Galileo’s Achievements

Galileo’s father had expected him to study medicine when Galileo entered the University of Pisa in 1581. Instead, Galileo became fascinated with mathematics and decided on a career in mathematical subjects and philosophy. He left the university without obtaining a degree. Yet Galileo showed his early genius by designing a new form of hydrostatic balance to measure small quantities. His short treatise “The Little Balance,” combined with his initial studies of motion, earned him recognition among mathematicians. In 1589 Galileo obtained the chair of mathematics at the University of Pisa, where he pursued his studies of motion.

Galileo used direct observation, experimentation, and mathematics to show that many of Aristotle’s ideas on motion, which had endured more than 1,900 years, were incorrect. In one of his most famous experiments, Galileo dropped objects of different weights off the Leaning Tower of Pisa. He found that the speed of fall of a heavy object is not proportionate to its weight, as Aristotle had claimed. His attacks on Aristotle made him unpopular with his colleagues in Pisa. In 1592 Galileo’s patrons secured a position for him at the University of Padua, where he taught until 1610. During this time he determined the law of falling bodies and calculated the curved trajectory, or parabola, of a projectile. Both conclusions contradicted Aristotle’s physics.

In the spring of 1609 Galileo’s career took a dramatic turn toward astronomy. He had learned about the telescope, invented in the Netherlands, and developed his own increasingly powerful instruments. When he turned his telescopes to the heavens, he made several startling discoveries. Galileo found that the Moon’s surface was rough and uneven, not smooth as had been thought. His telescope also detected far more stars than were visible with the naked eye. In January 1610 he observed four moons orbiting around Jupiter and later discovered that Venus went through phases just as the Moon does. He also observed spots on the Sun’s “perfect” surface. These astronomical discoveries confirmed Galileo’s belief that Polish astronomer Nicolaus Copernicus had been correct when he formulated a solar system centered on the Sun, with Earth and other planets moving around it. Galileo summarized his observations in his book The Sidereal Messenger.

Galileo’s increasing support of the Copernican theory began to cause him trouble with the Roman Catholic Church. In his Letter to the Grand Duchess Christina, Galileo discusses the problem of reconciling Copernican theory with passages in the Bible. However, the tide in Rome had turned against this theory; in 1615 the Inquisition declared it heretical. Galileo was admonished not to “hold, teach, or defend” the Copernican theory “in any way whatever, either orally or in writing.” Galileo did not entirely abandon the topic but approached it from another perspective. In 1623 he published a brilliant discussion on the nature of physical reality and a description of the new scientific method. Galileo argued that the “grand book, the universe” was written in the language of mathematics and geometry. This changed natural philosophy from a verbal account to a mathematical one in which experimentation became a recognized method for discovering the facts of nature. The next year Galileo received permission from Pope Urban VIII to write a book about theories of the universe. The result was Dialogue Concerning the Two Chief World Systems, Ptolemaic & Copernican, published in 1632. The book is a witty discussion among three characters: Salviati (Galileo); Sagredo, an intelligent layman; and Simplicio, a devout Aristotelian who is a figure of ridicule. In the book Galileo summarizes the arguments for the Copernican theory, based on his astronomical observations. Aristotle’s views are put in the mouth of the simpleton in the dialogue.

The Vatican’s reaction to the book was swift. In 1633 the Inquisition leveled a charge of heresy against Galileo and sentenced him to life imprisonment. Friends and patrons intervened, and he spent the rest of his life under house arrest in a villa near Arcetri, close to Florence. Galileo’s final book, Dialogues Concerning Two New Sciences, summarized his studies on motion and his work on testing the strength of different materials. The manuscript was smuggled out of Italy and published in the Netherlands in 1638. On January 8, 1642, Galileo died, at the age of 77.

Galileo has been called “the father of modern science.” Because of his work, experimentation and observation became a recognized scientific method for investigating the facts and laws of nature. He instituted fundamental changes in the study of motion, astronomy, cosmology, physics, biology, and material science. Galileo’s inventions, from balances to telescopes and microscopes, brought him widespread recognition. In 1992 Pope John Paul II officially declared, before the Pontifical Academy of Sciences in Rome, that Galileo had been right to support Copernicus.