Post-classical history

CHAPTER 20
Galileo and the New Astronomy

On 13 March 1610, Galileo went from obscure professor of mathematics to international sensation overnight. The book that brought about this transformation is called the Sidereal Messenger. On the very day of its publication, the English ambassador to Venice was writing home about it. Galileo, the ambassador concluded, ‘runs the risk of either being extremely famous or exceedingly ridiculous.’1

The Sidereal Messenger publicised the discoveries that Galileo had made with a new piece of scientific equipment – the telescope. It had been invented in Holland a couple of years earlier and one Hans Lipperhey (d.1619) had unsuccessfully tried to obtain a patent for it.2 By 1609, Galileo had built his own improved version. He quickly found that there were many more fixed stars than could be seen with the naked eye and that the planet Jupiter had four small companions in orbit around it. Most controversially, he revealed that the moon was not a perfect sphere, as Aristotle said all heavenly bodies must be, but disfigured by craters and mountains. He was not the only person who examined the heavens with the new instrument but he was the first to publish his observations, and he kept up the flow of new discoveries. Within a year he announced that Saturn had ‘ears’, which later turned out to be rings, and that Venus had phases like the moon.

This last observation was the most important. Galileo noted that sometimes, when he looked at Venus through his telescope, he saw almost a complete disk. At other times, only a semicircle or even less of the surface was visible. The periods of these phases were such that Ptolemy’s model of the heavens had to be wrong. Venus did not orbit the earth; it orbited the sun.

Galileo’s Discoveries

The controversy caused by these results was immediate. The first problem was that Galileo’s telescope, for one reason or another, was better than anyone else’s. He could see things that were not apparent to other observers, especially those who had decided in advance that he must be mistaken. One such critic was his colleague at the university of Padua, Cesare Cremonini (1550–1631). He was the university’s professor of Aristotelian philosophy and not very receptive to ideas that conflicted with his master’s teaching. However, he was no shirker of debate. His consistent refusal to contradict Aristotle’s denial of the soul’s immortality meant that the Inquisition were very keen to talk to him. Luckily, his residence in Venice, which only handed people over to the Vatican if it wanted to, kept him out of danger. However, Cremonini quickly became exasperated by the whole question of the telescope. ‘I do not wish to approve of claims about which I do not have any knowledge, and about things which I have not seen’, he said, ‘and then to observe through those glasses gives me a headache. Enough! I do not want to hear anything more about this.’3

While Cremonini was soothing his sore head, Giulio Libri (c.1550–1610), professor of Aristotelian philosophy at Pisa, was also having trouble seeing the moons of Jupiter. When he died shortly afterwards, Galileo sarcastically said of Libri, ‘never having wanted to see [the moons of Jupiter] on earth, perhaps he’ll see them on the way to heaven?’4 These remarks seem to be the source of the persistent legend that certain individuals refused even to look through the telescope. In fact, we know of no one who definitely declined to do so. The argument was over what they would see once they had peered through it.

As far as the Church was concerned, only one person’s opinion mattered – Christopher Clavius’s. He was now an old man, revered as the Jesuits’ most senior astronomer and famous throughout Europe. Initially, he was suspicious of Galileo’s discoveries. In 1610, no one had any idea how the telescope worked and it seemed very possible that it was distorting as well as magnifying the images. When one of Clavius’s students built his own telescope it was of insufficient power to show all the things Galileo claimed to see. The student set to work on an improved version and this time it worked very well.5

Cardinal Bellarmine wrote to Clavius to ask whether he could confirm Galileo’s discoveries. The Jesuits replied that they could, although they were not sure about how the results should be interpreted.6 Nevertheless, when Galileo visited Rome in 1611, he received a hero’s welcome and the Jesuits lauded him openly for his wonderful discoveries. In the same year, Johann Kepler drew on his experience of mathematical optics to explain how the telescope worked and suggest some improvements. Clavius added a section to his astronomy textbook outlining Galileo’s findings and ending with a note that ‘astronomers ought to consider how the celestial orbs should be rearranged to model these phenomena.’7 Even Clavius, a supporter of Ptolemy, could see that reform was now necessary. Unfortunately, he died shortly afterwards and never let on what he thought the reforms should be.

However, it is possible to make a guess. When Ptolemy’s system was rendered obsolete by Galileo’s discoveries, there were two candidates to replace it – the ideas of Copernicus and those of Tycho Brahe. Galileo and Kepler supported Copernicus while just about everyone else thought Tycho’s model the best. There were still overwhelming problems, both physical and religious, with the idea that the earth moved. This alone made Tycho’s theory the much more attractive one. Galileo realised the question was wider and more important than simply which scientific theory should be adopted. After all, if Tycho turned out to be wrong, then his ideas could be dropped just like Ptolemy’s had been. But the religious issues surrounding the heliocentric model were potentially toxic.

In 1610, cashing in his new-found celebrity, Galileo took up the post of official mathematician to the Grand Duke of Tuscany, Cosimo I Medici (1590–1621), a descendant of the Cosimo who had ordered Ficino to translate the Hermetic corpus. This meant that he no longer needed to take in students to make ends meet. He was being paid to produce books and research that would redound to the glory of the Medici family. Galileo had started well, naming the moons of Jupiter the ‘Medicean Stars’ in honour of his prospective employer. As a job application, this ploy of flattering the Grand Duke was completely successful. His old colleague, Cesare Cremonini, knew that Galileo was taking a risk leaving Venice for the Medicis’ home in Florence. Once there, Galileo would no longer enjoy the protection from the Inquisition that Venice afforded Cremonini. Of course, at the time Galileo had nothing to fear and ignored the warnings. Besides, he was going home.

The mother of Grand Duke Cosimo was called Christina (1565– 1637). She was an intelligent woman, interested in science and philosophy, who asked one of Galileo’s friends about the compatibility of Copernicanism and scripture. He passed the query to Galileo, who as scientific adviser to the Medicis, was well placed to answer her question. This he did, in great detail.

There is no denying that a completely literal reading of the Bible strongly supports the stability of the earth and the movement of the sun. For example, Ecclesiastes 1:5 reads: ‘The sun also arises, and the sun goes down, and hastens to the place where it arose’, while Psalm 103:5 (104:5 to Protestants) reads ‘He [God] laid the foundations of the earth, that it should not be moved forever.’ Back in the fourth century, St Augustine of Hippo had wrestled with the matter of what to do when the Bible and science said different things in his commentary on the book of Genesis. Genesis clearly conflicted with the best available Greek science of the time. Augustine was worried that Christians who read their Bible too literally risked making their religion look ridiculous. In his commentary he wrote:

Usually, even a non-Christian knows something about the earth, the heavens and the other elements of this world, about the motions and orbits of the stars and even their sizes and relative positions … Now it is a disgraceful and dangerous thing for an infidel to hear a Christian, presumably giving the meaning of the Holy Scriptures, talking nonsense on these topics, and we should take all means to prevent such an embarrassing situation, in which people show up vast ignorance in a Christian and laugh it to scorn.8

Augustine’s solution was to set out the circumstances when the Bible should be read in a figurative rather than literal sense.

Carefully developing these earlier ideas, Galileo showed that the Bible should not be read as a scientific document, but one written in the language of the common people. Thus, when it referred to the sun rising and setting, it was simply using the everyday idiom that everyone is familiar with. The same principle applies to the two references in the Bible to the ‘four corners of the earth’.9 This is simply a phrase that is used in common parlance, but not even the most one-eyed biblical literalist thinks the earth is flat. Galileo summed up his argument with the famous words: ‘The intention of the Holy Spirit is to teach us how one goes to heaven, not how the heavens go.’10 While this aphorism is pithy, the idea was not original. We have seen how William of Conches expressed exactly the same sentiment four centuries earlier.

Galileo made one further argument that in retrospect seems the most astute of them all. If, he said, the issue of whether or not Copernicus was correct was remotely uncertain, the Church should leave the matter well alone. If it made a ruling that later turned out to be wrong, the damage to its authority would be incalculable.11 Unfortunately, no one in the Vatican was listening.

The Church takes action against Copernicus

Matters came to a head in 1616. Galileo had been quite open about his support for Copernicus but, as it turned out, it was not his activities that pushed the Church into taking official action. Instead, a book appeared by an Italian friar called Paolo Foscarini (1565–1616), which argued along similar lines to Galileo that the earth’s motion was consistent with a proper reading of the Bible. The Church could not ignore Foscarini’s advocacy of Copernicus because he was a professional theologian.12 His opinions on Biblical interpretation carried far more weight than Galileo’s. At the centre of the Church’s response to Foscarini’s challenge was none other than Cardinal Bellarmine.

Bellarmine’s opinion about the Bible was completely different from Galileo’s and quite unusual among Catholics at the time. He believed that the Bible should always be treated as literally true unless there were ironclad reasons not to do so. Official Catholic doctrine laid down by the recent Council of Trent said that the Bible was only without error in matters of faith or morals. The clear implication was that incidental details might occasionally be wrong. Bellarmine disagreed. As the whole Bible was the word of God, then for him it was a matter of faith that it was completely without error.13 This was why he had rejected Aristotle’s natural philosophy – it conflicted with the Bible. He was also relaxed about the collapse of Ptolemy’s astronomy because it had no biblical support either. Crucially, though, the Bible did say that the earth is immobile and the sun moves. On this point, Bellarmine was himself immovable. Well, almost. He did concede that if Copernicus was ever proven to be correct, then he would just have to accept that the Bible was being figurative on this point.14 This attitude might sound commendably moderate, but this would mistake Bellarmine’s meaning. As far as he was concerned, there was absolutely no chance that Copernicanism would be shown to be demonstrably true. Irrefutable proof in science is a rare enough thing and Bellarmine was insisting on complete certainty before he would reconsider what the Bible seemed to say. Clearly, science cannot operate in such an environment.

In March 1616, the Congregation of the Index of Forbidden Books made its decision on Copernicus: that to assert that the earth orbited the sun was scientifically ‘foolish and absurd’ as well as being contrary to scripture. Foscarini’s book was banned outright and Copernicus’s Revolutions of the Heavenly Spheres suspended until corrected.15 As for Galileo, he was officially warned by Bellarmine that he could not defend, hold or teach the views of Copernicus. At the same time, he was assured that the Inquisition was not formally accusing him of doing anything wrong, still less making out that he was a heretic. Despite the fact that he was personally safe, the Church’s condemnation of Copernicus had realised Galileo’s worst fears. From that moment on, he seemed to be on a personal mission to have the decision reversed. It was a hopeless quest but Galileo’s self-belief was such that he was willing to try.

Prelude to Confrontation

On his return to Florence, Galileo could no longer publicly talk about Copernicus. Luckily, he had other controversies to take up his time. He had already been involved in a dispute with a Jesuit astronomer over who first discovered sunspots. Then, in 1618, three comets crossed the sky and these gave rise to another fierce argument. A Jesuit astronomer, Horatio Grassi (1583–1654), had measured the parallax of one of the comets and found that it was above the moon rather than being an atmospheric phenomenon. On this, Grassi agreed with the earlier findings of Tycho Brahe and others. Galileo, oddly enough, was not convinced and briefed a student to write a rebuttal that attacked the basis of saying anything definite about comets. From then on, the argument raged in an undignified fashion.16 In 1623, Galileo wrote a short book called the Assayer which was intended to scotch Grassi’s arguments. In this, he was resoundingly successful. The Assayer is a statement of what Galileo takes to be best practice in science; that is, to follow not the authority of other writers, but the authority of nature itself. He wrote:

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; without these, one wanders about in a dark labyrinth.17

Of course, there was nothing new about the metaphor of nature as a book. Nor was the idea that it was mathematical particularly novel – we have already encountered it in the work of Nicholas of Cusa and Kepler. However, mathematics had long been a poor relation to natural philosophy and Galileo was adding his weight to Clavius’s in order to ensure that it was now properly regarded. Unfortunately, the Assayer was primarily an attack on the Jesuits in Rome who took the whole affair quite badly. It is also worth noting that modern opinion agrees far more with Grassi than Galileo on the question of comets. Regardless, the Assayer was a literary tour de force and no one doubted that Galileo had won the debate.18

Alienating the Jesuits who had supported him in 1611 was probably not a good idea, but other things were going Galileo’s way. In 1620, The Congregation of the Index issued its corrections to Revolutions of the Heavenly Spheres. They were surprisingly modest – just ten amendments to a book that was several hundred pages long. The purpose of the corrections was to demote Copernicus’s ideas from a picture of reality to a mathematical hypothesis. Thus, when Copernicus wrote that he had no shame in ‘admitting’ that the earth moves around the sun, the Congregation of the Index changed this to ‘assuming’ that the earth so moves.19 Rather than order that existing copies of Copernicus’s work be destroyed, the Congregation ruled that their corrections be added as a special insert.

In 1621, Cardinal Bellarmine died and in 1623 there was a new Pope, Maffeo Barberini (1568–1644) who took the name Urban VIII. Barberini was already an admirer of Galileo. They were both from Tuscany and had known each other for many years. The new Pope had little time for the Jesuits and enormously enjoyed the Assayer, which was dedicated to him. This helped Galileo more than he ever knew because the Assayer supported the doctrine of atomism. This idea had landed Nicholas of Autrecourt in trouble back in the mid-fourteenth century and its close link to the Eucharist meant that it remained a touchy subject. A Jesuit assessor at the Congregation of the Index suggested that Galileo’s book should be censored, but Pope Urban put one of his nephews – who was newly created a Cardinal together with several other members of the family – in charge of the inquiry.20 Predictably, nothing came of it and Galileo remained of good standing.

The election of the new Pope presented an opportunity to see how far the ban on Copernicanism could be stretched. As Urban was sympathetic towards Galileo, the Pope was unlikely to throw the book at him if he tiptoed around the edges of the prohibition. Treating Copernicanism as a mathematical construction was quite acceptable as long as he did not assert that it represented reality. This meant that arguing about its virtues as a model would be legitimate, especially if he was comparing it to the other models available. Galileo planned a book that would do just that. In 1624, he came to Rome to meet Urban VIII. He was granted no less than six audiences with the Pope during his stay, as well as a papal pension for his son. While they wandered around the gardens of the Lateran Palace, Urban explained his opinion on the great cosmological debate. As far as he was concerned, it was beyond man’s ability to work out how the heavens really worked. Whatever mathematical model was used to describe the movement of the planets, God could easily have arranged things differently but so as to give the same result. Thus, no matter how exactly any model predicts the movement of the planets, we cannot be sure that it is true. Urban’s argument (technically known as the problem of underdetermination) is philosophically correct but falls down in practical terms. If we have a scientific theory that accurately explains the results of all our experiments, we are well justified in believing that the theory is true.

Galileo left Rome with enough encouragement to start writing his book. Urban had let on to a cardinal who was a friend of Galileo that he did not consider Copernicanism to be formally heretical anyway, merely rash.21 Besides, no one would ever prove it conclusively, so the Church could afford to be relaxed.

The Astrological Pope

Aside from his relationship with Galileo, Urban VIII is most famous as a patron of the arts. During his pontificate, Rome was rebuilt in the new Baroque style that signalled the Catholic Church’s resurgence after the Reformation.

A less well-known aspect of his character was his fervent belief in astrology. Despite a strong papal condemnation of horoscopes by one of Urban’s predecessors in 1589, astrologers were still very widely consulted at the start of the seventeenth century. The Pope’s enemies thought they could take advantage of his credulity by publicising their own version of his horoscope. They confidently predicted that a series of eclipses in 1628 and 1630 surely heralded the Pope’s demise. Almost everyone, including Urban, believed this and preparations discreetly got under way for the election of a new Pope.22

The aim of the conspiracy must have been to kill or at least incapacitate Urban purely through the power of suggestion. Luckily for the Pope, he had a defender against this magical attack languishing in the papal prison. Tommaso Campanella (1568–1639) was, like Giordano Bruno, a renegade Dominican who had invented an entire system of esoteric philosophy. Since 1599, he had been in jail for his part in a rebellion centred on Naples. Horribly tortured, he had only escaped execution by convincing his captors that he was insane.23 Like Bruno, Campanella believed that the earth orbited the sun for mystical reasons. In 1622 he wrote a Defence of Galileo from prison that echoed the Letter to the Grand Duchess Christina in saying that the Bible was the wrong place to look for information about how nature worked. For Campanella, though, the right place was in the neo-Platonic writings of Ficino and his followers.24

Campanella had convinced himself that Urban VIII was the universal monarch whom his astrological predictions had foreordained. The Pope, Campanella thought, would allow him to convert the world to his new religion of quasi-paganism. Whether or not Urban agreed, he badly needed Campanella’s magical skills to protect him from the dangers of the upcoming eclipses. The prisoner was summoned to the papal apartments and ordered to protect the Pope from the baleful influence of the stars. The ritual that Campanella used was something he had made up especially for the occasion. He and the Pope shut themselves in a sealed room, blocking up any air holes. They sprinkled perfume, burnt rosemary and draped the walls with white sheets. In the middle of the room, five torches and two candles were lit to represent the seven planets.25 As they believed that the eclipse had rendered the heavens defective, Campanella arranged that a miniature version of them should be created in the papal apartments to shield the Pope from the dangers outside. To Urban’s great relief, Campanella’s magic worked and the Pope survived. In return, he allowed the magician to set up a school in Rome to preach his ideas to whoever would listen, while ignoring his blatant heresies.

That Urban would ignore any unorthodoxy when it suited him boded well for Galileo. Not well enough, as it turned out.

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