text: This Greek word refers to an early Greek model of the universe , in which all matter was contained within rotating spheres centered on the Earth ; according to Aristotle , the rotation of the outermost sphere was responsible for the motion and change of everything within .
simplified: This refers to an early Greek model of the Universe . In that model , all matter was in rotating spheres centered on the Earth ; according to Aristotle , the rotation of the outermost sphere was responsible for the motion and change of everything within .