The NOVA documentary, Galileo's Battle for the Heavens, presents the struggle between Galileo and the church for his vision of the cosmos. This drama, the Galileo Affair, has been told and retold. It is the story of a man whose guide was fact and not inherited wisdom. A hero in the battle between faith and reason. In Against Method, Paul Feyerabend also presents Galileo as a heroic figure. 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. He used Galileo as an example since Galileo's commitment to Copernicism did not agree with facts known at the time. In other words, Galileo himself was going on faith.
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Much has been written about Galileo's problems with the church over his Dialogue Concerning the Two Chief World Systems. In the Dialogue, Galileo's argued for the Copernican Model against the Ptolemaic Model. This was Galileo's 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 wins by default. The problem with Galileo's argument was that there were at least 5 "world systems"! When Galileo wrote his Dialogue, the Ptolemaic model had been already supplanted by alternative models [_1_] .
The 5 major planetary models that were in play when Galileo published the Dialogue 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 five models mentioned were compatible with the Galileo's discovery. Most discussions of the Galileo Affair fail to mention this.
Straw man arguments aren't scientific arguments. Galileo narratives compound this flaw with shallow discussions of both the Copernican and Ptolemaic models. 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).
The problems identified by Feyerabend are only one issue with modern portrayals of the Galileo Affair (e.g. Galileo's Battle for the Heavens). They often share the same missing pieces:
There are necessary consequences of a moving earth. One is 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.
Stellar parallax was not the only problem with the Copernican Model. Planetary models are mathematical models. 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. This has been confirmed by modern computer-aided analyses [_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 the others but because it was so new, this was not obvious during Galileo's lifetime. The Kepler Model did have its successes, even during Galileo's lifetime. 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, asked astronomers around Europe to help verify the Transit. The Transit occurred within minutes of Kepler's predictions. Gassendi calculated the error of Kepler's model as 14 minutes (of an arc) while that of the Ptolemaic model was 4 degrees 25 minutes. The Copernican Model was worse than either at 5 degrees (see Nicolaus Copernicus Thorunensis). Galileo ignored this important experiment. He had announced his decision to ignore Kepler's work well before the experiment. (see Galileo's Contemporaries).
Galileo's Battle for the Heavens is all about Galileo's struggle with the Catholic Church over his support for the Copernican Model. It seems odd that no mention is made of Copernicus's own struggles with the Catholic Church over his Model. Copernicus's struggles are not mentioned because there were none. What happened after Copernicus died says much about what happened during his life. Instead of being buried in a cemetery, like most members of the diocese, he was honoured with a burial inside Fromborg Cathedral [_3_] . 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 an income (through sinecures) even while at university. In his last days, he was being cared for by a church canon, at the request of a Catholic bishop. About 10 years before his death Copernicus's ideas reached the Vatican. The result was a letter asking him to share his work with other scholars (see Schonberg's Letter). Copernicus ignored the request. It then fell to Tiedemann Giese, a Roman Catholic bishop and close friend of Copernicus, to convince Copernicus to publish. Copernicus finally agreed, but only to publish his mathematical tables. It was Geise and Copernicus's student, Rheticus, who convinced Copernicus to publish his theory as well. Geise, being one of Copernicus's closest friends, did warn him to expect pushback from other astronomers [_4_] . 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 and Geise.
Kepler is usually credited with our modern view of the solar system. 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 borrowing a telescope. Galileo ignored his requests. It would be left to the Catholic bishop of Cologne to lend him one. Over time Kepler developed a close 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 some Jesuits disagreed on 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. But not for long. Shortly after Galileo's death, astronomers discarded the Galilean design in favour of Kepler's. Scheiner was only one of many church scientists who made important contributions to the early development of telescopes. This included building the first crude reflecting telescope, inventing a telescope mount that is still used widely today and proposing the reflecting telescope design that would dominate in the twentieth century. Fathers of the Telescope details some of the contributions of church scientists to the early development of the telescope.
Narratives such as Galileo's Battle for the Heavens do Galileo a tremendous disservice. Galileo's greatness could be argued using only one of his works, Discourses and Mathematical Demonstrations Relating to Two New Sciences. Yet Galileo narratives unnecessarily embellish his record with myth and hyperbole. As a result, it is difficult to know where the real Galileo ends and where the mythical Galileo begins.
There are several examples of myth-making from Galileo's Battle for the Heavens. This from an award-winning documentary that is used widely in science education in the United States. The program's accompanying website stated "...Despite myriad embellishments, however, most optical telescopes in use in the 21st century derive from the two types developed in the 17th century by Galileo and Newton, on whose shoulders all astronomers, both amateur and professional, stand today.". Astronomical telescopes are based on Kepler's design, not Galileo's. The quote exaggerates Newton's importance as well. Newton's designs are still used by amateurs, but for about a century, almost all major research reflecting telescopes have been based on a design proposed by a 17th century Catholic priest, Laurent Cassegrain ( see Reflecting on History). In an ironic twist, Isaac Newton was the most important early critic of the design.
Galileo was not working from scratch. Galileo was not the first to apply mathematics to nature as the program's website suggests. This tradition had been established centuries before in Oxford (see The Oxford Calculators) and Paris (the Doctores Parienses) but had spread through Europe. We know that Galileo had been exposed to their work from his own notes as a student [_5_] . Galileo's time-squared law for free fall (distance is related to the square of time) is the same as Bishop Oresme's time-squared law for objects undergoing constant acceleration (distance is related to the square of time). Galileo's geometric proof for his theory is very similar to Oresme's geometric proof for his. Bishop Oresme was a Parisian academic. Galileo was not a lone voice for experimentation or a lone voice against Aristotle. Sadly, the program's educational materials use Galileo's Tower of Pisa experiment as an example of his belief in experimentation. We are still waiting for any evidence that the experiment ever happened (see Galileo's Contemporaries). We do know that several of Galileo's predecessors and contemporaries ( Borro,Varchi, Moletti, Stevin, Philiponus, Renieri) had conducted free-fall experiments from towers. Neither was Galileo able to determine the rate of acceleration due to gravity (unless you consider a 50% error close enough) [_6_] . Galileo's contemporaries amongst the Jesuits were the first to derive an accurate estimate of the acceleration due to gravity (see Galileo's Contemporaries).
Several myths surround Galileo's time at the Vatican. One of the documentary's myths seems to be pure invention. According to the program, "Galileo was remanded to a small room in the Palace of the Inquisition.". The floor plan below was done by a nineteenth century historian who had visited Galileo's five-room suite in the Palace [_7_] . It shows 3 large rooms for Galileo's personal use, one room for Galileo's valet, and an ante-room to receive visitors. One side of the apartment looked out on the Vatican Gardens, and from one corner Galileo had a view of St. Peter's. The "small room" was a suite of approximately 2500 square feet (230 square metres). This is larger than the average size of a home in the United States. While at the Palace, Galileo was provided with a personal valet and the finest of Tuscan cuisine (courtesy of the Tuscan Embassy).
The Galileo Affair has become a symbol for the conflict between church and science. This is curious. Science eventually adopted Kepler's model, not Galileo's favourite, the Copernican. Neither can cosmology be considered a mainstream science. If a symbol is needed, Gregor Mendel seems a better choice (see Gregor Mendel and Evolution). His work is core to any modern understanding of biology, agriculture or medicine. The problems don't go away even if we agree to base everything on early seventeenth century cosmology. Doesn't it make more sense to use the cosmologist from Galileo's time who had the most influence on the future astronomers. That would be Johannes Kepler. The image below is a word cloud (see wordle.net) of references to scientists in Newton's great work,Philosophiæ Naturalis Principia Mathematica.
Galileo's own problems with the church over the Copernican Model are well-known. 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 (the Martellinis). "House arrest" didn't mean quite the same thing to the Roman Inquisition as it does today. It was most 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 [_8_] . 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. Throughout his stay, he was wined and dined by his friend. In fact Galileo's daughter was very concerned concerned that her father may overindulge in 'prison' and thereby endanger his health [_9_] .
The Galileo Affair raises many questions that could be used to bring students a bit closer to the nub of science. What is the difference between a theory and a model? What constitutes 'proof' for a theory? How do you validate a model? Why are actual physical experiments considered the 'gold standard' when trying to prove a theory? Why "being right" is not good enough in science? These are not the questions that are asked by educators in their worksheets for "Galileo's Battle for the Heavens". They can hardly be blamed. Galileo's Battle for the Heavens, like many treatments of the Galileo Affair, do not consider the questions important. Scientists do. It seems that with the Galileo Affair, the story takes center stage and science is demoted to a sideshow.