  Since about 1700 theories about the nature and structure of the Universe were derived from Newtonian theory, most especially his theory of gravitation, which was used to account for the behavior of heavenly bodies and their systems. Newton’s theory hypothesized a force—gravitation—acting upon material bodies, free to move over time within the passive, inert ‘container’ of three-dimensional space. Bodies, paths, and space itself exemplified the classical geometry of Euclid. All these features changed with the publication of Einstein’s General Theory of Relativity, 1915–17.