Grand Duke of Tuscany, Ferdinand, died in January 1609 and was succeeded by his son, Cosimo II. Galileo had wanted to return to Florence for some time and he realised that his newly-won fame might assist him in effecting a change of residence. He christened the satellites of Jupiter Medicean stars in honour of Cosimo and, in July 1610, he was appointed Mathematician and Philosopher of the Grand Duke of Tuscany. Soon thereafter he discovered that Venus has phases like the moon, and that sunspots move across the surface of the sun.

Theological objections

In December 1613, theological objections were raised at a dinner at the court of the Grand Duke in Pisa. Galileo was absent but his disciple Benedetto Castelli defended his views when questioned by Christina of Lorraine, the Grand Duchess of Tuscany and the mother of the Grand Duke. Galileo felt that the matter was important enough to write a long letter to Castelli, dated December 21, 1613, in which he argued that the heliocentric system was not at variance with the Christian faith. On the fourth Sunday of Advent 1614, a Dominican friar, Tommaso Caccini, inveighed against the Copernican system from the pulpit of the church of Santa Maria Novella in Florence. Another Dominican, Nicolo Lorini, denounced Galileo to the Inquisition. Galileo then wrote a long letter to Christina of Lorraine, where he developed the view that God speaks through the book of nature as well as through the book of Scripture, and that the Bible teaches people how to go to heaven, not how the heavens go. In 1615, Cardinal Robert Bellarmine wrote a letter stating that in the absence of a conclusive proof for the motion of the earth, Galileo and astronomers should content themselves with speaking hypothetically. The Cardinal added that should such a proof become available then the passages in the Bible that seem to say that the earth is at rest would have to be reinterpreted. In 1616, Copernicus's On the Revolutions of the Heavenly Spheres was placed on the list of proscribed books and Galileo was privately, but nonetheless officially, warned not to teach orally or in writing that the earth revolves around the sun.

The debate on the comets and Galileo's trial

In 1618 great excitement was generated over the appearance, in rapid succession, of three comets. Galileo thought that they were merely optical phenomena caused by refraction in the atmosphere and he wrote a Discourse on the Comets to criticise the account of Father Orazio Grassi (1583–1654), a professor of mathematics at the Collegio Romano, who claimed the comets were real bodies beyond the moon. Grassi published a rejoinder, to which Galileo replied. The result was bitter enmity between himself and the Jesuits.

What changed Galileo's Copernican fortune was the election of Cardinal Maffeo Barberini to the Roman Pontificate in 1623. The following spring Galileo journeyed to Rome, and the new Pope, Urban VIII (1623–1644), granted him no less than six audiences. Galileo returned to Florence feeling that he could now write about the motion of the earth. In January 1630 his long awaited Dialogue on the Two Chief World Systems was ready for publication and the manuscript was sent to Rome where a friend, Giovanni Ciampoli, played a vital role in securing permission to print the book. Ciampoli exceeded his powers and was largely responsible for Galileo's subsequent trouble.

The Dialogue had gone to press in Florence in June 1631. The publisher had decided to print a thousand copies, a large edition for the time, and the work was not completed until February 1632. Copies did not reach Rome until the end of March or early April. Pope Urban VIII created a commission to investigate the licensing of the Dialogue. In the file on Galileo at the Holy Office the commission found an unsigned memorandum of 1616 stating that he had been enjoined not to teach that the earth moves. The commission concluded that Galileo had disobeyed a formal order of the Holy Office, and Galileo was summoned to Rome, arriving, after much delay, on February 13, 1633. Despite his vigorous denial, Galileo was judged to have contravened the orders of the Church. On the morning of June 22, 1633, he was taken to a hall in the convent of Santa Maria Sopra Minerva in Rome and was made to kneel while the sentence condemning him to imprisonment was read out aloud. Still kneeling, Galileo formally adjured his error. He was allowed to leave for Siena and later, in 1634, to return to Florence, where he was confined to his house in Arcetri.

Later years and modern assessment

Galileo sought comfort in work, and within two years he completed the Discourse on Two New Sciences, the book on which his lasting fame as a scientist rests. In this work Galileo studied the structure of matter and the strength of materials, and explained motion in the light of the timessquared law of falling bodies and the independent composition of velocities. Together these laws enabled him to give an accurate description of the parabolic path of projectiles. When he cast about for a publisher, he came up against a new problem: the Church had issued a general prohibition against printing or reprinting any of his books. Galileo's manuscript was sent to the Protestant Louis Elzevier in Holland, where it appeared in 1638. Galileo became blind in that year, and he remained under house arrest until his death on January 8, 1642, five weeks before his seventy-eighth birthday.

In contemporary times, the Roman Catholic Church has recognized that the trial of Galileo rested on a misunderstanding of the moral authority of the Church. This was clearly expressed by Pope John Paul II in 1983 at a commemoration of the 350th anniversary of the publication of the Dialogue on the Two Chief World Systems. The Pope declared that divine revelation does not involve any particular scientific theory of the universe, and that the Holy Spirit does not guarantee our human explanations of the physical constitution of reality. Galileo had made exactly that point in his letter to Christina of Lorraine.

See also ASTRONOMY; CHRISTIANITY, ROMAN CATHOLIC, ISSUES IN SCIENCE AND RELIGION; COSMOLOGY; GRAVITATION; MATHEMATICS; SCIENCE AND RELIGION, MODELS AND RELATIONS

WILLIAM R. SHEA