The Re-Trial of Galileo

The Galileo Affair has become, to use the words of ABCTV’s Compass host Geraldine Doogue, “a defining moment in the stormy relationship between religion and science.” Galileo, one of the greatest scientists of his time, the first to break free from the constraints of medieval superstition, the first to turn his telescope to the heavens, the first to see the phases of Venus and the moons of Jupiter, the first to understand how the universe really worked. Galileo, the devout Catholic who didn’t want his beloved church to look foolish in the face of advancing scientific knowledge. Picture him on his knees as he is forced to recant what he knows is the truth. Threatened with torture or even burning at the stake, he must say the words the Inquisitors want to hear, even though he doesn’t believe them. But as he leaves the chamber, he mutters under his breath, “eppur si muove”: “and yet it moves.”

Was he convicted justly? Or is this well-worn story a gross distortion? This is what a cast of churchmen, scientists, historians, lawyers and philosophers set out to determine in “The Re-Trial of Galileo”, originally performed at the University of New South Wales and broadcast on Australia’s ABC as “The Trials of Galileo”. The jury, headed by science  journalist Robyn Williams, found Galileo, played by astronomer Fred Watson, guilty of heresy, as did the Inquisition nearly 400 years earlier. Although defence counsel Julian Burnside stated that “Any sensible jury would acquit this man and would right the wrongs of four centuries,” it is difficult to see how any other verdict could have been reached. Galileo was guilty of heresy, as it was defined by the Roman Catholic Church of his day. As prosecution counsel Anna Katzmann pointed out in her closing, the issue in the trial was “whether the accused did as the Church required of him; the Church whose teachings he claimed to follow.”

When Galileo was born in 1564, the accepted view of the structure of the universe was derived from the natural philosophy of Aristotle and the astronomy of Ptolemy. The earth was at the centre, while the sun, moon, other planets and stars revolved around it. In 1543, the Polish astronomer Nicolaus Copernicus published his On the Revolutions of the Heavenly Spheres, in which he posed a heliocentric alternative, with the sun in the centre of the universe, and the earth circling around. When Galileo started actively promoting this viewpoint from around 1610, he quickly drew the attention of conservative philosophers and clergymen who accused him of heresy, claiming that the earth’s motion contradicted Scripture. Galileo argued that the Bible could be interpreted in ways consistent with the Copernican hypothesis, but such decisions were the place of theologians, not laymen. In 1616, the motion of the earth was declared to be physically false and contradictory to Scripture, and Galileo was warned by Cardinal Roberto Bellarmine (played in the Re-Trial by church historian and former Catholic priest Paul Collins) not to hold or defend the idea that the earth moved.

It is crucial to note that this warning did not mean that Galileo was forbidden to research or write about the Copernican hypothesis at all, only that he could not defend it as a physical truth. This was the central issue at Galileo’s trial before the Inquisition: in his Dialogue Concerning the Two Chief World Systems, did Galileo defend the Copernican system as a physical truth? In the recent retrial, astronomer Fred Watson as Galileo stated that he had taken the Copernican view “in the manner of a pure mathematical hypothesis.” That is, Galileo claimed to have employed the heliocentric view of the universe merely for the sake of convenience in mathematical calculations of the motions of the planets, but he did not consider it to be a literal representation of what the world was really like. The Inquisition, and most likely the majority of his readers both then and now, disagreed.

Contrary to popular belief, the Catholic Church was not dogmatically opposed to the possibility of revising their interpretation of Scripture based on developments in natural philosophy and astronomy. As Bellarmine wrote to Galileo’s friend Paolo Foscarini in 1615, if it were to be shown that the Copernican system were true, “one would have to proceed with great care in explaining the Scriptures that appear contrary, and say rather that we do not understand them than that what is demonstrated is false.” The problem was that Galileo had not been able to provide a conclusive demonstration. Most of the evidence from his telescope could also be accommodated within the Aristotelian-Ptolemaic system, and all of it also supported a third alternative, developed by the Danish astronomer Tycho Brahe, which was ignored by Galileo. This was touched upon in the examination of astronomer Christopher Clavius, played by astrophysicist Charley Lineweaver. Clavius was familiar with Galileo’s telescopic observations, and had looked through the telescope himself, but still was not convinced that there was sufficient evidence to abandon the Ptolemaic system.

The Galileo Affair took place at a dark time in the history of the Catholic Church, which was known to take extreme measures to ensure that her subjects conformed doctrinally. Although there is no evidence to suggest that Galileo was actually tortured or even imprisoned, there is little doubt that his interrogation took place under the cloud of potentially severe sanctions. Such incidents form a regrettable chapter in the history of Christianity. However, the Catholic Church was not opposing the Copernican system on merely theological grounds, but on the accepted scientific views of the day. It was not the case, contrary to the suggestion of Julian Burnside, that “the church fathers who have given evidence in this case wish to shut down any discussion of science in case it reveals the possibility that their interpretation of the Bible might need to be reconsidered.” Galileo was quite welcome to continue investigating Copernicanism as a hypothesis, but until he developed a more convincing demonstration, the existing interpretation of Scripture would be maintained.

Was Galileo justly convicted of heresy? At present, 62% of respondents in the Compass online poll have voted “no”. With hindsight, we know that Galileo turned out to be correct, on some points at least. But the situation at the time was not nearly so clear-cut. The Re-Trial of Galileo considered some of the questions raised by the trial, but an hour-long television programme can only do so much. It is likely, then, that the trials of Galileo will continue.

Dr Larissa Aldridge is a CPX Fellow who has recently completed a PhD in History and Philosophy of Science. She teaches Science and Religion at The University of New South Wales in Sydney.

“The Re-Trial of Galileo” was created and produced by Dr Peter Slezak of the School of History and Philosophy at the University of NSW. The Compass programme “The Trials of Galileo” may be viewed, along with a transcript, at