Astronomer and mathematician, born in Pisa, W Italy. He entered Pisa University as a medical student in 1581, and became professor of mathematics at Padua (15921610), where he improved the refracting telescope (1610), and was the first to use it for astronomy, discovering the four largest satellites of Jupiter. His bold advocacy of the Copernican theory brought severe ecclesiastical censure. He was forced to retract before the Inquisition, and was sentenced to indefinite imprisonment - though the sentence was commuted by the pope, at the request of the Duke of Tuscany. Under house arrest in Florence, he continued his research, though by 1637 he had become totally blind. Among his other discoveries were the law of uniformly accelerated motion towards the Earth, the parabolic path of projectiles, and the law that all bodies have weight. The validity of his scientific work was formally recognized by the Roman Catholic Church in 1993.
| Galileo Galilei | |
|---|---|
| Portrait of Galileo Galilei by Giusto Sustermans. | |
| Born |
February 15, 1564 Pisa |
| Died |
January 8, 1642 Arcetri |
Galileo Galilei (February 15, 1564 – January 8, 1642) was an Italian physicist, astronomer, and philosopher who is closely associated with the scientific revolution. According to Stephen Hawking, Galileo has probably contributed more to the creation of the modern natural sciences than anybody else. The work of Galileo is considered to be a significant break from that of Aristotle.
Biographical Sketch
Galileo was born in Pisa, in the Tuscany region of Italy, on February 15, 1564. Galileo was their first child out of seven (some people believe six).
Galileo was tutored from a very young age.
Although he was a devout Roman Catholic, Galileo fathered three children out of wedlock with Marina Gamba. She was Galileo's eldest child, the most beloved, and inherited her father's sharp mind. She died on April 2, 1634, and is currently buried with Galileo at the Basilica di Santa Croce di Firenze.
In 1612, Galileo went to Rome, where he joined the Accademia dei Lincei and observed sunspots. In 1612, opposition arose to the Copernican theories, which Galileo supported. In 1614, from the pulpit of Santa Maria Novella, Father Tommaso Caccini (1574-1648) denounced Galileo's opinions on the motion of the Earth, judging them dangerous and close to heresy. Galileo went to Rome to defend himself against these accusations, but, in 1616, Cardinal Roberto Bellarmino personally handed Galileo an admonition enjoining him to neither advocate nor teach Copernican astronomy as religious doctrine. In 1622, Galileo wrote the The Assayer (Saggiatore), which was approved and published in 1623. The court issued a sentence of condemnation and forced Galileo to abjure. In 1638, almost totally blind, Galileo published his final book, Two New Sciences, in Leiden.
Scientific methods
In the pantheon of the scientific revolution, Galileo Galilei takes a high position because of his pioneering use of quantitative experiments with results analyzed mathematically. the great experimentalist who immediately preceded Galileo, William Gilbert, did not use a quantitative approach. However, Galileo's father, Vincenzo Galilei, a lutenist and music theorist, had performed experiments in which he discovered what may be the oldest known non-linear relation in physics, between the tension and the pitch of a stretched string. Thus, a limited form of mathematics had long made its way into physical science at the point of music, and young Galileo was in a position to see his own father's observations generalize that relationship still further. Galileo himself would find credit as the first to plainly state that the laws of nature are mathematical, and (as he said) the idea that "the language of God is mathematics."
Galileo also contributed to the rejection of blind allegiance to authority (like the Church) or other thinkers (such as Aristotle) in matters of science and to the separation of science from philosophy or religion.
In the 20th century some authorities, in particular the distinguished French historian of science Alexandre Koyré, challenged the validity of Galileo's experiments.
Later research, however, has validated the experiments. The experiments on falling bodies (actually rolling balls) were replicated using the methods described by Galileo (Settle, 1961), and the precision of the results were consistent with Galileo's report. Later research into Galileo's unpublished working papers from as early as 1604 clearly showed the validity of the experiments and even indicated the particular results that led to the time-squared law (Drake, 1973).
Galileo showed a remarkably modern appreciation for the proper relationship between mathematics, theoretical physics, and experimental physics.
Due to the merit of his works, Einstein called Galileo the "father of modern science."
Astronomy
Contributions
The belief that Galileo invented the telescope is a common misconception. Based only on sketchy descriptions of the telescope, invented in the Netherlands in 1608, Galileo made one with about 3x magnification, and then made improved models up to about 32x.
In the week of January 7, 1610 Galileo discovered three of Jupiter's four largest satellites (moons): Io, Europa, and Callisto. Later astronomers overruled Galileo's naming of these objects, changing his originally named Medicean stars (after his patrons, the Medici) to Galilean satellites.
From September 1610 Galileo observed that Venus exhibited a full set of phases similar to that of the Moon. The heliocentric model of the solar system developed by Copernicus predicted that all phases would be visible since the orbit of Venus around the Sun would cause its illuminated hemisphere to face the Earth when it was on the opposite side of the Sun and to face away from the Earth when it was on the Earth-side of the Sun. Galileo's observations of the phases of Venus proved that it orbited the Sun and lent support to (but did not prove) the heliocentric model.
Galileo was one of the first Europeans to observe sunspots, although there is evidence that Chinese astronomers had done so long before. A dispute over priority in the discovery of sunspots led Galileo to a long and bitter feud with Christoph Scheiner;
Galileo was also the first to report lunar mountains and craters, whose existence he deduced from the patterns of light and shadow on the Moon's surface.
Galileo observed the Milky Way, previously believed to be nebulous, and found it to be a multitude of stars packed so densely that they appeared to be clouds from Earth.
Galileo observed the planet Neptune in 1612, but did not realize that it was a planet and took no particular notice of it.
Galileo, Kepler, and theories of tides
Galileo never accepted Kepler's elliptical orbits of the planets, despite Kepler's tremendous amount of data collected by Tycho Brahe, considering the circle a "perfect" shape.
Galileo attributed tides to momentum, as opposed to Kepler's theories which used the moon as a cause. this had to wait for the work of Newton.) Galileo stated in his Dialogue that, if the Earth spins on its axis and is traveling at a certain speed around the Sun, parts of the Earth must travel "faster" at night and "slower" during the day.
If his theory were correct, there would be only one high tide per day at noon. Galileo and his contemporaries were aware of this inadequacy because there are two daily high tides at Venice instead of one, and they travel around the clock. But Galileo dismissed this anomaly as the result of several secondary causes, including the shape of the sea, its depth, and other things. Against the assertion that Galileo was deceptive in making these arguments, Albert Einstein developed the opinion that Galileo developed his "fascinating arguments" and accepted them uncritically out of a desire for physical proof of the motion of the Earth (Einstein, 1952).
The noted author Arthur Koestler, in his book 'The Sleepwalkers', argued that Galileo was grossly unscientific and dishonest in his methods, and rarely gave credit where due. By the standards of his own time, Galileo was often willing to change his views in accordance with observation. Galileo's perceived dishonesty, then, is not abnormal.
Physics
Galileo's theoretical and experimental work on the motions of bodies, along with the largely independent work of Kepler and René Descartes, was a precursor of the Classical mechanics developed by Sir Isaac Newton.
One of the most famous stories about Galileo is that he dropped balls of different masses from the Leaning Tower of Pisa to demonstrate that their time of descent was independent of their mass (excluding the limited effect of air resistance). Though the story of the tower first appeared in a biography by Galileo's pupil Vincenzo Viviani, it is not now generally accepted as true. However, Galileo did perform experiments involving rolling balls down inclined planes, one of which is in Florence, called the bell and ball experiment, which proved the same thing: falling or rolling objects (rolling is a slower version of falling, as long as the distribution of mass in the objects is the same) are accelerated independently of their mass. (Although Galileo was the first person to demonstrate this via experiment, he was not — contrary to popular belief — the first to argue that it was true.
He determined the correct mathematical law for acceleration: the total distance covered, starting from rest, is proportional to the square of the time (). Galileo's Principle of Inertia stated: "A body moving on a level surface will continue in the same direction at constant speed unless disturbed."
Galileo also noted that a pendulum's swings always take the same amount of time, independently of the amplitude. While Galileo believed this equality of period to be exact, it is only an approximation appropriate to small amplitudes. It is good enough to regulate a clock, however, as Galileo may have been the first to realize. (See Technology below)
In the early 1600s, Galileo and an assistant tried to measure the speed of light. Galileo would open his shutter, and, as soon as his assistant saw the flash, he would open his shutter. At a distance of less than a mile, Galileo could detect no delay in the round-trip time greater than when he and the assistant were only a few yards apart.
Galileo is lesser known for, yet still credited with being one of the first to understand sound frequency.
In his 1632 Dialogue Galileo presented a physical theory to account for tides, based on the motion of the Earth.
Galileo also put forward the basic principle of relativity, that the laws of physics are the same in any system that is moving at a constant speed in a straight line, regardless of its particular speed or direction.
Mathematics
While Galileo's application of mathematics to experimental physics was innovative, his mathematical methods were the standard ones of the day. but by the end of Galileo's life it was being superseded by the algebraic methods of Descartes.
Galileo produced one piece of original and even prophetic work in mathematics: Galileo's paradox, which shows that there are as many perfect squares as there are whole numbers, even though most numbers are not perfect squares.
Technology
Galileo made a few contributions to what we now call technology as distinct from pure physics, and suggested others. This is not the same distinction as made by Aristotle, who would have considered all Galileo's physics as techne or useful knowledge, as opposed to episteme, or philosophical investigation into the causes of things.
In 1595–1598, Galileo devised and improved a "Geometric and Military Compass" suitable for use by gunners and surveyors.
About 1606–1607 (or possibly earlier), Galileo made a thermometer, using the expansion and contraction of air in a bulb to move water in an attached tube.
In 1609, Galileo was among the first to use a refracting telescope as an instrument to observe stars, planets or moons.
In 1610, he used a telescope as a compound microscope, and he made improved microscopes in 1623 and after.
In 1612, having determined the orbital periods of Jupiter's satellites, Galileo proposed that with sufficiently accurate knowledge of their orbits one could use their positions as a universal clock, and this would make possible the determination of longitude.
In his last year, when totally blind, he designed an escapement mechanism for a pendulum clock.
He created sketches of various inventions, such as a candle and mirror combination to reflect light throughout a building, an automatic tomato picker, a pocket comb that doubled as an eating utensil, and what appears to be a ballpoint pen.
Church controversy
Psalms 93:1; Galileo defended heliocentrism, and claimed it was not contrary to those Scripture passages.
By 1616 the attacks on Galileo had reached a head, and he went to Rome to try to persuade the Church authorities not to ban his ideas. The decree did not prevent Galileo from hypothesizing heliocentrism. For the next several years Galileo stayed well away from the controversy.
He revived his project of writing a book on the subject, encouraged by the election of Cardinal Barberini as Pope Urban VIII in 1623. Barberini was a friend and admirer of Galileo, and had opposed the condemnation of Galileo in 1616.
Pope Urban VIII personally asked Galileo to give arguments for and against heliocentrism in the book, and to be careful not to advocate heliocentrism. He made another request, that his own views on the matter be included in Galileo's book. Only the latter of those requests was fulfilled by Galileo. To add insult to injury, Galileo put the words of Pope Urban VIII into the mouth of Simplicius. Most historians agree Galileo did not act out of malice and felt blindsided by the reaction to his book. Galileo had alienated one of his biggest and most powerful supporters, the Pope, and was called to Rome to explain himself.
With the loss of many of his defenders in Rome because of Dialogue Concerning the Two Chief World Systems, Galileo was ordered to stand trial on suspicion of heresy in 1633.
After a period with the friendly Ascanio Piccolomini (the Archbishop of Siena), Galileo was allowed to return to his villa at Arcetri near Florence, where he spent the remainder of his life under house arrest. It was while Galileo was under house arrest when he dedicated his time to one of his finest works, Two New Sciences. As a result of this work, Galileo is often called, the "father of modern physics."
Galileo was reburied on sacred ground at Santa Croce in 1737. He was formally rehabilitated in 1741, when Pope Benedict XIV authorized the publication of Galileo's complete scientific works (a censored edition had been published in 1718), and in 1758 the general prohibition against heliocentrism was removed from the Index Librorum Prohibitorum. On 31 October 1992, Pope John Paul II expressed regret for how the Galileo affair was handled, as the result of a study conducted by the Pontifical Council for Culture.
In modern scientific terms, we consider Galileo's views on heliocentricity to be no fundamental advance. The heliocenticity model that Galileo presented was no more accurate than the Tychonic system model, the main competing theory at the time. Today, we know the Sun is no more the center of the universe than the Earth is, as it has its own orbit in the Milky Way Galaxy, just like the Galilean moons of Jupiter have orbits around Jupiter while Jupiter orbits the Sun.
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