Galileo Galilei

Galileo Galilei
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Galileo Galilei (1564-1642) was born in Pisa, Tuscany. His father was a nobleman, but poor, and Galileo had to leave the University of Pisa without taking a degree. He spent the next four years working on mechanics and hydrostatics, and in 1588 wrote a tract on the center of gravity in solids for his patron, the Marchese Guidobaldo del Monteso. Aged only twenty-five, he returned to the University as a professor.

	Traditionally, Galileo is said to have experimented at the Leaning Tower of Pisa - dropping balls of different weights from its top to disprove Aristotle's belief that heavier objects fall more quickly.

	In fact, this probably never happened there, but Galileo did perform experiments to try and confirm his theories about the velocity of falling objects.

In 1592, Galileo became professor of mathematics in the University of Padua. In 1597, he was already corresponding with Johannes Kepler and a firm believer in the Copernican system, although he remained silent on this point because the Aristotelian system was still generally accepted by academics.

In 1608, a Dutch spectacle-maker called Johann (Hans) Lippershey constructed a telescope that combined convex and concave lenses. Galileo heard of this, and invented an improved version. He used it to observe the stars and planets, and made amazing discoveries.

In 1610, he published Sidereus nuncius (Starry Messenger) detailing such important discoveries as that the moon was cratered, that Jupiter had four moons, and that there were vast thousands of stars invisible to the naked eye.

"…that the surface of the moon is not perfectly smooth, free from inequalities and exactly spherical, as a large school of philosophers considers with regard to the moon and the other heavenly bodies, but that, on the contrary, it is full of irregularities, uneven, full of hollows and protuberances, just like the surface of the earth itself, which is varied everywhere by lofty mountains and deep valleys".

	Galileo's Starry Messenger told the world that the ancient authorities were ignorant on many matters, and that not all celestial objects revolved around the earth - the moons of Jupiter orbited Jupiter. Moreover, Galileo wrote in simple concise language that everyone could understand (unlike the dense and technical prose of Copernicus and Kepler).
	Kepler wrote a glowing open letter of admiration to Galileo, and this helped Galileo obtain a post as court mathematician to Cosimo II Medici, Grand Duke of Tuscany, despite the hostility and skepticism of Italian astronomers about Galileo's findings. [Galileo had tried to increase his chances of the job by naming Jupiter's moons Sidera Medicea - "the Medicean Stars"].

Galileo's next important finding was the phases of Venus. The most obvious explanation of periodic phasing was that Venus revolved around the sun, just as the Copernican heliocentric system suggested.

Galileo had also observed that there were "spots" on the sun. This contradicted the Aristotelian belief that the sun was a perfect body, and a Professor of Mathematics at Ingoldstadt, Christoph Scheiner (1573-1650), questioned Galileo's interpretation. Galileo responded with his Letters on sunspots (Istoria e dimostrazioni intorno alle macchie solari e loro accidenti, 1613). In this letter he also endorsed the Copernican system for the first time in print.

In 1613, Galileo wrote a personal letter to his friend, Benedetto Castelli (1578-1643), a fellow mathematician and expert on hydraulics. Galileo agreed with Copernicus, and expressed the view that the bible was not to be taken literally, when its metaphorical expressions conflicted with reason and observation.

	The following year, Galileo expanded his letter to Castelli into a Letter to the Grand Duchess Christina (the mother of Cosimo II Medici) and circulated this widely. (It was published in 1636). Galileo also sent a copy of the Castelli letter for the attention of the eminent seventy-three year old theologian, Cardinal Robert Bellarmine (1542-1621).
	Galileo did not doubt the truth of the Copernican system, but Bellarmine did, and thought that undermining the authority of the Bible and the Church was very dangerous. He argued that Galileo should simply treat Copernican ideas as a working hypothesis, until there was solid unambiguous proof of its truth. [Bellarmine's reply to Galileo].
	Galileo's observations were in fact compatible with Brahe's system, which astronomers at the Roman College and the Catholic establishment were willing to accept.
	Galileo went to Rome to further his case, but the Inquisition condemned the idea that the sun was the fixed center of earth's orbit, and placed Copernicus' De revolutionibus on the Index of proscribed books until corrected. (Four years later in 1620, it was taken off the Index and reprinted, after nine sentences asserting the certainty of heliocentrism were expunged).

Galileo had many friends among the clergy, including Cardinal Maffeo Barberini (1568-1644), who became Pope Urban VIII in 1623. Galileo was quietly told not to insist publicly on the truth of the Copernican system and he returned to Florence.

	In 1619, Galileo became involved in a dispute with a Jesuit priest at the Roman College, Orazio (Horatio) Grassi who expressed the [correct] view that comets moves in regular orbits like planets. However, Grassi suggested that the the comets orbited the earth (not the sun) and this provoked Galileo (using one of his students) into an immoderate attack on the scientists of the Roman College.
	Emboldened by Barberini's election as Pope, in 1623 Galileo published Il saggiatore (The assayer). This mixed biting polemic against his opponents, with groundbreaking methodological and philosophical assumptions.

The universe "…cannot be understood unless one first learns to comprehend the language and read the letters in which it is composed. It is written in the language of mathematics, and its characters are triangles, circles and other geometric figures without which it is humanly impossible to understand a single word of it; without these one wonders about in a dark labyrinth."

Il Saggiatore not only stressed that quantification was the route to true knowledge of physical reality, it abandoned the Aristotelian stress on the qualitative aspects of bodies. Galileo argued that secondary qualities (like color and taste) were just names given by people to the impressions that bodies made on their senses. Science should concern itself only with the size, shape and relative motion of objects.

Galileo's mechanical philosophy undermined key aspects of traditional Aristotelianism.
Aristotle had differentiated between matter and form - a table, for example, was made of wood (its matter) but was only a table because of its "substantial form" (its table-ness). Galileo's theory ignored form.
Aristotle's philosophy was teleological - it considered "final causes" - the final cause of an acorn was an oak tree; the final cause of the acorn falling to the earth was its purpose, like that of all bodies, of moving to earth. Galileo's theory posited matter in motion, blindly responding to universal physical laws.

Virginio Cesarini

Galileo was encouraged when in 1623, Pope Urban VIII appointed two of Galileo's friends - Cesarini and Ciampoli - to important positions. Galileo hoped that this meant the Church would change its official position on the Copernican system.

Giovanni Ciampoli

Il saggiatore was examined by the Inquisition, but cleared in 1625. Galileo began work on his Dialogue on the great world systems (Dialogo di Massimi Sistemi del Mondo), and completed it by 1630. He asked for a license for its publication from the Inquisition and (in view of his known friendship with Urban VIII) this was granted. The Dialogue was published at Florence in 1632.

The Dialogue was written in the form of a discussion between three men - an advocate of Copernican system, another of the Aristotelian-Ptolemaic system (called "Simplicius"), and an uncommitted inquirer. By using this form, Galileo hoped to circumvent the ban on promotion of the Copernican hypothesis.

Urban VIII became convinced that he was the model for "Simplicius", and ordered that sales of the Dialogue be stopped and Galileo investigated.

Galileo was summoned to Rome in 1633, and put on trial for infringing the ban on upholding Copernicanism.

[Galileo's defense, & The Papal condemnation (1633)]

Under threat of torture and charges of heresy, Galileo agreed to abjure Copernicanism. He was sentenced to imprisonment, which in practice meant a comfortable house arrest in Siena. The Dialogue was condemned to be burnt.

"Eppur si muove"
(And yet it does move)

Galileo is supposed to have muttered this as he left the last session of the Inquisition after agreeing not to assert that the Earth orbits the Sun.

	Galileo remained in Siena, continuing his scientific work despite poor health and the onset of blindness, until his death in 1642.
	Galileo's treatment had a chilling effect on scientific research in Catholic Europe. Descartes decided not to publish his own Le monde, ou Traité de la lumière on hearing of Galileo's condemnation.
	The Roman Catholic Church did not finally reverse its ban on Copernican theory until 1758. Pope John Paul II reopened the Galileo case for consideration in 1979, and in 1992 reversed the sentence against him.

	Galileo also performed extremely important work on mechanics. He showed that projectiles moved in a parabola - an important contribution to the early science of ballistics.
	By reducing complex motion to a series of formulae describing each simple motion involved, Galileo started modern physics on its path to describing physical reality in abstract mathematical terms.