Coming of Age in the Milky Way (12 page)

Galileo was born in Pisa, on February 15, 1564, twenty years after the publication of Copernicus’s
On the Revolutions
. From his father, Vincenzo Galilei, a professional lute player and amateur mathematician, Galileo inherited a biting wit, a penchant for the dialogue form of argument, and a vehement distrust of authority. Vincenzo had written a book,
Dialogue of Ancient and Modern Music
, that encouraged Kepler in his search for Pythagorean harmonies. One of the characters in it utters a declaration that could have been the motto of the younger Galileo:

Galileo prospered so long as he remained true to that independent creed. Disaster beset him once he neglected it and began demanding that questions be decided on the pronouncements of his
own
authority.

As a young man, however, Galileo waged glorious campaigns against those who, as he was to write, “think that our intellect should be enslaved to that of some other man.”
³
An incandescent speaker and pamphleteer, he was known during his student days at the University of Pisa as “the wrangler” for the sarcastic aplomb with which he skewered the Scholastic professors.

At his parents’ behest Galileo studied medicine, but he found little there to gratify his appetite for empirical knowledge. Medical lecturers typically taught from a volume of Galen, who had been dead for fifteen hundred years, and their laboratory sessions were hindered by a Church prohibition against dissection of human bodies. Galileo soon dropped out. He then spent four irresponsible, productive years lazing about at home, reading Virgil and Ovid, building little machines, and studying mathematics with a tutor, Ostilio Ricci, with whom he shared a devotion to the works of Archimedes.

Galileo was twenty-five years old when a scientifically inclined nobleman, Francesco Cardinal del Monte, took an interest in his abilities and got him appointed professor of mathematics at Pisa. There he lectured on astronomy, poetry, and mathematics and resumed his hectoring of the Aristotelians, at one point circulating a satirical poem poking fun at the Scholastics’ habit of coming to school in togas, like little wax Aristotles. The students were delighted but the Scholastics were in the majority on the faculty, and when Galileo’s contract expired he was let go.

He then managed to gain an appointment to the chair of mathematics at the University of Padua, in the free Republic of Venice.
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(Another applicant for the post was Giordano Bruno, but he was in chains by the time Galileo arrived at the university in September 1592 and was burned alive eight years later for refusing to abjure many heresies, among them his insistence that the stars are suns.) Galileo remained at Padua for eighteen years, writing, lecturing, conducting experiments, and inventing scientific instruments, among them the thermometer.

During this time his financial troubles, always onerous, became insupportable. His father had died in 1591, leaving Galileo to pay his two sisters’ dowries, each of which equaled several years’ worth of his university salary. In addition he was obliged to send money to his brother Michelangelo, a wandering musician who demonstrated his contempt for cash by squandering it as rapidly as he could get his hands on it. By the age of forty-five, Galileo was a respected scientist and teacher with a couple of books to his credit, but his contract was coming up for renewal, his debts were mounting, and he needed something to elevate his career from the creditable to the extraordinary. It came to him in 1609. It was the telescope.

During one of his frequent visits to nearby Venice, Galileo learned that telescopes were being constructed in Holland. Quick to grasp the principles involved, he returned home to Padua and built a telescope for himself. “Placing my eye near the concave lens,” he recalled, “I perceived objects satisfactorily large and near, for they appeared three times closer and nine times larger than when seen with the naked eye alone. Next I constructed another one, more accurate, which represented objects as enlarged more than sixty times.”
⁴

Galileo did not need to be told that the telescope would have great practical value. Venice was an unwalled city, and its citizens depended for their defense upon their ability to spot approaching enemy ships in time to dispatch a fleet to engage them while they were still at sea; the telescope would greatly improve this early-warning system. The Venetians, furthermore, made their living from sea trade, and frequently kept an anxious watch, from the lookout towers
(campanili)
that dotted the city, for galleys returning with their holds full of cornmeal from the Levant, spices from Constantinople, and silver from Spain; an investor might be ruined if his ship were lost, or double his money once “his ship came in.”
A lookout using a telescope could spot the flag flying from an incoming trading ship much sooner than with the unaided eye.

Galileo accordingly arranged a demonstration for the authorities. On August 25, 1609, he led a procession of Venetian senators across the Piazza San Marco and up the Campanile for their first look through his first telescope. As he recalled the scene:

The senators, suitably impressed, doubled Galileo’s salary and granted him a lifelong appointment at Padua; as we would say today, Galileo got tenure. But his triumph was darkened by a cloud of deception. He permitted the senators to assume that he had
invented
the telescope. This was not strictly true, and his silence as to the stimulus of his greatest invention became embarrassing once telescopes produced by Dutch and Italian spectacle-makers began turning up in the marketplaces of Venice. In Bertolt Brecht’s play
Galileo
, Priuli the Venetian curator upbraids Galileo for his guile:

But while the senators trained their telescopes on the horizon, Galileo trained his on the night skies. He was the first scientist to do so (or one of the first; Thomas Harriot in England observed the moon through a telescope that same summer) and what he saw spelled the beginning of the end of the closed, geocentric cosmos, and the opening up of the depths of space.

As beginning observers have done ever since, Galileo looked first at the moon, and the sight of its mountains and craters immediately impressed him with the fact that it was not a wafer composed of heavenly aether, but a rocky, dusty, sovereign world. Aristotle to the contrary, the moon is “not robed in a smooth and polished surface,” wrote Galileo, but is “… rough and uneven, covered everywhere, just like the earth’s surface, with huge prominences, deep valleys, and chasms.”
⁷

Turning his telescope to Jupiter, Galileo discovered four moons orbiting that giant planet, their positions changing perceptibly in the course of just a few hours’ observation. Jupiter, he was to conclude, constituted a Copernican solar system in miniature, and proof as well that the earth is not unique in having a moon. Galileo called it

When Galileo observed the bright white planet Venus, he found that it exhibits phases like those of the moon, and that it appears much larger when in the crescent phase than when almost full. The obvious explanation was that Venus orbits the sun and not the earth, exhibiting a crescent face when it stands nearer to the earth than does the sun and a gibbous face when it is on the far side of the sun. “These things leave no room for doubt about
the orbit of Venus,” Galileo wrote. “With absolute necessity we shall conclude, in agreement with the theories of the Pythagoreans and of Copernicus, that Venus revolves about the sun just as do all the other planets.”
⁹

The greatest surprise was the stars. The telescope suggested, as the unaided eye could not, that the sky has
depth
, that the stars are not studded along the inner surface of an Aristotelian sphere, but range out deep into space. “You will behold through the telescope a host of other stars, which escape the unassisted sight, so numerous as to be almost beyond belief,” Galileo reported. Moreover, the stars were organized into definite structures, of which the most imposing was the Milky Way:

The phases of Venus, observed by Galileo through his telescope, proved that Venus lies closer to the sun than does the earth.

Galileo’s account of his visions through the telescope were first published in March 1610, in his
Sidereus Nuncius
, or
Starry Messenger
. The book was an instant success, and soon readers as far away as China were reading its reports of the rocky reality of the moon, the satellites of Jupiter, and the multitude of previously unseen stars in the sky. Here was observational evidence that we live in a Copernican solar system in a gigantic universe.

Galileo, who was principally a physicist and had been a Copernican before he ever looked through a telescope, understood that the task now facing science was to bring physics into accord with the reality of a moving Earth. The old anti-Copernican arguments had been turned inside out: Given that the earth really
does
rotate on its axis, why
don’t
arrows shot into the air fly off to the west, or east winds constantly blow across the land? Why, in short, does a moving Earth act
as if
it were at rest? Finding the answers to these questions would require a greatly improved understanding of the concepts of gravitation and inertia. Galileo struggled with both.

In Aristotelian physics, heavy objects were said to fall faster than light ones. Early on, probably while still at Pisa, Galileo had realized that this commonsensical view was wrong—that in a vacuum, where air resistance would have no effect, a feather would fall as fast as a cannonball.
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Having no means of creating a vacuum, Galileo tested his hypothesis by rolling spheres of various weights down inclined planes. This slowed their rate of descent as compared to free fall, making it easier to observe that all were accelerating at approximately the same rate.