Galileo's Battle for the Heavens

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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 were 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).

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 . A timeline of science contemporary with Galileo is found at Galileo's Contemporaries. 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. Like many Galileo discussions, it presents Giordano Bruno as an important scientific figure, mentioning him 7 times, and completely discounts Kepler's contributions, not mentioning him 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 (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. They were not clutching to some ancient model. 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. A measure of Kepler's and Brahe's importance is Newton's high regard for their work. The image below is a word cloud (see wordle.net) of references to scientists in Newton's great work,Philosophiæ Naturalis Principia Mathematica . References in the book's preface were not included.

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.

A major tool for cosmology is the Telescope; a device commonly associated with Galileo. In an ironic twist, Galileo's Jesuit contemporaries had made advances in telescope design and construction that would outlast Galileo's own contributions. Christopher Scheiner had opted for a Keplerian design of telescope instead of the popular Galilean design. This would be the design of choice by astronomers within a decade after Galileo's death. Galileo's Battle for the Heaven's does mention Christopher Scheiner, but only to highlight his mistake in believing that sunspots were satellites instead of solar phenomenon.

Modern discussions of the Galileo Affair present a distorted view of seventeenth century cosmology. More importantly, they present a distorted view of seventeenth century science. Galileo was an important scientist of the seventeenth century...he wasn't 'science'. If we look at who the scientists of the 1750's were citing in their work, most would be surprised. Galileo, Kepler and Tycho Brahe did not make 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. 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 not a perfect metric for the importance of a scientist but it is better than popularity with public.

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 that Galileo ever performed such an experiment. As with many myths there is a germ of truth to the story. There is documented evidence of a free fall experiment being conducted on the Tower of Pisa 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 just a dispute between an Olivetan monk and a Jesuit priest.

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.

Galileo was not the first to conduct experiments in free fall. Giuseppe Moletti, Galileo's immediate predecessor at the University of Padua, and the greatest names of 16th century physics, Simon Stevin and Girolamo Cardanus (see Classical Mechanics Timeline) all conducted free fall experiments. 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 Affair is certainly one of the most dramatic events in the history of the church and science. It is also the most widely discussed. But what part of these discussions is science, and what part is history, drama or religion.

The discussions don't seem to be about science, at least serious science. The science here is sixteenth and early seventeenth century cosmology. In Galileo's Battle for the Heavens it is a seventeenth century cosmology minus Tycho Brahe and Johannes Kepler. It went 117 minutes without a single mention of either cosmologist. Most discussions of the Galileo Affair do not fare much better. These discussions also ignore the scientific problems with the Copernican Model. Stellar parallax was an issue in the early seventeenth century. It was not to be observed for two centuries after the controversy. The most telling indicator that the Galileo Affair is not about science is the lack of interest in how the the various models performed. When faced with competing models of natural phenomenon, an obvious question for a scientist is how each perform against real world data. This question is very rarely asked, even though it has been answered (at least for the Ptolemaic vs. Copernican) [_4_] . The answer is that the Copernican Model did not seem to perform better than even the oldest of the models being argued at the time.

These discussions don't seem to be about history either. We see this from the same examples that tell us that it is not about science. If this is supposed to present a history of the battle for an idea, the least that can be expected would be to explain what the battle was against. If these discussions ignore the main models that competed with the Copernican model, and ignore the major criticisms from the day for the Copernican Model and Heliocentric theory, it is not only a problem with the science but a problem with the history. These are sins of omission. More blatant historical errors are found in the educational materials that support the program. They state "...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". None of the optical telescopes in use in the 21st century derive from Galileo. His design was abandoned by astronomers within a decade of his death. The replacement was the the Keplerian design first built by the Jesuit, Christopher Scheiner. And the most important reflecting telescopes of the 21st century do not derive from Newton's design but that of a Catholic priest, Laurent Cassegrain ( see The Church and the Early Telescope).

The program also doesn't spend much time on the religion involved. This is probably wise; delving into the subtleties of the theology involved was probably not wise in the short time allowed. What is left when you subtract the science, history and religion is a drama. What you really have is a soundbite of what actually happened. And it follows what journalism schools teach is the formula for a good soundbite [_5_] :

• 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.

Soundbites help make news interesting for a busy audience. They do not promise any deep understanding of news. No-one should think that the Galileo soundbite promises any deeper understanding of the relationship of the church and science.