The Trial of Galileo
Copernicus’s De Revolutionibus of 1543 was dedicated to the Pope; yet ninety years later (1633) Galileo was tried by the inquisition for espousing Copernican views. How did this come about?
Prior to the publication of De Revolutionibus, astronomical theories proposed that the earth was the centre of the universe and all the planets revolved around the earth. This was a view that was supported by both Aristotle and Ptolemy although Ptolemy’s work was based upon observations and scientific methods as opposed to Aristotle who was in effect theorising based upon religious belief. I shall outline the essential content of the De Revolutionibus and explain why it took so long for the church to condemn his book and then try Galileo for heresy as a result of his supporting Copernican ideas.
Copernicus was studying and writing during the Renaissance and arguably the Scientific Revolution. The Renaissance was a time of rebirth of old ideas and a new way of looking at things not just in the areas of science but throughout literature, arts and many other areas. It was a time when new ideas did not seem to provide solutions to all the questions that were being asked.( ) Copernicus proposed a new system of planetary motion that had the sun at the centre of the universe rather than the earth. However contrary to popular belief, this was not a new and revolutionary idea. The ancients had proposed such a solution, most notably from Aristarchus who argued that it was more plausible for the sun to be at the centre rather than the earth. However Copernicus makes no mention of Aristarchus in De Revolutionibus. Not long before Copernicus began writing, Cusa suggested this again, and it is argued that this may be where Copernicus got early inspiration from, although this is not proven. ( ) It was in the rest of his writing that Copernicus suggested ideas that were considered to be revolutionary. According to the Copernican system not only was the Earth revolving around the sun; it was revolving on its own axis. This was later to replace the idea that it was the stars that were revolving. Copernicus proposed that the earth revolved on its own axis once every day and orbited the sun throughout the period of a year. Copernicus hesitated in the publishing of the book as he was afraid that it may be heretical, even though the book when it was eventually published in 1543 was dedicated to Pope Paul the 3rd. At the time of his writing, Aristotelian physics were popular, and it was a difficult task to convince people that the heavens were not perfect, but were the same as the earth and that the earth was constantly moving. ( )
Many historians have argued that Copernicus initiated an astronomical revolution, which led to a whole new approach to looking at the heavens. This revolution was taken up by Galileo towards the end of the sixteenth century. Galileo believed in the Copernican theory that the Sun was the centre of the universe. It was this firm belief that eventually led to his trial for heresy.( ) The main question is what happened in the years between the publication of De Revolutionibus and the publication of firstly Sidereus Nuncius (1610) and the Dialago [Dialogue Concerning the Two Chief World Systems] (1632) I am firstly going to discuss some of Galileo’s main astronomical discoveries and then highlight the changes in the seventeenth century that led to the trial of Galileo for heresy.
Galileo admitted to Kepler as early as 1604 that he was a supporter of Copernicans, but at this time his field of study was not astronomy. However Galileo remained silent about this belief for a number of years, probably heavily influenced by the execution of Giordano Bruno in 1600 for heresy. He was more interested in the study of mechanics and motion, and upon overthrowing the Aristotelian view of motion.( ) Galileo only became interested in the field of Astronomy after hearing of the invention of the telescope although he made one contribution to astronomy in 1604. He observed the phenomenon of the Nova or new star, which of course played an important role in the demise of the Aristotelian system. According to Aristotle the heavens or celestial realm were perfect and unchanging. The fact that a new star appeared contradicted this completely. Whilst using the telescope, Galileo made a number of other discoveries that posed a direct contradiction to the Aristotelian system. Firstly he argued that the moon had mountains and craters, as there were variations in light and dark on the surface of the moon. As Galileo is quoted as saying, the moon??is not unlike the face if the earth. This of course contradicted the Aristotelian idea that the heavens were perfect. Secondly he observed that the sun had spots (a phenomenon also observed by Scheiner and Fabricius) which led to the argument between whether or not the sun was changeable or whether these spots were actually as a result of the planets orbiting around the sun. Whichever argument was to be believed, it contradicted old ways of thinking. Thirdly, one of Galileo’s most important discoveries was that of the moons of Jupiter. Galileo had observed that there were moons around the planet of Jupiter and that they were orbiting as their arrangement differed over time. Galileo saw this as a miniature model of the Copernican system of the universe and it of course proved that not all bodies in the solar system revolved around the earth. Galileo also observed that the planet Venus had different phases similar to that of the earth’s moon and therefore Galileo concluded that it must orbit the sun. ( )
I shall now address the question of what led to the trial of Galileo. The Vatican had a reputation for banning texts if they were in disagreement with church scriptures, although the problem was not serious due to high levels of illiteracy within the church. However in the sixteenth and seventeenth centuries the church became harsher. This was as a result of the reformation and the counter- reformation. This involved the Protestant church breaking away from Catholicism and the Catholic Church attempting to rein the Protestants back in. Another factor was the advent of printing presses, which were being utilized by the Protestant movement and therefore the Catholic church felt the need to take a more defensive position and ban certain books.( ) It was around 1542 when the Catholic church began to take a harsher stance on written material. It was at this time that Bernardino Ochino, a superior member of the Catholic church left Rome and turned to Protestantism which caused great of unrest both within the church and the general Catholic population. Pope Paul the third feared that more people would start to turn to Protestantism so began banning books from Italy which he felt where damaging to the Catholic religion. The powers of the Roman Congregation of the Index and they were increased to ensure heavy printing restrictions.( )
With regard to Galileo, the events that led to his summoning before the inquisition happened over a long period of time. In the seventeenth century a science professor informed the Medici family (Galileo’s employers) that the notion of the earth moving was contrary to church scripture and therefore heretical. Galileo responded to this with the circulation of a pamphlet titled Letters to Castelli in which he expressed his opinion on the relationship between the church and science. In December of 1614 a Florentine Dominican denounced Galilean thinking and posted a complaint with the inquisition in Rome. In 1616 Copernican books were argued to be heretical and were subjected to heavy censorship by the Roman Congregation of the Index of forbidden books. The result was Galileo being issued with a warning from Cardinal Robert Bellamine to discontinue his belief that the earth moved. Bellamine had earlier warned Galileo not to speak of Copernicanism as anything other than a method for calculation, i.e. hypothetical. After this ruling Galileo remained silent about his Copernican beliefs for a number of years. It was only in 1624 when Galileo wanted to write his book ‘Dialogue on the tides’ according to the Copernican and Ptolemaic systems of the universe did he clash with the church. The book was granted a license in 1630 but the title was altered to the Dialago [Dialogue Concerning the Two Chief World Systems.] As a result of a plague epidemic the book was published in Florence in 1632. Despite having been granted a license and holding the belief that Pope Urban the third would allow him to speak out, Galileo was called to trial for heresy. Although Galileo had made some attempt at complying with the ruling of 1616, it was clear that he had written a pro-Copernican book, discussing the ideas as probable as distinct from hypothetical. He had also increased the hostility of the situation by publishing the book in Italian so the general public could read it. Galileo was forced to renounce Copernican beliefs and was sentenced to life imprisonment (later reduced to house arrest.) The Dialogue was placed on the list of prohibited books and Galileo’s judgement and sentence was read aloud at every university in Italy.( ) The comment of the inquisition made the position of the church very clear; The proposition that the sun is in the center of the world and immovable from its place is absurd, philosophically false, and formally heretical; because it is expressly contrary to Holy Scriptures. The proposition that the earth is not the center of the world, nor immovable, but that it moves, and also with a diurnal action, is also absurd, philosophically false, and, theologically considered, at least erroneous in faith. ( )
In conclusion, the main change in the 90 years that led to Galileo’s trial for heresy was the increased pressure on the Catholic Church caused by the Protestant church’s split away. Another factor was the fact that Galileo treated Copernicanism as a believable theory as opposed to a hypothesis which could be used for calculations and provided convincing evidence to back up his claims. Yet despite Galileo renouncing his Copernican beliefs publically, it is said that whilst on his knees before the inquisition he muttered Eppur si muove translated as and yet it moves.( )
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