Galileo's Battle for the Heavens

The Nova documentary, Galileo's Battle for the Heavens, presents Galileo as a heroic figure who challenged the status quo. This Galileo was a man whose guide was fact and experiment and not inherited wisdom; the father of modern science. In Against Method, Paul Feyerabend, also presents Galileo as a heroic figure who challenged the status quo. 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. We now know that Copernicism was even contradicted by Galileo's personal observations (which he kept to himself). How do we reconcile these conflicting views of the same man.

The picture painted of a historical figure or event depends on which facts are considered and which are ignored. The NOVA documentary discussed Galileo's arguments for a sun-centered model of planetary motion. These arguments certainly had merit and were a challenge to the conventional view. What the program and website did not discuss was the scientific arguments against the sun-centered model. These arguments were equally compelling. There are necessary consequences of a moving earth. One of these would be the observation of stellar parallax (see 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.

There was another, more pragmatic, criticism; the Copernican model of planetary motion did not seem to work better than the geocentric Ptolemaic model. It is often forgotten that it was Kepler who made the Copernican model work, and Galileo knew of his work and rejected it. We now know using computer analysis and modern statistical techniques that the original Copernican model was approximately as accurate as the Ptolemaic but performed worse for some planets. Galileo and Copernicus used perfect circles to model planetary motion. This would prevent their models from ever becoming much better than the geocentric model. .

The issues surrounding the Copernican controversy are not simple. There were powerful scientifically valid arguments against the Earth-centered models. But there were also powerful scientifically valid arguments against the sun-centered models. But for biographies such as Galileo's Battle for the Heavens the issues were simple and clear. Serious treatments of the controversy are not nearly as conclusive. 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 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).

Galileo and his Contemporaries

Biographies such as Galileo's Battle for the Heavens commonly portray Galileo relationship with his contemporaries as a lone star in an otherwise dark sky. Discounting Galileo's contemporaries distorts the discussion of both church and science. Galileo had many important contemporaries including Kepler, Descartes, Pascal, Gassendi and Mersenne . After Galileo's death, when Newton took science the next giant step forward, it was Kepler's work that he used as the anchor for his greatest work (the Principia Mathematica). Newton's philosophy of science was also more influenced by the priest-scientist Gassendi than by Galileo. Galilean biographies rarely mention Kepler. In the case of Galileo's Battle for the Heavens this distortion reached extremes. It mentioned Giordano Bruno 7 times while not mentioning Kepler even once. Bruno did not contribute a single advance in fact or theory to the science of the day.

Early in Galileo's Battle for the Heavens we are warned that what we were about to see was another example of the "recurring clash between religion and science". Developing this premise was helped by ignoring Kepler and his relations with the Church. Although the Church never provided Kepler with ongoing research grants as they had Galileo [_1_] , they did provide something more important; access to resources and moral support. When Galileo ignored an early request from Kepler to borrow a telescope, it was the Archbishop of Cologne who leant him one. The last of Kepler's books to be published, Somnium, contained a gushing thank you to the Jesuit mathematician, Paul Guldin, an enduring advocate and friend of Kepler. The appendix also mentioned his joy over the gift of a telescope hand-made by the master Jesuit telescope-maker, Niccolo Zucchi. Between these early and later events there were many other events, including the Jesuits chasing down a manuscript stolen from Kepler and ensuring its return, and the Jesuits acting as a surrogate postal service for Kepler.

When modern biographies ignore Galileo's contemporaries it doesn't mean that scientists of the time did. The scientists of the day, including church scientists, were following Galileo's work, but also Kepler's. The priest-scientist Gassendi was a follower of Galileo's work. He conducted several of the experiments Galileo described in his books. But he was also a follower of Kepler. Kepler's model predicted that Mercury should pass between the earth and the sun (known as a Transit of Mercury) on November 7, 1631. The scientists of Europe were well-warned of this event in publications by Kepler and his assistant. Gassendi also published a pamphlet reminding interested scientists of this event. This was a watershed event; the first international experiment. The transit of Mercury was detected by Gassendi in Paris and other observers in Alsace, Austria, and Bavaria on November 7 but slightly earlier than predicted (see Gassendi's Transit of Mercury). Scientists around Europe, including Galileo, would have known of the experiment. Although the discovery by Gassendi that Mercury was much smaller than expected helped some of Galileo's arguments, this remarkable experiment gave credence to a model that competed with Galileo's own model; one that assumed elliptical orbits. It is Kepler's model that is taught in schools today. All this happened more than a year before Galileo's famous trial.

But Kepler was not the only contemporary of Galileo who was developing models to compete with the old Ptolemaic model. There were at least 6 models being proposed. The program, like so many other biographies of Galileo, builds a straw man, by suggesting that the choices were between Galileo's Copernican model and an archaic model inherited from Aristotle. Another important scientist of the day, Tycho Brahe, had developed the Tychonic System. The Jesuits mentioned in the program (e.g Scheiner) were not proponents of the old Ptolemaic system but of the newer Tychonic System. The program implies that all of Galileo's opponents were clutching to some ancient scheme. The Tychonic system had been published in 1587, more than 40 years after Copernicus' death. It was based on the best set of celestial data up to that time. The data set was eventually used by Kepler to propose our modern view of planetary motion.

Tycho Brahe's model was a hybrid system, where the sun circled the earth but the other planets circled the sun. The program describes important experiments where Galileo discovers that Venus actually revolves around the sun and not the earth. Galileo took this as proof of the Copernican model. But this behavior was completely consistent with the Tychonic model as well. This fact was lost on the viewers, since neither Tycho Brahe nor the Tychonic system were ever mentioned in the program. The Tychonic system has a significance beyond the controversies on planetary motion in the seventeenth century. One has to ask why Tycho Brahe would develop such an unusual system, a Geo-Heliocentric model. The answer was that he couldn't reconcile the Copernican model with the absence of visible stellar parallax. Stellar parallax was an issue for the scientists before and during Galileo's time. Modern discussions of Galileo and the church rarely mention this.

The program's theme of clash between religion and science really precludes any mention of positive contributions of church scientists. Galileo's Battle for the Heavens makes repeated mention of the Jesuits, including the Jesuit Christopher Scheiner. The Jesuits were presented as reactionary and the only mention of Christopher Scheiner was his erroneous belief that sunspots were actually satellites. The companion website has an entire section on the early development of the telescope. But these same Jesuits were critical to the early development of the telescope ( see Jesuits and the Telescope). The site mentions the man who proposed the telescope design that would quickly replace Galileo's, Kepler, but did not mention the first man to build one, Christopher Scheiner. It also mentions the innovation of adding an erector lens to Kepler's design . The website artfully dodges identifying the innovator, Christopher Scheiner, by anonymizing his contribution; "Some astronomers added a third convex lens to right the image". When the great scientists of the late 17th century looked back to help improve the telescope they weren't looking back to Galileo, but to the optical works of Kepler and Descartes and several priest-scientists (including Galileo's Jesuit contemporaries).

A discussion of Galileo would not be complete without mention of the Tower of Pisa experiment. Most people know the legend. A young professor from the University of Pisa climbs the Tower of Pisa in front of an audience of professors and students. In a direct challenge to the stodgy Aristotelian professors of the day, he proceeds to drop balls of unequal weight to show that they hit the ground at the same time. There is a growing consensus that this experiment was a myth, and the program's website questions whether the experiment ever happened. Neither Galileo nor anyone else in his lifetime ever mentioned the story. As with many myths there is a germ of truth to the story. There is documented evidence supporting only one Tower of Pisa free fall experiment in Galileo's lifetime. The twist is that the name of the young professor from the University of Pisa was Vincenzio Renieri, an Olivetan monk. Vincenzio, a friend of Galileo's, was not trying to disprove Aristotle. He was trying to disprove the work of the Jesuit, Niccolo Cabeo. Cabeo believed that two objects of different weights dropped from a height would reach the ground at the same time with the same velocity. This was based on observing the free fall experiments of Baliani. Vincenzio's experiment contradicted that of the Jesuit ( probably through experimental error) and Vincenzio promptly reported the results of his experiments to Galileo. Given how often Galilean biographies are presented as symbols of the clash between church and science, it is ironic that the Galileo's most famous experiment was really an attempt by an Olivetan monk to challenge the work of a Jesuit priest.

It is difficult to imagine a more dramatic set of events in the entire history of science than the Galileo Affair. Perhaps that is why there is so much written about it. We shouldn't confuse high drama with importance to the history of science, however. As the name, Galileo's Battle for the Heavens, suggests, the whole episode was about the heavens. But most science is very terrestrial. Statistical analysis of modern scientific activity shows that cosmology has almost no influence on the other disciplines of science ( see Home ). If these events and Galileo's other work were as important as these dramas suggest then we would see many references to it in the succeeding decades. But if we look at who the scientists of the 1750's were citing in their work, most would be surprised. Most would guess correctly that Newton was amongst the most commonly cited. Neither Galileo nor his contemporary cosmologists made it very high in the list. Galileo's contemporary, Gassendi was heavily cited, perhaps because he experimented in many areas of physics and also made important contributions to the philosophy of science. Also amongst the most commonly cited were several of Galileo's Jesuit contemporaries, Gaspar Schott, Giovanni Riccioli, and Claude-Francois Deschales [_2_] . Citations by scientists is definitely not a perfect metric for the importance of a scientist but certainly it is better than popularity with the public.

Galileo Predecessors

Popular Galilean biographies go beyond simply ignoring Galileo's contemporaries. They also ignore predecessors. In the 1630's Galileo had devised a brilliant experiment to prove the law of free fall using an inclined plane. But what he had really done is prove a law that had been taught in Jesuit schools across Europe for over a half century, and one that Galileo had accepted as true for 30 years. A Roman Catholic priest, Domingo deSoto had actually described the correct law of free fall in a textbook published 75 years before Galileo's famous experiment. The popular textbook had gone through 8 printings before Galileo finished university in Pisa. Galileo's Battle for the Heavens oversimplified Galileo's inclined plane experiment by repeating an old myth that Galileo had 'discovered by experiment' the law of free fall. There was no mention in the program of any preceding work.

The companion site also leaves the impression that the world had to wait for Galileo to perform simple experiments like dropping balls off a tower. There were literally thousands of high towers throughout Europe that would have been perfect for these experiments. The picture below shows the view from the top of one of these towers, the Torre Asinelli in Bologna. For reference, the smaller tower seen in the picture is the Torre Garisenda, itself only a few meters short of the height of the Tower of Pisa.

Torre Asinelli-Torre Garisenda

There had been considerable experimental study of falling objects before Galileo, including that by Galileo's immediate predecessor at the University of Padua, Guiseppe Moletti, and the greatest names of 16th century physics, Simon Stevin and Girolamo Cardanus (see Classical Mechanics Timeline). They had shown that light objects fall as fast as heavy objects. During Galileo's own lifetime, the Jesuits used a pendulum to time the fall of objects from the Torre Asinelli. This resulted in the first accurate estimate of the acceleration due to gravity. Galileo derived his own estimate from experiment, but his was about half the actual value [_3_] .

The Galileo Soundbite

Galileo's Battle for the Heavens is a made-for-TV docu-drama. Perhaps it is naive to expect either accuracy or balance from a TV program. However, the issues raised about the program can often be raised about many academic treatments of the Galileo Affair. In fact, the program and its companion website are often used to teach the history of science from grade school through to university.

When one looks at the program and many similar discussions one sees tell-tale signs of the soundbite. Journalists have a tried and tested formula for keeping people's attention in a soundbite [_4_] :

avoid or oversimplify any story that is complex.
build a story structure and exclude anything that doesn't contribute to that structure.
there must be conflict
story structure should include a beginning, middle and end.

It is easy to see what does and doesn't contribute to the story structure of Galileo's Battle for the Heavens. The "recurring clash between church and science" and Giordano Bruno does. Stellar parallax, scientific comparison of the competing planetary models, Galileo's refusal to accept Kepler's elliptical orbits, the long-term support of Kepler by the Jesuits, Tycho Brahe and the important early work on telescopes by the Jesuits doesn't. But the approach used in the program isn't restricted to just the popular media. It is surprising how many pages you will find on American university websites where Galileo and the Copernican Model are discussed without any mention of the major scientific criticisms against Copernicism presented at the time. Only 6% of pages from American university websites that discuss Galileo and the Copernican Model also discuss stellar parallax. That drops to 1% for the general public [_5_] .

The issues raised by the program go beyond critiquing a single television program, or the obvious concerns with mixing Hollywood and History. The program is an example of an approach to history known as "the Great Man Theory" (used very commonly in discussions that adopt the Conflict Thesis). This approach relates history through the biographies of the great men of history. The drawback of this approach is the loss of any form of perspective. In many Galileo biographies, the loss of perspective applies to the scientific discipline (cosmology), science itself, and the importance of these events to society as a whole. Within cosmology, these biographies typically contrast one flawed model, Galileo's, against another flawed model, the Ptolemaic. It is rarely mentioned that the Ptolemaic model had already fallen out of favor amongst Galileo's contemporaries. A more reasonable approach would have been to include all the key models. This would include the one that is used today, Kepler's, and the models that were supported by the different Jesuits (the Keplerian, Tychonic and Capellan). Within science itself, Galilean biographies often leave the impression that the Galileo Affair was pivotal to all future science. The assigns an importance to cosmology that is hard to support. You couldn't support it based on what scientists were citing and what they were doing 100 years later. And you can't support it based on what scientists are doing now.

Society tends to take a back seat in these discussions as well. It would take centuries before the work of many of the most famous seventeenth century scientists would truly benefit the average citizen of Europe. During Galileo's lifetime there were contributions by lesser known figures and anonymous citizens that would dramatically impact the life of the typical citizen. As Galileo was being called to Rome in 1632, Jesuit priests were returning to Rome from Peru with samples of Jesuit's Bark. This bark from the chinchona tree would eventually save thousands of lives from the scourge of malaria. The effective ingredient of chinchona bark is quinine. By the end of the seventeenth century its use had spread throughout Europe. Galileo also lived through the early stages of a Green Revolution started by the Columbian Exchange. After Columbus, several 'miracle plants' were discovered and brought back to Europe. One plant, the potato, would eventually represent the difference between life and death for millions of Europeans. Other important plants in the early stages of European cultivation included the tomato and maize plants. Most of the 'heroes' of this miraculous change were anonymous: Basque sailors, Spanish sailors, Carmelite monks, various unknown plant breeders and others. The only scientific figures of any note involved in the early history of this revolution were Bauhin, an important taxonomist, and Father Jose Acosta, a naturalist and ethnographer who had lived in South America for much of his life.

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