Galileo Discovers Inertia & the Relativity of Motion

Abstract

In the 1590s, while teaching at the University of Pisa, Galileo Galilei tried to solve a puzzle. It involved an apparent contradiction between what he was convinced was true about the world, but which our experience of the world implied was not true. The consensus among almost everyone, scientists and others, was that the Earth was not only the center of the universe, and that it remain fixed and unmovable in this place, but that our experience of everything going around us – Sun, Moon, stars, all things up in the sky – was proof that it could not be otherwise. It is impossible for the Earth to move, for if it did, we would experience that motion in various ways. At the very least, clouds and birds could not catch-up with a moving Earth. Or, a weight dropped from a tower would not fall vertically to the bottom, but would fall “behind” the tower. Of course, these things do not happen: therefore, not only is there nothing in our experience of the world that contradicts a stationary Earth, but everything we see and experience actually supports an immovable Earth. So why was Galileo puzzled? Because he was one of the few thinkers at this time who was increasing convinced, obstinately, that the Earth does move.