1564–1642 
INVENTOR AND PHYSICIST ITALY
Galileo, perhaps more than any other single person, was responsible for the birth of modern science. . . . Galileo was one of the first to argue that man could hope to understand how the world works, and, moreover, that we could do this by observing the real world.
—STEPHEN HAWKING, THEORETICAL PHYSICIST
Galileo was bored. After a week of studying math at the university, he had been looking forward to a good Sunday church service to fill his brain with more spiritual thoughts. Unfortunately, the visiting priest was so dull that Galileo couldn’t keep his head from dropping onto his chest. Snapping it to attention, he overcompensated and threw his head back too far. Something on the ceiling caught his eye. A lamp, hanging from a chain high overhead, was swaying in the air currents. Its rhythmic arcs almost put him back to sleep, but then Galileo noticed something that surprised him: there seemed to be a pattern to the swings.
Wide awake now, he used his own pulse to time how long it took the lantern to swing from one end of its arc to the other. He realized something: each swing took the same amount of time, whether the lantern had swung wide in a new breeze, or had settled into a barely noticed sway when the air currents quieted.
Duh, you might say; that seems obvious. But it wasn’t a duh then. People four hundred years ago had hardly a clue about what made the physical world work. With this observation, eighteen-year-old Galileo discovered the way to invent the first accurate mechanical clock, beginning a lifetime of experiments to figure out how the world works. He was the world’s first physicist (a scientist who studies matter and energy and how they interact).
Galileo said that a lock of wool and a piece of lead, if in a vacuum (with no air resistance), would fall at the same rate. In 1971, astronaut David Scott stood on the moon and dropped a feather and a hammer at the same time. They both fell side by side to the moon’s surface. He remarked: “This proves that Mr. Galileo was correct.”
Galileo’s curiosity would nearly get him killed later in life, but it also started humans down the road of knowledge to mechanics, electricity, radiation, and nuclear reactions. From a boring church service in Pisa in 1583 to a walk on the moon in 1969, and finally to nanotechnology today, there have been curious men and women, pulling more and more from the spool of scientific knowledge that Galileo started to unravel.
Galileo’s greatness came from his skepticism: he refused to believe something just because everyone else did. He came by this naturally; as a boy, Galileo had been taught by his father, who hated close-minded people, especially if they were in a position of authority.
By the time Galileo was eleven, his father could not keep up with his thirst for knowledge, so he sent his son to a monastery school. The peaceful life inside the monastery walls totally appealed to Galileo, so much so that, at thirteen, he volunteered to begin training as a monk. His dad was horrified and instantly nixed the idea: Galileo needed to pick a career that would generate enough money to help support the family. And four hundred years ago, just like today, doctors got paid big bucks. So, at his father’s insistence, when Galileo was seventeen he entered the University of Pisa to study medicine. But he was not interested in medicine, and he argued with his father to be allowed to study math—a profession that would help him figure out how the world worked. He must have been a good arguer because his father gave in. As Galileo later said of his passion for math:
The Catholic Church was very powerful in Italy in Galileo’s day. In Rome, everyone was Catholic, and one out of every twelve people was a priest or a nun.
. . . the universe cannot be understood unless one first learns to comprehend the language and interpret the characters in which it is written. It is written in the language of mathematics, and its characters are triangles, circles and other geometrical figures, without which it is humanly impossible to understand a single word of it . . .2
At Pisa, Galileo kept on arguing with people who supposedly knew more. He argued so much that his teachers nicknamed him Il Attaccabrighe, “the Wrangler.” What was he arguing about? Galileo felt that the facts they were teaching should not be accepted until someone had tested them.
When he was twenty-one, Galileo left school without earning a degree. Four years later, he was back, this time as an instructor. He began teaching math and went back to his old argumentative ways. At that time, universities were still following the teachings of Aristotle, who had lived 1,800 years earlier. One thing Aristotle had said was that the heavier an object was, the faster it would fall. Aristotle had never actually tried it; it just seemed to logically flow from other things he had observed.
Galileo easily proved this idea wrong: he climbed the Leaning Tower of Pisa and dropped two lead balls, one weighing much more than the other. As his critics watched, an 1,800-year-old “truth” was overturned: both objects fell to the earth at exactly the same speed. By using public stages like this, Galileo became popular and changed many people’s minds. But his popularity and ideas also created enemies, and he got fired from his job. Fortunately, friends got him a job at the University of Padua, near Venice. It had a reputation as being more open to new ideas, and Galileo was happy there. His fame grew as he invented and designed machines and instruments for various rulers and kings.
In 1609 the telescope was invented in Holland. It could magnify objects only up to three times, and it was merely used as a toy at parties. But Galileo saw other uses for the telescope and set out to improve it. By 1610 he had made a telescope so strong, it could be used in war to spy on approaching enemies. When he presented his telescope to the ruler of Venice, he was given a huge pay raise and a job for life. Orders poured in for his telescopes, and he became even more famous. He used his most powerful scopes—ones that could magnify an object thirty times—to look at the sky and discovered that the moon is full of mountains and craters. He also discovered another thing Aristotle was wrong about.
Aristotle had claimed that the Earth was the center of the universe—that the sun and all the other stars and planets revolved around the Earth. And the powerful Catholic Church agreed with him. If the Earth was the center of the universe, then that proved that the smartest creature on Earth, man, must be the center of the universe as well. Anyone who disagreed with this idea was considered an enemy of the church. And, at that time, the church was the same as the government. The punishment for disagreeing with it was torture or death.
Even though the Polish astronomer Nicolaus Copernicus had already said that the sun was the center of the universe, very few people believed him. Galileo did. His improved telescope allowed Galileo to prove that many of Copernicus’s ideas were right. Galileo wrote a book, The Starry Messenger, arguing that the Earth was not the center of the universe. Instead, he said the Earth revolved around the sun. This book got him in big trouble. At age fifty-one, Galileo was forced to withdraw his ideas or risk death. To save his life, Galileo said that he had been wrong.
For the rest of his life, Galileo battled the church over his beliefs. Church officials often threatened him with prison, torture, and death in order to force him to lie about his discoveries, but he never totally gave in. He always continued writing and teaching the truth, even when the pope and the Inquisition (the Catholic Church’s secret police) came after him. For the last eight years of his life, Galileo had to live under house arrest inside his home in Florence—but he never stopped conducting his experiments.
Some heroes would die rather than admit something that they don’t believe in. Why didn’t Galileo defend what he believed to the death? Maybe he wanted to live to make more discoveries. Or perhaps he knew that, whether he lived or died, the truth would eventually be known. And of course, it was. Today everyone, even the Catholic Church, believes that Galileo was right.
In the end, Galileo’s greatest legacy is not any one of his inventions or discoveries, but his search for truth, even in the face of ignorant laws and rulers. In Galileo’s day, the enemy of truth was people clinging to unproven beliefs. What is the enemy of truth today?