Galileo’s famous experiment dropping objects from the Leaning Tower of Piza probably did not happen quite the way we remember. But he did discover the existence of some force that causes a crumpled piece of paper to accelerate at the same rate as an apple. Gravitational acceleration on Earth does not depend on mass (at least not for two things of similar mass—the moon does not fall at the same rate as an apple would). This improved on Aristotle’s understanding of gravity, but it was not perfect. Newton later expanded the idea of gravity to something that exists everywhere in the universe. And then Einstein expanded it further with his theory of general relativity. Some time in the future, another scientific genius not yet born will make a new discovery to revolutionize our understanding of gravity. Our knowledge of science is always changing, and will always continue to change. Astronomer Laura Danly recounts the history of gravity.

Recorded June 2010; Posted August 2010