The Case of Galileo

A Closed Question?

Annibale Fantoli, George V. Coyne, S.J.

• Publisher: University of Notre Dame Press
• Year: 2012
• ISBN:
  9780268079727
• Topic: History
• Subtopic: European History
• Index: History

The "Galileo Affair" has been the locus of various and opposing appraisals for centuries: some view it as an historical event emblematic of the obscurantism of the Catholic Church, opposed a priori to the progress of science; others consider it a tragic reciprocal misunderstanding between Galileo, an arrogant and troublesome defender of the Copernican theory, and his theologian adversaries, who were prisoners of a narrow interpretation of scripture. In The Case of Galileo: A Closed Question? Annibale Fantoli presents a wide range of scientific, philosophical, and theological factors that played an important role in Galileo's trial, all set within the historical progression of Galileo's writing and personal interactions with his contemporaries. Fantoli traces the growth in Galileo Galilei's thought and actions as he embraced the new worldview presented in On the Revolutions of the Heavenly Spheres, the epoch-making work of the great Polish astronomer Nicolaus Copernicus.

Fantoli delivers a sophisticated analysis of the intellectual milieu of the day, describes the Catholic Church's condemnation of Copernicanism (1616) and of Galileo (1633), and assesses the church's slow acceptance of the Copernican worldview. Fantoli criticizes the 1992 treatment by Cardinal Poupard and Pope John Paul II of the reports of the Commission for the Study of the Galileo Case and concludes that the Galileo Affair, far from being a closed question, remains more than ever a challenge to the church as it confronts the wider and more complex intellectual and ethical problems posed by the contemporary progress of science and technology. In clear and accessible prose geared to a wide readership, Fantoli has distilled forty years of scholarly research into a fascinating recounting of one of the most famous cases in the history of science.

ONE

From Galileo’s Birth to His Teaching Years in Padua

Galileo was born in Pisa on February 15, 1564. At that time Italy was divided into many independent states, and Pisa, at one time a prosperous seafaring republic, was a part of the Grand Duchy of Tuscany, which was governed by the powerful Medici family, with its capital in Florence. At that time Florence was one of the richest cities in Europe. In the Middle Ages and especially in the Renaissance, Florence had made an incomparable contribution to Western art and culture. Galileo’s family was from Florence. There had been a renowned medical doctor in the family whose name was also Galileo Galilei. It is quite probable that Galileo’s father, Vincenzio, wished to give this name to his firstborn as a remembrance of his famous relative, and hoping that his son would follow in his footsteps in the medical profession. The family finances, at that time in a less than modest state, could thereby be put in order.

Vincenzio was a skillful lute player and an important member of the musical circle called the Camerata Fiorentina, where the theory of “drama in music” was developed. This eventually led to the Italian melodrama. But in order to make ends meet he was forced to engage in trading, and so, at Galileo’s birth, the family was in Pisa.

As he grew up, Galileo gave clear signs of his extraordinary talents, and this only strengthened his father’s plan to have him take up the profession of medicine. In September 1581 Galileo enrolled in the faculty of medicine at the University of Pisa. But to his father’s great chagrin he discontinued his studies without having completed the course work. It was not so much that he was not content with the courses in medicine, which were still based on the writings of the famous Greek doctor, Galen (129–199 CE). His decision was rather attributed to his growing interest in the geometry of Euclid and the mechanics of Archimedes. Galileo had begun these studies under the tutelage of Ostilio Ricci (1540–1603), the mathematician who taught the pages of the grand duke of Tuscany. Galileo became fascinated by the rigor of mathematics together with experimentation in physics. He sensed that here lay his true vocation.

During the next four years Galileo deepened his knowledge of Euclid and especially of Archimedes. These studies prepared him for a brief period of teaching at Siena (1586–1587) and later at the University of Pisa, where in July 1589 he was appointed lecturer in mathematics. He had to teach, in addition to the geometry of Euclid, the two “classical” medieval treatises: the Sphere of Sacrobosco and the Planetary Hypotheses. Whether or not he had already come in contact with astronomy, this provided him the occasion to do so. And, as in all other European universities at that time, it was Ptolemaic astronomy that he had to study and teach at Pisa.

Ptolemy’s astronomy (d. ca. 168 CE) came to be as an answer to many unresolved questions left by the theory of homocentric spheres that had been developed more than four centuries earlier by the Greek mathematician Eudoxus (409–365 BCE), who taught that the Earth is at the center of a complex system of spheres, the last of which had impressed upon it the so-called “fixed stars,” almost all of the objects visible in the sky to the naked eye. In its daily axial rotation from east to west this sphere dragged along the seven planets that lay under it. But these seven planets all had quite irregular motions that varied from one to the other with stopping points and backward motions with respect to their west to east direct motions. Eudoxus had imagined these irregular motions as due to a combination of simple circular motions of one or more concentric spheres for each planet.

Aristotle (384–321 BCE) had adopted this system, and in his treatise On the Heavens had taken it as the foundation of the structure of the movements of all heavenly bodies. But the great Greek philosopher had also and above all else tried to fit the mathematical system of Eudoxus into a complete astrophysics.

According to Aristotle the physical makeup of the heavenly bodies is clearly different from that of the sublunary bodies that are centered on the Earth. The sublunary world is made up of four fundamental elements: earth, air, fire, and water. Objects in this realm are generally made up of combinations of the four. Each of these elements has its own natural place. The natural place of the element earth is at the center of the universe. This is surrounded by a spherical shell of water, which in turn is surrounded by spherical shells of air and of fire, the latter of which extends out to just under the Moon. Should an element leave its natural place, it would tend to return to that place by its own natural motion, which is rectilinear towards the center for the heavy elements of earth and water and composites made mostly of them, and away from the center for the light elements of air and fire and composites made mostly of them. Since there are many bodies consisting of these elements and their compounds, and since there is a great contrast among their natural motions and their other characteristics, the sublunary world is subject to continuous changes.

The heavenly bodies, as well as the spheres that carry them along, are composed of a single element called the ether or the “fifth essence,” and their natural motion is circular, as shown by our everyday view of them. Since they are made up of a single element and are free of any contrasts in their circular motions, which go on indefinitely in the same direction, these bodies are immutable.

The Aristotelian universe is finite, bounded by the sphere of the fixed stars. And it exists from all eternity. Even if He did not create it, God is the ultimate source of its cosmic dynamism. All of the motions of finite and imperfect beings that populate the material world have, in fact, as the final cause the “desire” to be united with God, the perfect being and supreme good.

The fact that in this system the Earth is immobile at the center of the finite universe necessarily results from the “heaviness” of the element earth and of the composite bodies in which it is prevalent, and from its natural motion to go straight down to its natural place, the center of the universe. According to Aristotle this conclusion of “natural philosophy”—a term used until Newton’s time to designate a branch of study similar to what we now call “science”—is confirmed by the experience of our senses, which do not detect any motion of the Earth, neither an axial rotation nor an orbital revolution about another body.

With this conviction Aristotle criticizes the theories of the Earth’s motion developed by the school of Pythagoras. According to Philolaus (about 430 BCE) the Earth moves in the course of a day about a “central fire” (not to be confused with the Sun), which cannot be seen because the inhabited hemisphere (which contemporaries considered to be Europe, Africa, and Asia) of the Earth always faces away from it. That implied an axial rotation of the Earth. Later on the idea of a central fire was eliminated, but the axial rotation of the Earth remained. This idea was taken up by Heraclides Ponticus (388–310? BCE), a contemporary of Aristotle. These theories were labeled together as “Pythagorean,” a term that at Galileo’s time was used to denote also the more advanced theory of Aristarchus (see below), the only real forerunner of Copernicus’s heliocentrism in Greek antiquity.

None of these theories, including that of Aristarchus, had the support of justification at the level of natural philosophy similar to that given by Aristotle in his cosmology, which on the contrary offered a truly grandiose vision of the world. So fascinating was Aristotle’s system that it held sway in the teaching of natural philosophy in European universities right up to Galileo’s time and even beyond. But from a strictly astronomical point of view Aristotle’s system of homocentric spheres was readily seen as unsatisfactory. In fact, it required that each planet was at a constant distance from the Earth, and so it could not explain the increase and decrease of the apparent brightness of the planets with time, an explanation readily available if one posits changes in their distances from the Earth.

For a more satisfactory explanation of the heavenly motions it would be necessary to await the development of the mathematical concepts of eccentrics and epicycles by Apollonius (262–180 BCE) and by the great astronomer Hipparchus (d. 120 BCE). Relying upon those developments, Ptolemy, an astronomer and geographer from Alexandria, had written the greatest astronomical work of antiquity, the Sintaxis, which later became called the Almagest, meaning “the greatest,” by Arabian astronomers.

As to physics, Ptolemy followed the cosmological view of Aristotle, namely, geocentrism. But instead of the theory of Eudoxus, which had been followed by Aristotle, Ptolemy had introduced an explanation of planetary motions founded on three principles: eccentric motions, epicycles, and the equant. By the first principle, the Earth was in a position slightly removed (eccentric) from the center of the planetary orbits. This easily explained both the variation during the year of the brightness of the planets and also the apparent variation in their velocities and thus, considering the Sun, that the seasons had unequal lengths. By the second principle, the motion of each planet results from a combination of more than one circular motion: each planet moves on a circle (epicycle) whose center is located on and moves along another larger circle (the deferent) which may itself rotate on another deferent and so on. The largest and final deferent is not centered on the Earth but on a point slightly displaced (eccentric) from the Earth. The result of this combination of circular motions is a trajectory called an epicycloid, which explained the systematic direct and retrograde motion of the planets. The third principle, the equant, is intended to explain the change in the angular velocity of the planets during the year. While every planet moves with uniform motion on its own epicycle, the center of the epicycle moves on the deferent with a constant angular velocity with respect to a point (equant) displaced from the center of the deferent by the same amount, but in the opposite direction, that the Earth is displaced.

Based on these three principles, Ptolemy finally succeeded in constructing tables (ephemerides) that gave the positions of the planets with time and that agreed reasonably well with observations. In particular, the use of epicycles proved to be quite pliant. By varying, as required, the radius of an epicycle and by adding on other epicycles one could correct previously computed positions so as to better fit the observations. Because of this pliancy, the Ptolemaic system remained for fourteen hundred years the alpha and omega of theoretical astronomy.

But there was a lingering fundamental question. Although the Ptolemaic system was undoubtedly satisfactory as a mathematical scheme, what physical significance did it have? Ptolemy himself was aware of the difficulty, and he tried to give physical meaning to his theory in the book Planetary Hypotheses. But his attempt, as well as the similar ones by medieval Arabian authors, did not convince the so-called natural philosophers, namely, those whom we might call the scientists of the time. Following Aristotle they claimed to know the physical structure of the world and that which caused the movements of both the heavenly and the Earthly bodies. And so there came to be a “divorce” between the views of the philosophers and those of the astronomers, who, in the wake of Ptolemy’s thinking, continued to interest themselves in mathematical schemes that were useful for calculating celestial motions but were not very concerned about the physics behind those motions.

This situation lasted until the time of Galileo. Philosophy was considered superior to mathematics because it dealt with ultimate explanations, whereas mathematics was considered to be just a computing instrument. The difference became concretized in a higher academic status for philosophy in university teaching. The practical consequence was higher economic remuneration for philosophy teachers, including teachers of natural philosophy. And for a young reader in mathematics, such as Galileo, the salary was indeed meager.

Things being as they were, Galileo had to be careful not to push himself into the territory of his philosopher colleagues, but it was a situation that he was not prepared to endure forever. It was for him not just a question of prestige or economic well-being. He had a deep personal interest in enriching his knowledge of philosophy. He himself stated at a later date that he had “spent more years in studying philosophy than months in pure mathematics” (Galileo, Opere, 10:353). And certainly his key interest was in “natural philosophy.”

The writings of Galileo during his time in Pisa bear witness to his interest in deepening his knowledge of philosophy. It is evident from those writings that the teaching of philosophy and astronomy by the Jesuits at the Roman College had an influence on him. The Society of Jesus was founded in 1540 by the Basque Ignatius of Loyola (1491–1556). Very soon after its founding it dedicated itself predominantly, but not exclusively, to teaching. And at Galileo’s time the most active and well-known center of Jesuit teaching was that of the Roman College. Galileo had gone to Rome in the summer of 1587 and met there the famous Jesuit mathematician Christoph Clavius (1537–1612). They formed a friendship that would continue until Clavius’s death. Galileo must have been deeply impressed by the academic level of the Jesuit instruction.

Among Galileo’s writings during that period is the Treatise on Heaven. In this short treatise Galileo follows Aristotelian cosmology and makes it clear how much he depended on the texts used at the Roman College and, in particular, on Clavius’s commentary on the Sphere of Sacrobosco, a medieval treatise on the astronomy of Ptolemy. And it is right from Clavius that Galileo derives reasons why the Copernican theory must be wrong (Galileo, Opere, 1:47–50). But before we examine what, in truth, was Galileo’s personal position as regards Copernicanism, it would be useful to give a quick look at Copernicanism and at the history of its acceptance in the fifty years from Copernicus to Galileo’s teaching in Pisa.

The great work of Copernicus (1473–1543), On the Revolutions of the Heavenly Spheres was published in 1543. Aristarchus of Samos (310–230 BCE) had already proposed in ancient Greece a Sun-centered system, so Copernicus’s theory was not the first heliocentric system. But Copernicus gave a thorough mathematical treatment, so that his work was an absolutely new breakthrough in the world of science. The sweeping synthesis that it provided was such that the On the Revolutions could be compared to only one other such work, the Almagest of Ptolemy.

Copernicus claimed that to explain the phenomena in the heavens all that was required was to put the Sun, instead of the Earth, at the center and attribute three motions to the Earth: daily rotation on its own axis, which would explain the apparent daily motion of the heavenly bodies about the Earth; orbital motion about the Sun, which explains the apparent motion of the Sun along the ecliptic, the seasons, and the complex direct and retrograde motions of the planets; and the precession of the Earth’s axis of rotation, which, according to Copernicus, was required to explain the constant inclination of 23.5 degrees of the Earth’s rotation axis to the plane of the ecliptic.

These fundamental ideas, intended for nonspecialists, are found in book 1 of On the Revolutions, where Copernicus tried to answer the objections that Aristarchus’s system had already had to face and that had hindered its success among the majority of the Greek philosophers of nature and astronomers. As far as science goes, the weightiest objection against the Earth’s movement was undoubtedly the one based upon the absence of an observed parallax for the “fixed stars.” They should, if the Earth is truly moving, be seen in different positions in the sky during the course of the year. And this effect had never been observed. Copernicus repeated the response of Aristarchus: the dimensions of the sphere of the “fixed stars” were, in comparison to the size of the Earth and the distance of the Earth from the Sun, so much larger that, although the parallax was there, it was too small to be measured.

Although this heliocentric system presented a major and basic change in the way of thinking of the celestial motions, in many aspects it remained faithful to long-standing traditions. For instance, the idea that the universe had a spherical shape and that all celestial motions were circular, which had never been challenged in two thousand years by western philosophers and astronomers, still held. But this made inevitable the introduction of a series of epicycles and eccentrics so that theory would match observations. And so the great advantage of the simplicity of the Copernican theory over that of Ptolemy, as Copernicus himself emphasized in Book I, was lost for the most part in the later mathematical developments of On the Revolutions. On the other hand, because he had to introduce eccentric motions with respect to the Sun, Copernicus’s theory was strictly speaking no longer heliocentric.

To conclude, the Copernican system qualitatively had the undeniable advantage of simplicity. And it undoubtedly was better than the Ptolemaic system in the mathematical description of the motions of the inferior planets, Mercury and Venus, as well as that of the Moon. The result was that many of the most renowned astronomers of the time preferred Copernicanism as a mathematical theory to calculate planetary motions. But they refused to accept it as a physical explanation of how the world really worked. In fact, it apparently contradicted sense experience and the principles of Aristotelian cosmology. Of greater importance still it appeared to be in clear contradiction with scriptural statements about the stability of the Earth and the motion of the Sun.

Copernicus himself felt the weight of these difficulties and feared critical reactions from the Aristotelian camp, where the teaching of natural philosophy in European universities was still concentrated, as well as from theologians. Without a doubt, this was the main reason for his hesitation in publishing his work. In fact, however, the reactions he dreaded did not materialize, at least not with the virulence he feared. This fair-weather situation could be attributed in part to the influence of the “Note to the Reader,” an anonymous preface to the book by the Protestant editor Andreas Osiander (1498–1552), who wrote that Copernicus’s theory should be considered to be a pure mathematical hypothesis and not a physical explanation of the universe. Since it was only a mathematical theory, Osiander added, it was not more probable than any of the old theories. Still, it was published because of the “admirable hypotheses” it contained and, above all, because of its simplicity. “But as concerns hypotheses,” Osiander repeated, “no one expects any kind of certainty from astronomy, which is not capable of providing such certainties.” As we see, this harks back to the old thesis of the complete divorce between the areas of competence of natural philosophy and astronomical theories.

Copernicus was spared the sad experience of witnessing this betrayal of his real intentions. Having already suffered a cerebral paralysis some months before, he was dying when a copy of On the Revolutions was put in his hands. About five hundred copies of the book were printed. The second edition appeared only after twenty-three years and the third only after another fifty-one years. It would be without a doubt a mistake to state that the work of Copernicus received no attention from astronomers and the educated class in Europe. But, for reasons already mentioned, the theory appeared to be unacceptable as a real explanation of the structure of the universe. So the number of those who adhered to the new view of the world remained for the moment quite small. In Germany the principal promoter was Michael Mästlin (1550–1631), who probably deserves the honor of having introduced the ideas of Copernicus to his great disciple, Johannes Kepler (1571–1630). Even earlier than in Germany there were in England those who sympathized with Copernicanism. Among these were Robert Recorde (1510–1558), the greatest English mathematician of that period, and the famous William Gilbert (1544–1603), author of the treatise On Magnetism (1600). Even more clearly in favor of Copernicanism was Thomas Digges (ca. 1546–1595) in his work Wings or Mathematical Stairs (1572) and then in his appendix to the work on meteorology of his father Leonard, Prognostication Everlasting (1572). To this list of more or less declared supporters of Copernicus one should add the Frenchman Pierre de la Ramée (1515–1572) and the Italian Giovanni Battista Benedetti (1530–1590) and, of course, the famous Giordano Bruno, of whom I will write shortly.

The clearest proof that heliocentrism did not succeed as a physical explanation amo...

Table of contents

• Title Page
• Copyright Page
• Contents
• Presentation
• Preface
• Prologue
• Chapter 1. From Galileo’s Birth to His Teaching Years in Padua
• Chapter 2. Copernicanism and the Bible
• Chapter 3. The Scriptural Controversy Grows
• Chapter 4. The Copernican Doctrine Is Declared to Be Contrary to Holy Scripture
• Chapter 5. From the Polemics on the Comets to the Dialogue
• Chapter 6. The Trial and Condemnation of Galileo
• Chapter 7. The Burdensome Inheritance of the Galileo Affair
• Epilogue
• Bibliography
• About the Author