Died: 1642, Florence, Italy
Major Works The Sidereal Messenger (1610), The Assayer (1623), Dialogue on the Two Great World Systems (1632) Discourses on Two New Sciences (1638)
Observation bears out the truth of the Copernican theory that the earth is not the center of the universe. Aristotle's claim that heavier bodies fall faster than lighter ones can be disproved by observation.
Controlled experimentation and the use of quantitative methods of reporting observations yield better results than do casual observations and extended discussion of qualities and tendencies.
Authoritarian pronouncements about real phenomena must be tested against the evidence given us in nature. The universe is written in the language of mathematics.
Galileo Galilei is best known as the central figure in the great scientific revolution that transformed European thought in the seventeenth century. That revolution began hesitantly with the publication of a sun-centered cosmology in 1543 by Nicolaus Copernicus, whose, methods of argument were still distinctly medieval. It was completed with the work of Isaac Newton, who was first to achieve a full and clear formulation of the basic laws of motion and gravitation that became the foundation for the modern science of physics.
Galileo's birth into' the household of the well-known musician Vincenzo Galilei, following some years after the death of Copernicus, gave him the advantage of the mature flowering of the Renaissance. His death, within a few months of Newton's birth, was in a world beginning to feel the influence of Descartes and soon to see significant support for science as a deliberate enterprise through the formation of groups such as the Royal Society of London and the French Academie des Sciences. Where Copernicus had made a first tentative tug at the helm of natural philosophy, Galileo spun the wheel clear around to take the ship of thought out of the straits of authoritarianism and steer it toward the open seas of free scientific inquiry.
Galileo received a broad education, including some study of medicine at the University of Pisa. But his natural interests led him toward physics, and he left in 1585 without a degree. His talent and accomplishments became well enough known that he obtained a position teaching mathematics at the University of Pisa in 1589. But after conflicts with Aristotelian philosophers there, he moved to the chair of mathematics at the University of Padua in 1592, where he taught until 1610. He provides one of the first models for the modern consultant, having advised the city of Venice, among others, on such things as optics, ballistics, and fortifications.
Galileo might have simply lived another twenty years as a successful academic whose thoughtful experiments helped lay the foundations for the birth of physics had it not been for the advent of the telescope. Though Galileo did not invent this instrument, as soon as he saw one, he understood its working principles and quickly produced the first of a series of telescopes of increasingly better quality.
When he turned his telescope toward the skies in the summer of 1609, he made a stunning series of discoveries that transformed both his own life and the history of ideas in European civilization. He became a celebrity, both for good and for ill, and fell into a conflict with the Roman Catholic church that remains a touchstone for every discussion of the proper relation between science and religious belief.
Galileo's telescopes were good enough that within a matter of months he discovered spots on the sun, mountains on the moon, phases of Venus like those of our moon, four satellites orbiting Jupiter, "ears" on Saturn (later recognized as rings), and the starry makeup of the Milky Way. The image quality was still poor by modern standards, however, and many who looked through the first telescopes could not easily confirm Galileo's reports. In March of 1610, he published a small book, The Sidereal Messenger, describing some of these discoveries. He was shortly rewarded with an appointment as philosopher and mathematician to the Grand Duke of Tuscany, which enabled him to resign his duties in Padua and pursue his studies in whatever way he chose.
Galileo had already been sympathetic to the Copernican way of thought, but the new discoveries armed him with the first really compelling arguments in its favor. The paths of Jupiter's moons made it clear that objects other than the earth could be centers of motion, and the phases of Venus proved that it is sometimes beyond the sun, thus eliminating Ptolemy's earth-centered cosmology. Discussion of this new information caused quite a stir, with Galileo being at its center not only in his role as discoverer but also because he was very articulate. He took advantage of his celebrity to present both arguments and demonstrations in favor of his anti-Aristotelian views on falling bodies as well. He seems to have relished the attention, but his self-assurance bordered sometimes on arrogance, and he was not always gracious to his opponents. Of these he had a number, in several cases owing to other, extraneous disputes.
The opposition of the Catholic church was to some extent social or political as much as it was religious, since threats to its authority represented in church thinking an undermining of the entire social order. Neither was this opposition by any means monolithic. Leading Jesuit astronomers were among Galileo's friends in the early years, as was Maffeo Cardinal Barberini, who was to become Pope Urban VIII in 1623. Nevertheless there were denunciations to the Inquisition that led to Galileo's being instructed early in 1616 not to advocate the Copernican theory, though it remains difficult to determine precisely how strong a prohibition was imposed.
For some time Galileo turned to other things. He took what we see as the wrong side in an argument about several comets that were seen in 1618. A later stage in that dispute led to The Assayer, which appeared in 1623. It is seen by some as a masterpiece of polemical philosophy, including detailed exposition of the underlying principles of experimental science and the empiricist position. But for its physical thought it seems today a minor and relatively uninteresting little book--unless Pietro Redondi could be right in his recent (but generally disputed) proposal that Galileo's discussion of atomism here was in some people's eyes even more heretical than his Copernicanism.
In 1624, Galileo visited Rome and received what he took to be encouragement to undertake the project that, after several interruptions, finally appeared in 1632 as the Dialogue. In four "days" of Socratic conversations among its characters, Simplicio presents the traditional Aristotelian views while Salviati speaks for Galileo in advocating new thinking. Sagredo acts as a supposedly impartial listener, who of course is finally more impressed by Salviati's arguments. In its writing, the Dialogue was very effective; the wit, the style, and the use of vernacular Italian rather than Latin all helped it reach a wide audience. The quality of its physics is mixed. On the one hand, Galileo is very telling in his use of falling bodies to emphasize that proper understanding of inertia does away with the whole family of anti-Copernican objections that suppose a moving earth would leave loose objects behind. But on the other hand, he presents arguments about the movement of sunspots and about the origin of tides that ar e quite specious. So the real importance of this work lies not so much in any of its details as in its overall thrust of forcing the reader to seriously contemplate the Copernican possibility and to do so in physical rather than purely philosophical or authoritarian terms.
The book was hardly off the press before it was denounced, and within a few months the Holy Office ordered its sales stopped. Galileo was summoned to Rome for trial on charges of transgressing orders not to teach or defend the motion of the earth, and of falsely attributing the tides to the earth's movement. At first he attempted the defense that he had not really advocated the Copernican view at all, presenting it only as a hypothesis and a rather weak one at that; but no actual reader of the book would have gotten such an impression. In the end he was forced in 1633 to "abjure, curse, and detest the above-mentioned errors and heresies." He had always considered himself a loyal Catholic, and as Langford says, it was Galileo the scientist who wrote, but Galileo the believer who recanted.
In the tragedy of that trial, we can see one positive outcome: When Galileo returned to live out his life near Florence under house arrest, he resumed work on some less controversial problems in physics. His work in this area was largely done between about 1590 and 1610, and he had been planning to publish it when interrupted by the astronomical discoveries. Subsequent disputes as well as intermittent illness had kept him distracted. Now he finally took up these ideas again and integrated them into the Discourses on Two New Sciences, published at Leyden in 1638 away from the control of Catholic censors. Free from the emotional debate on Copernicanism, this is the work that best shows us Galileo as a worthy builder of the foundations of physics.
Two New Sciences is also in dialogue form, utilizing the: same three characters. But it is less consistent in style, less polished and accessible. This is partly due to the more technical subject matter, but also stems from its being completed as time was running out and Galileo's health was very poor. The subjects dealt with include the strength of materials, impacts, friction, floating bodies, motion through resisting media and through vacuum, string vibrations, and parabolic trajectories.
In the first day of Two New Sciences is a clever argument against Aristotle's claim that heavier bodies fall faster. We are asked to envision two small bodies falling slowly side by side; if joined together by even a tenuous connection they now constitute a larger body--but do we really believe that now they will fall twice as fast? The second day of the Dialogue similarly has ingenious arguments about motion on an inclined plane to clarify what should happen in vertical fall and in unimpeded horizontal motion. Both of these examples illustrate Galileo's great talent for using "thought experiments to mediate between vague theoretical expectations and the difficulties of real-life experiments, such as frictional forces and lack of precise timekeeping instruments. Galileo ranks with Einstein as one of the most creative users of this method of developing convincing physical theories.
Galileo deserves credit for advocating extended and well-controlled experiments, in preference to mere collection of assorted casual observations. He also emphasized the importance of quantitative methods over discussions of qualities and tendencies. As Ira Cohen has suggested, while Galileo was hardly the first scientist to do experiments, he was one of the first who made both experiments and mathematical analysis integral parts of his science. This does not mean, however, that he fully anticipated Newtonian physics. In spite of his extensive contributions, as Drake points out, Galileo did not have in mind the grand program we know as "the mechanical philosophy"; that is due more to Descartes. But he did pioneer something we are accustomed to expect in science today, placing a high value on unforeseen discoveries and novel explanations--a goal for which the universities of Galileo's time did not ordinarily strive.
An important part of Galileo's story is his personal style. In comparison with his slightly younger contemporary Kepler, Galileo impresses us less as a mystic and more as the first example of a modern scientific personality. He was no less concerned to achieve scientific results than to convey them effectively, taking great pains to rework his ideas into more and more convincing arguments. He was a skilled debater, not above exploiting opportunities to make his opponents look ridiculous. Unfortunately, as de Santillana has pointed out, Galileo's celebrity in his own time had all too little to do with real understanding: "His was the tragedy of an excess of gifts;...his contemporaries could easily recognize a master; but what remained with them of his 'incomparable demonstrations' was as dim as the memory of a symphony to the untrained ear."
Galileo's contributions to science have an important philosophical component. Most obvious is his insistence that authoritarian pronouncements about real phenomena must be tested against the evidence given to us in nature. This was not mere rebellion; he saw it as ultimately aiding true spirituality. When on trial, he said, "It would be to the greatest detriment of souls to be forbidden to believe that which is later made plain before their eyes." Salviati speaks powerfully for him in the first day of the Dialogue: "If what we are discussing were a point of law or of the humanities, in which neither true nor false exists, one might trust in subtlety of mind and readiness of tongue and in the greater experience of the writers, and expect him who excelled in those things to make his reasoning most plausible, and one might judge it to be the best. But in the natural sciences, whose conclusions are true and necessary and have nothing to do with human will, one must take care not to place oneself in the defense o f error; for here a thousand Demostheneses and a thousand Aristotles would be left in the lurch by every mediocre wit who happened to hit upon the truth for himself."
Galileo also insisted that natural philosophy could not disdain mathematics. One of his best-known statements comes from The Assayer: "Philosophy is written in this grand book, the universe, which stands continually open to our gaze. But the book cannot be understood unless one first learns to comprehend the language and read the letters in which it is composed. It is written in the language of mathematics, and its characters are triangles, circles, and other geometric figures without which it is humanly impossible to understand a single word of it." In the words of Langford, this is the divorce of science from philosophy--true science, demonstrative knowledge, must be mathematical; mere concepts of potency and final cause are practically useless.
Drake, Stillman. Gailileo at Work: His Scientific Biography. Chicago, University of Chicago Press, 1978. A wealth of detail on how Galileo did his physics, based on preserved papers and correspondence.
Finocchiaro, Maurice A. The Galileo Affair: A Documentary History. Berkeley: University of California Press, 1989. New English translations of some correspondence, minutes of the Inquisition, and other important documents. The 43-page introduction provides an excellent summary of Galileo's controversy with the Church; also valuable are a chronology of events, a biographical glossary of all the important characters involved, and a selected bibliography from the extensive literature on Galileo.
Gingerich, Owen. "The Galileo Affair." Scientific American (August, 1982): 132-43. Views of a modern astronomer.
Langford, Jerome J. Galileo, Science and the Church. Ann Arbor: University of Michigan Press, 1971. A more balanced evaluation than in biographies from the 1950s by Koestler (anti-Galileo) and de Santillana (pro-Galileo).
Redondi, Pietro. Galileo Heretic. Translated by Raymond Rosenthal. Princeton: Princeton University Press, 1987. A masterful portrayal of the "theater of shadows" that was the world of arcane theological dispute in 1620s Rome, even if its central conspiratorial theory is doubtful.
Santillana, Giorgio de. The Crime of Galileo. Chicago: University of Chicago Press, 1955. A sympathetic portrayal involving the theory that a key document used against Galileo in his trial was forged.
Shapere, Dudley. Galileo: A Philosophical Study. Chicago: University of Chicago Press, 1974.
Wallace, William A., ed. Reinterpreting Galileo. Studies in Philosophy and the History of Philosophy, vol. 15, Washington, DC: Catholic University of America Press, 1986.