Galileo

by Mario Livio

  “It is not from failing to take count of what others have thought that we have yielded to asserting that the earth is motionless… but (if for nothing else) for those reasons that are supplied by piety, religion, the knowledge of Divine Omnipotence, and a consciousness of the limitations of the human mind.” Naïvely, Galileo thought that these disclaimers would be sufficient.

  SALVIATI, SIMPLICIO, SAGREDO

  The Dialogo is one of the most engaging science texts ever written. There are conflict and drama, yes, but also philosophy, humor, cynicism, and poetic usage of language, so that the sum is much more than its parts.

  Fashioned after Plato’s dialogues, the Dialogo was presented as an imaginary discussion among three interlocutors, which takes place in a Venetian palace over a period of four days. Salviati, named for Galileo’s deceased Florentine friend Filippo Salviati, is a stand-in for Galileo’s Copernican opinions. Sagredo, named for Galileo’s great (also deceased) Venetian friend Gianfrancesco Sagredo, plays the role of the educated but nonexpert person who wisely judges between the Copernican and Aristotelian views expressed by the other two. Finally, Simplicio is an avid Aristotelian, who obstinately defends the geocentric worldview. He was supposedly named after Simplicius of Cilicia, the sixth-century commentator on Aristotle’s works, with the name being a double entendre, hinting at simplemindedness. Simplicio was fashioned partly after the conservative Cesare Cremonini and partly after Galileo’s nemesis, Lodovico delle Colombe.

  During the first three days, Galileo’s alter ego, Salviati, methodically demolishes Simplicio. Using examples ranging from dead cats falling out of windows to the illusion that the Moon follows us as we wander along a path, Galileo rejects any ancient authorities (such as Aristotle), “for our disputes are about the sensible world, and not one of paper.”

  In the first day, he demonstrates that there is no difference between terrestrial and celestial properties. In the second day, he intimates that all the observed motions in the heavens are explained more easily by assuming that it is the Earth that moves rather than the Sun and the rest of the world.

  Salviati devotes the third day to countering all the objections raised against the Earth’s revolution around the Sun and to providing evidence that it indeed moves. Perhaps most interesting in this discussion is Galileo’s new claim that he can prove the reality of the annual motion of the Earth from the observations of the paths of sunspots on the solar surface. Galileo’s and even more so Scheiner’s detailed observations of sunspots had revealed that the projected path of sunspots is not along a straight line parallel to the ecliptic. Rather, during one quarter of the year, they appear to ascend in a straight line inclined to the ecliptic. In the following quarter, they move along a path curved upward; in the next one, along a descending straight line; and, in the last quarter, they follow a downward curved path (as shown schematically in Figure 10.3). Galileo demonstrated that the root cause for the curve traced by these apparent motions was a rotation of the Sun about its axis, with a tilt of about 7 degrees of the solar spin axis with respect to a line perpendicular to the ecliptic plane. Relying then on Occam’s razor, that of two explanations to a given phenomenon the one that requires fewer assumptions is usually correct (in Galileo’s words: “whatever can be accomplished through few things, is done in vain through more”), he further claimed clear superiority of the Copernican system (over the Ptolemaic one) in explaining these observations. Since Galileo apparently hit upon this particular proof only a few months before submitting the Dialogo to press, his explanations are rather vague and certainly insufficient, which has caused many Galileo scholars to be skeptical about the proof’s validity. (Hungarian British author Arthur Koestler even went so far as to lambaste Galileo for both stupidity and dishonesty.)

  Figure 10.3. Schematic showing the directions of the observed paths of the annual motion of sunspots, in four quarters.

  More recent, thorough analyses of the proof, however, showed that while Galileo did not include all the relevant motions, the paths of sunspots could indeed be used as convincing evidence in favor of the Copernican system. More important, perhaps, even though Galileo hadn’t realized it, his proof militated as decisively against Tycho’s system as it did against the Ptolemaic scenario. It was certainly much stronger than the proof from the ebb and flow of the tides to which Galileo devoted the fourth day of the Dialogo. Interestingly, Galileo was fully aware of the explanations of the tides that relied on the Moon’s influence, but in the absence of a theory of gravitation, he regarded ideas such as those of Kepler—who talked specifically about “attractive forces” between the Moon and the Earth—as employing “occult properties,” even though Kepler’s concept happened to be a genuine forerunner to Newton’s theory.

  In his summary of the four-day marathon of discussions, Sagredo concludes:

  In the conversations of these four days, we have, then, strong evidences in favor of the Copernican system, among which three have been shown to be very convincing—those taken from the stoppings and retrograde motions of the planets, and their approaches toward and recessions from the earth; second, from the revolution of the sun upon itself, and from what is to be observed in the sunspots; and third, from the ebbing and flowing of the ocean tides.

  As we have seen, the third claimed piece of evidence (the tides) was, in fact, incorrect, and the second (the paths of sunspots) may have been an even stronger proof than Galileo realized or was able to articulate. With incredible foresight, Galileo added a fourth test: “The fourth, I mean, may come from the fixed stars, since by extremely accurate observations of these there may be discovered those minimal changes that Copernicus took to be imperceptible.” Galileo predicted here that the tiny parallax shift against the background stars due to the motion of the Earth around the Sun would eventually become measurable, as indeed it has.

  But, you may wonder, how could Galileo afford to finish his book with an advocacy for Copernicus? After all, the injunction imposed on him in 1616 by Seghizzi explicitly ordered him not to do so. Indeed, he could not. The risk of provoking a harsh punishment by the Church was just too high. Instead, he was forced into finishing with qualifications and reservations essentially negating the entire contents of the book! The renunciation was expressed most clearly by Simplicio:

  I know that if asked whether God in His infinite power and wisdom could have conferred upon the Watery element its observed reciprocating motion [the tides] using some other means than moving its containing vessels, both of you would reply that He could have, and He would have known how to do this in many ways which are unthinkable to our minds. From this I forthwith conclude, this being so, it would be excessive boldness for anyone to limit and restrict the Divine power and wisdom to some particular fancy of his own.

  These were, almost verbatim, the words of Pope Urban VIII. To complete this involuntary, unscientific admission, Galileo had Salviati agreeing completely with Simplicio and accepting that “we cannot discover the work of His hands,” and that “much less fit we may find ourselves to penetrate the profound depths of His infinite wisdom.”

  Galileo may have believed that by repeating the Pope’s own views on the human inability to truly fathom the cosmos, he’d paid his dues to the anti-Copernican philosophy—and Father Riccardi may have consented, at least to some extent. In doing so, however, Galileo underestimated the zeal of his enemies, who were sure to notice that the admission of the incomprehensibility of the universe was assigned to Simplicio, who had been ridiculed throughout the entire Dialogo.

  More important, the act of removing humans from their central place in the cosmos was too brutal to be remedied by some philosophical pleasantries at the end of a long debate with a very different tone.

  A few current historians of science have raised a different issue with the conclusion of the Dialogo. They regarded Galileo’s corrective “clarifications” as a sign of duplicity and cowardice. I cannot disagree more. The Dialogo courageously expressed Galileo’s genuine opin
ion on a topic that he had been warned not to discuss. There is little doubt that the delicate balancing act in the preface and the conclusion was imposed on him by his friends and those wishing to ensure that the book would be approved for publication. Galileo could have avoided all the misfortunes, grief, and suffering that were about to ensue by simply being less pugnacious and by not publishing the Dialogo. But he was only human, after all, and his sense of personal pride in his discoveries and an uncontrollable passion for what he regarded as the truth were too strong for him to just give up. To Galileo, the task of convincing everybody of the correctness of Copernicanism must have taken the shape of a historical duty. This was why he wrote the Dialogo (as he did with most of his other books) in Italian rather than Latin, so that it could be read by any literate and interested Italian. He did his best to convey the universe’s beauty and rational coherence, but he left the final judgment to the reader, as Salviati very clearly expresses toward the end of the third day:

  I do not give these arguments the status of either conclusiveness or inconclusiveness, since (as I have said before) my intention has not been to solve anything about this momentous question, but merely to set forth those physical and astronomical reasons which the two sides can give me to set forth. I leave to others the decision, which ultimately should not be ambiguous, since one of the arrangements must be true and the other false.

  History has indeed proved that Galileo was right, but being right is sometimes insufficient. It certainly did not save Galileo from the hardships and anguish that were in store for him the following year.

  CHAPTER 11 The Gathering Storm

  As one could have expected, Galileo’s fans greeted the publication of the Dialogo with great enthusiasm, none perhaps more so than Benedetto Castelli, who was not only a good mathematician and a firm Copernican but also a lifelong supporter of his former teacher. However, no more than four months had passed since the book hit the press, when some disturbing news started to arrive.

  It began in the form of a letter from Father Riccardi to the inquisitor in Florence, Clemente Egidi, asking the latter to immediately stop the distribution of the book until some corrections were sent from Rome. This ominous act was in itself the consequence of a series of events that accumulated to fuel in the Pope’s mind suspicion and hostility toward Galileo.

  The first incident involved Galileo’s friend Giovanni Ciampoli. By choosing to support Spanish-leaning cardinals, Ciampoli had put himself in the opposition to the Pope’s generally Francophile strategy, thus losing Urban VIII’s sympathy and trust. In addition, Ciampoli wrote a letter in which he criticized the Pope’s style, thereby appending a personal element to the Pontiff’s disapproval of him. Second, the Pope was starting to get word, especially from Jesuit opponents of Galileo, that the content of the Dialogo was different from what Urban VIII had expected. In particular, he was made aware of the fact that his own main argument about the incomprehensibility of the universe, and the inability of humans to ever prove the reality of any theoretical world system, had been treated disrespectfully in the Dialogo. Not only was it presented rather marginally and very briefly, but to add insult to injury, it was put in the mouth of Simplicio, who had been ridiculed throughout the entire book. Finally, due to the Pontiff’s generally paranoid state of mind at that time, Urban VIII even misinterpreted the printer’s seal on the book’s front page—composed of three dolphins, each holding the other’s tail in its mouth (see bottom of Figure 10.1, page 166)—to be an allusion to his own nepotism with his nephews. The upshot of all of these unnerving occurrences was that by August 1632, the talk in church circles in Rome already included options ranging from a delay in the book’s distribution, to its outright prohibition. In particular, the Jesuit fathers were reported to be actively trying to ban the book and to “execute him [Galileo] most bitterly.” In the meantime, Father Riccardi was trying diligently to obtain information on how many copies of the Dialogo had been printed and to whom they’d been sent, in order to recall all of them.

  What did Galileo do in response to all of these negative developments? Only the very little he could do: he asked both the Florentine ambassador to Rome, Niccolini, and the grand duke Ferdinando II himself to protest the restrictions imposed on a book that had previously received all the required permissions and licensing. Niccolini indeed met several times with the Pope’s nephew Cardinal Francesco Barberini, and upon hearing that a commission composed entirely of people unfriendly to Galileo had been appointed to examine the book, he requested that “some neutral persons” would be added to this commission. The ambassador received no assurances.

  In early September Filippo Magalotti, a relative of the Barberini family and a friend of both Galileo and Mario Guiducci, finally heard from Father Riccardi the main complaints against the Dialogo. In addition to the diminished role given to the Pope’s views in the book, the claim was that the preface was insufficient in providing the necessary balance to the Copernican opinions expressed in the main body of the Dialogo—especially since the preface appeared to be, and in fact was, an afterthought. At that stage, Magalotti still expressed cautious optimism that “with some small thing that is removed or added on for greater caution… the book will remain free.” His advice was to not try to force the issue but to wait for tempers to calm down. Through an unfortunate turn of events, however, exactly the opposite happened.

  Ambassador Niccolini had to meet with the Pope to discuss another topic, and that meeting deteriorated to the point of disastrous consequences, as the frustrated Niccolini described later: “While we were discussing those delicate subjects of the Holy Office, His Holiness exploded into great anger, and suddenly he told me that even our Galilei had dared entering where he should not have, into the most serious and dangerous subject which could be stirred up at this time.” Taken aback by this outburst—and not being aware of the fact that by that time Ciampoli had fallen out of favor with the Pope—Niccolini made the additional mistake of trying to argue that the Dialogo had been published with Riccardi’s and Ciampoli’s approval. This struck a nerve with Pope Urban VIII, who now shouted in rage that “he had been deceived by Galileo and Ciampoli,” and that “in particular, Ciampoli had dared tell him that Mr. Galilei was ready to do all His Holiness ordered and that everything was fine.” All of Niccolini’s attempts to convince the Pontiff to give Galileo a chance to explain his actions fell on deaf ears. The Pope screamed angrily that “such is not the custom,” and that “he [Galileo] knows very well where the difficulties lay, if he wants to know them, since we [using here the royal we] have discussed them with him, and he has heard them from ourselves.”

  Niccolini’s further efforts to at least soften the blow hit a brick wall. The Pope revealed that he had appointed a commission to examine the book “word for word, since one is dealing with the most perverse subject one could ever come across.” Finally, repeating his complaint that he had been deceived by Galileo, Urban VIII added that he had, in fact, done Galileo a favor by appointing a special commission and not sending the case directly to the Inquisition.

  Faced with this fiasco, Niccolini decided, also on Riccardi’s advice, to refrain from any additional steps to try appeasing the Pope, and to solely rely on Riccardi’s own endeavors to introduce some corrections into the book, to make it more palatable. Riccardi appeared to be less concerned about the composition of the commission (of which he was a member), estimating that at least two others would treat Galileo with fairness. In this assumption he was wrong, since the Jesuit Melchior Inchofer (most probably a commission member) was a devout anti-Copernican.

  At any rate, this was the situation at the beginning of September 1632, and although things looked far from encouraging, there were at least some grounds for mild optimism. However, that was when a new piece of information hit like a bomb.

  A GHOST OF THE PAST

  As you may recall, sixteen years earlier, Galileo had been summoned to Roberto Bellarmino’s palace, where, after a warning by Bell
armino, the Commissary General of the Holy Office, Michelangelo Seghizzi, unnecessarily issued a harsher injunction forbidding Galileo from holding or defending the Copernican system in any publication or in teachings. The document recording this injunction—and Galileo’s submission to it—was somehow recovered from the Holy Office’s archives around mid-September, and it was brought to the attention of the Pope’s commission. With this new evidence at hand, all hopes that the entire affair would be solved by a few corrections to the Dialogo were rapidly beginning to fade. In fact, at a meeting of the Congregation of the Holy Office on September 23, it was reported that Galileo had been “deceitfully silent about the command laid upon him by the Holy Office in the year 1616, which was as follows: to relinquish altogether the said opinion that the Sun is the center of the world and immovable and that the Earth moves, nor henceforth to hold, teach, or defend it in any way whatsoever, verbally or in writing, otherwise proceedings would be taken against him by the Holy Office, which injunction the said Galileo acquiesced in and promised to obey.” Seghizzi’s hand was now reaching for Galileo’s neck even from the grave. He’d died in 1625.

  In view of this new evidence, the Pope’s reaction was swift. He sent a message instructing the inquisitor of Florence to order Galileo to travel to Rome for the whole month of October and appear before the Commissary General of the Holy Office for questioning. Shocked to receive this jarring command, Galileo understood that he had to at least formally demonstrate obedience. At the same time, he was determined to do everything in his (or his friends’) power to dodge having to go to Rome, knowing only too well that nothing good could come out of such a trip. As part of these efforts and delay tactics—but also due to his genuinely poor health—he sent a letter on October 13 to Cardinal Francesco Barberini in which he complained that the fruits of his studies and labor “are turned into serious accusations against my reputation,” which, as he described, had caused him countless sleepless nights. Galileo made an emotional appeal to Barberini that the Church allow him to either send detailed explanations of all his writings or to appear before the inquisitor and his staff in Florence rather than in Rome.