by Mario Livio
“The great inequality of the Moon cannot be denied. But it appears to Father Clavius more probable that the surface is not uneven, but rather that the lunar body is not of uniform density and has denser and rarer parts, as are the ordinary spots seen with the natural light. Others think that the surface is indeed uneven, but thus far we are not certain enough about this to confirm it indubitably.”
The opinion of the Catholic Church’s most prestigious mathematicians marked an incredible victory for Galileo. Clavius’s thoughts on the interpretation of the lunar observations notwithstanding, the Collegio Romano scientists recognized the telescope as a bona fide scientific instrument that delivers reality in finer detail. One could no longer argue that the telescope deceives or presents a misleading picture of the cosmos. From then on, all serious discussion could concern only the interpretation and meaning of the results rather than the telescope itself or the reality of the discoveries made with it.
The current debate on global warming had to go (and to a large extent it is still going) through a similarly painful type of confirmation process. First, people have to be persuaded that the phenomenon itself is real; then they have to accept that the identification of its causes is correct; and finally, they have to embrace at least some of the recommended solutions.
As Galileo’s case (and, indeed, those of Darwin, Einstein, and other scientists) have demonstrated, we should trust the science—the stakes are simply too high not to. We can, and should, have a serious discussion on precisely what to do in order to address the consequences of scientific discoveries, such as the threats posed by climate change (for example, rising sea levels and the dramatic increase in the frequency of extreme weather events). There should, however, be no debate anymore on whether climate change is real, on what is causing it, and on whether doing nothing is an option.
Ironically, some climate change deniers have even tried to argue that the overwhelming consensus in the geoscience community about a human-caused climate change is in itself a “logical fallacy,” citing Galileo’s case. The argument goes as follows: because Galileo was mocked and persecuted for his views by a majority at his time but later proved to be right, current minority views on climate change that are being criticized must also be right. In fact, this false logic even has a name: the “Galileo gambit.” The flaw in the Galileo gambit is obvious: Galileo was right not because he had been mocked and criticized but because the scientific evidence was on his side. The reports on climate change by the leading scientific organizations represent, with obvious uncertainties which are clearly articulated, the up-to-date state of knowledge in this field. In science, we know that the near 100 percent consensus does not in itself guarantee that the conclusions are correct, but we know that this consensus is based on continually tested scientific evidence.
Returning to Galileo’s case proper, what happened—for a while, at least—was that he was showered with honors. Overall, some 400 books about Galileo, approximately 40 percent of them favorable, were published in the seventeenth century alone. Of those, about 170 appeared outside of Italy. Even his archenemy Martin Horky, impressed by Galileo’s observations of Saturn, declared his deep regret over having attacked such a magician of the heavens. In fact, he went so far as to say that he would have preferred to lose blood.
On April 14, 1611, during a banquet at which Galileo was elected as a sixth member of Cesi’s Accademia dei Lincei, the name telescopium was coined for the spyglass that revolutionized cosmology. The name was suggested by theologian and mathematician Giovanni Demisiani, and it didn’t take long for the first book on the history of the telescope to appear. It was written by the Milanese Girolamo Sirtori in 1612 and published in 1618 under the obvious title Telescopium.
Galileo’s triumphant reception in 1611 represented just one battle. It did not mean that he had won the war. While the veracity of the observations themselves had been accepted, this merely marked the starting point for the altercation over the interpretation of the results. It was to be expected that staunch, fervent geocentrists, compelled to reevaluate cherished beliefs about the cosmos and the Earth’s status within it, were not going to capitulate without a fight.
As we know today, the Copernican model as advocated by Galileo marked the introduction of a new concept, now known as the “Copernican principle”: the realization that the Earth, and we, human beings, are nothing special, from a physical perspective, in the grand scheme of things. In the centuries that have passed since Copernicus’s proposed scenario and Galileo’s discoveries, this principle of cosmic humility has only gained strength through a series of steps demonstrating that, indeed, we do not occupy any special place in the cosmos.
First, Copernicus and Galileo removed the Earth from its central position in the solar system. Then, in 1918, astronomer Harlow Shapley showed that in the Milky Way Galaxy, the solar system itself isn’t central at all. It is almost two-thirds of the way out; literally in the galaxy’s remote suburbs. And in 1924 astronomer Edwin Hubble discovered that there are many other galaxies in the universe. In fact, we know today that there are perhaps as many as two trillion galaxies in the observable part, according to the latest astronomical estimate. As if this wasn’t enough, some cosmologists now speculate that even our entire universe may be just one member of a huge ensemble of universes—a multiverse.
An interesting case illustrating what Galileo was up against in his endeavors to prove the superiority of the Copernican cosmology over the Aristotelian (or Ptolemaic) one was provided by Cesare Cremonini, a renowned philosopher and dogmatic Aristotelian. Cremonini was Galileo’s colleague at the University of Padua, where the two often engaged in a form of friendly rivalry. He was extremely opinionated when it came to natural philosophy, to the point that he apparently was afraid to even put William Gilbert’s book on magnets and the magnetic Earth on his shelf, for fear that it would contaminate his other books. While Cremonini was an atheist, and also forcefully defiant of censorship, he felt obligated to defend Aristotelianism in all its forms. Consequently, he challenged Galileo’s assertion that the nova of 1604 was farther out than the lunar orbit—because that went against Aristotle’s doctrine that all changes in the heavens were sublunar. When Galileo offered to show Cremonini his new discoveries, Cremonini was said to have refused to even look through the telescope (as did, by the way, the chief philosopher at Pisa, Giulio Libri). This behavior won Cremonini the dubious honor of Galileo patterning the stubborn Aristotelian Simplicio partly after him in the Dialogo. In reality, Cremonini wanted something deeper than what had been revealed by Galileo’s observations. He noted, for instance, that if the Moon was indeed a terrestrial-like body, as Galileo’s findings had implied, it should have fallen toward the Earth. In the absence of a theory that could explain why this was not happening (a situation that lasted until Newton), Cremonini was not prepared to give up his Aristotelian views.
Galileo was never a great believer in what he considered to be unseen spooky forces, such as what Newton would eventually identify as a gravitational force, acting at a distance. This fact played a role in his later theory of ocean tides. Even when discussing Gilbert’s experiments with magnetism, which involved a somewhat mysterious, unobserved magnetic force, he wished for Gilbert to have come up with an explanation “well grounded in geometry” for his findings, since he found the reasons given by Gilbert “not compelling with the strength which those adduced for natural, necessary, and eternal conclusions should undoubtedly possess.”
In short, Galileo was at that moment incapable of producing a genuine theory of gravity, and therefore he remained perpetually concerned that even if “something beautiful and true were discovered, it would be suppressed by their [the philosophers’] tyranny.”
There was another concept, by the way, with which Galileo had difficulties. Kepler had discovered that a circular orbit failed to fit Tycho Brahe’s very detailed observations of Mars, which had been collected for more than thirty-eight years. Consequently, he reluctan
tly altered his model for the orbit and made it an ellipse. To his surprise, he found that not only did an elliptical orbit explain the motion of Mars but also of the other planets. This turned out to be one of Kepler’s major discoveries, and he described it in his book Astronomia Nova, which was published in 1609.
Galileo never accepted the idea of elliptical orbits. In this, even he—arguably the founder of modern scientific thought—remained prisoner of the ancient Platonic concept that perfect motion had to be circular. Today we know that it is not the shape of the orbit that needs to be symmetrical (not change) under rotations. Rather, it is the law of gravity that is symmetrical—meaning that the orbit can have any orientation in space.
The enormous efforts during those years that Galileo had put into the observations themselves, the books describing the findings, and the propaganda campaign for the dissemination of the discoveries, took a heavy toll both on his health and his family life. Being as driven as he was, he probably cared more about the former than about the latter. As a result of heavy drinking and unhealthy food and lifestyle, he suffered from various rheumatic pains, fever, and irregular heartbeats during the winter of 1610 and the summer of 1611. Not just Horky noticed his sickly, sallow appearance—a Venetian ambassador who had not seen him for several years was shocked when he met Galileo in 1615.
On the family side, Galileo left his companion Marina Gamba behind when he moved to Florence. She died in August 1612, which left Galileo in charge of their three children. He promptly solved part of that problem by putting his two daughters in the convent of San Matteo in Arcetri. The Sisters of San Matteo belonged to the order of Poor Clares and were indeed in a state of miserable poverty most of the time. There was nothing unusual about young women being placed in convents at that time. This was particularly true in the case of illegitimate daughters, whose prospects for marriage were limited, given that the sizeable dowry that would have been required to ensure an acceptable husband was beyond Galileo’s means. Still, the choice of San Matteo of all places remains somewhat of a puzzle, given that particular convent’s extreme penury and its location outside the city, which made it much harder to supervise the everyday behavior of men inside the convent’s walls. Several cases of scandalous affairs between nuns and either unscrupulous father confessors or laymen who visited the convent have been known to occur. It is possible that the choice of the convent was imposed on Galileo by the fact that his daughters were really too young to be accepted as nuns. Galileo succeeded in getting them admitted only with the help of Cardinal Ottavio Bandini.
While we know very little about the life of Galileo’s daughter Virginia (Sister Maria Celeste) until 1623, about 120 letters she wrote to Galileo between 1623 and 1634 have survived. From these, a picture of an extremely sensitive and caring daughter emerges. Being an apothecary at the convent, Maria Celeste used to send Galileo herbal treatments for his numerous maladies, and she even restocked his house with wine when he finally returned home after his trial by the Inquisition. Sadly, she died at age thirty-three from dysentery. The brokenhearted Galileo wrote about his daughter that she was “a woman of exquisite mind, singular goodness, and most tenderly attached to me.”
Much less is known about Galileo’s other daughter, Livia (Sister Arcangela), and even that, only from Sister Maria Celeste’s letters to her father. It appears that Livia never adjusted to convent life, and her relationship with Galileo was seriously strained by the harsh conditions she experienced.
The fate of Galileo’s son, Vincenzo, was much happier, primarily because the gender bias prevailing at the time ensured that there were no special financial obligations involved with a son. Vincenzo was eventually legitimized by the grand duke and, ironically, completed medical school at the University of Pisa—the program from which his father had dropped out. In case you wonder, there are no descendants of Galileo today. His last great-great-grandson, Cosimo Maria, died in 1779.
MORE ADO TO INTERPRET INTERPRETATIONS
In 1613 Benedetto Castelli, Galileo’s former student, was appointed professor of mathematics at the University of Pisa. That December, as the Tuscan court implemented its customary annual move to Pisa, Castelli was invited several times to dine with the Medicis. This led to that famous breakfast at which Castelli was asked to explain the significance of Galileo’s discoveries and the merits of the Copernican system. To understand the backdrop to that event, we should realize that, in some sense, Galileo’s outreach campaign had been too successful. Having heard of his discoveries, various people began opposing his ideas on various grounds. In Florence, philosopher Lodovico delle Colombe challenged essentially every book Galileo had written up to that point. Between late 1610 and early 1611, he composed a treatise entitled Contro il moto della Terra (Against the Motion of the Earth), in which he listed numerous biblical quotations that supposedly showed that the Earth was motionless. He even went so far as to form a “league” hostile to Galileo. Scholars in Pisa were similarly lining up along ideologies unsympathetic to Galileo, with arguments for defending the Aristotelian system rapidly converging with reasons based on faith. Consequently, Castelli’s dining with the grand ducal family occurred during these already fairly charged times, and, significantly, present at the breakfast was also the Pisan professor of philosophy Cosimo Boscaglia, an expert on Plato, whose views on Galileo were suspect at the very least.
The initial conversation was friendly enough, general, and quite benign. Nevertheless, the Grand Duchess Christina, a strictly pious woman, was already wondering whether Jupiter’s satellites were real or just “illusions of the telescope.” Boscaglia, asked for his opinion, replied that their reality “could not be denied.” He did, however, whisper to Christina more privately that Galileo’s Copernican interpretation was more problematic, since “the motion of the Earth had in it something of the incredible, and could not occur, especially because the Holy Scripture was obviously contrary to that view.”
Following the meal, as Castelli was on his way out, he was recalled by Christina to her chambers, where he found, in addition to the duchess and the duke, a few other guests, including Don Antonio de’ Medici (an admirer of Galileo) and Professor Boscaglia. For the next two hours, Christina grilled Castelli on what she regarded as discrepancies between the concept of a moving Earth and Holy Scripture. From her manner, however, Castelli’s judgment was that she did this only to hear his replies. Boscaglia didn’t say a word.
While the entire event seemed to have ended favorably, Galileo was still concerned that Castelli might be placed in similar situations again. That was why he wrote his long and detailed Letter to Benedetto Castelli, in which he outlined his ideas about the handling of apparent contradictions between biblical texts and scientific discoveries. Even though written more than four hundred years ago, this Letter to Benedetto Castelli and the subsequent expanded version—Letter to the Grand Duchess Christina—both written by a serious scientist who, having lived in seventeenth-century Italy, was also a “sincere believer” (in the words of Pope John Paul II)—remain remarkable documents on the relationship between science and Scripture. We shall return to this topic, which is still of great current interest, in chapter 17.
Galileo started his letter by praising Castelli for his success as a professor, adding, “What greater favor could you desire than to see their Highnesses taking pleasure in reasoning with you, raising questions, hearing their solutions, and finally resting satisfied with your replies?” He then explained that the incident caused him to think more generally about “the carrying of Holy Scripture into disputes about physical conclusions”—in particular the passage in Joshua about the Sun stopping in its course, which appeared to contradict “the mobility of the Earth and stability of the Sun.” Galileo’s opening statement about the usage of biblical texts powerfully sets the stage for his subsequent arguments:
“Holy Scripture could never lie or err… its decrees are of absolute truth” (emphasis added). Nevertheless, Galileo added, “some of its i
nterpreters and expositors may sometimes err in various ways, one of which may be very serious and quite frequent, [that is,] when they would base themselves always on the literal meaning of the words. For in that way there would appear to be [in the Bible] not only various contradictions but even grave heresies and blasphemies, since [literally] it would be necessary to give to God feet and hands and eyes, and no less corporeal and human feelings, like wrath, regret, and hatred, or sometimes even forgetfulness of things gone by and ignorance of the future.”
Galileo continued by insisting that for it to be understood by common, uneducated people, Scripture had to use a language that could be accessible. Consequently, he argued: “Physical effects placed before our eyes by sensible experience, or concluded by necessary demonstrations, should not in any circumstances be called in doubt by passages in Scripture that verbally have a different semblance.” Especially, Galileo noted, since one cannot have a situation where two truths contradict each other. “Hence,” he suggested, “apart from articles concerning salvation and the establishment of the Faith, against the solidity of which there is no danger that anyone may ever raise a more valid and efficacious doctrine, it would be the best counsel never to add more [articles of faith] without necessity.” To which he added that (already mentioned) compelling, powerfully cogent reasoning that he did not believe that “the same God who has given us our senses, reason, and intelligence wished us to abandon their use.”