Galileo Galilei (1564–1642), known simply as Galileo, was born at Pisa, Italy, into a family of impoverished nobility. He was a brilliant mathematician who, at the age of 25, was appointed professor of mathematics at the University of Pisa. Like Copernicus and Kepler, Galileo viewed the uni- verse as a perfect machine whose workings could be understood only in mathematical terms:
Philosophy is written in that great book which ever lies before our eyes—I mean the universe—but we cannot understand it if we do not first learn the language and grasp the symbols in which it is written. This book is written in the mathematical language, and the symbols are triangles, circles, and other geometric figures, without whose help it is impossible to comprehend a single word of it; without which one wanders in vain through a dark labyrinth.
Also like Copernicus and Kepler, Galileo saw his task as explaining the true mathematical reality that existed beyond the world of appearances. Armed with these Pythagorean-Platonic beliefs, Galileo set out to correct a number of misconceptions about the world and about heavenly bodies. He challenged Aristotle’s contention that heavy objects fall faster than lighter ones by demonstrating that both fall at the same rate. He accepted the Copernican heliocentric theory and wrote a book in which he demolished all arguments against it. In 1609, Galileo used his modified version of the newly invented telescope to discover the mountains of the moon, sunspots, and the fact that the Milky Way is made up of many stars not visible to the naked eye. He also discovered four moons of Jupiter, which meant that there were at least 11 bodies in the solar system instead of 7, as claimed by the church.