Encyclopedia
Galileo Galilei was an
Italian physicist,
astronomer, astrologer and
philosopher who is closely associated with the scientific revolution. His achievements include improvements to the
telescope, a variety of astronomical observations, the and laws of motion, and effective support for
Copernicanism. He has been referred to as the "father of modern
astronomy," as the "father of modern
physics," and as the "father of
science."
The work of Galileo is considered to be a significant break from that of
Aristotle. In addition, his conflict with the
Roman Catholic Church is taken as a major early example of the conflict of authority and freedom of thought, particularly with
science, in
Western society.
Biographical sketch
Galileo was born in
Pisa, in the
Tuscany region of
Italy, on February 15 1564. He was the son of Vincenzo Galilei, a mathematician and musician born in Florence in 1520, and Giulia Ammannati. Galileo was their first child out of seven.
Galileo was tutored from a very young age. Later, he attended the
University of Pisa but was forced to cease his study there for financial reasons. However, he was offered a position on its faculty in 1589 and taught mathematics. Soon after, he moved to the
University of Padua and served on its faculty, teaching
geometry, mechanics, and
astronomy until 1610. During this time he explored science and made many significant discoveries.
Although he was a devout Catholic, Galileo fathered three children out of wedlock: two daughters and one son. All were the children of Galileo and Marina Gamba. Because of their illegitimate birth, both girls were sent to the convent of San Matteo in Arcetri at early ages.
- Virginia who took the name Maria Celeste upon entering a convent. 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.
- Livia took the name Suor Arcangela, she was sick for most of her life at the convent.
- Vincenzio was later legitimized and married Sestilia Bocchineri.
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 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 , which was approved and published in 1623. In 1624, he developed the first known example of the
microscope. In 1630, he returned to Rome to apply for a license to print the
Dialogue Concerning the Two Chief World Systems, published in
Florence in 1632. In October of that year, however, he was ordered to appear before the Holy Office in Rome. The court issued a sentence of condemnation and forced Galileo to abjure. As a result, he was confined in
Siena and eventually, in December 1633, he was allowed to retire to his villa in
Arcetri. In 1634, he was deprived of the support of his beloved daughter, Sister Maria Celeste , who died prematurely. In 1638, almost totally blind, Galileo published his final book,
Two New Sciences, in
Leiden. He died in
Arcetri on January 8, 1642, in the company of his student
Vincenzo Viviani.
Scientific methods
To the pantheon of the scientific revolution, Galileo Galilei takes a high position because of his pioneering use of quantitative experiments with results analyzed mathematically. There was no tradition of such methods in European thought at that time; 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. These observations were in the Pythagorean tradition of music, well-known to instrument makers, that whole-number mathematical relationships define harmoneous scales. 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 the idea that "the language of God is mathematics." This was a sharp break with earlier traditions of science: up until this point, following
Aristotle, logic, not
mathematics had been seen to be the basic intellectual tool of science.
Galileo also contributed to the rejection of blind allegiance to authority or other thinkers in matters of science and to the separation of science from
philosophy or religion. These are the primary justifications for his description as the "father of science".
In the 20th century some authorities, in particular the distinguished French historian of science
Alexandre Koyré, challenged the validity of Galileo's experiments. The experiments reported in
Two New Sciences to determine the law of acceleration of falling bodies, for instance, required accurate measurements of time, which appeared to be impossible with the technology of the 1600s. According to Koyré, the law was arrived at deductively, and the experiments were merely illustrative thought experiments.
Later research, however, has validated the experiments. The experiments on falling bodies were replicated using the methods described by Galileo , 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 .
Galileo showed a remarkably modern appreciation for the proper relationship between mathematics, theoretical physics, and experimental physics. For example:
- He understood the mathematical parabola, both in terms of conic sections and in terms of the square-law.
- He asserted that the parabola was the theoretically-ideal trajectory, in the absence of friction and other disturbances. More remarkably, he stated limits to the validity of this theory, saying that it was appropriate for laboratory-scale and battlefield-scale trajectories. He went on to point out, on theoretical physics grounds, that the parabola could not possibly be correct if the trajectory were so large as to be comparable to the size of the planet.
- He recognized that his experimental data would never agree exactly with any theoretical or mathematical form, because of the imprecision of measurement, irreducible friction, and other factors.
Due to the merit of his works, Einstein called Galileo the "father of modern science."
Astronomy
Contributions
That Galileo invented the
telescope is a popular misconception. However, he improved the device, was one of the first to use it to observe the sky, and for a time was one of very few people able to construct one good enough for that purpose. 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. On August 25 1609, he demonstrated his first telescope to
Venetian lawmakers. His work on the device also made for a profitable sideline with merchants who found it useful for their shipping businesses. He published his initial telescopic astronomical observations in March 1610 in a short treatise entitled
Sidereus Nuncius is a short treatise published in Latin [i] by Galileo Galilei [i] in March 1610 [i] ...
.
On January 7 1610 Galileo discovered three of
Jupiter's four largest
satellites : Io, Europa, and Callisto. He discovered
Ganymede four nights later. He noted that the moons would appear and disappear periodically, an observation which he attributed to their movement behind Jupiter, and concluded that they were orbiting the planet. He made additional observations of them in 1620. Later astronomers overruled Galileo's naming of these objects, changing his originally named
Medicean stars to
Galilean satellites. The demonstration that a planet had smaller planets orbiting it was problematic for the orderly, comprehensive picture of the
geocentric model of the universe, in which everything circled around the
Earth.
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. In contrast, the
geocentric model of
Ptolemy predicted that only crescent and new phases would be seen, since Venus was thought to remain between the Sun and Earth during its orbit around the Earth. Galileo's observations of the phases of Venus proved that it orbited the Sun and lent support to 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. He also reinterpreted a sunspot observation from the time of
Charlemagne, which formerly had been attributed to a transit of Mercury. The very existence of sunspots showed another difficulty with the unchanging perfection of the heavens as assumed in the older philosophy. And the annual variations in their motions, first noticed by Francesco Sizi, presented great difficulties for both the geocentric system and that of
Tycho Brahe. A dispute over priority in the discovery of sunspots led Galileo to a long and bitter feud with Christoph Scheiner; in fact, there is little doubt that both of them were beaten by David Fabricius and his son Johannes.
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. He even estimated the mountains' heights from these observations. This led him to the conclusion that the Moon was "rough and uneven, and just like the surface of the Earth itself," rather than a perfect
sphere as Aristotle had claimed.
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. He also located many other stars too distant to be visible with the naked eye.
Galileo observed the planet
Neptune in 1612, but did not realize that it was a planet and took no particular notice of it. It appears in his notebooks as one of many unremarkable dim stars.
Modern claims of scientific errors and misconduct
Although Galileo is generally considered one of the first modern scientists, as evidenced by his position in the sunspot controversy, he is often said to have arrogantly considered himself to be the sole proprietor of the discoveries in astronomy.
Furthermore, he never accepted
Kepler's elliptical orbits for the planets, holding to the circular orbits of Copernicus, which still employed
epicycles to account for irregularities in planetary motions. For this reason, Galileo's "heliocentric" theory is incorrect, since there is, by definition, no geometric "center" to an elliptical orbit.
Galileo attributed
tides to momentum, despite his great knowledge of the ideas of relative motion and Kepler's better theories using the
Moon as the cause. 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. This is true in the Sun's frame of reference; but it is by no means adequate to explain the tides.
Since this theory was not based on any real scientific observations, many commentators believe Galileo developed the position to justify his own opinion. 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 .
Arthur Koestler argues for the case of Galileo's scientific misconduct in his book
'The Sleepwalkers'. Others argue that it is unfair to hold him to modern "scientific standards" with which he himself was only beginning to experiment. By the standards of his own time, Galileo was often willing to change his views in accordance with observation, as contrasted with a few notable men who refused even to look through their telescopes at celestial objects for fear of what they might see. It may also be argued that all modern scientists filter their observations and beliefs through pre-conceived notions. Although this may appear "dishonest," some of it is actually required for the scientific process to function . 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. He was a pioneer, at least in the European tradition, in performing rigorous experiments and insisting on a
mathematical description of the laws of nature.
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 . This was contrary to what Aristotle had taught: that heavy objects fall faster than lighter ones, in direct proportion to weight. 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. Moreover, Giambattista Benedetti had reached the same scientific conclusion years before, in 1553. However, Galileo did perform
experiments involving rolling balls down
inclined planes, which proved the same thing: falling or rolling objects are
accelerated independently of their mass. .
He determined the correct mathematical law for acceleration: the total distance covered, starting from rest, is proportional to the square of the time . He expressed this law using geometrical constructions and mathematically-precise words, adhering to the standards of the day. He also concluded that objects
retain their velocity unless a force — often friction — acts upon them, refuting the generally accepted Aristotelian hypothesis that objects "naturally" slow down and stop unless a force acts upon them . Galileo's Principle of Inertia stated: "A body moving on a level surface will continue in the same direction at constant speed unless disturbed." This principle was incorporated into
Newton's laws of motion .
Galileo also noted that a
pendulum's swings always take the same amount of time, independently of the
amplitude. The story goes that he came to this conclusion by watching the swings of the bronze chandelier in the cathedral of Pisa, using his pulse to time it. 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.
In the early 1600s, Galileo and an assistant tried to measure the
speed of light. They stood on different hilltops, each holding a shuttered
lantern. 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. While he could reach no conclusion on whether light propagated instantaneously, he recognized that the distance between the hilltops was perhaps too small for a good measurement.
Galileo is lesser known for, yet still credited with being one of the first to understand sound frequency. After scraping a chisel at different speeds, he linked the pitch of sound to the spacing of the chisel's skips .
In his 1632 Dialogue Galileo presented a physical theory to account for
tides, based on the motion of the Earth. If correct, this would have been a strong argument for the reality of the Earth's motion. His theory gave the first insight into the importance of the shapes of ocean basins in the size and timing of tides; he correctly accounted, for instance, for the negligible tides halfway along the
Adriatic Sea compared to those at the ends. As a general account of the cause of tides, however, his theory was a failure. Kepler and others correctly associated the Moon with an influence over the tides, based on empirical data; a proper physical theory of the tides, however, was not available until Newton.
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. Hence, there is no absolute motion or absolute rest. This principle provided the basic framework for Newton's laws of motion and is the infinite speed of light approximation to
Einstein's
special theory of relativity.
Mathematics
While Galileo's application of mathematics to experimental physics was innovative, his mathematical methods were the standard ones of the day. The analyses and proofs relied heavily on the Eudoxian theory of proportion, as set forth in the fifth book of
Euclid's Elements. This theory had become available only a century before, thanks to accurate translations by
Tartaglia and others; 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. Such seeming contradictions were brought under control 250 years later in the work of
Georg Cantor.
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. This expanded on earlier instruments designed by
Niccolo Tartaglia and
Guidobaldo del Monte. For gunners, it offered, in addition to a new and safer way of elevating
cannons accurately, a way of quickly computing the charge of
gunpowder for
cannonballs of different sizes and materials. As a geometric instrument, it enabled the construction of any regular
polygon, computation of the area of any polygon or circular sector, and a variety of other calculations.
About 1606–1607 , 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. This appears to be the
first clearly documented use of the compound microscope.
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. He worked on this problem from time to time during the remainder of his life; but the practical problems were severe. The method was first successfully applied by
Giovanni Domenico Cassini in 1681 and was later used extensively for large land surveys; this method, for example, was used by
Lewis and Clark. .
In his last year, when totally
blind, he designed an
escapement mechanism for a pendulum clock. The first fully operational pendulum clock was made by
Christiaan Huygens in the 1650s.
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
- Main article: Galileo affair
Psalms 93:1 and Psalm 104:5, and Ecclesiastes 1:5 speak of the "firm" and "established" position of the earth. Galileo defended
heliocentrism, and claimed it was not contrary to those Scripture passages. He took Augustine's position on Scripture: not to take every passage too literally, particularly when the scripture in question is a book of poetry and songs, not a book of instructions or history. The writers of the Scripture wrote from the perspective of the terrestrial world, and from that vantage point the sun does rise and set. In fact, it is the earth's rotation which gives the impression of the sun in motion across the sky.
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. In the end,
Cardinal Bellarmine, acting on directives from the Inquisition , delivered him an order not to "hold or defend" the idea that the Earth moves and the Sun stands still at the center. 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. The book, Dialogue Concerning the Two Chief World Systems, was published in 1632, with formal authorization from the
Inquisition and papal permission.
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. Whether unknowingly or deliberate, Simplicius, the defender of the Aristotelian Geocentric view in
Dialogue Concerning the Two Chief World Systems, was often caught in his own errors and sometimes came across as a fool. This fact made
Dialogue Concerning the Two Chief World Systems appear as an advocacy book; an attack on Aristotelian geocentrism and defense of the Copernican theory. 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. However, the Pope did not take the public ridicule lightly, nor the blatant bias. 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. The sentence of the Inquisition was in three essential parts:
- Galileo was required to recant his heliocentric ideas; the idea that the Sun is stationary was condemned as "formally heretical".
- He was ordered imprisoned; the sentence was later commuted to house arrest.
- His offending Dialogue was banned; and in an action not announced at the trial and not enforced, publication of any of his works was forbidden, including any he might write in the future.
After a period with the friendly Ascanio Piccolomini , 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. This book has received high praise from both
Sir Isaac Newton and
Albert Einstein. 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 , and in 1758 the general prohibition against heliocentrism was removed from the
Index Librorum Prohibitorum is a list of publications which the Catholic Church [i] ...
. 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. Stellar
parallax, the first evidence from outside the solar system that the Earth does indeed move, would be not observed until the 1838 . 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. The Catholic Church held to the prevailing theological opinion of the day, which was that the Earth was the center of the universe.
Galileo's writings
- Two New Sciences 1638 Lowys Elzevir Leiden
- Letters on Sunspots 1613
- The Assayer 1623
- Dialogue Concerning the Two Chief World Systems 1632
- The Starry Messenger is a short treatise published in Latin [i] by Galileo Galilei [i] in March 1610 [i] ...
1610 Venice - Letter to Grand Duchess Christina 1615
Writings on Galileo
