Transforming natural philosophy into modern science, thereby creating civilization’s first scientific revolution
Galileo Galilei
(1564–1642)
A man of deep religious faith, Galileo nevertheless defied the Catholic Inquisition to emerge as the archetype of the modern rational man of science. He was an adept experimentalist and observer as well as an incisive theorist, who used his telescope—which he himself built, improving on a Dutch original—to discover the moons of Jupiter and the mountains on Earth’s moon. He made important observations of Kepler’s supernova and of Venus, Saturn, and Neptune. His discovery of sunspots challenged religious-based theories of the literally spotless “perfection” of that heavenly body. He discovered that the Milky Way was not the nebulous cloud it was thought to be, but a multitude of stars. Using his telescope and his own development of mathematical physics, he supported and popularized the Copernican model of the solar system, in which the earth was but one of several planets orbiting a central sun. Turning from the heavens down to the earth, Galileo invented the compound microscope and made pioneering observations with it. He made discoveries foundational to mathematical physics, especially concerning the motions of bodies and the basic principle of relativity—by which the laws of motion are the same in any system moving at a constant speed in a straight line. This became the baseline assumption central to Albert Einstein’s epoch-making special theory of relativity in the twentieth century.
Galileo Galilei was born on February 15, 1564 in Pisa, Italy. At the time of his birth, “science” did not exist. By the time of his death seventy-eight years later, science was a rapidly emerging discipline—thanks to him.
After moving with his parents and siblings to Florence in 1572, Galileo began studying to become a priest, but soon returned to Pisa and the university there to study medicine. Before completing the work for this degree, however, he changed focus yet again and embarked on the study of mathematics. In 1589, he obtained an appointment to the chair of mathematics at the University of Pisa. Just three years later, he accepted a more prestigious and remunerative professorship in mathematics at the University of Padua. In this city, he met Marina Gamba, whom he married. Together, they had three children, Virginia (1600), Livia (1601), and Vincenzo (1606).
In Padua, Galileo did much of his work in physical mechanics and commenced his observations with the telescope. In 1610, he published his Sidereus Nuncius (The Starry Messenger), product of the world’s first telescopic observations of the heavenly bodies. Partly due to the fame generated by this publication, Galileo was offered a position as mathematician at the University of Pisa and the official post of philosopher to the Grand Duke of Tuscany, which ushered him into the powerful court of the Medici. (A scientist not above politics, Galileo named Jupiter’s moons, which he had discovered, after the Medici.) In 1611, he was honored by membership in the Academia dei Lincei, generally recognized as the world’s first scientific learned society.
In 1612, Galileo published Discourse on Floating Bodies, which, among other things, reported his discovery of sunspots and his observations on the phases of Venus, the strange shape of Saturn (his telescope lacked sufficient resolution to reveal the planet’s rings; Galileo saw them as “ears”), and the periods of the orbit of Jupiter’s moons. A year later, he published his Letters on the Sunspots, in which he presented his support for the bold assertion of the Polish astronomer Nicolaus Copernicus (1473–1543) that the planets, including the earth, orbit the centrally located sun.
During 1613–1614, Galileo further developed his thoughts on the heliocentric Copernican solar system, and in 1616 expressed these in his Letter to the Grand Duchess Christina. At this time, the Sacred Congregation of the Index, an arm of the Grand Inquisition of the Catholic Church, condemned Copernicus’s book On the Revolution of the Heavenly Orbs. Galileo was summoned to an audience with Cardinal Robert Bellarmine, who warned him neither to teach nor further defend Copernican theory, which the Church believed challenged scripture.
Galileo did not publish again until 1623’s The Assayer (Il Saggiatore), which argued that comets were sublunary phenomena. He also asserted the basis for mathematical physics with the claim that “the book of nature is written in the language of mathematics.” Historically, The Assayer is considered the first developed statement of the scientific method of empirical inquiry. Although the Church never condemned this work, it was actually Galileo’s most powerful challenge to faith-based knowledge.
The year 1623 also saw the election of Maffeo Barberini—whom Galileo considered a great friend and was a longtime supporter of Galileo—as Pope Urban VIII. This encouraged the scientist to resume his work in support of Copernican theory. Titled Dialogues Concerning the Two Great World Systems, the geocentric universe and the heliocentric universe, it was not published until 1632. Galileo presented further proof that Copernicus was correct: the sun, not the earth, was the center of the known universe.
Very soon after the publication of Dialogues, the Inquisition banned its sale and summoned Galileo to Rome for an ecclesiastical trial. He was condemned as a heretic the following year and held under house arrest. He used this enforced seclusion as an opportunity to write his final work, Discourses and Mathematical Demonstrations concerning Two New Sciences, which was smuggled out of Italy and published in Protestant Holland. The “new sciences” that are the subject of the book concern the strength of materials and the motion of objects—predecessors of the foundational modern fields of material engineering and kinematics, the study of points, objects, and bodies in motion.
Galileo died on January 8, 1642. Because he was still under condemnation as a heretic, he was buried in an obscure corner of Florence’s Basilica of Santa Croce, only to be reinterred in the main portion of that Basilica, under a magnificent monument to him, in 1737.
Galileo was posthumously rehabilitated by the Church, signified by his reburial and by Pope John Paul II’s official expression of regret on behalf of the Church on October 31, 1992. This was a long-overdue resolution to a dispute between the Church and a man of sincere faith (Galileo’s two daughters had, with his enthusiastic blessing, become nuns) who nevertheless could not deny the truth as his new scientific method delivered it to him. He had been summoned by the Inquisitors to four hearings during 1633, at the last of which, on June 21, he was compelled to recite and to sign a written “abjuration” for “having held and believed that the sun [is] in the center of the universe and immoveable, and that the earth is not at the center of same, and that it does move.”
Popular legend has long held that, after uttering this abjuration, denying that the earth moves, Galileo muttered under his breath “And yet it moves.” He almost certainly said no such thing, but his work spoke for him and for the enduring triumph of rational inquiry as systematized by the scientific method despite subsequent assault by religious zealots and political deceivers and tyrants.