Our universe is defined by the way it moves, and one way to describe the history of science is through our increasing awareness of the restlessness of the cosmos.
For millennia the brightest scientific minds in Europe and the Middle East believed that the Earth was perfectly still and that the heavens revolved around it, with a series of nested crystal spheres carrying each of the heavenly objects. Those early astronomers busied themselves with attempts to explain and predict the motion of those objects – the Sun, the Moon, each of the known planets, and the stars. Those predictions were excellent, and their systems able to explain the data well into the 16th century.
But that cosmological system of motion, initially developed by Claudius Ptolemy in the 2nd century, wasn’t perfect. In fact, it was an ungainly mathematical mess, relying on small circular orbits nested within larger ones, with some centered on the Earth and some centered on other points. On his deathbed in 1,543, the Polish astronomer Nicolas Copernicus published On the Revolutions of the Heavenly Spheres, a radical reformulation of the old Ptolemaic system that put the Sun at the center of the universe – still and motionless – with the Earth set in motion around it along with all the other planets.
