Galileo: The great disruptor

Galileo Galilei was born in Pisa in 1564, and became a professor of mathematics at the city’s university in 1589 — aged 25. Initially, he didn’t show much interest in astronomy, devoting himself instead to discrediting Aristotle’s views on the physics of motion.

When his three-year contract in Pisa expired, Galileo moved to become the chair of mathematics at Padua, at the time one of the most important intellectual centres in Europe. It was here in around 1597 that he began to develop an interest in the astronomical model developed by Nicolaus Copernicus, which made the then-extraordinary proposition that the sun was at the centre of the universe with the earth and other planets rotating around it. 

In 1633 the great Renaissance scientist Galileo Galilei was forced by the Roman Inquisition to recant his assertion that the earth rotated around the sun, and accept the view based on Holy Scripture that the earth was fixed in place.

Legend has it that even in the moment of recanting, he muttered the words ‘eppur si muove’ (‘and yet it moves’) — a phrase that has come to stand as a symbol of the unshakeable truths of the new age of science.

On 13 July, Christie’s will offer six key first editions of Galileo’s works from the Giancarlo Beltrame Library of Scientific Books, works which collectively trace the remarkable life of one of the great disruptors of intellectual and scientific history.

It was also in 1597 that Galileo began production of a mathematical instrument — the sector, or proportional compass. Not dissimilar to the humble compass still used by schoolchildren worldwide, it was ingeniously transformed into an elaborate calculating instrument that revolutionised and democratised practical mathematics in the same way that the pocket calculator has done in our own time.

It is this compass which is the subject of Galileo’s first published work, Operazioni del compasso, privately printed in 1606 in an edition of only 60 copies. This extremely rare work by an obscure 42-year-old university professor gave little indication to the reading world that one of Europe’s greatest intellectual figures was taking his first steps in the public arena. 

In 1609, Galileo learned of the invention by Hans Lipperhey, a Dutch lens-grinder, of an ingenious device for making distant objects appear closer — what we now know as the telescope. He set out to construct his own instrument, and within a few months had produced a device that was capable of magnifying objects by a then unthinkable 30 times.

In early January 1610 — one of the turning points in man’s relation to our universe — Galileo first directed his telescope to the heavens. The results were startling. Not only was the moon revealed to be mountainous, but the Milky Way was seen to be a disorderly scattering of individual stars. Also, and contrary to the Aristotelian principles which had been accepted as the basis of science for two millennia, a host of new fixed stars and four satellites of Jupiter were discovered.

Galileo’s announcement of these extraordinary findings, published with remarkable speed only two months later, in his work Sidereus nuncius [An announcement about the stars], exploded upon the scientific world with the force of an intellectual bombshell. Everything that had been believed since the most ancient times about the structure of the universe was proved to be false. 

Galileo’s work immediately came under attack from all sides, but he had not yet openly associated himself with the Copernican model, which placed the sun at the centre of the universe.

However in 1613 Galileo published his Istoria e dimostrazioni intorno alle macchie solari (Letter on Sunspots), a work in which he proposed that, rather than being tiny satellites of the sun, sunspots actually appeared on the surface of the sun, and that the sun rotated on a fixed axis. Crucially, the work also included his explicit endorsement of the Copernican system. 

In a few short years, Galileo had moved from the status of an obscure university professor with an interest in calculating machines to being at the epicentre of an intellectual storm. He was by now the leading standard-bearer of the Copernican model, and at the centre of the debate over whether the Bible or scientific findings could provide the most faithful representation of the universe.

Two years later he travelled to Rome in order to argue, in vain, against the official suppression of Copernican theory. On 26 February 1616 a papal commission under Pope Paul V outlawed Copernicanism, and ordered Galileo to abandon his defence of the doctrine.

In 1618 the appearance of three comets attracted attention in Europe and became the subject of numerous pamphlets and books. Comets were a significantly problematic phenomenon for the traditional model of the universe, since Aristotelian orthodoxy dictated that objects beyond the moon could not change shape or state. 

Suffering from ill health, and perhaps cautious after his unsuccessful challenge to papal authority, Galileo entered the debate somewhat tangentially, dictating his views to his pupil Guiducci in the form of a critique of a work on the comets by the leading Jesuit mathematician, Orazio Grassi. 

Although Grassi was not named in Galileo’s critique, he still responded with a savage attack on Galileo. It was this attack which provoked Galileo’s great polemic, Il Saggiatore [The Assayer], published in 1623. 

Galileo had been forbidden since 1616 from defending Copernican theory and therefore could not take on Grassi in any direct discussion on the earth’s motion. Instead, he chose to establish a general scientific approach to the investigation of celestial phenomena — namely that no theory of comets should be advanced unless it was proved that comets were concrete moving objects and not solar-generated optic effects.

In essence, Galileo was asserting the primacy of the scientific method — that nature was to be approached through mathematical tools, rather than through biblically-inspired scholastic philosophy.  

In the year of the publication of Il Saggiatore, the short-lived papacy of Gregory XV gave way to that of one of the great Renaissance figures, Urban VIII. One of Galileo’s closest friends and patrons, Virginio Cesarini, became the new pontiff’s chamberlain. Encouraged by what seemed to be a more favourable intellectual climate, Galileo began to believe that he could finally expound openly the heliocentric structure of the universe.

Published in 1632, after almost ten years of silence, Dialogo sopra i due massimi sistemi del mondo (Dialogue Concerning the Two Chief World Systems) is Galileo’s crowning work on the Copernican debate. Although expressed at the request of Urban VIII in the form of an equal debate between proponents of the Copernican system and the traditional earth-centred model, Galileo’s work masterfully exposed the absurdities and contradictions inherent in the Ptolemaic-Aristotelian world view, and revelled in the simplicity and good sense of the Copernican system.

In the intellectual history of Europe, Il Dialogo marks the moment when the heliocentric system became a commonplace. Yet for Galileo personally, it was a disaster. Provoked by the depiction of him in the work as the simple-minded Aristotelian ‘Simplicius’, Urban VIII summoned Galileo to Rome.

Placed on trial by the Inquisition, he was forced to recant his support for Copernicanism, and formally state that the earth was fixed — provoking his legendary muttered rejoinder, ‘eppur si muove’.

Il Dialogo was placed on the list of prohibited books, and Galileo was sentenced to life imprisonment, commuted to house arrest. He was to remain under the sentence until his death — at his villa in Arcetri, in the hills above Florence — in 1642.