Galileo

by Mario Livio

  The first appearance of the legendary motto in a printed book was in the eighteenth century, in The Italian Library by an Italian living in London, Giuseppe Baretti. Galileo could not have muttered these words in front of the inquisitors, but it is not impossible that he did utter some version of this phrase, which was surely on his mind, to one of his friends. At any rate, Galileo’s bitterness about the trial and his contempt for the inquisitors continued to occupy his mind for the rest of his life.

  Today the phrase “And yet it moves” has become a symbol of intellectual defiance, implying that “in spite of what you believe, these are the facts.” Unfortunately, in an era of “alternative facts,” there appear to be more and more occasions where the use of the phrase is appropriate.

  Did the Church act within its legal authority in terms of the charges brought against Galileo? From its very narrow point of view, most probably yes, given the warning of Bellarmino and the injunction issued to Galileo by Seghizzi. Galileo was convicted essentially because of two facts: first, for having violated the 1616 injunction, and second, for having obtained the imprimatur to print the Dialogo “artfully and cunningly” by not revealing the injunction to Riccardi and Egidi. In this sense, the conviction was justified. The abjuration was also a necessary step, since without it, the “suspicion of heresy” would have turned into actual heresy, for which, as we know, Giordano Bruno had been burned at the stake.

  Judging the affair from a broader perspective, however, there is a more important point to be made. Putting Galileo on trial, imprisoning him, and forbidding his book, was wrong not just because Galileo was right about the science of the solar system. These actions against intellectual freedom and, by implication, even against religious beliefs, would have been wrong even if the geocentric model were the correct one. The much bigger lesson from the Galileo affair is that no officialdom, be it religious or governmental, should have the authority to impose punishments on scientific, religious, or any other type of opinions (whether correct or incorrect), as long as those neither harm, nor incite others to harm, anybody else. This is precisely why the real Galileo affair was planted in humanity’s conscience after the verdict and abjuration in Galileo’s trial. In that further-reaching affair, the inquisitors became the culprits, and the affair itself remains a constant reminder that the freedom to express truths should never be taken for granted.

  CHAPTER 14 One Old Man, Two New Sciences

  Galileo’s sentence included detention. He therefore had to be informed where that would take place. Fortunately, the Pope commuted his sentence to house arrest and, on June 30, 1633, allowed him to start the imprisonment at the house of Ascanio Piccolomini, the archbishop of Siena, where Galileo spent about a half year. In spite of the restriction on his personal freedom, Galileo enjoyed his stay in the house of the receptive and learned archbishop, who regarded Galileo as “the greatest man in the world.” It was in Piccolomini’s house where Galileo started to work on his last great book, Discorsi, which summarized all of his experimental work in Padua and his insights in mechanics. With an ironic historical twist, Galileo’s mechanics were precisely the tools that Sir Isaac Newton later needed to prove Copernicanism correct.

  Throughout his time in Siena, however, what Galileo really wanted more than anything was to return to his home in Arcetri, near Florence. In his absence, the home was managed by his daughter, Sister Maria Celeste, from her convent nearby. From her wonderful letters, Galileo learned that lemons, beans, and lettuce were thriving, and that the wine from his casks tasted good. This young woman was able to comfort her old father even at his darkest hours with her remarkable yet affectionate calm. Having given up other forms of love, she lavished her most tender love on Galileo and wrote to him following his trial:

  As much as the news of Your Honor’s new affliction was sudden and unexpected, that much more my soul was pierced with extreme grief in hearing the decision finally taken both about your book and Your Honor’s person… now is the time to avail yourself more than ever of that prudence which the Lord God has granted you, bearing these blows with that strength of spirit which your religion, your profession, and your age demand.

  In December 1633 the Pope finally allowed Galileo to return to Arcetri, where he was to be in perpetual house arrest and strictly forbidden from turning the place into a gathering center for intellectuals, scientists, and mathematicians. While Galileo was very happy to be back home and close to his loving daughter, this happiness was rather short-lived. Sister Maria Celeste died at age thirty-three only three months after Galileo’s return. Galileo was devastated. “I had two daughters whom I much loved, especially the elder, a woman of fine mind and singular goodness and most affectionate to me,” he wrote to his friend Elia Diodati in Paris.

  Seeking comfort in his work, Galileo managed to complete Discorsi in 1635, and his original intention was to publish the book in Venice. This turned out to be easier said than done. All the local inquisitors in Italy had received from the Roman Inquisition the full text of Galileo’s sentence and abjuration. The inquisitor of Venice informed Galileo’s friend (and Paolo Sarpi’s biographer) Fulgenzio Micanzio, that Rome had issued an order prohibiting the publication of any book by Galileo, including the reprinting of previously published books. Consequently, Galileo clandestinely sent copies of Discorsi to friends outside of Italy with the hope of securing a publisher somewhere outside the circle of dominance of the Catholic Church and the Jesuits.

  One of those friends, military engineer Giovanni Pieroni, tried unsuccessfully to publish the book in Prague. He expressed his frustration in a letter to Galileo: “What an unhappy place we live in,” he complained, “where there reigns a determined resolution to exterminate all novelties, especially in science, as if we already knew everything knowable.” Indeed, what eventually marked the scientific revolution, in which Galileo played a major role, was the recognition that humans did not know everything, and that exploration, observation, and experimentation offered the best way to acquire new insights and knowledge. Eventually Louis Elsevier, an able publisher in the Protestant university city of Leiden, the Netherlands, published the book in 1638. Elsevier managed to obtain one copy of Discorsi when he visited Venice. A second copy was smuggled to him by the French ambassador to Rome, a loyal admirer of Galileo’s who received permission to stop at Galileo’s home upon his return to France.

  DISCORSI

  Discorsi marked the final chapter of Galileo’s scientific story (Figure 14.1 shows the title page). Like the Dialogo, it again involved the cast of Salviati, Sagredo, and Simplicio, this time discussing topics in mechanics rather than lofty world systems. The “two sciences” mentioned in the title referred to a mathematical description of the nature of matter and of material strength, and to the topic of the principles of motion.

  The book included Galileo’s important discoveries in mechanics, such as the fact that in the absence of air resistance heavy and light bodies fall at the same rate (rather than heavier bodies falling faster, as Aristotle had pronounced). To prove this point, Galileo used a beautiful “thought experiment.” Imagine, he said, that you join together a light body and a heavy one. According to Aristotle, since the lighter body falls slower, it should slow down the heavier body, and the combined body should fall slower than the heavy body by itself. On the other hand, Galileo pointed out, one could consider the two joined bodies as one body that is even heavier than the original heavy body; therefore, according to Aristotle, they should fall faster than the individual heavy body—a clear contradiction.

  Figure 14.1. Title page of Discorsi.

  To justify his Paduan experimental results with balls rolling down inclined planes as opposed to truly free-falling, Galileo had to show how the motion of such rolling balls is related to a body in free fall. To this goal, he noted that the speed balls reach after rolling down an inclined plane depends only on the vertical distance the balls had covered, and not on the angle at which the plane was tilted. In this sense, a free
-falling body could be thought of as a ball rolling down a vertical plane.

  One of Galileo’s crowning achievements was calculating the trajectory traced by projectiles. This came out of an experiment conducted in 1608, which looked something like this: An inclined plane was placed on top of a horizontal tabletop. A ball rolled down the inclined plane, then on the horizontal table, eventually shooting off the table’s edge along a trajectory that finally hit the ground. By measuring the horizontal and vertical distances traveled, and by understanding that the horizontal motion (while in the air) is nearly at a uniform speed (since only the air resistance acts to slow it down slightly), while the vertical motion is in free fall, he was able to determine the geometrical shape of the trajectory. Basically, the vertical distance through which the body falls is proportional to the square of the horizontal distance traveled. That is, a ball that travels twice farther horizontally falls four times farther vertically. The trajectory precisely delineates the curve known since antiquity as a parabola.

  Overall, the “New” in the title of Galileo’s book didn’t refer so much to the subjects discussed in the book. After all, people had used beams of wood for construction (and were therefore interested in their strength) thousands of years before Galileo, and bows and catapults shot projectiles into the air in ancient Greece—not to mention the biblical story of David and Goliath. What was new in Galileo’s discussion was the way in which mechanics was treated. Through an ingenious combination of experimentation (for example, with inclined planes), abstraction (discovering mathematical laws), and rational generalization (understanding that the same laws apply to all accelerated motions), Galileo established what has since become the modern approach to the study of all natural phenomena.

  Perhaps the best demonstration of the evolution in Galileo’s thoughts on mechanics was provided by his law of inertia, which later became known as Newton’s first law of motion. Starting from Aristotle’s notions of “natural” and “violent” motions, and realizing that even fire would move downward if not for the buoyancy provided by the air, Galileo started thinking about how a body would behave if no force whatsoever acted upon it. Finally, in Discorsi, he found the answer:

  “Along a horizontal plane, the motion is uniform [constant speed], since here it experiences neither acceleration nor retardation.” Then came the punchline: “any velocity imparted to a moving body will be rigidly maintained as long as the external causes of acceleration or retardation are removed, a condition which is [experimentally, approximately] found only on horizontal planes.” This velocity, he added, “would carry the body at a uniform rate to infinity.”

  Newton’s first law of motion indeed states that an object will remain at rest or in uniform motion along a straight line unless acted upon by an external force. Formulating this law required on Galileo’s part imagining a world without friction, which is much harder than it may seem. Friction is such a common feature in all of our everyday experiences—it allows us to walk and to hold objects in our hands, and it slows down every motion we see—that to envisage what would happen without it required a truly phenomenal power of abstraction.

  This was Galileo at his best. He established the belief in the existence of what we call today the laws of nature, which are universally valid and perpetually reproducible. Nature cannot be deceitful, or, as Einstein put it several centuries later: “The Lord God is subtle, but malicious he is not.” In the introduction to the discussions of the third day of Discorsi, Galileo wrote what could be regarded as his own summary of his contributions:

  My purpose is to set forth a very new science dealing with a very ancient subject.… I have discovered by experiment some properties of it which are worth knowing and which have not hitherto been either observed or demonstrated… what I consider more important, there have been opened up to this vast and most excellent science, of which my work is merely the beginning, ways and means by which other minds more acute than mine will explore its remote corners.

  CHAPTER 15 The Final Years

  The year 1634 was one of the worst in Galileo’s life. In addition to him being under house arrest, not only did his beloved daughter die, but Galileo also had to support the few members of his brother Michelangelo’s family who survived the plague in Munich. All that the distraught Galileo could do was to send some money and invite them to come to Arcetri to be together.

  Galileo’s eyes were also starting to bother him. At first, he attributed his failing vision to the grueling readings he had to put in while preparing the Dialogo. Although he continued to work on problems related to navigation at sea—and he even embarked on a series of experiments with pendulums—Galileo was rapidly losing his eyesight, first in his right eye, then in the left. From his descriptions of the progression of his blindness, modern ophthalmologists diagnosed his condition as bilateral uveitis—an inflammation in the middle layer of the eye—or creeping angle closure glaucoma. He was totally blind during the last four years of his life.

  Not being able to look through his precious telescope anymore, the distressed Galileo wrote to his friend Diodati:

  Alas, my good sir, your dear friend and servant Galileo is irreparably and completely blind, in such a way that the sky, that world and that universe, which with my wondrous observations and clear demonstrations I amplified a hundred and a thousand times over what was believed most commonly by the learned of all past centuries, is for me now so diminished and narrowed that it is no greater than what my body occupies.

  It was during that agonizing period that poet John Milton visited him, in 1638. Following the general perception that “travel broadens the mind,” Milton was on a European tour in which he tried to meet with as many intellectuals as he could. Having met Galileo’s son, Vincenzo, at a literary society meeting in Florence, Milton jumped at the opportunity to be introduced to the most famous scientist in Europe. Not much is known about what transpired at the meeting, but there is no doubt that Galileo’s discoveries, his trial, and the condemnation of his book had a great influence on Milton. In Paradise Lost, Milton refers to the “glass of Galileo,” and to the innumerable stars discovered by him:

  Of amplitude almost immense, with stars

  Numerous, and every star perhaps a world

  Of destined habitation.

  In 1644 Milton published a pamphlet entitled Areopagitica—the title inspired by the name of a hill in ancient Greece where the Council of Athens used to meet—in which he argued against censorship of books. This essay is still regarded today as one of the most impassioned pleas for freedom of speech, and the US Supreme Court referred to it in interpreting the First Amendment to the US Constitution.

  In Areopagitica, Milton wrote ardently:

  And lest some should persuade ye, Lords and Commons, that these arguments of learned men’s discouragement at this your order, are mere flourishes, and not real, I could recount what I have seen and heard in other Countries, where this kind of inquisition tyrannizes; when I have sat among their learned men, for that honour I had, and been counted happy to be born in such a place of Philosophic freedom, as they supposed England was, while themselves did nothing but bemoan the servile condition into which learning amongst them was brought; that this was it which had damped the glory of Italian wits; that nothing had been there written now these many years but flattery and fustian [pompous speech]. There it was that I found and visited the famous Galileo grown old, a prisoner to the Inquisition, for thinking in Astronomy otherwise than the Franciscan and Domican licencers thought.

  Sadly, Milton diagnosed the situation correctly. For a while, at least, Galileo’s fate exerted a chilling, impeding effect on progress in deciphering the cosmos. The great French philosopher René Descartes wrote in November 1633 a letter to his and Galileo’s friend the polymath Marin Mersenne, in which he lamented:

  I inquired in Leiden and Amsterdam whether Galileo’s World System was available, for I thought I had heard that it was published in Italy last year. I was told that it had i
ndeed been published, but that all the copies had immediately been burnt at Rome, and that Galileo had been convicted and fined. I was so astonished at this that I almost decided to burn all my papers, or at least to let no one see them.

  Mercifully, Galileo eventually prevailed. Already in 1635 a Latin translation of the Dialogo was published in Protestant Strasbourg, France. Slowly but surely, the Church itself started changing. In 1757 Pope Benedict XIV, realizing that the Catholic astronomers themselves were using the Copernican scenario, rescinded the prohibition against books that discussed the central tenets of Copernicanism: the Earth’s revolution around the Sun and the Sun’s immobility. In 1820 the master of the Sacred Palace refused to allow printing for a book that described the heliocentric model, but he was overruled by Pope Pius VII, who decreed that “no obstacles exist for those who sustain Copernicus’s affirmation regarding the earth’s movement.” In 1822 the Church even declared penalties for prohibiting the publication of books that presented the Earth’s revolution around the Sun as an established scientific fact. Finally, in 1835 both Copernicus’s book and the Dialogo were removed from the Index of Prohibited Books.

  Physically, Galileo was deteriorating rapidly during his last four years. Modern medical researchers have speculated that he suffered from an immune rheumatic disease, reactive arthritis. An inquisitor who was sent to check on whether Galileo’s complaints were justified found that he was suffering from severe insomnia and that “he looks more like a cadaver than a living person.” Still, even though the Pope allowed Galileo to move to his son’s house to be able to receive better medical care, he insisted on prohibiting him from discussing Copernicanism under any circumstances. Galileo contracted fever in November 1641, and he died on the evening of January 8, 1642, presumably of congestive heart failure and pneumonia. His son, Vincenzo, and his students Vincenzo Viviani and Evangelista Torricelli, a talented experimentalist who invented the barometer, were at his side. Figure 8 in the color insert shows Viviani and Galileo. Viviani movingly described Galileo’s passing: