Galileo Galilei

Galileo Galilei was born in Pisa, Italy, in 1564. His father was a noble of Florence, and Galileo was well-educated. He studied medicine at the University of Oisa until he became distracted by two different events. One day while daydreaming in church, he watched a lamp swing back and forth as a result of its being pulled aside for lighting. He timed the swings with his pulses and noticed that each lasted the same amount of time, even though the swings were decreasing in size. Later he attended a lecture on geometry at the university. As a result, Galileo's interest in physics and mathematics was aroused, and he changed his major.

At age twenty five, Galileo was appointed professor of mathematics at the University of Pisa, where he began experimenting with motion, especially motion due to gravity. His finding contradicted the accepted teachings of Aristotle. Other professor were shocked that Galileo would consider contradicting Aristotle and refused to even consider Galileo's experimental evidence. Science at that time was based solely on 'logical' thingking, with no attempt to support conclusion by experimentation. Galileo was forced to resign his position, and he became a professor at the University of Padua, where he pursuits found greater acceptance.


Meanwhile in Holland, an apprentice lens grinder had discovered that if he looked through two lenses held an appropriate distance apart, objects appeared to be closer. His master used this principle to make a toy that he then displayed in his window. The toy came to the attention of Prince Maurice of Nassau, commander of the armed forces of the Netherlands (and, coincidentally, Descartes's commander), who envisioned military uses for it.

Galileo heard of this device two years later and started building telescopes. His fiifth telescope was large enough and accurate enough to enable him to observe sunspots and the mountain on the moon and to see that Jupiter had four moon that seemed to circle around it. These observations again contradicted the accepted science of Aristotle, which held the sun is without blemish and that all celestial bodies revolve around the earth, Galileo chose to publicly support the Copernican system, which stated that the planets revolve around the sun. His foes would not accept his evidence; he was even accused of falsifying his evidence by placing the four moons of Jupiter inside his telescope. The Church denounced the Copernican system as being dangerous to the faith and summoned Galileo to Rome, warning him not to teach or uphold that system.

Galileo responded by writing a masterpiece, Dialogue on the Two Chief Systems of the World, in which he compared the strength of the two theories of celestial motion. This work was written so that the nonspecialist could read it, and it became quite popular. Galileo was again summoned to Rome, where he was tried by the Inquisition and forced to recant his finding under threat of torture. It is said that after his forced denial of the earth's motion he muttered 'e pur si muove' ('nevertheless it does move'). He was imprisoned in his home and died nine years later. As a result of Galileo's experience, most scientist left Italy and went to Holland, where new scientific views were viewed with a more tolerant attitude.

A note in Galileo's handwriting in the margin of his personal copy of the Dialogue states: "In the matter of introducing novelties. And who can doubt that it will lead to the worst disorders when minds created free by God are compelled to submit slavishly to an outside will? When we are told to deny our senses and subject them to the whim of others? When people devoid of whatsoever competence are made judges over experts and are granted authority to treat them as they please? These are the novelties which are apt to bring about the ruin of commonwealths and the subversion of the state."

It is interesting  to note that in 1992 the Roman Catholic church admitted that it was wrong in condemning Galileo and opposing the Copernican system.

Galileo is called the father of modern science because of his emphasis on experimentation and his interest  in determining how things work rather than what cause them to work as they do. He insisted that a theory was unsound, no matter how logical it seemed, if observation did not support it, He invented the pendulum clock and the thermometer; he constructed one of the first compound  microscopes; and he greatly improved the design of telescopes. His last work, Dialogues Concerning Two New Sciences, contain many of his contributions to science, including those concerning motion and the strength of materials. In that work, he showed that a projectile follows a parabolic path and came to conclusions that foreshadowed Newton's law of motion. He also held that motion does not require a force to maintain it (As Aristotle claimed), but rather the 'creation or destruction of motion' (that is acceleration or deceleration) requires the application of force. Thus, he was the first to appreciate the importance ot the concept of acceleration.