Cosmological Revolution IV: Galileo

Galileo is one of the most fascinating of the renaissance cosmologists. He made important contributions to physics, especially mechanics, and indeed, he developed a new physics, effectively replacing the old Aristotilean physics as a basis for astronomy. He was important both as an experimentalist and mathematician. Secondly, he made important astronomical discoveries with an invention of his own: the telescope. We have here the introduction of a new technology for the first time in cosmology, other than aids to calculation and representation which had existed before (transits, astrolabes etc.) The telescope would lead to major new discoveries, and for the first time distinguish between the Copernican and Ptolemaic systems observationally. Finally, his life and especially his trial and condemnation by the inquisition, bring out the problem and the complexity of the relation between science and religion, and between scientific freedom and institutional constraints (which is not the same problem).

Galileo's life (1564-1642) overlapped that of Kepler (1571-1630); they were thus contemporaries. Perhaps this is one reason that Galileo did not use Kepler's elliptical orbits: they were still in the process of gestation when he had already begun his career. Galileo (born in Pisa and raised in Florence) initially went to university to study arts and medecine, but chancing upon a lecture on Euclid's geometry, he switched to the study of mathematics. He was soon appointed, at age 25, to a post at Pisa, where he remained some 20 years, during which time he developed his mathematical skills and became a defender (though in private) of Copernicus. He did considerable work on Archimedes mechanics at the same time. It was there that he did his experiments on the free fall of bodies, from the leaning tower in that city, of course. In 1592, he was appointed to a chair at Padua. Galileo's academic career was successful, but he continued to search for new ways to make discoveries, not content to sit back and enjoy his station.

Galileo's Telescopic Observations

In 1609, Galileo was angling for a more prestigious and better paid apointment at Florence, he heard of a new invention: a spy glass, probably first developed in Holland, which allowed the observation of distant objects at sea as if one were close by.

The spy-glass was first described in October of 1608, and within a year news had gotten to Galileo and he adapted the lens system to produce a crude but effective 30x magnification in a telescope. The combination of lens involved a convex objective lens: () which focuses the light rays at a point, and a concave eyepiece lens: )( which spreads the rays to the eyes. This is known as a refracting telescope.

He began his observations in January 1610, in March 1610 pubished his book, the Starry Messenger, detailing the amazing discovery he had made: the moons of Jupiter. Here are his own words: "On the seventh day of Janaury in this present year 1610, at the first hour of the night, when I was viewing the heavenly bodies with a telescope, Jupiter presented itself to me; and because I had prepared a very excellent instrument for myself I perceived... that beside the planet were three starlets, small indeed, but very bright" (D/O of Galileo, p. 51). At first he thought they were part of the stellar background, but their arrangement and brilliance caught his attention.

The sitings could not be interpreted as fixed stars, for at the same time on different nights their positions and brightness (leftmost Jan 12) were different. Galileo continued his nightly observations till early March (2nd). His conclusion was that these must be moons of Jupiter, four in number, and he was able to compute their periods of revolutions. He named them the Medecian planets in honour of his patron.

By this time, Galileo's fame had spread, in part at least on his own doing. Soon after his construction of a telescope, he had hurried to Venice, the major seafaring city, to show his invention. The Venetian senate was impressed by the possible military application, and granted him a life tenure at their university and a big pay increase. But this did not keep Galileo in Venice, and in July 1610, he took up residence as court mathematician and philosopher at Pisa, at the court of Grand Duke Cosimo II de Medici. He desired to be considered as a philosopher as well as mathematician, because of his growing desire to criticize the Aristotilean physics then considered as part of philosophy; the Grand Duke wanted him to calculate artillery paths as well.

The observation of the moons of Jupiter was a blow to the Aristotilean and Ptolemaic world views, still dominant. For now another planet had moons, just like the earth, and four of them. How could this be squared with the privileged place of the earth as the center of the universe. Indeed, as Copernicus had claimed, there was no single center, with the earth and Jupiter now centers of their own, along with the sun. The observation of novas had already pointed to a problem with the old view, now this was confirming and reinforcing that position.

Other observations of Galileo's include:

(1) The phases of Venus. This had been predicted by the Copernican theory, but not observed with the naked eye. On the Ptolemaic model, Venus is between the central earth and the sun, and should not show phases like the moon (only a crescent shape); on the Copernican model, it should, because there are times when the earth and Venus are on opposite sides of the sun (in this case, Venus is far away, but full). These phases were observed and mapped by Galileo, also in 1610.

(2) The "moons" of Saturn, of which Galileo found two, which did not, however, move, as did those of Jupiter. Galileo was puzzled, and sent a brief summary in anagram form (coded) to Kepler, the correct decoding being "I have observed the furthest planet to be triple". The motionless moons were of course the opposite sides of Saturn's rings.

(3) The mountains on the moon. Galileo was able to even calculate their probable height (a few miles, up to five) by measuring the shadows he observed through the telescope.

(4) Many more stars then previously believed in the heavens, in particular because the milky way was now seen to be a mass of many stars.

Galileo's work, The Starry messenger, was published in Venice in 1610. It was subtitled "Revealing great, unusual and remarkable spectacles, opening these to the consideration of every man, and especially of philosophers and astronomers; as Observed by Galileo Gaililei, Gentleman of Florence, Professor of Mathematics in the University of Padua, with the Aid of a Spyglass, lately invented by him, in the surface of the Moon, in innumerable fixed stars, in nebulae, and above all in Four Planets, swiftly revolving about Jupiter at differing distances and periods, and known to no one before the Authro recently perceive dthem and decided that they should be named the Medecean Stars". Books had real subtitles then. Incidently, the term telescope was only coined the year after, in 1611

Another discovery Galileo made was that of spots on the sun. This discovery was made simulaneously by Fabricius in Holland and Scheiner, in Rome, and there was much controversy over priority. In 1613 he published in Rome, History and Demonstrations Concerning Sunspots and their Phenomena. By this time, however, he was already embroiled in the religion/science controversy that would lead to his trial and condemnation.

Galileo on Religion and Science: Letter to Princess Christina

Galileo himself was not opposed to religion. He expressed himself quite clearly on the subject in his 1615 text, Letter to Madame Christina of Lorraine, Grand Duchess of Tuscany, Concerning the Use of Biblical Quotations in Matters of Science. He sets out his view rather clearly from the start: "I hold the sun to be situated motionless in the center of the revoluton of the celestial orbs while the earth rotates on its axis and revolves about the sun." (p. 177). There is no saving the hypotheses here, but a full Copernican realism. Note that the orbits are still circular.

Some had criticized his defence of Copernicus (unadorned by an Osiander type deflection) for contradicting the bible, which says that the sun moves and the earth stands still. Indeed, there are passages to that effect, saying that verbastim. The way out for Copernicus is the following:

(1) Nature is "innexorable and immutable: she never transgresses the laws imposed upon her, or cares a white whether her abstruse reasons and methods of operation are understandable to men." (p. 182). Whatever is evidenced by sense perception and for which necessary demonstrations (ie mathematical presentations) exist cannot be contradicted by a literal reading of the Bible.

(2) But "the holy Bible and the phenomena of nature proceed alike from the divine Word, the former as the dictate of the Holy Ghost, and the latter as the boservant executrix of God's commands" (p. 182). The Bible "can never speak untruth-whenever its true meaning is understood". (p. 181) Contradictions between the two over physical matters arise because, "propositions uttered by the Holy Ghost were set down in that manner by the sacred scribes in order to accomodate them to the capacities of the common people, who are rude and unlearned." Hence, the earth not moving and the sun moving, which is how the common people observe and perceive things.

(3). But "for the sake of theose who deserve to be separated from the herd, it is necessary that wise expositors should produce the true senses of such passages, together with the special reasons for which they were set down in those words." (p.182). Sticking only to the "unadorned grammatical meaning" may lead one into error. Galileo wishes to find the "true senses", which in his opinion is never and never be in contradiction with science. The Bible is intended for our salvation, not as a science textbook, and references to physical descriptions in contradiction to science may be re-interpreted with impunity.

Galileo was therefore a believer in the reconciliation of religion and science, and he distinguished the literal words of a passage which were obstensively about a physical phenomena, and its real import, which was related to moral edification and religious salvation. This latter was the essential, and where discrepancies occured with the letter of the scripture and the book of science, the former had to be reinterpreted, in the context of the original moral lesson to be given.

But this did not impress others. Some continued to polemicize against him. Others, like Cardinal Bellarmine, warned him to confine himself to presenting the Copernican sysem as an hypothesis as Osiander had himself done. But in 1632, Gaileo published his Dialogue Concerning the Two Chief World Systems. His condemnation would come the next year, 1633.

The Conflict between Galileo and the Inquisition

Galileo was not opposed to religion, but he was opposed to the interference of organized religion in science. The distinction between the two is important. Organized religion, in counterpart, had some growing doubts about Galileo. The conflict, in large part one of authority and power: who has the right to make pronouncements in what domains of knowledge, grew in stages from the early 1600s, through the 1610s, to the culmination in 1633. It pits Galileo and the Church, especially Cardinal Bellarmine.

Robert Cardinal Bellarmine was not an ignorant religious zealot, but rather a highly educated churchman. Bellarmine had, however, been one of the cardinals who had condemned Bruno to death. He and Galileo had met in the early 1600s at the home of a common acquaintance. Once Galileo had attained fame and attention with the publication of his Starry Messenger and the work on the sunspots, he also drew increasingly the attention of the Inquisition. In February of 1616, the Inquisition decided the following propositions were to be censured:

(1) "That the sun is the center of the world, and totally immovable as to locomotion". Censure: This proposition is "foolish and absurd" in philosophy, and "formally heretical" in theology, contradicting the holy scriptures in its exact wording and in learned commentators of church fathers and theologians.

(2) "That the earth is neither in the center of the world nor immovable, but moves as a whole and in daily motion." Censure: as for the above proposition in philosophy, "and with regard to Theological verity it is at least erroneous in the faith." (Drake, p. 64 short bio).

Note the terms "foolish and absurd" attached to the proposition that the sun is motionless at the center of the world, and "erroneous in the faith" attached to the propositon that the earth moves. It appears that the latter condemnation is even stronger.

The above decisions were adopted by the weekly meeting of the Inquisition on Feb. 24, 1616; Bellarmine was instructed by the Pope to notify Galileo that he could no longer hold or defend the censured propositions. If he did not accept the warning, he was to be told that he may not hold, defend or teach the proscribed propositions, on penalty of action by the Inquisition against him. Galileo was indeed summoned two days later, and met with Bellarmine, acquiescing to the warning according to Bellarmine's report to the next meeting of the cardinals of the Inquisition. Note acquiescing: accepting the authority, but not necessarily agreeing to the content. On March 5, a decree was issued banning a book by Foscarini which attempted to defend Copernicus as consistent with the text of the bible, while Copernicus' work and another on commentaries to the book of Job were suspended pending correction.

Galileo continued on his own work and in 1630 he sent to the printers his masterpiece, Dialogues Concerning the Two World Systems-Ptolameic and Copernican. This is a wonderful book, probably the most litterary of scientific books, written in dialogue form. The speakers are Salviati, Galileo's spokesman or persona, Sagredi, an educated lay person who wishes to be informed of the debate and is sympathetic, but not yet convinced of the Copernican system, and Simplicio, the defender of Aristotle's physics and the geocentric cosmology. Salviati and Sagredi were names taken from friends, then dead, of Galileo's. Simplicio, which might seem a derisive name, is actually that of a commentator on Aristotle from later antiquity. The debate goes over four days, dealing with (1) the critique of the Aristotilean distinction between the earthly and heavenly domains; (2) problems surrounding the earth's rotation; (3) the daily and yearly motion of the earth; (4) the tides as an argument for the earth's daily motion. I won't go into the details, but encourage some at least of you to actually read parts or the whole of this book. The advantage of the three-way dialogue is that argument, counterargument, persuasion and doubts are clearly and beautifully expressed.

But the upshot of the publication of the book in 1632, after initial difficulties in getting a licence to publish, was Galileo's convocation by the Inquisition. In August of that year, distribution of the book was ordered halted, and Galileo was summoned to appear before the Inquisition. The trial began on April 12. Galileo argued that Bellarmine had told him that Copernicanism contradicted the Holy Scripture, "it could not be held or defended, but that it might be taken hypothetically and made use of." (p. 77). He did not recall being instructed not to teach it as well. The Inquisition claimed that he had been so instructed, but this was not in fact the case, for Bellarmine had been told to say that only if Galileo refused to acquiesce, which he had not. Still, and quite unjustly in terms of principle and also in terms of detail, Galileo was convicted. He was sentenced to life imprisonment, an old man of 69. Eventually he was allowed to return to his villa in house arrest, where he died in 1642, but not before publishing his second great work, Dialogues on the Two New Sciences, recounting his work in physics. Galileo's work, both in astronomy and physics, was completed by Newton, the subject of the next unit.