Galilei, Galileo

views updated

Galileo Galilei

February 15, 1564
Pisa, Italy
January 8, 1642

Mathematician, physicist, astronomer

"All truths are easy to understand once they are discovered; the point is to discover them."
Galileo.

The Italian mathematician, physicist, and astronomer Galileo Galilei (called Galileo) was the foremost scientist of the Renaissance. (The Renaissance was a cultural movement that began in Italy in the mid-1300s and was initiated by scholars called humanists who promoted the human-centered values of ancient Greece and Rome.) Now considered the "father of modern science," Galileo made revolutionary contributions to astronomy, physics, and scientific philosophy. In 1612 he shook the foundations of the scientific world by supporting the Sun-centered theory of the universe, which the Polish astronomer Nicolaus Copernicus (1473–1543; see entry) had formulated nearly seventy years earlier. This daring assertion brought Galileo into direct confrontation with the Roman Catholic Church.

The Sun-centered theory of the universe was controversial because it contradicted the seventeenth-century belief that the Sun and all the planets revolved around the Earth. Since the second century a.d., astronomers (scientists who study the stars and planets) had accepted the Earth-centered view, which was stated by the ancient Egyptian scholar Ptolemy (Claudius Ptolemaeus; c. a.d. 100–c. 170). Ptolemy followed earlier Greek thinkers such as Aristotle (384–322 b.c.), who concluded that the Earth is the center of a fixed and perfectly balanced heavenly system. Ptolemy's ideas were enforced by the church, which found supporting evidence in the Bible (the Christian holy book).

Copernicus gave proof of the Sun-centered universe in De revolutionibus orbium coelestium (On the revolutions of the heavenly orbs), which was published only hours before he died in 1543. At the time the book was not a source of controversy because the preface stated that the theory was not presented as fact. Although some church officials expressed concern about Copernicus's ideas, action was never taken against the book. The problem did return, however, after Galileo proved the Sun-centered theory. In 1616 church officials forbade Galileo to defend or teach De revolutionibus orbium coelestium. Although he agreed to follow church orders, he nevertheless continued to gather evidence that supported Copernican theory. In 1532 the church put Galileo on trial, unleashing a controversy that continued into the twentieth century.

States theory of natural motion

Galileo was born in Pisa, Italy, the first child of Vincenzio Galilei, a merchant and musician who championed advanced musical theories of the day. The family moved to Florence in 1574, and that year Galileo started his formal education in the nearby monastery (house of a religious order for men) of Vallombrosa. Seven years later he entered the University of Pisa as a medical student. In 1583, while Galileo was at home on vacation, he began to study mathematics and the physical sciences. Galileo ended his medical studies and pursued the sciences, but financial difficulties forced him to leave the University of Pisa in 1585 before he completed his degree.

After returning to Florence, Galileo spent three years vainly searching for a suitable teaching position. During that time he wrote works that gained him a reputation as a mathematician and natural philosopher (physicist). He then secured a teaching post at the University of Pisa in 1589. From the beginning of his academic career, he was an eager participant in disputes and controversies. For instance, he made fun of the custom of wearing academic gowns. He was willing to condone ordinary clothes, he said, but the best thing was to go naked.

When Galileo's father died in 1591, Galileo was left to care for his mother, brothers, and sisters. As a result of this additional responsibility, he had to look for a better position. He found one in 1592 at the University of Padua in the Republic of Venice. In 1604 Galileo publicly declared that he supported Copernicus's theory of a Sun-centered universe. He then gave three public lectures before overflow audiences in Venice. He argued that a new star, which had appeared earlier that year, was major evidence in support Copernicus's views. More important was a letter in which he stated his theory of natural motion. By natural motion Galileo meant that a body will fall freely in space, and he proposed the law of free fall to account for this phenomenon. This concept contradicted the accepted view that the universe was a perfectly ordered and fixed system in which no body can freely move on its own.

Comes into conflict with church

In 1609 Galileo learned about the success of some Dutch spectacle (eyeglass) makers in combining lenses (pieces of glass used for forming an image by focusing rays of light) into what later came to be called the telescope (an instrument used for viewing distant objects such as stars and planets). He feverishly set to work, and on August 25 he presented to the Venetian Senate a telescope as his own invention. The success was tremendous. He obtained a lifelong contract at the University of Padua, but he also stirred up resentment when it was learned that he was not the original inventor. Within a few months, however, Galileo had gathered astonishing evidence about mountains on the Earth's Moon and about moons circling the planet Jupiter through the use of his telescope. He also identified a large number of stars, especially in the belt of the Milky Way (a galaxy, or very large group of stars, of which the Earth's solar system is a part). On March 12, 1610, all these sensational findings were printed in Venice under the title Sidereus nuncius (Starry messenger). The booklet took the world of science by storm. The view of the heavens drastically changed, and so did Galileo's life.

In 1610 Galileo accepted the position of mathematician in Florence, Italy, at the court of Duke Cosimo II de' Medici (1590–1621). He left behind in Padua his common-law wife (a woman to whom he was not legally married), Marina Gamba, and his young son, Vincenzio. He placed his two daughters, aged twelve and thirteen, in the convent (house of a women's religious order) of Saint Matteo in Arcetri. Galileo's move to Florence turned out to be highly unwise. In the beginning everything was pure bliss. He made a triumphal visit to Rome in 1611, and the next year his Discourse on Bodies in Water was published. In this work he disclosed his discovery of the phases of the planet Venus, which proved the truth of the Copernican theory that celestial bodies travel around the Sun. Two years later Galileo published his observations of sunspots (the dark spots that appear from time to time on the surface of the Sun), which embroiled him for many years in bitter disputes with the German astronomer Christoph Scheiner (1573–1650). A member of the Jesuit order (Society of Jesus) and based at the University of Ingolstadt, Scheiner had published observations of sunspots in 1612 under the pseudonym (pen name) Apelles.

Church issues stern order

Galileo's aim was to make a detailed description of the universe according to the theories of Copernicus and to develop a new form of physics. A major obstacle was the traditional belief, stated in the Bible, that the Earth is the center of the universe. To deal with the difficulties raised by the Scripture, Galileo addressed theological (religious) issues. He was assisted by church leaders, such as Monsignor Piero Dini and Father Benedetto Castelli, his best scientific pupil. In letters to Dini and Castelli, Galileo produced essays that now rank among the best writings of biblical analysis of those times. His longest letter was addressed to Grand Duchess Christina of Tuscany. In all of the letters he discarded the idea of an Earth-centered universe in favor of the theory that the Earth revolves around the Sun. As the letters were more widely circulated, a confrontation with church authorities became inevitable. In 1616 Cardinal Robert Bellarmine issued an order that forbade Galileo to continue teaching or writing about the Copernican doctrine of the motion of the Earth.

Galileo agreed not to promote Copernicus's views. Nevertheless, he was determined to have the order overturned. In 1623 Galileo dedicated Assayer, a work on the philosophy of science, to the new pope (supreme head of the Roman Catholic Church), Urban VIII (1568–1644; reigned 1623–44). The next year Galileo had six audiences (formal meetings) with the pope. Urban promised a pension for Galileo's son, Vincenzio, but he did not grant Galileo permission to resume his work on a new description of the universe. Before departing for Florence, Galileo was informed that the pope had remarked that he did not believe the Roman Catholic Church would ever declare the Copernican theory to be heretical, but he was also certain the theory could never be proven. This news gave Galileo encouragement to go ahead with the great undertaking of his life, the Dialogue Concerning the Two Chief World Systems (known as Dialogue).

Called before the Inquisition

Galileo's Dialogue was published in 1632. The book features four main topics discussed by three speakers on four consecutive days. The speakers are Simplicius, Salviati, and Sagredo, Simplicius represents Aristotle, Salviati is a spokesman for Galileo, and Sagredo plays the role of an arbiter (one who makes the final judgment on an issue), who leans heavily toward Galileo. The First Day is devoted to the criticism of the alleged perfection of the universe, as claimed by Aristotle. Here Galileo made use of his discovery of the "imperfections" of the Moon, namely, its rugged surface as revealed by the telescope. (Aristotle contended that the Moon's surface is perfectly smooth.) The Second Day is a discussion of the rotation of the Earth on its axis (an imaginary line extending through the center of the Earth from north to south) as an explanation of various celestial phenomena.

Starry Messenger

In 1610 Galileo published Starry Messenger, a booklet in which he recorded the results of observations with his newly invented telescope. He had gathered evidence about mountains on the Earth's Moon and about moons circling the planet Jupiter. He also identified a large number of stars. At the conclusion of Starry Messenger he summarized the evidence that supported the Copernican theory of a universe with the Sun, not the Earth, at its center. With a bemused tone he noted that some people were quite happy to accept the idea that planets revolve around the Sun. Yet they seemed to be offended by any notion that the Earth might move around the Sun along with the planets.

Galileo wrote:

Here we have a fine and elegant argument for quieting the doubts of those who, while accepting with tranquil mind the revolutions of the planets about the sun in the Copernican system, are mightily disturbed to have the moon alone revolve about the earth and accompany it in an annual rotation about the sun. Some have believed that this structure of the universe should be rejected as impossible. But now we have not just one planet rotating about another while both run through a great orbit around the sun; our own eyes show us four stars which wander around Jupiter as does the moon around the earth, while all together trace out a grand revolution about the sun in the space of twelve years.

The Achievement of Galileo. James Brophy and Henry Paolucci, editors. New York: Twayne Publishers, 1962, p. 30.

During the Third Day the orbital motion of the Earth around the Sun is debated. A main issue is the undisturbed nature of the surface of the Earth in spite of its double motion—that is, its revolving on an axis while at the same time orbiting around the Sun. The discussion on the Fourth Day shows that the tides (the rhythmical rising and falling of oceans and other bodies of water) are proof of the Earth's twofold motion. In this section Galileo seemed to contradict the contention of the Third Day discussion, that the surface of the Earth remains undisturbed by its double motion. The tides, which cause the regular movement of oceans, show that the Earth's surface is in fact affected by the twofold motion.

Church officials were outraged by the Dialogue, which proved that Galileo supported Copernicus's ideas. Galileo was summoned to Rome to appear before the Inquisition, a church court set up to punish heretics (people who violate or oppose the teachings of the church). The proceedings dragged on from the fall of 1632 to the summer of 1633. During that time Galileo was allowed to stay at the home of the Florentine ambassador in Rome. He was never subjected to physical force. Nevertheless, he had to inflict torture upon himself by publicly rejecting the doctrine that the Earth moved around the Sun. At the end of the trial, church officials ordered that Dialogue be placed on the Index of Prohibited Books by the Holy Office. The Holy Office was a branch of the church established as part of the Inquisition to review the content of all publications. The Index of Prohibited Books was a list of works that the church considered to be heretical.

Remains a Christian

Galileo was confined to house arrest (he was not permitted to leave the premises) in Siena, a province in western Italy. He then received permission in December to live in his own villa at Arcetri. He was not supposed to have any visitors, but this order was not obeyed. The church was also unable to prevent the printing of Galileo's works outside Italy. Over the next five years translations of his writings were published in France and Holland. In 1638 his Two New Sciences was printed in Leiden, Holland. Like the Dialogue, this work is in the form of discussions over a period of four days. Topics included the mechanical resistance of materials, the atomic composition of matter, the nature of vacuum, the vibrations of pendulums, uniform and accelerated motion, and the projectile motion of a cannonball.

Although Galileo proposed a radically new concept of the universe, he remained a Christian to the end of his life. He believed that the world was made by a rational creator (God) who gave order to everything according to weight, measure, and number. Galileo stated this faith in the closing pages of the First Day of the Dialogue. He described the human mind as the most excellent product of the creator, because it could recognize mathematical truths. Galileo spent his last years partially blind, and he died in 1642.

Would It Be "imprudent or unreasonable"?

In 1835 the Holy Office of the Roman Catholic Church removed Galileo's Dialogue from the Index of Prohibited Books. Yet more than one hundred fifty years would pass before the church officially made amends for the treatment Galileo himself had received at the trial in 1633.

On November 10, 1979, Pope John Paul II (1920– ; elected 1978) acknowledged that the church had caused Galileo to suffer a great. The pope called for a frank reexamination of the famous trial. On July 3, 1981, he appointed a special commission to study and publish all available documents relating to the trial. The pope presented the results of the commission's work to the Pontifical (Pope's) Academy of Sciences on October 31, 1992. The report made clear that astronomy was in a state of transition when Galileo was silenced in 1616 and when he was forced to withdraw his theory in 1633. Furthermore, scripture scholars were confused about cosmology (the study of the universe). The report stated that Galileo had not demonstrated the Earth's motion, and theologians had erred in their assessment of his teachings. But in the 1990s, the pope continued, science is so complex it is almost impossible to certify scientific discoveries as being absolutely true. The best one can hope for, he said, is that discoveries be "seriously and solidly grounded." He went on to state that the function of the Pontifical Academy was to advise the church if the degree of probability of a discovery is such "that it would be imprudent [unwise] or unreasonable to reject it." In other words, a scientific discovery should not be rejected if there is any possibility that it can be proven. Historians note that if such advice had been available to Pope Urban VIII, Galileo might have been spared the unhappiness of his final years.

The aftermath

In 1820 the condemnation of Copernicanism was revoked (withdrawn) by the Holy Office. This action was taken on the basis of discoveries made by two little-known Italian astronomers. The first, Giovanni Battista Guglielmini, offered proof of the Earth's rotation by conducting experiments with bodies falling from a high tower. In Bologna, between 1789 and 1792, he made measurements and observed that the bodies deflected slightly to the east, thus proving that the Earth moves in a twofold motion. The second astronomer, Giuseppe Calendrelli, measured the parallax (the angular distance in direction of a celestial body, as measured from two points on Earth's orbit) of star Alpha in the constellation Lyra, also confirming such motion. He presented his findings to Pope Pius VII (1742–1823; reigned 1800–23) in a work published in 1806. During a debate over whether to approve an astronomy text in 1820, Benedetto Olivieri, head of the Holy Office, determined that the experiments of Guglielmini and Calendrelli demonstrated the Earth's twofold movement. Galileo's Dialogue was finally removed from the Index of Prohibited Books in 1835. But it was nearly one hundred sixty more years before the Catholic Church issued an official report stating that theologians had been wrong in their assessment of Galileo's teachings (see accompanying box).