Galileo (1564-1642) is a key character, perhaps the key character, in the founding of modern science. While best known for his trial by the Inquisition, he changed our view of astronomy and established physics as an experimental science. Galileo was born in Pisa, near Florence, and not much is known about his childhood, except that his father was a musician and he apparently was educated by priests. He attended the University of Pisa to study medicine, but did not get a degree. In mathematics, Galileo was mostly self-taught and he set out to get an appointment as a professor in that subject. He did this by writing several essays using mathematics to understand the world, one on measuring the proportions of the different metals in alloys and another on finding the center of gravity of solids. These papers impressed leading mathematicians and he was given a position at the University of Pisa. Much of Galileo’s research at Pisa was on motion. He showed, for example, that objects of the same shape and size, but of different weights, fall at the same speed. This ran counter to the prevailing thought of the time.
The dominant figure in science at the time was Aristotle and his 2000 year old explanations were considered absolutely true by many. In astronomy, Aristotelians felt that Earth was the center of the universe, and that all heavenly bodies circle Earth. Galileo wanted to improve scientific knowledge by showing that using mathematics and evidence is superior to the philosophical approach of Aristotle. Galileo’s hero from classical times was not Aristotle, it was Archimedes, the mathematician and engineer.
In 1591, Galileo’s father died, leaving him as head of the family. This added to his financial obligations, especially in providing dowries for his two sisters. The following year he moved to the more prestigious and better paying University of Padua. To increase his income, he taught students privately, took in boarders in his home, and set up a shop to manufacture instruments. He never married, but fathered a son and two daughters during a ten year relationship with Marina Gamba, a Venetian. He paid for his son’s education and put his two daughters into a convent when they were still children. (At the time, girls with unmarried parents would have great difficulty finding respectable husbands.) Both daughters became nuns, one rather unhappy her whole life while the other remained close and supportive of her father.
Galileo was a leader in the movement to discredit Aristotle’s dominance over science and replace it with mathematics combined with an empirical approach to gaining knowledge. He was not opposed to Aristotle personally, but to the tendency for scholars to assume that Aristotle’s conclusions were correct and there was no need to improve on that knowledge.
The Aristotelian understanding of astronomy was mostly associated with the Greek geographer and astronomer Ptolemy (Second Century AD), who worked out the details of how all heavenly bodies traveled in perfect circles around the stationary Earth. While Aristotle and Ptolemy were neither Jews nor Christians, their system was compatible with the few astronomical references in the Old Testament and was assumed correct by the Catholic Church. Astronomers after Ptolomy predicted the positions of the heavenly bodies, especially the planets. Perfect circles did not work for such predictions, though. In science today, if a model makes poor predictions we assume that it needs to be modified. But before Galileo explanations and predictions did not have to agree–the Ptolemaic model was still assumed to be correct. Polish astronomer Nicholas Copernicus (1473-1543) found that predictions were much improved if the planets, including a rotating Earth, revolved around the Sun. His book explaining this theory was published after he died and a friend added a preface stating that the Copernican system was merely a calculating device, not a change in the Earth-centered theory of Ptolemy. In this way, there was no challenge to the Ptolemaic system, and the Catholic Church was not threatened.
Over time, the Copernican system was refined and found by some to be a more accurate representation of planetary motion. In the sixteenth century, Danish astronomer Tycho Brahe kept detailed records of planetary positions and German astronomer and mathematician Johannes Kepler analyzed Tycho’s data and greatly improved on the Copernican system. He showed that the planets revolve not in circular orbits, but in elliptical ones. It was Galileo who set out to explain these orbits and show that the Copernican model was not just a predictive device, but was fundamentally correct.
Telescopes were newly invented and Galileo built one to study astronomy. According to the Ptolemaic system, heavenly bodies were perfect unchanging spheres and all revolved around Earth. Galileo looked at the Moon and saw that it is not perfect, there are mountains and craters. He looked at Jupiter and saw moons that circled that planet, not Earth. He observed sunspots. Each of these suggested that something is wrong with the Ptolemaic system in addition to the orbital findings of Copernicus and Kepler. Galileo published essays suggesting that the Copernican system is correct and these writings got him in trouble with the Church.
Galileo preferred to argue using evidence and mathematics, but at the time science had to be reconciled with Scripture. Using reasoning going back to St. Augustine (around 400 AD), he suggested that God condescends to human limitations and therefore explained things in ways ancient people could understand. He continued by arguing that since most astronomy in the Bible is incidental to the story, it should not be taken literally. In 1616, he went to Rome to defend his ideas. He felt that if he could show, using evidence, that he was correct, then Scripture should be reevaluated. The Church did not agree and ordered him to not believe in or teach Copernicanism.
In 1624, Galileo met with the new Pope, Urban VIII; the two had been friends for years. They had a friendly discussion and Urban declared that Copernicanism could never be proved true. Galileo wrongly interpreted this statement as encouragement to write a book comparing the two astronomical systems, making it clear that he was not preferring one side over the other. His Dialogue Concerning the Two Chief Systems, written as a series of conversations between three characters, was published in 1632. In it, he clearly argued that Copernicanism was correct. The Pope was not pleased. Adding to the Pope’s displeasure was that the character in the Dialogue most closely associated with the Church position was the rather ignorant Simplicio, perhaps a veiled reference to a simpleton. A commission was convened to investigate Galileo’s actions and since he clearly violated his orders from 1616, he was sent to trial by the Inquisition, the Church tribunal that tried people for heresy during the Middle Ages. Torture and death were not unusual in both the trial and punishment phases.
People charged with lesser offences had been imprisoned and killed by the Inquisition, so Galileo feared for his life. First he argued that the book was not strongly Copernican, then he claimed that it was Copernican, but he did it in a vain attempt to sound clever. Later he changed his story again in that the book shows that neither side had conclusive proof. His inquisitors did not believe him and gave him two more chances to tell the truth, the second under the threat of torture. At the end of the trial, he stuck with the story that he never believed in Copernicanism after 1616. Galileo was convicted, declared “vehemently suspect of heresy.” Imprisonment was not imposed, instead he was sentenced to house arrest for the rest of his life. In 1637, he was in poor health and went blind, possibly from looking at the sun through his telescope too many times. His house arrest was lifted under condition that he not discuss the movement of Earth.
But that was not the end of Galileo. He went on to pull together his research on other matters and published a book (Discourses and Mathematical Demonstrations Relating to Two New Sciences) in 1638 that can be seen as the foundation of modern physics. He covered motion and the strength of solids, both with mathematically based explanations and discussions of the engineering applications of such knowledge.
Galileo died in 1642. Over time, scientists and others agreed that he was correct in his astronomy and built on his physics. His greatest contribution to science, though, is that he was a great scholar who insisted that empirical evidence and theory should drive the quest for scientific knowledge. While he lost his personal battle on the matter, science eventually won.
In 1992, 350 years after Galileo’s death, Pope John Paul II gave a speech in which he made it quite clear that the Catholic Church erred in the trial of Galileo. The Pope went on to state that the purpose of science is to explain the physical universe and the purpose of religion is to explain spiritual matters. The two complement each other and are not in conflict.
- Galileo: Decisive Innovator, Michael Sharratt, Blackwell Publishers, 247 p. (1994) ISBN: 0521566711.