 However, medieval philosophers differentiated empty worlds by the power of places within those worlds (Grant 1981). The Condemnation of 1277 forced Aristotelian philosophers to acknowledge the possibility of a void (to respect God’s omnipotence and the Christian doctrine of creation from nothing). Most thinkers retained Aristotle’s assumption that there was a unique center of the universe. If rocks were introduced into such a world, they would all head toward their natural location at the center of the universe. (Aristotle used this point to provide a spectacular explanation of why there are not two earths; they would have collided!) However, Nicole Oresme imagined a world without any center. He predicted the rocks would head toward each other. Since air, fire, earth, and water each had their own places in Aristotle’s physics, fourteenth century philosophers could imagine worlds that differed as to which of these places to retain. The void was rarely pictured as homogeneous.