The NOVA-PBS documentary, Galileo's Battle for the Heavens, presents the story of a heroic Galileo battling for truth. This Galileo was a man whose guide was fact and experiment and not inherited wisdom. But the NOVA documentary might be more of a story than a true history. In Against Method, Paul Feyerabend also presents Galileo as a heroic figure. But for Feyerabend, Galileo's guide was often intuition not fact. Feyerabend believed that great science does not work the way it is painted in textbooks, and one support for this was that Galileo's commitment to Copernicism did not agree with facts known at the time.
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Much has been written about Galileo's problems with the church as a result of the publication of the Dialogue Concerning the Two Chief World Systems. Typically they present Galileo's arguments for the Copernican Model against an opposing and archaic Ptolemaic Model. Galileo provided some compelling criticisms of the Ptolemaic Model. Given these criticisms, those who disagreed with Galileo (including church scientists) are made to look very foolish. The problem with Galileo's Battle for the Heavens, like so many treatments of the Galileo Affair, is that they have fallen for a straw man argument. In a straw man argument, you create or choose an opposing argument that is easy to defeat, then proceed to destroy it. Your own argument is the victor by default. When Galileo wrote his Dialogue, the Ptolemaic model was not a "Chief World System" [_1_] . In fact, Galileo was proposing the Copernican Model against 4 other systems, including the one we accept today, the Keplerian Model.
There were at least 5 major planetary models in play when Galileo published the Dialogue. They were the Tychonic, Ursine, Capellan, Copernican and Keplerian. Three were geo-heliocentric ( Tychonic, Capellan, Ursine) where some bodies circled the sun and some the earth. Two were heliocentric (Copernican and Keplerian). Early on, Galileo's Battle for the Heavens describes Galileo's discovery that Venus went through phases. This could only be explained if Venus was orbiting the Sun and not earth. If the choice was between a Copernican model ( sun-centred ) and Galileo's straw man ( the earth-centred Ptolemaic) it was clear proof for the Copernican Model. But it wasn't a two-way choice. All 5 of the models mentioned above are compatible with the Galileo's discovery of the phases of Venus. This is lost on viewers because opposing models other than the Ptolemaic are never mentioned.
Straw man arguments aren't scientific arguments. Other clues that tell us that Galileo narratives aren't about science is the poor job done on listing the pros and cons of the various systems. In Against Method, Paul Feyerabend spends several chapters discussing Galileo and both the arguments and counter-arguments for Copernicism from a philosophical and scientific point of view. The noted philosopher's conclusions are at odds with the digested version of the controversy presented in the typical biography:
...while the pre-Copernican astronomy was in trouble (was confronted by a series of refuting instances and implausibilities), the Copernican theory was in even greater trouble (was confronted by even more drastic refuting instances and implausibilities).
There are necessary consequences of a moving earth. One of these would be the observation of stellar parallax (see Copernicus and Stellar Parallax). If the earth was moving relative to the sun it demands that viewers on earth be able to see some change in the relative positions of nearer and distant stars over the course of a year. No-one in Galileo's time was able to detect any change in the positions of the different stars. Stellar parallax was eventually detected, but not until 1838.
The Copernican Model had an even bigger problem than stellar parallax. Planetary models are mathematical models. This means they can be used to predict the position of any planet at any time during a year. Deciding on a model should have been as easy as comparing predicted positions with actual positions for each of the different models. But it seemed that all the models (excepting the Keplerian) were observationally equivalent. Modern computer-aided analyses of the Copernican Model and the Ptolemaic model confirm that there is little statistical difference between the two [_2_] . Galileo narratives ignore the fact that the Copernican Model used perfect circles, and the problem required the use of Kepler's ellipses. Kepler's model would prove better than all the other models but because it was so new, this was not obvious during Galileo's lifetime.
Although the observational data didn't prove that Kepler's Model was superior to the other models, it certainly showed that Kepler's Model should be taken seriously. Kepler's model predicted that Mercury would pass between the Earth and Sun on November 7,1631. This is known as a Transit of Mercury (see Gassendi's Transit). A Catholic priest, Pierre Gassendi, arranged for astronomers around Europe to attempt to verify the Transit. The Transit occurred within minutes of when the Keplerian Model said it would. Gassendi calculated the Kepler's model had an error of only 14 minutes (of an arc). He also calculated that the Alphonsine (Ptolemaic) model had an error of 4 degrees 25 minutes, and the Copernican Model was worse still with an error of 5 degrees (see Nicolaus Copernicus Thorunensis). Galileo ignored this important experiment. He had made the decision decades earlier to ignore Kepler's work since he considered his work erratic (see Galileo's Contemporaries).
Galileo's dispute with the church over Copernicism has become a symbol for the incompatibility of the church and science. This is curious. The Copernican model was never fully accepted by the scientific community (they eventually chose Kepler's model) and cosmology is hardly mainstream science. If finding a symbol is that easy, why wouldn't Gregor Mendel be the choice (see Gregor Mendel and Evolution). His work is core to any modern understanding of biology, agriculture or medicine. And his work was used to rescue Darwinism from obscurity. Even if we agree that seventeenth century cosmology can stand in for all of science we have problems. Wouldn't it make more sense to use the cosmologist from Galileo's time who had the most influence on the future of astronomy. That would be Johannes Kepler. A measure of Kepler's importance is Newton's high regard for his work. The image below is a word cloud (see wordle.net) of references to scientists in Newton's great work,Philosophiæ Naturalis Principia Mathematica.
Kepler was not a Catholic. Born a Lutheran, he had been excommunicated from the Lutheran church for some of his beliefs. He remained a devout Christian, but outside of any formal tradition. Nothing seemed to come easy for Kepler. Early in his career, Kepler had trouble gaining access to a telescope. Galileo ignored his request to borrow one. It would be left to a local Catholic bishop to lend him one. Over time Kepler developed a very special and long-lasting relationship with the Austrian Jesuits (especially Paul Guldin). Kepler would use the Jesuit network of institutions as his private postal service. The Jesuits chased down and returned a manuscript that was stolen from him. Niccolo Zucchi, a master Jesuit telescope builder, built a telescope for Kepler, at Guldin's request. Kepler acknowledged the help with a gushing thank you to the Jesuits in his last book, the Somnium.
Galileo, Kepler and the Jesuits were involved in a dispute over the design of telescopes. Galileo's preferred design used a convex objective and a plano-concave eyepiece. A few years after Galileo introduced his telescopes, Kepler proposed a design with a convex objective and a convex eyepiece. This design was largely ignored; except for a group of Jesuits, led by Christopher Scheiner. Scheiner started building and using telescopes using Kepler's design. He detailed this in his work, Rosa Ursina, in 1630. Astronomers remained skeptical. Within twenty years, however, astronomers had made a complete about face, discarding the Galilean design in favour of Kepler's design. The advantages of the Keplerian design had become obvious. Scheiner was only one of many church scientists who made important contributions to the early development of telescopes. One of Galileo's contemporaries, Father Marin Mersenne, proposed a design of a reflecting telescope that is still in use today. This was thirty years before Newton 'invented' the reflecting telescope. Another contemporary, the Jesuit Niccolo Zucchi, is commonly credited with building the first crude reflecting telescope. Fathers of the Telescope details some of the contributions of church scientists to the early development of the telescope.
The Galileo Affair is all about Galileo's problems with the church over his support for the Copernican Model. Copernicus himself had no problems with the church over his model. Copernicus was either in the care or employ of the church from the time he was orphaned at age 10 to his death at age 70. The church funded his university education, and provided him with three sinecures. Sinecures are effectively "money for nothing"; a regular stipend given to an individual with no associated responsibilities. In his last days, he was being cared for by a church canon, at the request of a Catholic bishop. Although Copernicus published his major works on the Copernican Model very late in life his ideas were floating around academic circles in Europe well before that. About 10 years before his death, they reached the Vatican. Shortly afterward the Vatican sent him a letter asking him to share his work with other scholars (see Schonberg's Letter). A key figure in the final publication of his work was Tiedemann Giese, a local bishop. Copernicus's workload as a canon was reduced to help him complete his manuscript. When the manuscript was finally published, it contained a copy of Schonberg's Letter, the imprimatur of the pope, and an expression of thanks to the pope. Due to his long service to the church, Copernicus was buried in a privileged location in the local Cathedral after his death.
Galileo's own problems with the church over the Copernican Model are well-known. The Vatican's reaction to the Dialogue was extreme. He was eventually placed under house arrest in a large summer villa, Il Gioello, that Galileo had been renting from one of the richest banking families in Florence. "House arrest" didn't mean quite the same thing to the Inquisition as it does today. It was more often a restriction of movement. If the sentence really involved a house arrest, there would have been no need to specify that he shouldn't cross the Arno, which was about 2 kilometers from his villa. At the time Galileo was 69. Until that time, Galileo had enjoyed the favour of the church. This included monetary support for his research. When Pope Urban VIII was elected pope, he arranged for two prebends for Galileo. Prebends are similar to sinecures, a recurring grant with little associated responsibilities. Galileo did have disputes with several Jesuits but for the most part these were scientific disputes, as happen even today. Throughout his life he remained close to many Roman Catholic clergy. Two priests, Pierre Gassendi and Marin Mersenne, could be considered Galileo's ambassadors outside of Italy. One of his 'prisons' during his trial was the palace of one of his best friends, Archbishop Piccolomini of Siena. Although the Inquisition considered his stay there as a "formal prison", few others would. He was wined and dined by his friend. In fact, Galileo's daughter wrote him about her concern that the wine might affect his health, and that she feared that when he was finally allowed to return to Il Gioello, he would not want to.
Galileo's Battle for the Heavens makes things simple for its viewers. Galileo was the voice for reason, and those opposing him were voices for the status quo. Things are rarely that simple. Each planetary model in play in 1632 had its strengths and its weaknesses. Galileo was not as logical as he was made to be; Galileo's disdain for Johannes Kepler was probably more a product of Galileo's pride than his logic. Conversely, those who championed one of the geo-heliocentric models had logical reasons to question heliocentric systems. Those questions were answered in the following centuries. We should not judge them on what we know now, but on what was known then.