Galileo Galilei 1564-1642

Galileo was born in 1564 in Pisa, which was then part of the Duchy of Tuscany. He began studying medicine in Pisa but abandoned his studies after 4 years. In 1589, he returned to the university as a lecturer on mathematics, but dealt mainly with physics. We do not know if Galileo really placed one of his students on the leaning tower of Pisa in order to demonstrate before the university students and teachers that a large ball will fall at the same velocity as a small light one, as is related in one of the stories about him. We certainly know that this experiment indeed demonstrates Galileo's first important discovery: that the velocity at which bodies fall does not depend on their weight. This claim of Galileo's contradicts the law of Aristotle who claimed that the velocity of falling bodies is relative to their weight. Thus, at the very outset of his career, Galileo already opposed parts of Aristotle's Physical Theory, a theory which he eventually totally rejected.

The Padua Period

In 1592, Galileo moved to the famous university of Padua, where he was offered a higher salary. In Padua, he continued his physics research particularly in the area of mechanics. During the last decade of the 16th century he was involved in the study of motion, and even wrote a book, which he did not publish, entitled De Moto. Galileo's ideas during this period were not particularly revolutionary. He adhered to the main Aristotelian concepts accepted by his contemporaries, but was already developing his opposition to Aristotelian physics, particularly to the philosophical tradition of the study of physics, which was unwilling to deviate from the ideas of the Greek philosopher. In Padua, Galileo was also involved in the invention and perfection of various technological devices.

The Law of Fall

During the first decade of the 17th century, Galileo began conducting experiments and working with various precise measurements in the search for mathematical equations capable of describing the movement of bodies. Galileo's use of mathematics and experimentation for physical research were one of the central innovations of his scientific activity. Galileo was deeply influenced by Archimedes principles of statics (the theory of equilibrium) which he expanded on for his discussion of moving bodies. Through his use of mathematics and physical experimentation, Galileo was able to formulate the Law of Fall in 1604, which is related to the Law of Inertia which he first formulated in 1612. These laws stand in marked contradiction to Aristotelian physics and all that was accepted up to then. From this period on, Galileo made distinct efforts to refute Aristotelian theory.

The observations of the heavens.

The appearance of the new star (Nova) in 1604, provided an excellent opportunity to point out the weaknesses of Aristotle's physics, which claimed that nothing ever changed in the heavens. Galileo's observations of the star, in combination with the observations of astronomers throughout Europe, showed that this star indeed exists in the heavens, thus constituting proof of change in the heavens, contrary to the Aristotelian claim. The appearance of the new star led to Galileo's interest in astronomy and to his active support of the Copernican theory, which obviously also contradicts Aristotelian theory and the claims of its adherents who controlled the universities. Galileo's improvement of the telescope in 1609, provided him with a powerful new tool for observing the heavens. With the telescope's help, Galileo discovered in 1610 the mountains and valleys on the moon, the moons of Jupiter and the sun spots, as well as many stars which had not previously been observed. These findings made Galileo the most famous scientist in Italy. In 1610, Galileo became the court philosopher and mathematician of the Medici family, the Dukes of Tuscany - a position which assured him a comfortable income and absolved him of teaching duties. He spent the rest of his life in Florence, the capital of the Duchy.

The heliocentric theory versus the geocentric theory.

Galileo's publications on celestial phenomena supported the heliocentric theory (according to which the sun is at the center of the world), and explained that this physical theory presents the world as it is. This claim contradicted the Church interpretation of Scripture. These publications and Galileo's attempts to interpret Scripture according to this new theory, were not acceptable to the Church. In 1616, he met inquisition officials a number of times and they forbade him to support the Copernican theory (See the Prohibition of the Copernican theory). This was the first part of his conflict with the Church, which reached its climax at his trial conducted 17 years later.

For a number of years Galileo refrained from directly addressing the question of the earth's movement. He continued to be involved in scientific discussions and continued writing. In 1623, he published his book The Assayer - Il Saggiatore, which was a great attack on the Aristotelian philosophers who base their theories on Aristotle's authority rather than their observations. In this book Galileo claimed that the language of nature's book is mathematics and that the way to understand nature is through mathematics. The book was highly successful, even with the new Pope Urbanus XIII, and among the higher echelons of the Christian church. Encouraged by his success, Galileo began writing his comprehensive book on the Copernican theory, The Dialogue A Bout Two Ch ief World Systems, which was published in 1632. The book presents the claims favoring the Copernican theory and shows that the motion of the earth is possible. The book is full of harsh attacks against Aristotelian physics.