Galileo Galilei (15 February 1564 - 8 January 1642) is considered one of the most important figures of the Scientific Revolution as an Italian mathematician, physicist, astronomer, and philosopher. By observing the sky with the telescope he developed, he discovered Jupiter’s moons, the phases of Venus, sunspots, and the rugged surface of the Moon; in the field of physics, he conducted groundbreaking studies on the motion of falling objects, the laws of the pendulum, and mechanics. His defense of Copernicus’s heliocentric universe theory led to his conflict with the Catholic Church, causing him to spend his final years under house arrest. Galileo’s experimental approach laid the foundation for modern science and earned him the title “Father of Modern Science.”

Early Life and Education

Galileo was born on February 15, 1564, in Pisa, Italy, in the Duchy of Florence. He was the eldest of six children. His father, Vincenzo Galilei, was a renowned musician and music theorist; his mother, Giulia Ammannati, came from a family involved in the textile trade in Pisa. The family moved to Florence in 1574, where Galileo began his formal education. He first received lessons from private tutors, then studied at the Camaldolese monastery in Vallombrosa, and although he considered a religious career for a time, he eventually abandoned this path.

In 1581, at the age of 16, he enrolled at the University of Pisa to study medicine. However, he soon developed an interest in subjects like mathematics and physics. During that period, he took courses on the prevalent Aristotelian worldview. Due to financial difficulties, he left the university in 1585 without obtaining a degree. He supported himself by giving private mathematics lessons in Florence and Siena, establishing connections with leading mathematicians during this short period. In 1589, he began teaching mathematics at the University of Pisa; in 1592, he became a professor of mathematics at the University of Padua in the Venetian Republic.

Family Life

In Padua, Galileo met Marina Gamba and although they never married, they had three children together: Virginia (1600), Livia (1601), and Vincenzo (1606). Due to financial and social concerns, he did not formally marry Marina. Concerned that his daughters might not find good marriages, Galileo placed them in the San Matteo Convent near Florence during their adolescence. Virginia, upon becoming a nun, took the name Maria Celeste and maintained a close relationship with her father; Livia took the name Arcangela. Vincenzo's birth was later legitimized, and he too became a successful musician.

Scientific Works and Discoveries

Physics and Mechanics

Galileo worked on mechanics for 18 years while in Padua. In his work De Motu (On Motion), written in the 1590s, he disproved Aristotle's view that falling objects move at different speeds according to their weight. He showed that falling objects accelerate at the same rate and would reach the ground simultaneously if there were no air resistance. He also studied the motion of pendulums, discovering that their periods are independent of weight and depend only on their length (isochrony). These findings matured in his work Discourses Concerning Two New Sciences, published in 1638, and he put forth the law of free fall, one of the fundamental laws of modern physics.

Galileo attempted to mathematically describe the motion of objects and correlated acceleration with time through inclined plane experiments. He also developed the idea that an object could move indefinitely on a smooth surface in a frictionless environment (inertia); this formed the basis of Newton's first law of motion. Two New Sciences represents the pinnacle of Galileo's career, addressing both the structure of matter and the laws of local motion.

Telescope and Astronomy

Hearing about the telescope invented in the Netherlands in 1609, Galileo developed his own design, creating an instrument with a 33x magnification capacity. With this telescope, he made crucial observations by examining the sky. His Sidereus Nuncius (Starry Messenger), published in 1610, revealed that the Moon was covered with mountains and valleys, that Jupiter had four large moons (now known as the Galilean moons), and that Venus had phases like the Moon. By observing sunspots, he proved that the Sun rotated and was not perfect. These findings shattered Aristotle's view that celestial bodies were perfect and unchanging and supported Copernicus's heliocentric model.

Galileo dedicated his discoveries to the powerful Medici family of Tuscany, naming Jupiter's moons the “Medici Stars.” This strategy allowed him to earn the title “Chief Mathematician and Philosopher” at the Medici court in Florence in 1610.

^{Representative image of Galileo Galilei doing his scientific work. Created with artificial intelligence support.}

Conflict with the Church

Galileo’s defense of the Copernican theory led to his conflict with the Catholic Church. At that time, the Church supported Ptolemy’s geocentric model of the universe. In a letter to his student Benedetto Castelli in 1613, Galileo argued that the Copernican theory did not contradict the Holy Scripture; he expanded on this view in his 1615 letter to Grand Duchess Christina. According to him, nature and the Holy Scripture represented different realms of truth, and scientific findings might necessitate a reinterpretation of religious texts.

In 1616, the Church placed Copernicus’s work De Revolutionibus on the Index of Forbidden Books, and Galileo was ordered “not to defend, teach, or hold” this theory. Galileo complied with this order for seven years. However, encouraged by his friend Cardinal Maffeo Barberini’s election as Pope Urban VIII in 1623, he published his work Dialogue Concerning the Two Chief World Systems in 1632. The book was written through three characters discussing the heliocentric and geocentric systems, but it showed a clear leaning towards the Copernican model. This drew the Church’s reaction.

In 1633, Galileo was tried before the Inquisition in Rome and condemned on “vehement suspicion of heresy.” Under threat of torture, he was forced to publicly recant his theories and was sentenced to life imprisonment; this sentence was immediately commuted to house arrest. Remaining in his villa in Arcetri near Florence, Galileo, despite being forbidden from receiving visitors and publishing his works outside Italy, had Two New Sciences printed in Holland in 1638.

Final Years and Death

During the years of his house arrest, Galileo lost his eyesight and his health deteriorated. The death of his eldest daughter, Maria Celeste, in 1634 deeply affected him. Despite this, he continued his scientific work and completed his last major work, Two New Sciences, summarizing his ideas on mechanics and motion. On January 8, 1642, at the age of 77, he died in Arcetri from heart palpitations and fever. Due to the Church's objection, he was initially buried modestly; in 1737, he was reburied in the Santa Croce Church in Florence.

Legacy

Galileo's work was crucial in the birth of modern science. His integration of the experimental method and mathematics into natural inquiry influenced later scientists like Isaac Newton. His discoveries in astronomy accelerated the acceptance of the heliocentric model. The Church lifted the ban on works supporting the Copernican theory in 1758, and in 1992, Pope John Paul II expressed regret for how the Galileo case was handled.

Galileo secured an important place in history with his scientific courage, innovative thoughts, and efforts to understand the universe. His legacy continues to live on, not only through his discoveries but also through his methodological approach that guided the advancement of science.