Galileo’s Book of Nature

In 1971, astronaut David Scott, standing on the Moon, dropped a hammer and a feather and found that both reached the surface at the same time. This popular experiment during the Apollo 15 mission was a dramatic demonstration of a prediction made by Galileo three centuries earlier. Galileo was born in Pisa on 15 February 1564, just 454 years ago today [TM133 or search for “thatsmaths” at].


Image: NASA

During the time when he held a teaching post at the University of Pisa, Galileo wrote a series of essays on motion, De Motu, which advanced an idea that is obvious to us today but that was very innovative at that time: one can test scientific theories by conducting experiments. De Motu describes the important idea that theories about falling bodies could be tested using an inclined plane to slow down the rate of descent. This enabled Galileo to deduce that acceleration is the same for all bodies subject to gravity, so that heavy and light objects should fall at the same speed. And it was this hypothesis that was confirmed by the experiment on the Moon in 1971. Of course, on Earth, air resistance complicates matters, but there is no atmospheric drag on the Moon.

Galileo’s Telescope

Galilean-MoonsIn May 1609, Galileo, having heard about an optical instrument devised by a Dutch eyeglass maker named Hans Lippershey, quickly designed a telescope that could magnify objects 20 times. Galileo was the first person to point a telescope towards the sky. His findings were dramatic and ultimately had a revolutionary effect on science. He could see the mountains on the moon, spots on the Sun, the phases of Venus and the myriad stars in the Milky Way. He also discovered the four major moons rotating around Jupiter.

As a result of his observations, Galileo became convinced that the Sun was at the centre of our planetary system, in accordance with the ideas of Copernicus but in conflict with orthodox interpretations of Holy Scripture. Galileo wrote a book “Dialogue Concerning the Two Chief World Systems, Ptolemaic and Copernican” comparing the old and new world models. It was published in 1632 but, although he dedicated this work to Pope Urban VIII, Galileo’s ideas were deemed to be heretical and he was sentenced to house arrest, which endured until his death ten years later.

Galileo-Galilei-SmallGalileo made dramatic discoveries in mechanics, studying inertia, velocity, the effects of gravity, the principle of relativity and the motion of projectiles. He also worked in practical applications of science, describing the properties of pendulums and hydrostatic balances and inventing the thermometer. His student Evangelista Torricelli is credited with the invention of the barometer, triggering major developments in the physics of the atmosphere. Galileo’s work had an enormous significance for Newton and he is undoubtedly one of the “giants” upon whose shoulders Newton stood.

The Book of Nature

Galileo has been called the father of observational astronomy, the father of modern physics and even the father of science. Perhaps his greatest contribution was the “mathematization” of science. He wrote that the Book of Nature is “written in mathematical language, and its characters are triangles, circles and other geometric figures, without which it is impossible to humanly understand a word; without these, one is wandering in a dark labyrinth.”

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