In the history of culture, Galileo stands as a symbol of the battle against authority for freedom of inquiry.

 

 

 

 

 

 

 

ARISTOTELIAN PHYSICS OF GALILEO’S TIME

 

Aristotelians made a sharp division between Earth and the heavens. In the heavens there could be no change except the recurring patterns produced by the circular motions of the perfectly spherical heavenly bodies. The sublunar world (the universe below the Moon) was the region of the four elements—earth, water, air, and fire—and was subject to its own distinct laws of natural motion. Fire, for instance, had lightness, which made it rise vertically, away from the centre of Earth. Earthy objects fell naturally downward toward the centre of Earth: the heavier the object, the faster its fall. “Natural” motions of the elements took them to their natural place, where they rested. Rest was the natural state of an element; it was motion that needed explaining, since every motion must have a cause.

 

This common-sense physics held sway until Galileo began to undermine it.

Italian physicist and astronomer Galileo maintained that the earth revolved around the sun, disputing the belief held by the Roman Catholic church that the earth was the centre of the universe. He refused to obey orders from Rome to cease discussions of his theories and was sentenced to life imprisonment. It was not until 1984 that a papal commission acknowledged that the church was wrong.

 

Copernicus was a Polish astronomer, best known for his theory that the Sun and not the Earth is at the centre of the universe.

 

Early in 1616 Copernican books were subjected to censorship by the church’s Index of Forbidden Books.The ruling of 1616 similarly laid down that Catholics could use Copernicanism as a calculating device but could not say that it was the true system of the universe.

 

In 1609 Galileo heard that a telescope had been invented in Holland. In August of that year he constructed a telescope that magnified about ten times and presented it to the doge of Venice. Its value for naval and maritime operations resulted in the doubling of his salary and his assurance of lifelong tenure as a professor.

 

By December 1609 Galileo had built a telescope of 20 times magnification, with which he discovered mountains and craters on the Moon. He also saw that the Milky Way was composed of stars, and he discovered four satellites circling Jupiter. It was therefore undeniable that at least some heavenly bodies move around a centre other than Earth, a finding that did not prove that Copernicus had been right but did fit in well with the Copernican system of the universe. Galileo published these findings in March 1610 in a book called The Starry Messenger. Galileo believed that his scientific findings fell far outside the theological realm.

 

 

Jesuit cardinal Robert Bellarmine instructed Galileo that he must no longer hold or defend the opinion that Earth moves.

 

In 1624 Galileo began a book he wished to call Dialogue on the Tides, in which he discussed the Ptolemaic and Copernican hypotheses in relation to the physics of tides. In 1630 the book was licensed for printing by Roman Catholic censors at Rome, but they altered the title to Dialogue on the Two Chief World Systems. It was published at Florence in 1632. Despite the book’s having two official licenses, Galileo was summoned to Rome by the Inquisition to stand trial for “grave suspicion of heresy.”

 

Although Galileo had made considerable efforts to conform to the letter of the ruling of 1616, he had clearly written a pro-Copernican book. He had occasionally also slipped up by explicitly treating the Copernican system as “probable,” meaning that, although it was yet unproven, sooner or later it could well be shown to be true. Such a position was incompatible with the ruling of 1616, as was pointed out at his trial: Catholics were allowed to use Copernicanism as a helpful calculating device, provided that they did not treat it as having any truth. 

 

The charge against Galileo was grounded on a report that Galileo had been personally ordered in 1616 not to discuss Copernicanism either orally or in writing. Cardinal Bellarmine had died, but Galileo produced a certificate signed by the cardinal, stating that Galileo had been subjected to no further restriction than applied to any Roman Catholic under the 1616 edict. No signed document contradicting this was ever found, but Galileo was nevertheless compelled in 1633 to abjure (formally renounce his beliefs) and was sentenced to life imprisonment (swiftly commuted to permanent house arrest). The Dialogue was ordered to be burned, and the sentence against him was to be read publicly in every university.