This Week in History: The trial of Galileo

Italian scientist convicted of heresy and confined by the Pope to house arrest in 1633 for teaching that the Earth orbits the sun.

September 24, 2010 13:33
4 minute read.
Galileo faces the Roman inquisition

Galileo 311. (photo credit: Courtesy)

On September 20, 1633, the Italian scientist Galileo Galilei is tried by the Church for teaching that the Earth orbits the sun. As a result, on the Pope’s order, he was confined to house arrest for the remainder of his life until his death in 1642, at the age of 77.

One century earlier, Nicolaus Copernicus had published On the Revolutions of the Celestial Spheres, the first book to outline a comprehensive heliocentric cosmology. This revolutionary theory placed the sun at center of the universe, rather than the Earth.

Geocentricism, the theory placing the Earth at the center of the Universe, had been vastly accepted since the 2nd century AD, when firmly established by Claudius Ptolemy.

What is known as the “Galileo affair” began in 1610 when he came out against the Ptolemaic scientific view in his book Starry Messenger. Using the new telescope he had developed, he made observations supporting Copernican astronomy.

In reaction, many scientific and theological scholars attacked the theory because it seemingly contradicted Ptolemy's model of the universe, as well as several passages of Holy Scripture.

Galilei responded to that criticism in his letter to Kepler in August 1610 saying “My dear Kepler, I wish that we might laugh at the remarkable stupidity of the common herd. What do you have to say about the principal philosophers of this academy who are filled with the stubbornness of an asp and do not want to look at either the planets, the moon or the telescope, even though I have freely and deliberately offered them the opportunity a thousand times? Truly, just as the asp stops its ears, so do these philosophers shut their eyes to the light of truth.”

While Church officials were willing to let heliocentrism be taught as a hypothesis and discussed in scientific circles, the faith of the ordinary people was to be safeguarded. However, Galilei argued that his telescopic observations favored the Copernican heliocentric theory as a physical truth.

As the Inquisition started taking serious notice of Galilei’s work in 1615, he sent a letter to Grand Duchess Christina, which was an essay on the relation between the revelations of the Bible and the new discoveries then being made in science. His general stance was that the relevant passages of the Bible, which he was accused of contradicting, should not be interpreted literally, especially when taken from poetic or allegorical texts.

By 1616, the attacks on Copernicus’ ideas had reached a peak, to which Galilei responded by going to Rome in order to persuade the Catholic Church authorities not to ban heliocentrism. Ultimately, the Inquisition delivered him with an order not to "hold or defend" the idea that the Earth moves and the Sun stands still at the centre. The decree did not prevent Galileo from discussing the controversial subject.

Pope Urban VIII, elected in 1623, was a friend and supporter of Galilei who opposed his condemnation in 1616.  And thus, with the Pope’s formal authorization along with that of the Inquisition, Galilei published Dialogue Concerning the Two Chief World Systems in 1632. Previously, the Pope had personally asked Galilei to give arguments for and against heliocentrism in the book, and to be careful not to advocate the controversial theory. He also requested that his own views on the matter be included in Galileo's book. Only the latter of those requests was fulfilled by Galilei.

Whether unknowingly or deliberately, Simplicio, the defender of the Geocentric view in the book, was often caught in his own errors and sometimes came across as a fool. Indeed, although Galileo states in the preface of his book that the character is named after a famous Aristotelian philosopher, the name "Simplicio" in Italian also has the connotation of "simpleton.” This portrayal of Simplicio made it appear as an advocacy book: an attack on Aristotelian geocentrism and defence of the Copernican theory.

Unfortunately for his relationship with the Pope, Galileo put the words of Urban VIII into the mouth of Simplicio. Most historians agree Galilei did not act out of malice and felt blindsided by the reaction to his book.

However, the Pope did not take the suspected public ridicule lightly, nor the Copernican advocacy. Galileo had alienated one of his biggest and most powerful supporters, the Pope, and was called to Rome to defend his writings.

With the loss of many of his defenders in Rome because of Dialogue Concerning the Two Chief World Systems, Galilei was ordered to stand trial on suspicion of heresy in 1633.

As a result, Galilei was found “vehemently suspect of heresy” and was required to "abjure, curse and detest" those opinions. He was sentenced to formal imprisonment at the pleasure of the Inquisition. On the following day, this was commuted to house arrest, which he remained under for the rest of his life.

Aside from his theoretical works, Galilei made several contributions to “technology” such as an improved telescope, a thermometer, a military compass and many many others. So great was his legacy that he was called by Einstein the “father of modern science.”

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