The story of Galileos defense of Copernicuss heliocentric cosmology, leading to trial and condemnation by an intolerant Catholic church, has, for many people, become symbolic of a long-standing pattern of Christian hostility toward scientific conclusions that are inconsistent with a literal interpretation of the Bible. Galileo has thus come to be viewed as a martyr in a drama of perennial warfare. When the myths are stripped away, however, we find a truth far more complicated and a great deal more interesting than the myths it replaces.
In the summer of 1609, Galileo Galilei (1564-1642), professor of mathematics at the University of Padua in northern Italy, learned of a newly-invented scientific instrument the telescope. He produced one for himself and turned it to the heavens, with remarkable results: ten times the number of visible stars; mountains, valleys, and craters on the moon; four moons circling Jupiter; a ring around Saturn; and a full set of phases for Venus. Galileo quickly wrote a small book on the subject, The Starry Messenger (1610), followed three years later by Letters on Sunspots (1613) books in which he deployed his telescopic discoveries as evidence for the heliocentric (sun-centered) model of the universe. In 1611, Galileo traveled to Rome to display his new instrument. His telescopic discoveries were confirmed, and he was acclaimed by a variety of dignitaries, including the astronomers at the Jesuit College in Rome. Contrary to myth, Galileo encountered no reluctance on the part of church officials to look at the new celestial wonders through his telescope.
None of Galileos telescopic discoveries offered proof of the heliocentric model, but such discoveries as the phases of Venus, the rough topography of the lunar surface, and the satellites of Jupiter did contribute to its plausibility. Galileos books did not make many converts to heliocentrism. Indeed, worries about their compatibility with scripture, literally interpreted, became an issue around which opposition to heliocentrism could coalesce among a variety of conservative opponents. Aware of the back-stage maneuvering that was taking place and the mischief that such opposition could make, Galileo defended himself in an open letter, in which he argued that the Bible is not a scientific textbook and should not be interpreted literally when it appears to address scientific matters. However, rather than calming troubled waters, this open letter exacerbated Galileos problems, for here was a layman claiming the right to interpret Scripture. Indeed, the open letter motivated several of his critics to lodge accusations against Galileo with the Inquisition in Rome.
Aware that trouble was brewing, Galileo returned to Rome in the winter of 1515-1516, to fight smoldering fires of resentment and back-stage maneuvering against him. He was convinced that he could best his opponents in argument and convince them of the truth of the heliocentric model. While in Rome, he had frequently opportunities to make his case at dinners and other social gatherings of the Roman intelligentsia. Passionate, arrogant, and quick to display his argumentative prowess, Galileo made an occasional convert, but he also alienated some of the very people whose favor he ought to have been cultivating.
Galileo was still in Rome on 26 February 1616, when the Holy Office (the Inquisition) completed its review of the accusations made previously against Galileo and heliocentrism. On that day, he was summoned to the residence of Cardinal Robert Bellarmine (head of the Holy Office and the most powerful Catholic theologian of his day). Galileo was informed that the Copernican model had been judged false and contrary to Holy Scripture. He was admonished to abandon these opinions and forbidden to hold, teach, or defend them in any manner or form, either verbally or in writing. Galileo had no choice but to acquiesce.
On what grounds did the decision of the Holy Office rest? The ecclesiastical officials who decided the case argued (rightly) that neither Galileos telescopic observations nor the ability of the heliocentric model to make accurate astronomical predictions constituted proof that the Copernican model represented physical reality. Against this conclusion stood, first of all, church tradition, which the Roman theological establishment was not going to abandon without good reason. There were also biblical passages that apparently addressed the cosmological question:
Psalm 19:4-6: In [the heavens God] has set a tent for the sun, which comes forth like a bridegroom leaving his chamber and, like a strong man, runs its course with joy. Its rising is from the end of the heavens, and its circuit to the end of them.
Ecclesiastes 1:5: The sun rises and sets and hastens to the place of its rising.
Joshua 10:12-13: Then spoke Joshua to the Lord in the day when the Lord gave the Amorites over to the men of Israel; and he said in the sight of Israel, Sun, stand thou still at Gibeon, and thou Moon in the valley of Aijalon. And the sun stood still, and the moon stayed . . .
Were ours a heliocentric cosmos, Joshua would have commanded the earth to stop rotating on its axis.
Added to the evidence of these and several other biblical passages was a philosophical argument widely accepted by both astronomers and members of the church hierarchy namely, that astronomical models were designed merely to predict planetary positions, with no pretense of describing physical reality. We cant get up into the heavens to find out whats really going on; only God knows the mechanism that underlies the celestial motions.
However, Galileo was convinced that proof was possible. In the first place, his telescopic observations comported perfectly with the heliocentric model. The phases of Venus were just what the heliocentric model predicted, as was the periodic reversal of the planets in their course through the fixed stars. The moons of Jupiter, and the earthlike topography of the moon helped to undercut objections to the heliocentric model. Galileo regarded these pieces of evidence as sufficiently convincing. But in case they failed to persuade, he believed that his theory of the tides provided the needed physical proof. The tides, he claimed, could only be the result of a double motion of the earth (rotation on its axis and simultaneous orbital motion about the sun), which caused the seas to slosh back and forth in their basins.
The ecclesiastical authorities acknowledged that, if presented with a genuine proof of the heliocentric model, they would need to reexamine their interpretation of biblical passages that seemed to teach the motion of the sun and the stability of the earth; but in the absence of a proof, there was no reason for them to tamper with the traditional, common sense interpretation of Scripture. To obtain a proper perspective on the choice, as it presented itself to Galileos opponents, we must recognize that the community of astronomers (or scientists more generally) overwhelmingly supported the geocentric model, and it would have been an extraordinary thing for the church to abandon its traditional interpretation, common sense, and majority scientific opinion, in order to leap onto Galileos lonely bandwagon. This struggle did not pit the church against Galileo and the scientific community, but the church and most of the scientific community against Galileo and a small band of disciples.
Despite the condemnation of heliocentrism by the Holy Office, Galileo was not personally threatened, nor even named in the decree just admonished not to hold or teach the condemned theory. In 1623, a new pope was elected Maffeo Barberini (Pope Urban VIII). This was a stroke of luck, for Barberini was considered a moderate on the subject of heliocentrism; moreover, Galileo had a history of friendly relations with him. In the course of several audiences, Urban made clear his belief that humans were, in principle, incapable of achieving certainty regarding cosmological matters. Nonetheless, he gave Galileo permission to explore the pros and cons of heliocentrism, so long as he treated it merely as an unproven hypothesis. Galileo set to work and completed his Dialogue on the Two Chief World Systems in 1629. In the book, he presented extensive, powerful arguments in favor of heliocentrism, unmistakably defending it as true. In order to adhere formally to Urbans demand for neutrality, near the end of the Dialogue Galileo portrays his book merely as a drama, not intended to promote any particular cosmological belief a very risky strategy. And on the final page of the book, Galileo put the Popes admonition about the hypothetical character of heliocentrism into the mouth of Simplicio, the slow-witted Aristotelian laughing-stock of the Dialogue.
The Dialogue did not pass smoothly through the licensing process, but after various revisions it was published in 1632, with the imprimatur of the Catholic Church. The book was an instant sensation among the literati of Rome and Florence. Urban discovered his words in the mouth of Simplicio and became convinced that Galileo had betrayed his trust and, indeed, intentionally ridiculed him. Such insubordination could not be overlooked, and it was inevitable that the machinery of the Inquisition would be set in motion against Galileo.
The principal issue in the subsequent trial was the question of the churchs authority and flagrant disobedience on Galileos part. Galileo was accused of violating the injunction of 1616, which forbad him to hold or defend the heliocentric model; and of this it must have been clear to everybody concerned that he was guilty. Sentence was passed, and Galileo was forced to recant. For the remaining 10 years of his life, he was under house arrest, comfortably housed in a villa just outside Florence, with few restrictions on who could come and go. He was never tortured or imprisoned simply silenced.
What can we learn from this story? The Galileo affair was not merely an ideological conflict, but an event that had enormous human and political dimensions. After all, science and religion cannot interact. Scientists and theologians interact, and when human beings are involved, human interests are inevitably present. There were political events that were undermining Urbans authority and made him extremely irritable, suspicious, and intolerant. And, of course, Galileos personality looms large in the story. If Galileo had learned diplomacy; if he had walked softly, been willing to compromise, and understood the value of strategic retreat, it is likely that he could have carried out a significant campaign on behalf of heliocentrism without condemnation.
It follows that the outcome of the Galileo affair was a contingent event, powerfully influenced by local circumstances. It was not merely about universal or global aspects of science and religion, but about the local circumstances impinging on individual historical actors--fear, jealousy, revenge, greed, bias, ambition, personality, rivalry, alliances, and political context. Historical events are situated in time and space; they are contingent, local events, and our analysis must respond to this feature of science-religion interaction.
Finally, was this, in fact, a battle between Christianity and science, an episode in the alleged warfare of science and religion the view that has dominated understanding of the Galileo affair? In fact, every one of the actors called himself a Christian, and every one of them acknowledged the authority of the Bible. Every one of the major actors also had well-considered cosmological views, to which he and in one case she was entitled. Bellarmine had actually taught astronomy at the University of Louvain as a young man and fully understood the issues. Looked at closely, the battle turns out not to have been between science and Christianity, but within Christianity: between opposing theories of Biblical interpretation--the one progressive, the other traditional; and within science, between the proponents of competing cosmologies. The battle lines simply did not fall along a divide separating science from religion.
Finally, a wider view of science/religion conflict reveals that all parties generally prefer peace to warfare and manage to find means of compromise, accommodation, and peaceful coexistence. The Galileo affair is one of that minority of cases in which one party to the struggle was sufficiently powerful to dictate the terms of armistice.
It might seem odd to our eyes for the church to have prosecutorial jurisdiction, but, in matters of orthodoxy and faith, it probably made sense. Also, let's keep in mind that the courts of the Papacy once had appellate jurisdiction from all courts so it was a real legal system at the time.
