Titans of History

GALILEO

1564–1642

I do not feel obliged to believe that that same God who has endowed us with senses, reason and intellect has intended to forgo their use and by some other means to give us knowledge which we can attain by them.

Galileo Galilei, “Letter to the Grand Duchess Christina” (1615)

Galileo Galilei helped to transform the way that people looked at the world—and the universe beyond. A physicist, mathematician and astronomer, Galileo made fundamental discoveries about the nature of motion and the movement of the planets. He realized the importance of experimentation and held that the physical world was best understood through mathematics. His insistence that the universe should be analyzed via reason and evidence brought him into conflict with the Church, but his discoveries long outlasted the Inquisition that sought to suppress them.

Galileo’s father was a musician, and the young man may well have helped with paternal experiments into the tension and pitch of strings. His formal education took place at Pisa University, where he matriculated in 1581, initially to study medicine. To his father’s disapproval, Galileo spent most of his time on mathematics and left the university without a degree in 1585.

Galileo continued to study mathematics for the next four years, earning money through private tuition until he was appointed to a chair at the university in 1589. It was during this time that he supposedly demonstrated his theory of the speed of falling objects by dropping weights from Pisa’s leaning tower.

His unorthodox views earned him the disapproval of the university authorities, and in 1592 Galileo was forced to move to Padua, where he taught until 1610. Crippled by his family’s financial demands after his father died, Galileo earned extra money by selling home-made mathematical compasses and continuing to tutor private pupils.

In 1609 Galileo heard of a strange device invented in the Netherlands that could make distant objects appear close. It was the telescope, and Galileo immediately set about building his own. Within a year he was investigating the heavens with a device that provided 20x magnification. It was a turning point in his career.

With his telescope Galileo discovered Jupiter’s four moons and noted that their phases indicated that they orbited Jupiter. This evidence dented the Church-approved Ptolemaic model of the universe, in which all heavenly bodies orbit the earth. Galileo also saw stars that were invisible to the naked eye. He immediately published his findings in a short book dedicated to one of his illustrious pupils, Cosimo II de Medici, grand duke of Florence. As a reward, Cosimo brought him back to Tuscany in triumph.

With greater financial freedom, Galileo was able to move his investigations on apace. He studied the rings of Saturn and discovered that Venus, like the moon, went through phases—an indication that it moved around the sun. These discoveries committed him to the theory—proposed by Nicolaus Copernicus a century before—that it was the sun, and not the earth, that was at the center of the universe.

Copernicanism was a dangerous concept for Galileo to flirt with, and around 1613 it earned him the attention of the Inquisition. He traveled to Rome to defend Copernicus’ heliocentric model but was silenced, and in 1616 he was warned explicitly not to promulgate such ideas any further.

By 1632 Galileo felt unable to keep silent on Copernicanism any longer and published his Dialogue, which drew together all of the major strands of thought about the nature of the universe and discussed them through the mouths of several fictitious characters.

When he was dragged to Rome the next year and asked to explain himself to the Inquisition, Galileo argued that he had obtained ecclesiastical permission to discuss Copernicanism in a hypothetical way. Unfortunately, he had not obtained permission to ridicule the papal attachment to older arguments, which he had done quite unashamedly. The Inquisition sentenced him to life imprisonment.

Fortunately for Galileo, his imprisonment amounted to little more than enforced internal exile to the Tuscan hills, where he was free to continue his work in a more muted form. Though he was going blind, he continued to study, concentrating on the nature and strength of materials and smuggling another book out of Italy to be published in the Netherlands in 1638. He died four years later, at age seventy-seven.