Michael Fowler
UVa Physics Department
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NOTE: Many books have been written about Galileo, and,
in particular, about his interaction with the Church. An excellent
short biography is Galileo, Stillman Drake, Oxford. One
classic is The Crime of Galileo, Giorgio de Santillana,
1955, University of Chicago Press. A recent "popular"
biography is Galileo, a Life, James Reston, Jr., HarperCollins.
(I am certainly no expert in this complex field of study, and
just present a collection of facts below to try to give the flavor
of Galileo's life and times.)
Galileo was born in Pisa, Tuscany in 1564, the son of Florentine
musician Vincenzo Galilei. Actually, Vincenzo was a revolutionary
musician-he felt the formal church music that then dominated the
scene had become sterile, and that classic Greek poetry and myths
had a power the church music lacked, that perhaps could be translated
into modern music. He attempted some of this, and his work began
the development that culminated in Italian opera.
To understand something of Galileo's early upbringing, here is
a quote from his father, Vincenzo Galileo:
"It appears to me that those who rely simply on the weight of authority to prove any assertion, without searching out the arguments to support it, act absurdly. I wish to question freely and to answer freely without any sort of adulation. That well becomes any who are sincere in the search for truth."
(I took this from Reston, Page 9)
At age 17, Galileo went to the University of Pisa. He enrolled
as a medical student, following his father's advice, but turned
to math, after persuading his father that he didn't want to be
a doctor. His father allowed him to be tutored by the Tuscan court
mathematician, Ricci, who designed fortifications, which no doubt
impressed Galileo (Reston, page 15).
Galileo proved to be an extremely talented mathematician, and
in his early twenties he wrote some tracts extending results of
Archimedes on centers of gravity of shapes. At age 25, he was
appointed to the Chair of Mathematics at Pisa.
At age 28, in 1592, Galileo moved to a better position at Padua,
in the Venetian Republic, where he stayed until the age of 46.
Reston's book certainly paints a vivid picture of the Venetian
Republic at the time Galileo moved there! Venice, a city of 150,000
people, apparently consumed 40 million bottles of wine annually.
There were more courtesans than Rome. In 1599, Galileo met one
Marina Gamba, 21 years old. He had three children by her, greatly
upsetting his mother. Galileo also spent a lot of time with Sagredo,
a young Venetian nobleman, both in the town and at Sagredo's very
fancy house, or palace. Sagredo is features as one of the disputants
in Dialogue Concerning the Two Chief World Systems, and
Two New Sciences. Another close friend during this period
was Fra Paolo Sarpi, a Servite friar, and official theologian
to the Republic of Venice in 1606, when Pole Paul put Venice under
the interdict. Tensions between Venice and Rome were partly generated
because Venice wanted to be able to tax churches built in Venice
by Rome. Sarpi advised the Venetians to ignore the interdict,
and the Jesuits were expelled from Venice. A nearly successful
attempt on Sarpi's life was generally blamed on the Jesuits (from
Drake, page 28).
When Galileo was 46 years old, in 1610, he developed the telescope,
secured tenure and a big raise at Padua, then went on to make
all the discoveries announced in Sidereus Nuncius: mountains
on the moon, the moons of Jupiter, phases of Venus, etc. By naming
the moons of Jupiter after the Medici family, Galileo landed the
job of Mathematician and Philosopher (meaning Physicist) to the
Grand Duke of Tuscany, and was able to return to his native land.
This move upset his friends in Venice who had worked so hard to
secure his promotion at Padua only months before.
Of course, Galileo's belief that his discoveries with the telescope
strongly favored the Copernican world view meant he was headed
for trouble with the Church. In fact, his Venetian friends warned
him that it might be dangerous to leave the protection of the
Venetian state.
In 1611, Galileo went to Rome and met with the Jesuit astronomers. Probably he felt that if he could win them over, he would smooth his path in any future problems with the Church. Father Clavius, author of Gregorian Calendar and undisputed leader of Jesuit astronomy had a hard time believing there were mountains on the moon, but he surrendered with good grace on looking through the telescope (Sant., pages 18, 20)
One archbishop wrote (p 20): "Bellarmine asked the Jesuits
for an opinion on Galileo, and the learned fathers sent the most
favorable letter you can think of … " Bellarmine was
chief theologian of the Church, and a Jesuit himself. Bellarmine
wrote in a letter to A. Foscarini, 12 April 1615:
Third, I say that if there were a true demonstration that the
sun is at the center of the world and the earth in the third heaven,
and that the sun does not circle the earth but the earth circles
the sun, then one would have to proceed with great care in explaining
the Scriptures that appear contrary, and say rather that we do
not understand them than that what is demonstrated is false. But
I will not believe that there is such a demonstration, until it
is shown me."
(Quote from Feldhay, Galileo and the Church, Cambridge,
1995, page 35)
This was far from a mindless rejection of the Copernican picture-it
just demanded a more convincing demonstration.
Somewhat earlier-Dec 1613-Galileo had written a letter to Castelli
(a Benedictine abbot and former pupil of Galileo's) saying in
essence that Scripture cannot contradict what we see in nature,
so scripture, written for the business of saving souls and readable
by everybody, sometimes is metaphorical in describing nature.
It seems that Bellarmine and Galileo might have been able to come
to some agreement on a world view.
Incidentally, Galileo was thinking about quite a different series of physics problems at this same time-trying to understand when things will float and when they sink. He believed Archimedes' Principle, that denser objects than water sink in water.(To be precise, the Principle states that the buoyant supporting force from the water on an immersed object is equal to the weight of the water displaced by the object. That is, it is equal to the weight of a volume of water equal to the volume of the object.So if the object is denser than water, its weight is greater than the buoyancy force and it sinks.)
It was
pointed out to him that a ball made of ebony sinks in water, but
a flat chip of ebony floats. We now understand this in terms of
surface tension, but that had not been understood in Galileo's
time. Nevertheless, Galileo gave an essentially correct answer:
he observed that the chip floated somewhat below the previous
level of the surface, dragging the water down slightly around
its edges, so one should consider the floating body to be the
chip plus the thin sheet of air over it, and putting these together
gives an average density equal to that of water. Galileo discussed
problems of this kind with a Florentine patrician, Filippo Salviati,
and a group of his acquaintances. As usual, Galileo's style and
ability to pulverize the opposition did not win many friends.
(see Drake, pages 49-51). Salviati appears as one of the three
disputants in Galileo's Dialogue.
One more source of tension between Galileo and the Jesuits arose
at this point. Since 1611, Galileo had been observing the motion
of sunspots-small dark spots on the surface of the sun, easily
visible through a telescope at sunset. They were observed independently
at about the same time by Christopher Scheiner, a German Jesuit
from Ingoldstadt. (It is possible that Scheiner had somehow heard
of Galileo's observations.) Scheiner thought they were small dark
objects circling the sun at some distance, Galileo correctly surmised
they were actually on the sun's surface, another blow to the perfect
incorruptibility of a heavenly body. Galileo published his findings
in 1613, with a preface asserting his priority of discovery. This
greatly upset Scheiner.
About this time, some members of another order of the Church,
the Dominicans, were becoming aware of the Copernican world view,
and began to preach against it. In 1613, Father Nicolo Lorini,
a professor of ecclesiastical history in Florence, inveighed against
the new astronomy, in particular "Ipernicus". (Sant
p 25). He wrote a letter of apology after being reproved. In 1614,
another Dominican, Father Tommaso Caccini, who had previously
been reprimanded for rabble-rousing, preached a sermon with the
text "Ye men of Galilee, why stand ye gazing up into the
heaven? He attacked mathematicians, and in particular Copernicus.
(In the popular mind, mathematician tended to mean astrologer.)
It should be added that these two were by no means representative
of the order as a whole. The Dominican Preacher General, Father
Luigi Maraffi, wrote Galileo an apology, saying "unfortunately
I have to answer for all the idiocies that thirty or forty thousand
brothers may or actually do commit".
According to De Santillana (page 45) in 1615 Father Lorini sends
an altered copy of Galileo's letter to Castelli (mentioned above)
to the Inquisition. He made two changes, one of which was to go
from "There are in scripture words which, taken in the strictly
literal meaning, look as if they differ from the truth" to
"which are false in the literal meaning". Still, the
inquisitor who read it thought it passable, although open to being
misconstrued.
Nevertheless, in February 1616, the Copernican System was condemned.
According to Drake (page 63): "A principal area of contention
between Catholics and Protestants was freedom to interpret the
Bible, which meant that any new Catholic interpretation could
be used by the Protestants as leverage: if one reinterpretation
could be made, why not wholesale reinterpretations? A dispute
between the Dominicans and the Jesuits over certain issues of
free will was still fresh in the pope's mind, as he had to take
action in 1607 to stop members of the two great teaching orders
from hurling charges of heresy at each other. These things suggest
that Paul V, if not temperamentally anti-intellectual, had formed
a habit of nipping in the bud any intellectual dispute that might
grow into factionalism within the Church and become a source of
strength for the contentions of the Protestants."
The pope asked Bellarmine to convey the ruling against the Copernican
system to Galileo. Bellarmine had a meeting with Galileo, and
apparently there were also some Dominicans present. Just what
happened at this meeting is not quite clear, at least to me. Later
(in May) Galileo was given an affidavit by Bellarmine stating
that he must no longer hold or defend the propositions
that the earth moves and the sun doesn't. Another document, however,
which was unsigned (and therefore perhaps of questionable accuracy),
stated that the Commissary of the Inquisition, in the name of
the pope, ordered that Galileo could no longer hold, defend
or teach the two propositions (Drake, page 67). This second
document was not given to Galileo. The inclusion of teach was
a crucial difference-it meant Galileo couldn't even describe
the Copernican system. A week later (early March) books describing
a moving earth were placed on the Index of Prohibited Books, some
pending correction.
In the fall of 1618, three comets appeared. A book by a prominent
Jesuit argued that the comets followed orbits close to those of
planets, although they had short lifetimes. Galileo knew the comets
moved in almost straight line motion much of the time. As usual,
Galileo could not conceal his contempt of the incorrect views
of others:
In Sarsi I seem to discern the belief that in philosophizing
one must support oneself on the opinion of some celebrated author,
as if our minds ought to remain completely sterile and barren
unless wedded to the reasoning of someone else. Possibly he thinks
that philosophy is a book of fiction by some author, like the
Iliad … . Well, Sarsi, that is not how things are. Philosophy
is written in this grand book of the universe, which stands continually
open to our gaze. But the book cannot be understood unless one
first learns to comprehend the language and to read the alphabet
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 wanders in a dark labyrinth.
(This is from The Assayer, 1623)
Naturally, this further alienated the Jesuits.
In 1623, Galileo's admirer the Florentine Maffeo Barberini becomes
Pope Urban VIII. The new pope saw himself as a widely educated
man, who appreciated even Galileo's current theories. He had written
a poem "In Dangerous Adulation" about Galileo's ideas.
He also suggests his own pet theory to Galileo: even though the
universe may be most simply understood by thinking of the sun
at rest, God could have arranged it that way, but really with
the earth at rest.
Galileo felt that with his friend and admirer as pope, and his
affidavit from Bellarmine that didn't actually forbid him from
describing the Copernican system, it was safe to write further
about his world view. His ambition was to prove that the Copernican
system must be correct, even though the more cumbersome Ptolemaic
system might be fixed up to describe observations. (For example,
the Danish Astronomer Tycho Brahe suggested that the sun went
around the earth, but all the other planets went around the sun.
That would account correctly for the phases of Venus.) Galileo
was searching for some real proof that the earth was moving. He
thought he found it in the tides. Why should all the water on
the surface of the earth slosh around once or twice a day? Galileo
decided it was because the earth was both rotating and moving
around the sun, so for a given place on earth, its speed varies
throughout the day, depending on whether its speed from the daily
rotation is in the same direction as its speed from the earth's
moving around the sun. This constant speeding up and slowing down
is what Galileo thought generated the tides, so the tides were
proof the earth was moving! (Actually this is not a good argument-the
tides are really caused by the moon's gravity.)
Galileo worked on his new book, which he intended to call "Dialogue
on the Tides", from 1624 to 1630. He was warned as he completed
the work that that title seemed to imply he really held the view
that the earth was moving, so he changed the title to Dialogue
Concerning the Two Chief Systems of the World-Ptolemaic and Copernican.
As usual, Galileo spared no-one in the book. He gratuitously insulted
Scheiner, calling him vain. He mocked the pope himself, by putting
Urban's suggestion (see above) in the mouth of Simplicio, then
dismissing it contemptuously (Reston, page 195).
The book was published in March 1632 in Florence. In August, an
order came from the Inquisition in Rome to stop publication, and
Galileo was ordered to stand trial. Apparently, someone-probably
Scheiner, now living in Rome-had shown the pope the unsigned memo
from the 1616 meeting, forbidding Galileo even to describe the
Copernican system. Galileo was not too upset at the thought of
a trial, because he held a trump card-the affidavit from Bellarmine.
At the trial, Galileo said he had no memory of being forbidden
to teach, and no signed document could be found to support the
unsigned memo.
The trial did not address the scientific merits of the case, it
was about whether or not Galileo had disobeyed an official order.
It was suggested that he admit to some wrongdoing, and he would
get off lightly. He agreed to tone down the Dialogue, pleading
that he had been carried away by his own arguments. He was condemned
to indefinite imprisonment, and, after some negotiation, was confined
to his villa until his death in 1642. During this period, he wrote
Two New Sciences, a book on the strength of materials and
on the science of motion.
Galileo wrote in his old age, in his own copy of the Dialogue:
Take note, theologians, that in your desire to make matters
of faith out of propositions relating to the fixity of sun and
earth, you run the risk of eventually having to condemn as heretics
those who would declare the earth to stand still and the sun to
change position-eventually, I say, at such a time as it might
be physically or logically proved that the earth moves and the
sun stands still.
(Quoted in Drake, page 62).
It's perhaps worth adding one last word from the Jesuits (Reston, page 273)
:
"If Galileo had only known how to retain the favor of the fathers of this college, he would have stood in renown before the world; he would have been spared all his misfortunes, and could have written about everything, even about the motion of the earth."
Index of Lectures and Overview of the Course