reasonable answers

Brief Synopsis (ie the "Cliff Notes" version)

When it comes to the debate between heliocentrism (the Earth goes around sun) versus geocentrism (the Sun goes around Earth), the Church was not the primary opponent to Galileo and Copernicus. The chief opponents of heliocentrism were the secular Aristotelean scientists. The Church simply subscribed to what was the reigning scientific paradigm at the time. And though today it seems obvious that the Earth moves around the sun, back then it seemed just as obvious that the Earth did not move. Empirical evidence that the Earth really did move around the sun didn’t come until the 18th century with the discovery of stellar aberration and later stellar parallax. Galileo’s own “proofs” could either be explained by the Tychonian model (phases of Venus) or were simply wrong (the motion of the tides). So the whole thing about heliocentrism versus geocentrism was not a case of science versus the church, but rather scientific theory versus scientific theory.

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The Trial of Galileo is the most commonly cited example of the conflict between science and faith, or at least the conflict between men of science and men of faith. Galileo is touted as the hero of science through his willingness to take a stand for scientific truth in defiance of the religious threats of the Church. But who was Galileo really fighting? Who was it that really opposed the idea of heliocentrism? Indeed, the story of how heliocentrism won over geocentrism can be seen as a conflict between men of science and men of faith, but in contrast with the usual perspective, I would argue that it was Galileo who was the man of faith, and in promoting heliocentrism, his fight was against the secular scientists of his day.

This entry will address the first of three popular myths about Galileo and the debate between heliocentrism and geocentrism.

Popular Myths about the Galileo and Heliocentrism versus Geocentrism

• Galileo was able to prove scientifically that the Earth moved around the sun.
• The Church tortured, burned at the stake, excommunicated, or otherwise banned all who tried to promote heliocentrism.
• Galileo was trying to undermine the authority of the church through his scientific work.

Myth #1. Galileo was able to prove scientifically that the Earth moved around the sun.

The first and foremost assault against the credibility of the Church is the idea that heliocentrism was a proven scientific theory during Galileo’s time, and thus the Church was placing dogma and superstition over reason and fact.  Much is made of the notion that the Church thwarted the work of Copernicus, Galileo, and the rest of the scientific establishment by insisting against the evidence that the Earth was at the center of the solar system and that the sun and all the planets orbited the Earth.

However, it wasn’t Christians who invented the geocentric model of the solar system. The Greeks began representing the universe with the Earth at the center as early as the 6^th century BC, with Aristotle seizing this concept as one key aspect of his cosmology.  However, it was Ptolemy in the 2^nd century AD who established the detailed workings of a geocentric system, and thus the primary geocentric model became known as the Ptolemaic system. Eventually, Aristotelian cosmology became the established scientific worldview in the West, with the Church incorporating more than a few aspects into its theological interpretations, and the Ptolemaic system became the chief astronomical model.  So it was the case that when Nicolas Copernicus presented his heliocentric (sun centered) system, he was going up against a geocentric worldview that had already been dominant for over a thousand years.  The Church was simply subscribing to what was the reigning scientific model of the time, which seemed to be in keeping with Scriptural interpretation and Church tradition.

 

Galileo’s contribution to the debate was showing that the Copernican system could explain phenomena that the Ptolemaic system could not—such as the phases of Venus. He also argued that his telescopic observations showing that Jupiter had its own system of moons provided circumstantial evidence that not all bodies in the solar system were required to orbit the Earth. However, these were not considered to be conclusive proofs for the Copernican system, as the Tychonian system—which featured the sun orbiting the Earth but all the other planets orbiting the sun—could also preserve the appearances and explain the same phenomena.

In addition, the Tychonian system had the advantage of not having to answer the obvious (at the time) question: If the Earth was actually moving around the sun, why was this motion not felt or observed by any means? Why did falling objects not get left behind or take a curved path as the Earth moved? To most scientists at the time the inability to detect the motion of the Earth seemed to be the conclusive evidence favoring a geocentric rather than a heliocentric model.

Notice that up to this point, no mention has been made of any theological or scriptural arguments against a heliocentric cosmos.  This is because for the most part the debate between heliocentrism and geocentrism was a scientific argument between Galileo and the Aristotelian scientists, with both sides claiming observational evidence for their respective position, but with the majority of scientists at the time believing that the geocentric model (Tycho’s version) agreed better with reality, especially since no demonstration had yet been made that the Earth moved.

This is an essential point that is oft neglected or ignored: the fact that heliocentrism was first opposed by the scientists of Galileo’s time, and that Galileo’s fight was with other scientists, not the Church.  And even when the Church did become involved—through the political maneuverings of said Aristotelian scientists who were fed up with trying to silence Galileo on the scientific playing field—it is erroneous to hold that Christians involved in the debate turned a blind eye to the evidence. It is due to the lack of conclusive evidence for heliocentrism that the Church continued to stick to the traditional position that the Earth was immovable and the sun and planets moved around the Earth.

The Lack of a Conclusive Demonstration

Key members of the Church who were cognizant of the issues involved showed reasonable consideration on the matter of heliocentrism. Cardinal Robert Bellarmine first consulted with Jesuit astronomers, who informed him that Galileo's proofs were more probability than established fact, before advising Galileo that heliocentrism was to be considered only a theoretical or mathematical model and not a true representation of reality, an injunction which later served as the basis for the trial against Galileo. His 1615 Letter on Galileo’s Theories showed that he was open to the possibility that heliocentrism could later be proven true:

I say that if there were a true demonstration that the sun was in the center of the universe and the earth in the third sphere, and that the sun did not travel around the earth but the earth circled the sun, then it would be necessary to proceed with great caution in explaining the passages of Scripture which seemed contrary, and we would rather have to say that we did not understand them than to say that something was false which has been demonstrated. But I do not believe that there is any such demonstration; none has been shown to me. It is not the same thing to show that the appearances are saved by assuming that the sun really is in the center and the earth in the heavens. I believe that the first demonstration might exist, but I have grave doubts about the second, and in a case of doubt, one may not depart from the Scriptures as explained by the holy Fathers.

He seemed well aware of the implications if there was a true, conclusive demonstration that the Earth moved around the sun, and he was ready to take the necessary steps of re-examining those passages in Scripture that, taken literally, seemed to imply an immovable Earth.

Galileo himself adopted Augustine’s hermeneutic which affirmed the need for a conclusive demonstration before considering that Scripture required re-interpretation. Galileo wrote, “Yet even in those propositions which are not matters of faith, this authority [of the Bible] ought to be preferred over that of all human writings which are supported only by bare assertions or probable arguments, and not set forth in a demonstrative way” (quoted in The Galileo Connection by Charles Hummel,p. 107).

Galileo’s “Killer Proof”

And so Galileo set out to find the definitive demonstration which would prove that the Earth actually moved.  He spent months experimenting with his theory involving the motion of the ocean tides, his idea being that the ocean waters sloshed back and forth due to the motion of the Earth in the same way that water in a bucket sloshes as the bucket is moved. He finally published his “killer proof” that the Earth moves around the sun in his Treatise on the Tides (1616).

The only problem was, his proof was wrong. Other scientists who considered his argument concluded that it made no sense. Galileo’s explanation would have resulted in only one tide per day, but there were two tides per day, 12 hours apart. Galileo tried to dismiss this by attributing the second tide to other factors, such as the shape and depth of the sea, etc.

He rejected the alternative explanation proposed by Kepler, that the moon caused the tides. Galileo also rejected Kepler’s evidence that the shape of planetary orbits was elliptical rather than circular, both of which were later proved to be correct.

It is an example of Galileo's acerbic attitude that in his Dialogue Concerning the Two Chief World Systems, Galileo makes this statement through the character Salviati, “Among all the famous men who have philosophized [about the tides], I wonder more at Kepler than any of the rest. Though he is a free and acute genius, he has lent his assent to the moon's dominance over the oceans and to other occult happenings and other such trifles.”

It seems that even the greatest scientist can fall prey to dogmatic assertion at times.

Thus, we can see that it is incorrect to believe that heliocentrism was scientifically proven during the time of Galileo, with the added implication that the Church was denying clear evidence in continuing to uphold geocentrism. Heliocentrism was accepted as a plausible theoretical or mathematical model, but with no empirical demonstration that the Earth was in fact moving, the scientists and theologians at the time saw no reason to abandon the geocentric model, especially in the form of the Tychonian system.

True observational proof of the motion of the earth didn’t come until the 18th century with the observation first of stellar aberration, and later stellar parallax. Stellar parallax is the observation that some stars in the sky seem to “shift” position with respect to the background due to the different location of the Earth as it orbits the sun. To visualize this, hold your thumb up at arms length and observe how it appears to “move” side to side as you view it with just your left eye and then your right eye. In fact, the concept of stellar parallax was known to astronomers at the time, and the inability to observe this phenomenon was yet another scientific argument against heliocentrism. It wasn’t until 1838 that instruments became sensitive enough to discern stellar parallax, and by this time the idea that the Earth orbited the sun was already widely accepted by both scientists and theologians.

The other two myths, which involve more of the theological and political issues surrounding the trial of Galileo, will be addressed in the next entry.

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For Further Reading
The trial of Galileo is much more nuanced and complex than the simplistic “science versus the church” caricature painted by the popular press. For a highly readable account of the trial of Galileo as well as the stories of Copernicus, Kepler, and Newton, I highly recommend Charles Hummel, The Galileo Connection: Resolving Conflicts between Science and the Bible.

The Galilean Library has some good resources, including an article by Paul Newall called The Galileo Affair.

James Hannam of Quodlibeta has an article on Deconstructing Copernicus.