A Little History Of Science: Leaning Towers and Telescopes Galileo
One of the strangest buildings in the world must be the 850-year- old bell tower of the cathedral in the city of Pisa in Italy. You may know it as the Leaning Tower of Pisa. It’s fun to take photographs of a friend in front of it pretending to hold the tilting tower from falling. There are also stories about how Galileo used the tower to perform his own experiments – dropping two balls of different weights from the top to see which would land first. In fact, Galileo didn’t use the tower, but he did other experiments that showed him what the result would be, and he found that a ten-pound ball and a one-pound ball would hit the ground at the same time. Like the sun not moving around the earth each day, this experiment seemed to go against our everyday experience. After all, a feather and a ball dropped from the tower do not fall at the same rate. Why would the differently weighted balls drop to earth together?
Galileo Galilei (1564–1642) was born in Pisa. (Galilei was the family name, but our hero is always known by his first name.) His father was a musician and Galileo actually grew up in nearby Florence. He returned to the University of Pisa as a young man, starting to study medicine, but he was always more interested in mathematics, and he left the university with a reputation for cleverness and quick wit. In 1592, he went to Padua to teach mathematics and what we would call physics. He was there when William Harvey, whom we shall meet shortly, was a student, and it’s a shame that the two probably never met each other.
Galileo attracted controversy throughout his life. His ideas always seemed to challenge accepted views, especially the physics and astronomy of Aristotle and the other Ancients. He was a good Catholic, but it was also his belief that religion is about morality and faith, whilst science deals with the observable, physical world.
As he put it, the Bible teaches how to go to heaven, not how the heavens go. This brought him into conflict with the Catholic Church, which was energetically defending itself against those who dared to challenge either its ideas or its authority. The Church also started policing the growing number of books that were produced by the printing presses, placing unacceptable ones on a list they called the Index Librorum Prohibitorum – the ‘List of Banned Books’. Galileo, who had many friends in high places (including princes, bishops, cardinals and even popes), had the support of many churchmen, but others were determined not to allow his ideas to upset their teachings, which were centuries-old.
Galileo’s early work was with the forces involved in moving objects. From the very beginning he was someone who wanted to observe and measure things for himself, and if possible to express his results mathematically. In one of his most famous experiments, he carefully rolled a ball down a tilted surface and measured how long it took to reach certain distances. As you can imagine, the ball picks up speed as it moves down the slope (we would say it accelerates). Galileo saw that there was a special relationship between the speed of the ball and the time that had passed since it started moving. The speed was related to the square (a value multiplied by itself, such as 3 × 3) of the time taken.
So, after two seconds, Galileo discovered that the ball would be travelling four times as fast. (The square of the time taken also appears in later scientists’ work, so look out for it. Nature seems to like things squared.) In all these, and many more experiments, Galileo showed himself to be a very modern scientist, because he knew that his actual measurements were not always exactly the same; sometimes we blink at a bad moment, or it takes time for us to record what we see, or the equipment isn’t perfect. However, these are the kinds of observations we can make about the real world, and Galileo was always most interested in the world as we find it, not in some abstract world where everything was always perfect and exact.
Galileo’s early work on moving objects showed how differently he saw the world as compared with Aristotle and the hundreds of thinkers who had come after, despite Aristotle’s continuing importance in the universities, which were governed by religious groups.
In 1609, Galileo learned of a new instrument that would challenge the ancient way of thinking even more seriously. This instrument was soon to be called the ‘telescope’, a word that means ‘to see far’, just as ‘telephone’ means ‘to speak far’, and ‘microscope’ means ‘to see small’. Both telescopes and microscopes have been very important in the history of science.
The first telescope that Galileo constructed offered only a little magnification, but he was very impressed with it. He quickly improved it by combining two lenses, so that he could get the kind of magnifying power that we expect from an ordinary pair of binoculars today, about fifteen times. That doesn’t sound like much, but it created a sensation. Using it, one could spot ships coming in from the sea long before they were visible to the naked eye. More importantly, Galileo turned his telescope to the heavens and was amazed at what he found there.
When he looked at the moon, he realised that it was not the perfect, smooth, circular ball that people had supposed. It had mountains and craters. Turning his telescope towards the planets, he observed their movements more closely, and discovered that one planet, Jupiter, had ‘moons’ just as the earth had its moon.
Another planet, Saturn, had two big blobs which didn’t look like moons and which we now call its ‘rings’. He could see the movements of Venus and Mars much more clearly, and agreed that they changed their direction and speed in a regular and predictable way. The sun had dark areas or spots, which moved a bit each day in regular patterns. (He learned to look at it indirectly, to protect his eyes, as you must.) His telescope revealed that the Milky Way, which appears as a wonderful, fuzzy blur of light when looking with the naked eye on a clear night, was actually composed of thousands and thousands of individual stars, very far away from the earth.
With his telescope, Galileo made these and many other important observations. He wrote about them in a book called Starry Messenger (1610), which created a stir. Each revelation called into question what people thought about the heavens. Some thought Galileo’s ideas were based on tricks played by his new ‘tube’, as the telescope was often called, because what could not be seen by the naked eye might not be there. Galileo had to try to convince people that what his telescope showed was real.
Much more awkwardly, and dangerously, was that Galileo’s observations were good evidence for Copernicus being right about the moon revolving around the earth, and about the earth, moon and the other planets all orbiting around the sun. By this time, Copernicus’s book had been in print for almost seventy years, and he had a number of followers, Protestants as well as Catholics. The official position of the Catholic Church was that Copernicus’s ideas were useful to work out the movements of the planets, but they were not literally true. If they were, too many passages from the Bible would be complicated, and have to be thought about again.
But Galileo wanted to tell people about his astronomical findings. He went to Rome in 1615 hoping to get the Church’s permission to teach what he had learned. Many people – even the Pope-sympathised with him, but he was still forbidden to write about, or teach, Copernicus’s system. He didn’t give up entirely, going to Rome again in 1624 and 1630 to test the waters, though he was getting old and unwell. He became convinced that as long as he was careful to present the Copernican system only as a possibility then he would be safe. His work on astronomy, Dialogue on the Two Chief World Systems, is written as a conversation between three people: one representing Aristotle, another representing Copernicus, and the third acting as the host. That way, Galileo could discuss the pros and cons of old and new ideas about the universe without having to say which was right or wrong.
It is a wonderful book, full of jokes, and written, like most of Galileo’s works, in his native language, Italian. (Scholars from all over Europe still usually wrote their books in Latin.) From the start, it was pretty obvious which side Galileo was on. For one thing, the Aristotelian character was named Simplicio. Now, there was in fact an ancient commentator on Aristotle called that, but just as in English, in Italian it sounds like ‘simpleton’, and this character isn’t very bright. The Copernican (called Salviati, a name that suggests ‘wise’ and ‘safe’) has by far the best lines and arguments.
Galileo tried very hard to get the Church’s official approval for his book. The censor in Rome, who controlled which books could be published, was sympathetic to Galileo, but he knew there would be problems and so delayed his decision. Galileo went ahead and had the book printed in Florence. When the high churchmen in Rome read it, they were not pleased, and summoned the old man to Rome. Someone dug out a copy of the old ban against him teaching the Copernican system, and after a ‘trial’ in 1633 that went on for three months, Galileo was forced to say his book was an error and the product of his vanity. The earth, he said in his signed confession, does not move and is the centre of the universe.
There is a legend that immediately after being convicted, Galileo muttered, ‘Eppur si muove’ (‘And yet it moves’). Whether or not he did say it out loud, he certainly thought it, for the Church could not force him to change his beliefs about the nature of the world.
The Church had the power to throw Galileo in prison and even torture him, but his jury recognised that he was a very unusual man, and put him under house arrest instead. His first ‘house arrest’ in the city of Siena wasn’t all that strict – he was the life and soul of many dinner parties – so the Church insisted that he return to his home outside Florence, where his visitors were carefully policed. One of Galileo’s daughters (a nun) died soon after, and his last years were lonely. But he continued his work, returning to the problems of falling objects and the forces that produce the kinds of movement we see around us every day. His great work, Two New Sciences (1638), is one of the foundations of modern physics. He looked again at the acceleration of falling bodies, and used mathematics to show that acceleration could be measured in a way that anticipated Isaac Newton’s later famous work on gravity. He also offered a new way of thinking about the paths of things shot through the air, like cannon-balls, showing how it could be predicted where they would land. With this work, the concept of ‘force’ – what influences something to move in a particular way – took its place in the study of physics.
If you’ve ever heard the phrase ‘rebel without a cause’, then Galileo was a rebel with a cause. The thing he fought for was science as knowledge that can explain the way the world works in its own terms. Some of his rebellious ideas were later abandoned because they were wrong, or did not fully explain things. But that’s the way science always works, and no area of science is a closed book containing all the answers. Just as all modern scientists should, Galileo knew this.