One thing that quickly becomes apparent in discussions about science and religion is that there are a lot of stories out there. Some of them are quite good. Too good, even. Consider, for instance, Myth #8 in Galileo Goes to Jail, an essay anthology edited by historian of science Ronald L. Numbers. According to this myth, Galileo was imprisoned in an inquisition dungeon, and tortured there, for teaching the heliocentric theory. As the inquisition was pronouncing its sentence, he is supposed to have looked down at the earth and muttered, “and yet it moves.” The inquisition could silence a scientist, but not science, and not truth. It’s a paradigm case of the medieval church’s fear of science, its resort to force when challenged by free-thinking rationalists. But free thinkers can take heart. Just as science ultimately forced a retreat in religious dogma in the past, so too will it do in the present, and in the future. The truth will out, and mere force can’t stop that. So science progresses, religion retreats. It’s a zero-sum game, as we see in the case of the Galileo trial.
Like most good myths, this one has an element of truth to it. The early modern Catholic Church was nobody’s idea of a liberal, democratic institution. There were rules about what could and couldn’t be taught, Galileo violated them, he was tried by the inquisition, and he was condemned by it. But he was not tortured or sent to a dungeon. He lived the final nine years of his life under house arrest. But the story of how this happened, and why the heliocentric theory was controversial, is, as we often find in the history of science and religion, more complex and interesting than the myth.
Galileo was never tortured, and he was never sent to a dungeon.
The myth that Galileo was tortured in a dungeon arose from the Papacy itself. At the time (the early seventeenth century), the Catholic Church was involved in a fierce contest with the Protestant Reformers. Starting in the early sixteenth century, Protestants had been attacking Catholic belief and institutions throughout Europe. They denounced the Pope as anti-Christ, and were denounced in turn as heretics. There were cataclysmic wars in Germany, France, and England. Kings were overthrown, towns destroyed, tens of thousands of people massacred, and many more slain by disease and starvation, in what came to be called the Wars of Religion. In this crisis, Pope Urban VIII wanted to show other Catholics that he was up the challenge of defending the church, and that he was prepared to take a hard line in enforcing Catholic orthodoxy. When Galileo was condemned, he had documents sent to the lords and Bishops throughout Europe, to the effect that Galileo had been tortured and imprisoned. The people of the day can be forgiven for believing that it actually happened. But although historians have long known that these events did not in fact occur, the myth persists to this day. Galileo was never tortured, and he was never sent to a dungeon.
The Protestant Reformation is relevant to another aspect of the Galileo affair. When Copernicus proposed the heliocentric theory, one objection that was raised referred to a story in the book of Joshua, where the Sun miraculously stands still in the middle of the sky. Theological conservatives argued that Joshua says that the Sun stands still, implying that its normal condition is motion. Hence, in their view, the sun revolved around the earth, not the earth around the sun, and Copernicus’s heliocentric theory was false. So this is a clear-cut case of science vs. religion, right? Well, not so fast.
It’s easy to laugh at their naivety, but the science of the time was actually on the side of the conservatives. There were serious arguments on offer against the motion of the earth. One has to do with the stellar parallax. Parallax is the differential, apparent motion of two objects relative to a single observer. Suppose, for instance, you’re driving down a highway. As you look out your side window, you see a sign by the side of the road, a town beyond that, and a range of mountains beyond the town. Your motion down the highway appears as the relative, differential motion of the sign, the town, and the mountains. Each of them appears to be moving, but not at the same rate. More distant objects appear to be moving more slowly, and that’s a parallax effect.
We need to know another fact about science in order to appreciate the argument from stellar parallax: careful observation of the night sky is one of the oldest scientific activities known to history. The reason is that it’s important for two very old, very important activities. One is agriculture. An agricultural society is one in which most of the people are employed in producing food items, and where the economy is based, ultimately, on food production. In such a society it’s extremely important to have a good, reliable harvest every year. If the harvest fails, the bottom falls out of the economy, there’s mass starvation, and the ruling dynasty might even be overthrown. Everyone in an agricultural economy has an interest in good, reliable harvests. In order to get the best harvest, one needs to know when to plant the crops. Too early, and they can grow up stunted from too little light, or get wiped out by a late-winter cold snap. Too late, and they don’t have enough time to grow. Thus, having the best harvest depends on being able to accurately predict the transition from winter to spring, that depends on keeping accurate calendars, and that depends on keeping accurate astronomical records. Hence in the most ancient societies, we tend to find astronomy as a highly developed (relative to their capabilities) area of knowledge.
The other reason that astronomy was so important is astrology. I can hear some of you, dear readers, laughing at the mention of astrology as something important. Well, I’m not saying that astrology is true, that the stars exert a mystical pull on our destinies, that we can know the future by taking horoscopes, or anything like that. What I am saying, however, is that belief in astrology was extremely widespread in premodern times, and, as you’ve probably observed, is not exactly extinct in ours. Astrology was a well-paid, well-developed, well-respected profession because people really did believe that the stars exerted this kind of influence on their lives. I should note, in passing, that Augustine ridiculed astrology in his book, the Confessions. He pointed out that twins born under the same sign could have very different life outcomes, and that that falsifies astrology. So, it’s not that everyone believed in astrology, but many people did. In any case, from a historical point of view, if people think something is important, it is. Whether their beliefs are true is beside the point, if we’re just asking about why people did the things they did. And the other reason, besides the importance of agriculture, that astronomy was such a well-developed science in agricultural societies, is that astrology was taken so seriously. “Accurate” astrological prediction depends on accurate knowledge of the stars, and that, in turn, depends on astronomy.
So, astronomy was a well-developed science in Galileo’s time. His contemporaries had highly detailed, accurate star charts to work from. And that brings us back to stellar parallax. If the earth moved around the sun, the geocentric astronomers argued, we ought to see differential movement of the stars. Stars that are closer should appear to be moving more quickly, stars that are farther, more slowly, just as the sign outside your car window appears to be moving more quickly than the mountains in the distance. But if we look at the night sky, and we check our astronomical records, we don’t see this. All the stars appear to be moving at the same rate, with the exception of the planets, whose motion was already incorporated in the geocentric system. Since the stars all move at the same rate, it seems to follow that there is no stellar parallax, and hence no motion of the earth. Today we know that there is a stellar parallax effect, but it's very small. Nobody at the time realized just how far away the stars were, and they didn’t have instruments capable of detecting the very small differences in relative motion that actually occur.
Relative motion also caused another problem for the heliocentric model. If I throw a rock strait up, it comes straight down, more or less. If the earth were moving underneath it, geocentric astronomers reasoned, then it shouldn’t come back to the place from where it was thrown, but rather to another location all together. After all, the earth is moving, right? So if the earth is moving underneath a thrown object, we ought to see that reflected in the place it falls. But we don’t observe this at all. So, again, no relative motion, no heliocentrism. Another problem has to do with the atmosphere. Why doesn’t it all just fly off? If the earth is moving, what keeps it in place? The same thing goes for birds. If the earth were moving, wouldn’t they just get sucked out into space the moment they took off? Obviously, nothing like this happens, hence the earth is not moving, according to the geocentric astronomers.
At the time, the geocentric model seemed a better match with observation—it was the best science of the day.
Well, the answer here has to do with gravity, which we know about, but early modern astronomers didn’t. They knew that objects fell, of course, but Aristotle had explained this as the result of a natural tendency of objects to seek the lowest point. All objects were attracted to the center, according to Aristotle—not to each other, as Newton held. We have information that the premodern astronomers didn’t, which enables us to answer the objections of the geocentric astronomers. But at the time, the geocentric model seemed a better match with observation—it was the best science of the day.
So, if we return to the conservative theological argument against Galileo, that Joshua says the Sun moves and not the earth, I think we can see that it wasn’t just a case of science vs. religion. The science was on the theological conservatives’ side. True, they got their fingers burned when the science went in another direction, and could be made to seem pretty foolish in retrospect. And let that be a lesson on invoking sacred texts as scientific authorities. Still, it’s not really accurate to portray the dispute as one of simply science vs. religion. Not only was the science on the theological conservatives’ side, but Galileo himself was a believing Catholic. The issue was less a matter of science vs. religion than whose science, whose religion. The variety of modern, skeptical atheism that looks to science as its guiding star had nothing to do with the Galileo affair one way or another.
Oh, I nearly forgot! I promised earlier to show that Protestantism was relevant to this dispute, and so it was. The reason is that when Galileo was confronted with the passage in Joshua, and some others that seemed to support the geocentric model, he offered his own interpretation of those passages, which accorded with the heliocentric model. This was a dangerous thing to do at the time because Europe had been engulfed for a century in deadly wars, revolutions, and persecutions between Protestants and Catholics. One of the principal points of contention between them had to do with the nature of Biblical authority. Both agreed that the Bible was authoritative in some sense, but they disagreed about what that sense was. For Catholic theology, the correct interpretation of the Bible is that which accords with the traditions of the Church. They see an unbroken line of continuity stretching from the present all the way back to the early church. Not just anybody is supposed to interpret the Bible and come up with their own theological opinions; rather, it is the responsibility of the clergy to interpret Scripture, and of the laity to accept and believe that interpretation. God presides over the clergy’s interpretation to ensure that it will not lead the rank-and-file believers astray, according to Catholic theology.
Protestant theology rejects this way of thinking. It presupposes discontinuity between the early and the modern church. For Protestant Christians, the early church was rightly guided, but then traditions, abuses, and errors crept in, and gradually it lost its way altogether. That’s why there had to be a Reformation. The Church was literally re-formed, purged of erroneous doctrine and arbitrary authority, according to Protestant theology. A good Protestant is not supposed to admit the right of some external authority to tell him or her what the Bible means. They are supposed to read it, and interpret it, for themselves.
You see the trouble that Galileo was stepping into, when he offered his personal interpretation of the Bible. He sounded like a Protestant, and that was dangerous at a time when Catholics and Protestants were fighting bloody wars all over Europe. The Catholic authorities were not interested in his private interpretation of Scripture, and were not in a mood to listen to someone who presumed his right to tell them what it meant. He was usurping their responsibility. It made him sound arrogant and unreasonable.
Well, perhaps Galileo had the right to his opinions. That’s a sentiment that I think most of us would agree with. For the purpose of historical understanding, though, it’s not our opinions about right and wrong, but those of the historical actors themselves, that matter. By the standards of our time, Galileo was in the right, the Catholic Church in the wrong. By the standards of Galileo’s time (at least in Catholic Italy!) things were quite the reverse. But I don’t write any of this to apologize for the Catholic Church. In fact, John Paul II issued a formal apology in 1992, so, in a sense, it would be superfluous. When he did, the New York Times implied that Catholics were just now realizing the truth of heliocentrism: “After 350 Years,” the headline ran, “Vatican Says Galileo Was Right: It Moves.”
This essay is part of a series; the previous essay can be found here.
Daniel Halverson is a graduate student studying the History of Science and Technology. He is also a regular contributor to the PEL Facebook page.