Galileo Galilei | Biography

Galileo Galilei, known best as simply "Galileo," was a scientist at a most difficult time in history: the time of the Inquisition, when the Roman Catholic Church was still furiously resisting evidence from new discoveries. Galileo is one of the Inquisition's most famous victims; he supported Copernicus's discovery that the Earth revolves around the Sun. Although he was not killed for his beliefs, Galileo was silenced and placed under house arrest from the time of his trial to the end of his life.

Galileo was born February 15, 1564, in Pisa, Italy. His father, Vincenzio Galilei, was a scientist, investigating acoustics and musical theory. His mother was Giulia Ammannati. Galileo, the oldest of seven children, began his studies with Jacopo Borghini, but had to leave his tutor when his father moved the family back to his native Florence about 1575. Galileo then studied at the monastery of Santa Maria, and entered the order as a novice. His father removed the young man from the order and tried to get him a scholarship to the University of Pisa, but failed. Galileo returned to the monastery to study until entering the University of Pisa as a medical student in 1581, following his father's wishes.

It was that year Galileo made the first of a lifetime of great discoveries. While sitting in church, he noticed a swinging lamp. No matter how great the swing's arc, they all seemed to take the same amount of time, he realized. After the service, Galileo began experimenting with different weights and lengths of string, and devised a simple device that would measure a patient's pulse. Pisa faculty members improved on the device and the pusilogia was used for many years afterward. Despite this invention, Galileo was not interested in medicine. He was a difficult student, often challenging his professors, who gave him the nickname "The Wrangler." Mathematics did interest him, however; quite possibly sparked by his father's work with acoustics, particularly the study of the effects of the length of musical strings on consonance. Although still officially a medical student, Galileo began his mathematical studies outside of the University with Ostillio Ricci, mathematician to the grand duke of Tuscany. Despite his father's objections and his suffering medical studies, Galileo persisted. He finally left the university in 1585 to study on his own, partly because his misbehavior made him unsuitable for a scholarship that would have allowed him to continue his medical studies.

Galileo went home to Florence and began tutoring students in mathematics. It was during this time that he became interested in Archimedes' experiment that disclosed that a crown was indeed not solid gold, but gold and a base metal (Archimedes had placed the crown in water and measured the amount of water it displaced, which turned out to be less than a solid-gold object of the same side would have). Galileo created a hydrostatic balance, a small scale that could perform the same measurement more accurately, and this invention led to his first published piece of scientific writing, a booklet describing it, which appeared in 1586.

Galileo apparently enjoyed debunking famous myths and regularly set about deflating the ideas of the ancient Greeks, particularly Aristotle. His work with falling bodies damaged Aristotelian physics beyond repair. Going contrary to the widely held belief of the time, Galileo demonstrated that Aristotle was incorrect in his claim that light objects fell more slowly than heavy ones. From this work arose the legend about Galileo dropping two cannon balls, one heavier than the other, off the Tower of Pisa.

In another experiment, he challenged Aristotle's idea that force had to be continually applied in order to keep a body in motion. Some had taken this idea and explained that the source of this force was hardworking angels. However, Galileo's experiment with a body rolling down an inclined plane showed that if force were continuously applied, the body would continue to accelerate.

Among Galileo's other discoveries in the field of mechanics were the fact that two forces can act on a body simultaneously, causing the body to move in a parabolic curve (the base of the mathematical science kinematics), and studies concerning the strength of materials. He discussed both of these ideas in his book Discourses and Mathematical Demonstrations Concerning Two New Sciences. Galileo's text forms the basis of modern physics because it shows the use of mathematics in understanding motion and the value of physical experiment and mathematical analysis in solving problems. Although the calculations he made regarding projectiles used low speeds, Galileo's tables and ideas would be further refined by others who came later, and made gunnery a science.

Throughout his investigations, Galileo's proofs used only the same geometric methods that had been available to the Greeks. Algebra and other more complicated methods of calculation would not be available until the time of René Descartes and Isaac Newton. However, Galileo believed mathematics was superior to logic. In 1592 he was named Chair of Mathematics at the University of Padua.

Galileo was not a man of all work. He had a mistress, Marina Gamba, for 10 years and had three children by her. The daughters, Virginia and Livia, entered the Franciscan convent in their mid-teens, taking the names Sister Maria Celeste and Sister Arcangela. Galileo did eventually recognize his son, Vincenzo.

Galileo's attention was diverted from his studies of mechanics by the invention of the telescope. Over the years he built hundreds of telescopes, many of which he gave as gifts to persons of influence. Some of his telescopes that have survived to this day have nearly perfect optics.

With his telescopes, Galileo observed the face of the moon and showed that it was not smooth as had been thought, but rather rough-surfaced. He found that constellations such as Orion and formations like the Pleides comprised far more stars than had ever been guessed; in Orion alone he counted 500 stars. He also observed the planets, including Jupiter and Saturn.

Galileo's discovery of Jupiter's moons was of groundbreaking importance. On January 7, 1610, he saw three small but bright stars near the planet, two east and one west. Observations on successive nights found that the stars moved--eventually with all three west of the planet. "My confusion was transformed to amazement," he wrote. "I had now decided beyond all question that three stars were wandering around Jupiter, as do Venus and Mercury around the sun." Three nights later, he found another "star" circling Jupiter. Over the next six weeks he continued to watch, and the evidence was irrefutable: here was a perfect example of smaller heavenly bodies circling a larger one, just as Copernicus had said that the Earth circled the sun.

Quickly Galileo wrote and published his observations in a book called Siderius nuncius (The Starry Messenger). It became the most important book of the 17th century, and set the stage for Galileo's downfall.

Galileo's discoveries made him reluctant to continue teaching his students the old Ptolemaic system (Earth-centered) and he resigned his chair at Padua and turned to Florence, where he became the Grand duke of Tuscany's mathematician and philosopher and the University of Pisa's chief mathematician, a non-teaching position. By 1614, his stance on the question of an Earth-centered solar system had earned him attacks from Church leaders. In 1616, Pope Paul V summoned Galileo to Rome and ordered him to stop disseminating this theory called Coperinicism. Angry, Galileo nevertheless obeyed; there was no other choice, for if he had defied the Church he would have been imprisoned or tortured (in 1600, philosopher Giordano Bruno had been burned at the stake for refusing to recant his scientific views).

On August 6, 1623, Urban VIII was named pope. Somehow, Galileo was persuaded that Urban would be open to his ideas, and so he wrote Dialogue on the Two Chief World Systems. In the Dialogue, Galileo pitted an Aristotelian, Simplico, against a quick-minded Salviati, who got the best of the argument. Galileo wrote the book in Italian, not Latin, the language of scholars, and so it was accessible to anyone who could read, and was quickly translated into other languages.

Unfortunately for Galileo, one of his most bitter enemies, Father Christopher Scheiner, convinced Urban that the Simplico character was a buffoonish caricature of himself. Galileo was in trouble again. The Pope called him to Rome in 1633 and forced him to renounce any views that were at odds with the Church's belief.

Galileo was nearly 70 years old at this time. With the example of Bruno in his mind, he agreed. The church placed him under house arrest in his villa at Arcetri for the remainder of his life. By Christmas 1637, Galileo became completely blind. He died January 8, 1642.

On October 31, 1992, over 350 years after Galileo's trial, the Roman Catholic Church acknowledged that it had been in error and acknowledged the validity of his work.