Gravity is weird. On the one hand, gravity is a good thing, because it keeps me from floating away into space and makes possible my building stable shelters from the storm. On the other hand, gravity is a major cause of natural evil, as when buildings collapse during earthquakes or people fall through cracks in the ice and drown. The quirky American businessman, Roger Babson, was so alarmed by the evil consequences of gravity that in 1948 he founded the Gravity Research Foundation in New Boston, New Hampshire with the explicit aim of understanding gravity so as to defeat it. So how does gravity work? What keeps my feet planted firmly on the ground but then sends me tumbling painfully to the earth when I trip over a rock?

Aristotle on Free Fall

In the fourth century, BCE, Aristotle thought that he had the answer. He taught that every element had a natural place in the universe and a corresponding natural tendency to seek that place. The natural place of the element earth was a sphere at the center of the universe, and earth, by its very nature, tended always to seek that natural place unless something interfered with its natural motion. Since heavy bodies, on his analysis, consisted mainly of earth, albeit mixed with some water, air, and fire, they fall simply because that’s what earth naturally does. For its time, this was not a bad theory. It explained free fall and other noteworthy “facts,” such as why, as Aristotle and his contemporaries thought, the planet, Earth, happened to be located in the centre of the universe.