Galileo Galilei was one of the main pioneers of the Scientific Revolution. Thanks to his discoveries with the telescope, Galileo caused the old world view to be called into question. But his fierce and sometimes untactical demeanor eventually caused him to clash head-on with the Catholic Inquisition. Kennislink did a 'fictional interview' with the world-famous Tuscan.
"The book of nature is written in the language of mathematics." According to the Italian scholar Galileo Galilei (1564-1642), whoever wants to understand nature had to be prepared to learn a new language, that of mathematics. The Bible as a source of knowledge about nature had become obsolete as far as Galileo was concerned. “The Bible tells you how to get to heaven, but not how heaven moves.”
Galileo's work marked the beginning of the "mechanisation of the worldview," a process that culminated in the work of Isaac Newton. Galileo also discovered that you can learn much more about the world by observing yourself than by reading the same ancient authorities over and over.
Mr Galilei, how nice of you to receive us at home. You were unable to come to our editorial office because you have been under house arrest for a number of years. We'll come back to that later. Let's talk about your childhood first. As for your later scientific career, you owe a lot to your father Vincenzo Galilei, don't you? “Welcome, sit down. What you say is correct. My father earned a living as a lutenist and composer. He literally played all the time and everywhere. When I think about my childhood, I hear his music. He also wrote books on music theory and harmony. Very interesting, because music is full of math. A good example is the question of the mathematical relationship between the tension on a string and the tone that the string produces. This provides insight into the structure of the octave. I well remember my father doing experiments at our house by hanging weights from strings. Partly because of this I discovered that you can solve theoretical problems by experimenting yourself.”
Did you already know that you wanted to become a researcher yourself? No, that's not how it went. In 1574, our family moved from my hometown of Pisa to Florence. My mother lodged me in the monastery of Vallombrosa, where very learned monks lived. The peace and life in the monastery appealed to me enormously. It felt so familiar that I applied as a novice for my official probationary period as a monk. I completely envisioned a retired life as a monk. However, it was my father who took me away after a short time. He hated the idea that I would spend my whole life tucked away in the monastery. He preferred that I go to medical school and become a doctor, because our family desperately needed money."
“When I turned sixteen, my father enrolled me in the Faculty of Medicine at the University of Pisa. One of the most important skills of a doctor was knowledge of astrology to be able to draw horoscopes. After all, the position of the stars tells a doctor exactly what the best medicine is for an ailment, you will of course agree with me. The little bit of geometry and math we got for that interested me much more than medicine. Despite the low reputation of the subject – because it was about abstractions it was mainly seen as a tool for physics and astrology – I decided to specialize in mathematics.”
Like probably everyone else in your day, you have always been a religious man. Did that influence your early math work? "Secure. I will give an example. The great writer Dante Alighieri had given a description of hell in his Divine Comedy (1314). Dante's hell consisted of a gigantic underground funnel-shaped cavern, created when God threw the rebellious Lucifer from heaven. The city of Jerusalem is exactly above the center of that space. Within that space are several concentric circles where the sinners are punished.”
“On the basis of the scant information Dante gave about the geometry of hell, several mathematicians had tried to determine its dimensions. A certain Antonio Manetti thought he had the solution. According to his calculations, Dante's hell was a gigantic cone-shaped space, extending to the center of the earth. However, I was able to show that such a large cone would collapse under its own weight. If hell does indeed reach to the center of the earth and has a cone shape, then the concentric circle division must be calculated quite differently in order to support its own weight. They hadn't considered that something big couldn't be put together in the same way as something smaller."
We can hardly imagine the importance of this kind of discussion anymore, but at least you discovered an important mathematical and architectural principle. What else did you do during that time? "Everything. As a student I discovered that the time in which a weight swings back and forth is regular, it is and independent of the amplitude of that pendulum. I immediately realized that this had applications in timekeeping. But more important are my ideas about movement.”
“According to the prevailing Aristotelian world view (see box, ed.), the fall speed of an object was determined by its mass. A ten-pound object would already be on the ground while a one-pound object would have traveled only a tenth of that distance. But what if you were to attach those two objects together? Would the lighter object then slow down the heavier object? Or should you add the two weights together? Strangely enough, no one had ever tried that.”
The sublunary was subject to change, transience, life and death. It consisted of four elements:water, fire, earth and air. Each element had its fixed place, or at least aspired to it. The element earth was the heaviest. A stone mainly consists of the element earth and therefore falls down to its natural resting point in the middle of the cosmos. The heavier an object is, the harder it strives for its permanent place and the faster it falls. The superlunar consisted of a fifth element, which Aristotle called ether. The supermoon was the domain of the immutable and the divine. It consisted of 'spheres', which were represented as concentric, perfectly round, hard crystal balls in which the planets, the sun, and the fixed stars revolved around the earth.
Aristotle had great authority, but it soon became apparent that the motion of the planets along the expanse did not match its perfect circular orbits. Planets apparently sometimes moved faster or slower, or even backwards. To explain these movements, the astronomer Claudius Ptolemy used all kinds of mathematical tricks with extra auxiliary circles. which made the whole thing very complicated.
“I put it to the test by dropping heavy and lighter balls of the same volume from a great height – the Leaning Tower of Pisa lent itself perfectly for this – and measuring the time it took them to hit the ground . It turned out that regardless of their mass, they landed on the ground almost simultaneously. That to me was the first strong proof that something was wrong with Aristotle's ancient ideas.”
Just in between, it seems as if you were mainly working as a young man, did you have time for the pleasures of life? “Like anyone who proposes anything in my time, I liked to immerse myself in art and poetry. But I was indeed never married, if that's what you mean. On one of my trips to Venice I met a very sweet woman, Marina Gamba. But I never married her, and therefore no children…”
We are in your own home, can you admit that you have given her three children? “You're right (slow down, ed.). I gave her three children, two daughters and a son. Because Marina and I never married, it was difficult to give the daughters a good life. They are in a monastery. I also have good contact with my daughter Maria Celeste. She writes me long letters, in which she supports me in my work or when I am sick again, which unfortunately happens often in recent years.
Thank you for your openness. Back to science then. One of the unshakable ideas of Aristotelian philosophy was that the Earth was the center of the universe (geocentrism). Tell us about the great discoveries you made with the telescope? “Anyone who took the trouble to think could see that that image wasn't quite right! According to Aristotle, the planets moved in perfect circles around the Earth. But everyone could see that the planet Mars sometimes seemed to move backwards across the sky. Also, the tables astronomers used to predict solar and lunar eclipses were not accurate enough.”
“Polish physician and mathematician Nicholas Copernicus largely solved these problems by writing in his De revolutionibus orbium coelestium (about the revolutions of the heavenly bodies) to propose a system in which not the earth but the sun was the center. Copernicus' work caused little controversy because it went against everything we thought we knew about the cosmos. Mathematically, however, it was elegant, which is why I wanted to defend his work. After all, the book of nature is written in the language of mathematics.”
That's one of your famous quotes! But what role does the telescope play in this? “In 1608, the Dutchman Hans Lipperhey discovered how you can magnify distant objects by placing lenses in succession. His original telescope magnified three times. I improved the instrument a year later so that it magnified no less than twenty times. I discovered four moons around the planet Jupiter, craters and mountains on the moon and phases of Venus.”
“The old idea that the superlunar was thought to be perfect and immutable has been unequivocally refuted. Moreover, the phases of Venus could only occur if the planet revolved around the sun, and was illuminated from different angles. In my book Sterrenbode I wrote down all my findings for the widest possible audience. I dedicated the Star Herald to my friend Cosimo de Medici.
And you claimed the right to name the moons. You chose Medici stars. Did you sometimes want something from the influential Medici family? “Come on, let me admit it, I was looking for a job as court mathematician to the Duke of Florence. The Medicis had connections there. Since my father's death in 1591, I had to support my mother and siblings. As a mathematics professor, I actually didn't earn enough for that. I hope you understand that I was always trying to get higher. Sliming down with influential types was very important in my time.”
Soon there was heated discussion everywhere about your Sterrenbode. And you went on, for you also discovered that even the sun was not as perfect as was always thought. “I saw strange dark spots on the surface of the sun, which seemed to come out of nowhere, rotate with the sun and then disappear again. About this I had an intensive correspondence with a certain Christoph Scheiner, a Jesuit astronomer from Ingelstadt. He desperately tried to save the old worldview by arguing in all sorts of ways that the spots were planets orbiting the sun. Ridiculous! In my letters to him I remained polite, but actually I thought he was a simple soul, and I also told that to those around me.”
You are fierce and perhaps a bit untactical for someone with daring ideas for the time… “Yes, I am once very convinced that I am right. Unfortunately with my performances made enemies. Some conservative clergy in Florence tipped off the Church Inquisition in 1616 about my defense of the Copernicus system. I tried to explain to them that they really got it wrong, but that went down the wrong way. Copernicus' work, the idea that the sun was actually at the center of the universe was labeled heresy. I was forced to stop proclaiming his ideas”
And that's the end of the matter? “Initially yes. I was allowed to continue to use and defend Copernicus' mathematical work, as long as I didn't claim that the sun really was at the center of the universe. However, I knew I was right and thought I could count on influential friends to protect me. In 1632 I therefore published Dialogo sopra i due massimi sistemi del mondo (Dialogue on the two major world systems). In it I had two figures, Salvati and Simplicio, debate the old and the new image of the cosmos.”
“Simplicio, of course, was in favor of the old, and he lost the dispute. By order of the Inquisition I was locked up in my own house, where we have now spoken. I will probably die under house arrest. People still cling too much to the old ideas, and for the Church there is simply a lot at stake. But still I think she moves! (the earth, ed.)”