Post-classical history

CHAPTER 19
Galileo and Giordano Bruno

According to the traditional history of science, Galileo was a man of unparalleled originality. He was, supposedly, the first person to show that objects of different weights fall at the same speed, the first to claim that vacuums could really exist and the first to realise projectiles move in curves. He rejected Aristotle when everyone else followed him slavishly. It is said that he proved Copernicus was right and that the Inquisition cast him into prison as a result. As it turns out, none of these things is exactly true. Galileo never proved heliocentricism (as we have already seen, it was Kepler who effectively did that) and his trial before the Inquisition was based more on politics than science. Galileo’s scientific achievement was solidly based on the natural philosophy that came before him. Appreciating that fact should not diminish our admiration of his genius. While almost all his theories can be traced back to earlier sources, he was the first to mould them into a coherent whole and the first to show how they could be experimentally demonstrated. In that sense, the long road to modern science really does start with him.

The Early Career of Galileo

Galileo Galilei was born in the city of Pisa on 15 February 1564. His father was a distinguished musician by profession who had acquired some business interests in Pisa through his wife. Galileo entered the university of Pisa to study medicine (although the family had moved back to Florence by this stage), but left without a degree in 1585.1 He had no great interest in medicine but the preliminary courses in mathematics and natural philosophy encouraged him to devote himself to the study of numbers. The astronomy textbook that Galileo would most probably have used during his student days was Clavius’s. This would have introduced him to the ideas of Copernicus but also demonstrated why they were wrong. At the same time, Galileo would have covered Aristotle’s natural philosophy. The aspect that interested him most was the theory of motion, which he was convinced Aristotle had got badly wrong. His lifetime of opposition to Aristotle’s physics certainly arose during his days as a Pisan student.

Despite lacking a degree, young Galileo’s talent for mathematics was obvious. His family also had friends in high places and this was enough to secure him a mathematics professorship at Pisa in 1589.

The greatest monument of Pisa, its leaning tower, was begun in 1173 to function as a bell tower for the local cathedral. According to one of his early biographers, Galileo used the leaning tower to strike a mighty blow against Aristotle’s ideas about free fall. The story goes that Galileo, together with a gaggle of his students, summoned the Aristotelian professors to the base of the tower. The followers of the Philosopher all insisted that heavy objects fall faster than light ones. In fact, they thought an object that is twice as heavy should fall twice as quickly. To prove this wrong, Galileo mounted the tower armed with two lead balls of very different sizes. They were of high enough density that air resistance would not be a significant factor. He dropped the balls from the belfry at the top of the tower and, to the consternation of the Aristotelians, both hit the ground at the same time. In this way, Galileo refuted the doctrine of Aristotle and showed how his experimental method trumped the rational analysis of the philosophers.

Nowadays, many historians dismiss the story as a myth, but it is entirely possible that something similar did happen.2 For example, we know that Galileo was dropping wooden and lead balls together at around this time, although his results were not that they both landed at the same time. Instead, he reported that the wooden ball began by falling faster and was then overtaken by the lead ball that reached the ground first. Modern physics cannot explain this result and it shows that even the great Galileo’s experiments were fallible.3 He was also not the only one at Pisa carrying out this sort of work. The Aristotelian professors were doing experiments of their own to prove their theories. They too achieved results that are clearly wrong.

The conclusion that objects of differing weights fall at the same speed was hardly new. John Philoponus had, we noted in chapter 11, made this observation in the sixth century and Thomas Bradwardine had later suggested that it also held true in a vacuum. Giovanni Battista Benedetti (1530–90), an Italian mathematician and student of Nicolò Tartaglia,4 published the result as his own discovery in 1553 and his book was translated into English and German. Benedetti incorrectly said that the speed at which an object fell depended on its density – a point on which Galileo agreed with him.5 Jean Taisnier, the priest who had plagiarised Peter the Pilgrim’s treatise on magnetism, also claimed to have made Benedetti’s breakthrough himself.6 Taisnier’s fraudulent work inspired Simon Stevin (1548–1620), a Dutch engineer, to carry out his own experiment on the matter. In a book of 1586, Stevin wrote:

The experiment against Aristotle is this: let us take (as the very learned Mr Jan Cornets de Groot, most industrious investigator of the secrets of nature, and myself have done) two spheres of lead, one ten times larger and heavier than the other, and drop them together from the height of thirty feet on to a board or something on which they give a perceptible sound. Then it will be found the lighter will not be ten times longer on its way than the heavier but that they fall together on to the board so simultaneously that their two sounds seem to be one and same.7

He went on to refute Benedetti’s conjectures on density, thinking they were Taisnier’s. So, by the time Galileo came to address the question, just about every natural philosopher would have heard the evidence that Aristotle was wrong.

Clearly, Galileo’s early doubts about Aristotle’s account of motion were not the thoughts of a lone radical, but part of a scientific milieu where experimentation and criticism of Greek natural philosophy were becoming increasingly common. Of course, we know that this began with John Buridan way back in the fourteenth century and that the Jesuits had published well-regarded books on motion with which Galileo was familiar. His earliest attempt to explain projectile motion (that is, what happens to a cannon ball after it is fired, or when you throw something), drew directly on the concept of impetus that Buridan had found so useful.8 Galileo’s ideas are similar to those of Arabic thinkers who had in turn found inspiration from John Philoponus.9 We also know from Galileo’s own writings that he had not figured out the truth about free-falling bodies at this early stage of his career. That would come later.

Domingo de Soto and Falling Objects

Although Galileo did not yet understand how falling bodies actually move, someone else did. He was a Spanish Dominican called Domingo de Soto (1494–1560). After his early education was completed in his home country, Domingo moved to the university of Paris to study theology.10 He had first to complete the course of Aristotle’s philosophy and basic mathematics, which were both still viewed as an essential introduction to the ‘queen of the sciences’. His course would have been dominated by the works of John Buridan and his contemporary followers such as Thomas Bricot. We know that Juan de Celaya (d.1558), Soto’s teacher and compatriot at Paris, published a highly technical book on the science of physics in 1517 which makes full use of the work of the Merton Calculators and John Buridan.11 Clearly, the discoveries of the masters of the fourteenth century were still found to be relevant in the sixteenth. Domingo himself returned to Spain before he completed the theological course but gained his degree shortly afterwards. In 1525, attracted by the order’s academic reputation, he joined the Dominicans and spent the rest of his life teaching at their school in Salamanca. His interests included ethics – he criticised the treatment of Native Americans by Spanish colonists – and theology, as well as physics. The resulting textbooks sold so well that they financed a good deal of building work at his home priory.12

In 1545, the Dominicans sent Domingo to Italy to attend the Council of Trent, where the Catholic Church was laying the ground for the Counter Reformation, as one of their representatives. While he was there, he would have had the chance to learn about the work of Italian critics of Aristotle’s theory of motion who had already been carrying out experiments to show that the ancient Greek was wrong. Domingo returned to Salamanca in 1551 and published his textbook on Aristotle’s Physics. In it, he gives the first accurate description of how objects fall under gravity.13

We know today that the distance that a falling object travels is described by the mean speed theorem developed by the Merton Calculators and Nicole Oresme. What no one had managed to do up until the time of Domingo was relate the theorem to what actually happens to falling bodies. Domingo finally did so and reported the result in his textbook. It was widely distributed around southern Europe, especially in the schools run by the Dominican order.14 His ideas were thus current during the period when Galileo was developing his own theories.

Galileo’s Family Life

During his time at Pisa, Galileo had already marked himself out as a thinker of note and needed only suitable patronage to advance his career. In 1592, he left Pisa and used his connections to gain a job at the much more prestigious university of Padua, situated in the hinterland of Venice. He stayed there for eighteen years. At some point during this period, he met a local woman called Marina Gamba. She moved in with him and bore him three children, but they never married and parted when he left Padua in 1610. His son, Vincenzo, received a good education and was eventually decreed a legitimate child so that he could become Galileo’s heir. The two girls were less lucky. Their father tried to have them packed off to a nunnery as early as possible. The law stated that a girl could not profess as a nun until she was sixteen and old enough to make an informed decision. Galileo was impatient and called on his influential friends to get both girls into a convent near Florence when they were barely thirteen. The elder one, Virginia, seemed quite content with this arrangement and remained close to her father until she died in 1634. The younger, Livia, was deeply unhappy at effectively being forced into a religious life that she was unsuited for.15

The main reason for Galileo’s questionable treatment of his daughters was money. He never had enough of it. After his father had died in 1591, he had become head of the family and was responsible for finding dowries for his two sisters. He was not keen on taking on similar obligations for his offspring. His salary as a mathematics professor was not substantial and he was expected to supplement it by taking on extra pupils privately, some of whom also rented their lodging from him.

Galileo’s research during his time at Padua was constantly interrupted by these other calls on his time. He also had to deal with plagiarism of his work and the task of keeping his ultimate masters, the Venetian senate, on side. Despite all these distractions, he made considerable progress in trying to formulate a realistic law of motion and what we would today call a scientific method. For while Galileo thought that Aristotle’s conclusions were almost always wrong, he was a great admirer of his system of analysis. Italian philosophers had been arguing about and fine-tuning Aristotle’s methodology since 1400 in an effort to explain exactly how to relate theory to physical reality.16 Galileo’s work comes at the end of this tradition. Essentially, Galileo believed that a scientific proposition was proved if it could be derived from properly grounded causes and then demonstrated by experience.

Today we have a much less demanding test for a valid scientific theory. Nothing is ever proved absolutely in science because there is always the possibility that some new evidence will come along and show that the old theory is inadequate. We now know that even some of the most famous scientific theories are not exactly correct, including Newton’s laws and Kepler’s model of the solar system. Galileo wanted to believe that science can discover things with certainty and this, as we will see, eventually got him into serious trouble. Another, more direct reason for his later problems was that while he was in Padua he became one of the few people to believe that Copernicus might be right in saying that the earth orbited the sun.

We first hear Galileo enthusiastically espousing Copernicanism in 1597 in a letter he wrote to Kepler acknowledging a copy of one of Kepler’s books that he had received from a mutual acquaintance. Kepler was thrilled to find an ally, even one he had never heard of, and immediately wrote back, enclosing another couple of copies of the book for Galileo to distribute. By that time, though, Galileo had decided that he really had little in common with Kepler. The latter’s religious mysticism was not to the Galilean taste and the text was probably just too opaque to bother with.17 Galileo was a masterful writer and valued limpid prose in others. This had the unfortunate consequence that Galileo ignored Kepler’s great discoveries and never made much use of them in his own work.

The Church Discovers the Theory of Copernicus

Religious reaction to Copernicus before 1600 had been subdued largely because so few people thought that his theory was correct. A few writers had pointed out that the idea of a moving earth clearly contradicted scripture, but the point was moot because no one believed it anyway.

In 1584, Didacus à Stunica (1536–97) a Spanish friar, wrote a biblical commentary in which he explained that all the passages in the Bible that said the earth did not move could easily be interpreted figuratively. He explained that the Bible was written from the point of view of an observer on earth rather than from a ‘god’s-eye’ view of the heavens as a whole. This is, of course, exactly the same argument as Oresme had made 250 years earlier. Then, in 1597, Stunica wrote another book, this time actually about natural philosophy rather than a biblical commentary. By then, he had decided that even though the issue could not be settled from the Bible, Copernicus’s ideas were physically absurd.18 In other words, he thought a moving earth was religiously unobjectionable but scientifically untenable.

A Platonic philosopher by the name of Francisco Patrizi (1529–97) suggested that the earth rotated for very similar reasons to those suggested by Nicole Oresme. This was not even the most radical aspect of his work, which sought to replace Aristotelian materialism with a mystical Platonic alternative. The Catholic Church’s censorship body, the Congregation of the Index, ordered him to amend his work but allowed the rotation of the earth to stand, despite initially questioning it. A revised version of Patrizi’s book appeared two years later and he kept his job as professor of Platonic philosophy, having been appointed by the Pope himself.19

Patrizi’s most fruitful suggestion was that vacuums might actually be real.20 Since 1277, Christians had admitted that they were possible, if only through God’s absolute power to do what he liked, but few natural philosophers had postulated that they really existed. This aspect of Patrizi’s thinking may well have influenced Galileo, who was also becoming receptive to the possibility of vacuums.

Giordano Bruno: Martyr for Magic

No early proponent of Copernicus’s hypothesis is more famous than a renegade Dominican and magician by the name of Giordano Bruno (1548–1600). He was born near Naples in 1548 and joined the local Dominican monastery in 1563. We know very little about his early career except that in 1576 he clashed with his superiors over his strange doctrines. Bruno cast off his friar’s cloak and embarked upon a life on the road. His travels took him through France and then on to England where he arrived with a letter of recommendation addressed to the French ambassador in March 1583.21 Within a few months, he was in Oxford arguing with the local professors about his magical philosophy.

Bruno went further than many of the magicians of his time by trying to add an entirely new religion of his own creation to the existing magical doctrines. His beliefs were loosely based on the same neo-Platonic writings that had inspired Ficino, but Bruno made no effort to conform his ideas to Christianity. He even referred to such controversial writers as Cecco D’Ascoli whose previously banned books were now in print.22 He was also monumentally conceited, with a habit of writing about himself in the third person as some kind of genius. The combination of newfangled and absurd theology with an unerring ability to rub people up the wrong way meant that he could rarely stay put for long. People had a habit of running him out of town.

Among his various ideas, Bruno was right about at least one thing – the earth goes around the sun. He lauded Copernicus for realising this, even though he certainly could not handle the mathematics upon which Copernicus built his system. Instead, Bruno shared a veneration of the sun with other neo-Platonists. By way of explanation, he wrote:

The cause of such motion [of the earth] is the renewal and the rebirth of this body, which cannot last forever under the same disposition. Just as things which cannot last forever through the species (speaking in common terms) endure through species, substances which cannot perpetuate themselves under the same countenance do so by changing their configuration.23

Don’t worry if this doesn’t make any sense. It is certainly not scientific in the way that we might understand today. What Bruno seems to be saying here is that the earth moves so that it will benefit from the seasons. But before we write it off as complete lunacy, it did have some influence on William Gilbert.24 As we have seen, Gilbert equated the earth’s magnetic field with its soul. That was the kind of thinking that Bruno inspired and it is entirely possible that Gilbert’s mystical speculation was built on Bruno’s.

Needless to say, none of this went down well in Oxford. Bruno decided to give some lectures and harangued his audience about how ignorant and backward-looking they were. This was how he treated everyone who disagreed with him. The trouble was that the Oxford masters were far from ignorant. They had been discussing Copernicus for at least the previous ten years and had come to the same conclusion as everyone else – he was wrong.25 The denouement of his Oxford visit went badly for Bruno. One of his audience realised that he was plagiarising Ficino and brought his own copy of Ficino’s book with him to the next lecture. He caught Bruno misrepresenting his source and, after some procrastination, the magician slunk off back to the continent.26 He wandered around Europe hawking his thoughts for almost another decade before, in 1591, he made the fateful decision to return to Italy into the arms of the Inquisition. A Venetian patrician had invited him to the city and after a few months, denounced him to the local inquisitor as a heretic.27 It has been suggested that the invitation to Italy was a trap, but perhaps the experience of having Bruno in his house for a few months was quite sufficient to cause any sensible Catholic to hand him over to the authorities.

Initially, the Venetian Inquisition knew little about Bruno. They had arrested him on the say-so of an aristocrat who also made a series of hair-raising allegations. Bruno denied almost everything and without further evidence, the case looked like it would go nowhere. If he recanted the minor errors he admitted to, he would be given a penance and they would have to release him. Then things started to go wrong for Bruno. First, it turned out he had previous. His exit from the Dominican order in 1576 had generated a file in Rome and the inquisitors there wanted him extradited. Usually, the authorities in Venice refused to hand over prisoners, but Bruno was not a citizen and not their problem, so he was sent to Rome.

Bruno’s difficulties started to mount. He had discussed his ideas with his fellow prisoners who started making depositions that needed to be investigated. Worse, the inquisitors got hold of his books which were full of alarming ideas. In the end the file ran to 600 pages and it took nine years for the case to be concluded.28 Throughout, Bruno insisted on his innocence.

Eventually the file was handed to a Jesuit professor by the name of Robert Bellarmine (1542–1621). He drew up a list of eight heretical statements that no one could doubt Bruno held. The list has not survived and this leaves us free to speculate about what the eight statements were. The choice from Bruno’s extant works alone is very considerable. Those who imagine that Bruno was a martyr for science assume that his support for a moving earth and an infinite universe featured on the list. This is impossible. As we will see in the next chapter, Copernicanism was not declared a heresy until 1616 and as for an infinite universe, he was simply echoing Cardinal Nicholas of Cusa. Both these beliefs were discussed in the Inquisition’s files, but that in no way proves that they were deemed formally heretical.

In any case, Bruno agreed to recant the statements on Bellarmine’s list and do penance. At the same time he wrote a sealed letter to the Pope claiming that the statements were not heresies at all. In doing so, he undermined his own confession. Now, finally, the inquisitors lost patience. He was given 40 days to repent or face the stake as an impudent and recalcitrant heretic. With incredible bravery, Bruno stuck to his guns and was burned alive in Rome on 17 February 1600. Nobody deserves this terrible fate and the Inquisition should not even have taken him seriously.29

As for Robert Bellarmine, historians agree on three things. He was in possession of a brilliant intellect, he was a religious fundamentalist and you could not hope to meet a nicer bloke.30 His manners and kindness were legendary. If sentencing a man to be burnt alive sounds less than nice, we may be sure that he felt the same. Instead, like so many other people in history, he had a misguided sense that he had to do his duty, however unpleasant.

Although physically a very small man, Bellarmine was a big fish in the Vatican pool. He was Italian by birth and the nephew of a pope, but he had no need for nepotism to advance up the ecclesiastical ladder. He completed his education at the university of Louvain in the Netherlands where he lectured on natural philosophy. Bellarmine was no unquestioning follower of Aristotle but instead thought that science should be based on the Bible. As there is very little science in the Bible, many scientific questions were, for Bellarmine, unanswerable. The certainties of Aristotle were unacceptable, especially his claim that the heavens never changed and were made of the fifth element, ‘ether’. The Bible hinted nothing of this and so, in Bellarmine’s eyes, the theory was unfounded. As for the motion of the planets, Ptolemy’s theory was no good because it could not exactly describe the phenomena we observe. Bellarmine himself seemed to think that the movements of the planets were simply too complicated to be accurately modelled.31 The reality of their motion was beyond the ken of man.

In 1576, Bellarmine was recalled to Rome and put in charge of the Jesuits’ offensive against Protestantism. His analysis of the various threats to the Catholic Church, published as the book Controversies, made him the number one target of Protestant propaganda. He was a worthy opponent because he had no time for the superstitions popular with the Catholic laity, such as ringing church bells to ward off thunderstorms, which also enraged Protestant theologians.32 Bellarmine upset the Pope too by downgrading his political power to merely ‘indirect’.33 But he was able to shrug off papal disapproval and the next pontiff promoted him. In 1599, he became a cardinal and in 1606 narrowly escaped becoming Pope himself, something he did not want at all. However, he remained in Rome as the most important thinker in the Vatican and the first man to whom the Pope turned when he needed intellectual advice. Thus, when Galileo’s new ideas about the planets became an issue, Bellarmine was closely involved in formulating the official response.

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