Galileo Galilei
Key Facts
- Tourne son télescope perfectionné vers le ciel en 1609 : découverte des lunes de Jupiter et des phases de Vénus
- Confirme le modèle héliocentrique de Copernic grâce à ses observations télescopiques
- Publie le «Dialogue sur les deux grands systèmes du monde» en 1632
- Condamné par l'Inquisition en 1633 : contraint d'abjurer, assigné à résidence à Arcetri jusqu'à sa mort
- Rédige les «Deux nouvelles sciences» (1638) : fondements de la mécanique moderne
- Réhabilité par l'Église catholique en 1992 sous Jean-Paul II, 360 ans après sa condamnation
Biography
Galileo Galilei was born on 15 February 1564 in Pisa, Tuscany, the eldest of six children of a musician and music theorist. Enrolled in medicine at the University of Pisa, he was far more drawn to mathematics and mechanics. Around 1583, he observed the isochronism of pendulum oscillations and laid the foundations of a science of motion based on measurement and experiment rather than Aristotelian authority. Appointed professor of mathematics in Pisa and then in Padua, he quickly became one of the most renowned scholars in Italy.
In 1609, learning of the invention of a magnifying lens in the Netherlands, Galileo built an improved version and turned it towards the sky. His observations overturned traditional cosmology: he discovered that the Moon was not a perfect sphere but had mountains and valleys; that the Milky Way was made up of a multitude of stars; that Jupiter was surrounded by four moons (the "Medicean stars", dedicated to the Medici); and that Venus showed phases similar to those of the Moon. These observations confirmed the Copernican heliocentric model: if Venus had phases, it must orbit the Sun, not the Earth.
Galileo openly championed the Copernican system and in 1632 published his "Dialogue Concerning the Two Chief World Systems", which transparently pitted the advocate of geocentrism (named Simplicio) against the heliocentric champion. The Church felt mocked — the character of Simplicio even seemed to parody Pope Urban VIII. In 1633, Galileo was summoned before the Inquisition, forced to abjure his convictions and sentenced to house arrest at his villa in Arcetri, near Florence. The phrase attributed to him — "And yet it moves" — symbolises his inner resistance.
Despite his condemnation, Galileo continued his scientific work. He wrote his "Two New Sciences" (1638), a synthesis of his research on motion and the resistance of materials, which directly influenced Newton. He died on 8 January 1642 in Arcetri, blind and under ecclesiastical supervision. The Catholic Church officially rehabilitated him in 1992, under the pontificate of John Paul II, acknowledging the error committed three hundred and sixty years earlier.
Galileo is considered the father of modern physics and of the experimental method. His conviction that nature is written in mathematical language and that every theory must be tested against experiment is the very foundation of science as it is still practised today. His tragic fate, caught between scientific truth and religious power, remains one of the most powerful symbols of freedom of thought.