Galileo Galilei (1564-1642)

Quotation

I do not feel obliged to believe that the same God who has endowed us with sense, reason, and intellect has intended us to forgo their use.

Books

Please browse our Amazon list of titles about Galileo Galilei. For rare and hard to find works we recommend our Alibris list of titles about Galileo Galilei.

Research

Lecture: The Starry Message
COPAC UK: Galileo
Library of Canada: Galileo
Library of Congress: Galileo
Other Library Catalogs: Galileo

Biographical

Galileo Galilei, Italian philosopher, physicist and astronomer, was born in Pisa on February 15, 1564 and died January 8, 1642. He has been called the father of modern astronomy, and along with Bacon was one of the pioneers of the scientific method.

Scientific achievements

Galileo was one of the first people to use a telescope to observe the sky. He acquired a 10x telescope and promptly made an improved 20x one. Galileo discovered the four largest satellites of Jupiter. He also observed that the planet Venus exhibited a full set of "phases" like the Moon. Both of these discoveries lent support to the heliocentric model of the solar system developed by Copernicus. (see below) He was the first westerner to report sunspots (there is evidence that Chinese astronomers had already observed them). He also argued from the occultation of stars (visible only through a telescope) that the Moon is not a perfect sphere (like a billiard ball) but has mountains. His experimental work in dynamics paved the way for Kepler's and Newton's laws of motion, and he is often credited with being one of the first scientists to fully exploit the experimental method and to insist on a mathematical description of the laws of nature. His study of balls rolling down inclined planes convinced him that falling objects are accelerated independent of their mass, and that objects retain their velocity unless a force acts on them. Galileo also described that a pendulum's swings always take the same amount of time, independent of the amplitude, a discovery which made later precise clocks possible. Galileo wrote several long books which were circulated widely, at least outside of Italy, although several of Galileo's inventions exist today only in his notes and drawings. He created sketches of imaginary devices such as a candle and mirror combination to reflect light through an entire home, an automatic tomato picker, a pocket comb that doubled as an eating utensil, and what appeared to be a crude form of ballpoint pen.

Church Controversy

Galileo was a devout Catholic, yet his writings on the Copernican model of the universe (incorporating a heliocentric, or sun-centered solar system) disturbed the Church, which, like most everyone else at the time, held to a Ptolemaic or Aristotelian Earth-centered theory of the universe. Church fathers argued extensively that any other view would contradict scripture. The late-nineteenth and early twentieth century historian Andrew Dickson White, writing from an anti-clerical perspective, wrote:

The war became more and more bitter. The Dominican Father Caccini preached a sermon from the text, "Ye men of Galilee, why stand ye gazing up into heaven?" and this wretched pun upon the great astronomer's name ushered in sharper weapons; for, before Caccini ended, he insisted that "geometry is of the devil," and that "mathematicians should be banished as the authors of all heresies." The Church authorities gave Caccini promotion. Father Lorini proved that Galileo's doctrine was not only heretical but "atheistic," and besought the Inquisition to intervene. The Bishop of Fiesole screamed in rage against the Copernican system, publicly insulted Galileo, and denounced him to the Grand-Duke. The Archbishop of Pisa secretly sought to entrap Galileo and deliver him to the Inquisition at Rome. The Archbishop of Florence solemnly condemned the new doctrines as unscriptural; and Paul V, while petting Galileo, and inviting him as the greatest astronomer of the world to visit Rome, was secretly moving the Archbishop of Pisa to pick up evidence against the astronomer. But by far the most terrible champion who now appeared was Cardinal Bellarmin, one of the greatest theologians the world has known. He was earnest, sincere, and learned, but insisted on making science conform to Scripture. The weapons which men of Bellarmin's stamp used were purely theological. They held up before the world the dreadful consequences which must result to Christian theology were the heavenly bodies proved to revolve about the sun and not about the earth. Their most tremendous dogmatic engine was the statement that "his pretended discovery vitiates the whole Christian plan of salvation." Father Lecazre declared "it casts suspicion on the doctrine of the incarnation." Others declared, "It upsets the whole basis of theology. If the earth is a planet, and only one among several planets, it can not be that any such great things have been done specially for it as the Christian doctrine teaches. If there are other planets, since God makes nothing in vain, they must be inhabited; but how can their inhabitants be descended from Adam? How can they trace back their origin to Noah's ark? How can they have been redeemed by the Saviour?" Nor was this argument confined to the theologians of the Roman Church; Melanchthon, Protestant as he was, had already used it in his attacks on Copernicus and his school. [1]

Despite his continued insistence that his work in the area was purely theoretical, despite his strict following of the church protocol for publication of works (which required prior examination by church censors and subsequent permission), and despite his close friendship with Maffeo Barberini who later became Pope Urban VIII and presided throughout the ordeal, Galileo was forced to recant his views repeatedly and was put under life-long house arrest (1633-1642).

The Inquisition had rejected earlier pleas by Galilei to postpone or relocate the trial because of his ill health. At a meeting presided by Pope Urban VIII, the Inquisition decided to notify Galilei that he either had to come to Rome or that he would be arrested and brought there in chains. After two weeks in quarantine, Galilei was detained at the comfortable residence of the Tuscan ambassador, as a favor to the influential Grand Duke Ferdinand II de' Medici. In April 1633 he was formally interrogated by the Inquisition. He was not imprisoned in a dungeon cell, but detained in a room in the offices of the Inquisition for 22 days. On June 22, 1633, the Roman Inquisition started its trial against Galilei, who was then 69 years old and pleaded for mercy, pointing to his "regrettable state of physical unwellness". Threatening him with torture, imprisonment and death on the stake, the show trial forced Galileo to "abjure, curse and detest" his work and to promise to denounce others who held his prior viewpoint. Galileo did everything the church requested him to do. That the threat of torture and death Galileo was facing was a real one had been proven by the church in the earlier trial against Giordano Bruno, who was burned at the stake in 1600 for holding a naturalistic view of the universe.

Galileo was put under life-long house arrest, for the most part (1634-1642) in his own villas in Arcetri and Florence. Because of a painful hernia, he requested permission to consult physicians in Florence, which was denied by Rome, warning that further such requests would lead to imprisonment. Under arrest, he was forced to recite penitentiary psalms regularly, and his social contacts were highly restricted, but he was allowed to continue his less controversial research and publish under strict rules of censorship. He went totally blind in 1638 (his petition to the Inquisition to be released was rejected, but he was allowed to move to his house in Florence where he was closer to his physicians). His Dialogue was put on the Index librorum prohibitorum, a black list of banned books, until 1822. [2]

According to Andrew Dickson White and many of his colleagues, Galileo's experiences demonstrate a classic case of a scholar forced to recant a scientific insight because it offended powerful, conservative forces in society: for the church at the time, it was not the scientific method that should be used to find truth -- especially in certain areas -- but the doctrine as interpreted and defined by church scholars, and this doctrine was defended with torture, murder, deprivation of freedom, and censorship.

More recently, the viewpoints of White and his colleagues have become less-generally accepted by the academic community, partially because White wrote from a perspective that Christianity is a destructive force. This attitude can also be seen in the works of Bertolt Brecht, whose play about Galileo is one of the chief sources for popular knowledge on the scientist. Moreover, deeper examination of the primary sources for Galileo and his trial shows that claims of torture and deprivation were likely exagerrated. Dava Sobel's Galileo's Daughter offers a different set of insights into Galileo and his world, in large part through the private correspondence of Maria Celeste, the daughter of the title, and her father.

In 1992, 359 years after the Galileo trial, Pope John Paul II issued an apology, lifting the edict of Inquisition against Galileo: "Galileo sensed in his scientific research the presence of the Creator who, stirring in the depths of his spirit, stimulated him, anticipating and assisting his intuitions."

References:

[1] Andrew Dickson White: A History of the Warfare of Science with Theology in Christendom. New York 1898. Public domain text, online version.

[2] Hal Hellman: Great Feuds in Science. Ten of the Liveliest Disputes Ever. New York: Wiley, 1998. [This article is licensed under the GNU Free Documentation License and uses material adapted in whole or in part from the Wikipedia article on Galileo Galilei.]


The Starry Message
Russell McNeil, PhD (Copyright 2005)
[Logos Exclusive]

Over the course of his lifetime more or less single-handedly reinvented natural philosophy -- the science of physics. The burden of doing that -- reinventing physics -- was required to make that that model there -- the Copernican sun-centered universe -- that he so dearly loved -- some badly needed support. As elegant and sensible as that model seemed to Galileo -- and Copernicus before him -- and Aristarchus before him -- the dam thing just would not fly.

Yet, Galileo grew quite attached to this radical world view--an attachment that was to get him in a whole heap of trouble in later years--but his attachment, trust, belief, faith, in this new view--needed justification. Physics, before Galileo, had advanced little since Aristotle had basically written the book on Physics 2,000 years earlier. Aristotle had disallowed that sort of thing by virtue of the ways that it has attributed and defined motion--a dusty, musty, and rusty hodge podge of concepts which had kept the heavens in heaven and the earth at the centre of the universe for those two millennia. Aristotle was in Christian eyes a pagan philosopher -- of course -- but, the early Christian church -- in a legitimate and frankly liberal response to reconcile science with scripture --- had assimilated much of Aristotle's cosmology and physics centuries before. Aristotle's cosmology had by Galileo's day merged into the very core of Christian doctrine.

Galileo Galilei was born in Pisa in 1564--the same year as William Shakespeare and the same year Michelangelo died. He was the son of Vincenzo Galilei, well known for his studies of music, and Giulia Ammannati. Galileo's family moved to Florence when he was 10 in 1574. It is helpful to reflect a moment on those early years and the family atmosphere that contributed to the formation of the character of the man.

The same year the young Galileo began his life in Florence, his father Vincenzio had formed a little band of renegade artists, musicians, literati, scholars, book-lovers and scientists, the Florentine Camerata, an amazingly inquisitive group of revolutionary activists and musical amateurs who met to discuss literature, science and the arts. In fact, their work is linked closely with the development of opera. Unknowingly, the Camerata became the crucible not only of the opera but of modern science as well! The boy Galileo was often witness to these free-wheeling, highly argumentative and experimentally based weekly inquiries. It was there Galileo learned how to learn.

The musical ideas emerging from the crucible of this passionate group included the exploration of new musical theories, theories that were often tested against a backdrop of careful experiment. Vincenzio was a skilled lutenist and exponent of new music. He was trying to break out of medieval form by forging ties with the Greek past while pushing through to the future, a future that was to be the renaissance in music. The most important treatise on music that emerged from this group was Vincenzio's Diologo della musica. This work is important not only for its contribution to the musical theory of the Renaissance but because it contributed to the development of experimental science. The knowledge of mathematics and the use of experiment which is evidenced in his writings suggest important early influences on Galileo.

Vincenzio, influenced Galileo in one other important way -- his father was a Renaissance thinker in music, mathematics, and classical languages--true, but he also had a biting wit and sarcasm -- and an independent judgment which led him -- Vincenzio -- to reject the principle of authority which formed the basis for so much of the knowledge of medieval thinking.

Galileo's mother Giulia Ammannati, was equally influential. She has been described as: sharp and quarrelsome, prone to polemical aggressiveness, impatient, and prone to sudden fits of anger which she expressed in derisive diatribes. That maternal role modeling -- honed by a lifetime of practice -- expresses itself the in mature Galileo's highly effective and frankly dangerous writing style -- evident particularly in his later works. The style became synonymous with an attitude that would not suffer fools; would accept nothing short of the truth -- and above all rejected authority. A rebel with a cause!

Like many modern fathers, Vincencio had ambitions for his son. He wanted Galileo to study medicine. The dutiful now 17 year old Galileo -- registered in medicine at the University of Pisa in 1581. But Galileo loathed the Galenist medicine -- as then taught and practiced -- bored Galileo. Galileo preferred reading Aristotle and Plato -- and was especially awed by the works of Euclid and Archimedes. The clear, crisp, deductive, mechanical, mathematical precision was more to his liking.

Galileo dropped out -- he abandoned medicine and at 21 returned to Florence at with no degree and no prospects. No matter. Galileo had his wits -- became self taught -- wrote a tiny scientific work called The Little Balance a modified invention designed to measure specific gravity, and, through effort and ambition, after four years, managed to land himself a teaching job, without a degree, back at Pisa, the same university he abandoned as a student.

He was now 25. He later moved Pisa to the University of Padua where he remained until 1610 when he published this work, the Starry Message. During these years he carried out studies and experiments in mechanics. He also invented a thermoscope.

This device emerged from Galileo's contention that heat and cold were not -- as Aristotle would have them -- fundamental qualities that combine with wet and dry to form earth, air, water and fire. For Galileo heat was an accidental property of matter. Heat might be in matter but matter was not defined by heat. Heat could thus be measured by the degree or degrees of its effects. In this understanding cold could be seen as a measure of heat -- very little or none at all. When heat entered fluids or gases they expanded. When heat was removed, they contracted.

Galileo's approach to motion was quite similar. Motion -- like heat -- was also an accidental property -- not something inherent to the thing as Aristotle's physics demanded. Circular motion and straight line motion for Aristotle were not accidentals. They were desires determined by the nature of matter. Earth -- for example -- could never move in a circle because it had no natural desire to do so. Stars could never fall to the earth or move in straight lines because, as quintessence, they had only one desire -- to move in circles.

The idea of somehow allowing earth or the Earth to move in circles naturally (i.e. Heliocentric model) -- as Copernicus' new system required, or combining straight line motion with circular motion as Galileo's later explanations of projectile motion required (toss chalk) -- would be impossible under Aristotle's physics. Such a combination of straight and circular motion would be possible only for an element that was a compound of say earth and quintessence -- and such combinations were not permitted.

Galileo's reflections on motion were carefully argued in the Dialogue on the two chief world systems. Although promised in the Starry Message in 1610, the Dialogue itself was not published until 1632 when Galileo was in his 69th year. In October of that year Galileo was summoned by the Holy Office in Rome. The tribunal there passed a sentence condemning him for his ideas and compelled Galileo to solemnly renounce his theory. He spent his remaining years under house arrest where he completed one more massive work, the Dialogue on Two New Sciences. By 1638 Galileo was completely blind. He died in 1642, the same year Isaac Newton was born. In 1992 -- just six years ago, after a 13 year re-examination of the Galileo Affair, the Roman Catholic Church admitted it had erred -- acknowledged -- among other mistakes -- that false evidence had been proffered in Galileo's trial, and finally reversed the conviction that had taken place 350 years before.

But the critical moment in this whole story -- a story that gave birth to modern times -- was the publication of his little book the Starry Message. The Starry Message is not a story about motion -- it is rather a document of observation: a summary of a short series of observations in which Galileo uses his newly invented celestial spyglass or telescope. Galileo praises the device in the first paragraph of this book. It -- this artifact, this technology -- is as great in excellence as the things he has begun to observe! Why is this man in love with his technology? He says, all these things were discovered with the aid of a spyglass I devised, after first being illuminated by divine grace.

What Galileo euphemistically calls divine grace is his unique understanding of how basic principles of nature can be harnessed to enhance the human capacity for reason. Galileo is a Platonist. He is in love with reason. His fundamental goal is to illuminate the understanding: to seek the good. How to we get there? We get there through reason. Is reason aided by sense? Obviously it must be. It may be that the natural world is but a reflection of the divine, but to aid in the approach to the divine, it helps to have a clearer picture of the material world. Is human sense limited? Of course it is. Will technology extend the sense? Obviously it does. Is the telescope an extension of the sense of sight? Certainly it is. The telescope -- this sense extension -- may never peer across Plato's divided line. But it can get us a lot closer. And that I think is what Galileo is ultimately trying to do: It seems to me to be a matter of no small importance to have ended the dispute about the Milky Way by making its nature manifest to the very senses as well as to the intellect.

How did Galileo harness basic principles to develop this extension of sense and reason? It was rooted in an ancient metaphysical principle: nature does things simply -- nature is economic. But how does this economy of nature apply to the idea of light? A Greek named Heliodorus developed the idea in antiquity to explain the apparent bending of light in water. The path light does follow is the most economic path that light does follow.

This simple but powerful notion -- known in Physics today as the Principle of Least Time has all the earmarks of an evident truth. Applied to nature it works as Heliodorus showed us. A simple technology like the lens can harness the curvature of the surface of glass in such a way that light passing through the lens from distant objects will converge to form images onto a plane located at a geometrically determined distance from the lens called the focal length. We know that is so because that is exactly how the eye works. Note here that the function of the lens depends on both the principle of economy and the geometry of the lens. Of course the very geometry defining the shape of the lens is -- like the principle of least time -- something Galileo would see as yet another manifestation of a divine truth. Euclid was one of Galileo's heroes.

When Galileo trained this divinely inspired extension of sense onto the heavens he was awestruck. The heavens opened up. The skies were filled with an infinitude of never before seen stars. The moon's surface was rough and pitted with ridges and mountains soaring miles above the lunar surface. This was proof incontrovertible that the heavens -- like the earth were made of the same stuff. The earth was not the sink of all dull refuse of the universe, as the older cosmologies would have it. The earth was -- like this beautiful moon -- a splendid and wandering body. If the heavens were divine in character -- so now was the Earth thanks to the spin Galileo places with this interpretation.

When Galileo turned his attention to the planet Jupiter, on the 7th day of January in the year 1610 at the first hour of night, he was in for a surprise. In a carefully documented series of observations over two months he witnessed an astonishing sight. Jupiter had first three and then four companion starlets -- moons as they are now called -- Galileo named them the Medicean stars. Here they are today: Io, Europa, Ganymede and Callisto.


This was direct sensible evidence that the earth was not alone in the universe as the single centre of all circular motion. It confirmed that the sort of system Copernicus had proposed was indeed possible. But it was still not proof enough that the earth revolved about the sun like these planets about Jupiter.

That evidence came later. When Galileo trained his telescope on the planet Venus he discovered that Venus in its motions displayed phases and those phases were identical to the phases of the moon. This observation could only be explained by a Copernican model. The Aristotelian model would now account for all of the phases of Venus.

How was this work received? Ironically, the reaction to Galileo's discoveries was not what popular history would have us expect. Two types of responses began to emerge. From the Church -- the response was cautious but generally favorable. The church in this era had vested responsibility for the investigation of scientific matters in the hands of an Institution in Rome known as the Roman School -- run by the Catholic order called the Jesuits. Galileo was very interested in ensuring that the Jesuits were fully informed of his discoveries and that they had opportunities to see what he saw. And they did. In Rome, one of the leading theologians of the day, Cardinal Robert Bellarmine -- himself a Jesuit -- wrote the Roman College and asked them five questions:

2. Was Saturn really composed of three stars?
3. Did Venus really have phases like the moon?
4. Was the moon's surface really rough?
5. Did Jupiter really have four satellites revolving around it?

The response to Bellarmine's questions in a letter signed by the top four mathematicians and scientists there was yes on all counts except for the moon. On the moon they said that they could not confirm beyond all doubt that its surface was rough, but that they leaned to believing so.

In this same year Galileo traveled to Rome, had a very cordial meeting with the then Pope Paul V, met a man named Maffeo Barbarini -- who was later to succeed Paul V as Pope Urban VIII, and attended an academic assembly at the Roman College in Galileo's Honour to hear presentations about the material contained here and to confirm its observational contents. A large number of church officials attended and there was no coolness at all towards Galileo.

The Jesuits were restrained in openly accepting the Copernican interpretation. They were at the time constrained by a religious obligation to conform to Aristotelian doctrine. However, there was private discussion that a reconciliation of Copernicanism with scripture and theology was possible. As scientists however, the Jesuits were troubled by a very real problem -- of which Galileo was aware -- that the Copernican system was not allowed by then known physical laws. And that was quite understandable.

The problem of reconciliation with scripture was one that could be addressed. After all, it was just such a reconciliation with the literal interpretation of clearly allegorical biblical passages that had moved the church centuries earlier to accept Aristotle in the first place. But the church had not baptized Aristotle completely. Aristotle's idea of incorruptibility, for example, was not a problem. The problem was motion. The theological view at the time went thus: if a biblical passage should be understood as literal -- it ought not to be understood differently. A private and friendly letter to Galileo from a Cardinal Conti in 1612 addressed the problem: he noted that the motion of the Earth was NOT consistent with scripture, but that the motion of the Earth could be reconciled if in those instances the Bible was regarded as using, the language of the common people. He noted however that such a reconciliation should not be done unless it was really necessary.

The other response over the Starry Message came from outside the Church. And this reaction was frankly hostile. The furor began with the academics -- an extraordinarily conservative group or University-based Aristotelian philosophers who began to attack Galileo mercilessly. Worse, it was they -- not the Church -- who brought scripture into the debate. Their philosophic position was bizarre. The man who lead this attack, the University of Padua philosopher Columbe, wrote a treatise in 1611 in which he characterized Galileo's opinions as: rash, dangerous for the faith, and designed to show cleverness rather than to aid philosophy. His philosophical position was twofold: 1: Cite Aristotle as authority, and 2: Reject -- a priori -- anything seen through any telescope. According to a treatise written by Plutarch in antiquity, such images could be nothing other than optical illusions. The academic philosophers simply refused to even look -- although Galileo had invited them personally, in his own words: an infinitude of times. No Jesuit or Cardinal ever refused Galileo's offer to see what he saw.

This debate between the Aristotelians and Copernicans became highly charged and politicized in the ensuing decades. At one point early on Galileo and Columbe were involved in a debate in Florence on the question of why ice floats. Columbe -- ascribing to Aristotle's theory of cold -- argued that ice was of necessity heavier than water -- more dense -- but floated because its flat surface prevented its sinking. Galileo who identified with Archimedes argued that ice floated because it was less dense -- lighter. Galileo won the debate -- one in which the future pope Urban the VIII was actually in attendance and who had sided with Galileo! The humiliation Columbe suffered in this instance led to the formation of an Academic League against Galileo. Galileo's friends called them the pigeons. Sadly, the pigeons were more powerful than Galileo. They were out to get the man -- and eventually -- they did. For two decades they hammered at the theological establishment in Rome -- undermined Galileo's credibility on all fronts. There are many more elements to this story. Galileo's relationships with the Jesuits soured -- not because of science but around mis-communications with a prominent Jesuit named Scheiner over who first documented the sunspots.

History has of course vindicated Galileo and the Church has admitted its error and found a way to reconcile scripture with science. Reason and revelation can not contradict.

As to Galileo's legacy, he will be remembered for much. But for me, Galileo is relevant because he saw technology as an extension of sense; science as an extension of reason; and reason as directed fundamentally towards the seeking of Truth. Galileo also understood the role of the natural philosopher in the scheme of philosophy overall. He knew that science and its discoveries would provoke a profound shift in consciousness. He understood that that shift would provoke a crisis. It is clear in the tone of his writings that he understood that the scientist has a responsibility to be aware of where his reasoning might lead -- and the inevitable consequences that reasoning might have on the moral plane.

I think at the end of the day he was successful. He uncovered new and magnificent and I think eternal truths. The fundamental ideas of conservation and eternal inertial motion, reflected in the idealized swinging pendulum and orbiting Earth reveal fundamental aspects of nature that continue to inform our understanding of the cosmos not only in physical terms but in moral terms as well.

Books from Alibris: Galileo