The author examines the theoretical effects of the three-dimensionality of the universe on Galileo’s and Copernicus’ cosmology. This conception coincides with the choice to suspend judgment on the boundaries of the whole and plays a key role in the fundamental notion of the preservation of order, seen as the stable relations of mobile bodies to the center of their motion that determine their perfection. It follows that not only the plurality of centers does not prejudice "the best arrangement" of the parts of the universe, but also that for bodies, whatever they are, it is the same to move in a circle or to be at rest. Furthermore, three-dimensionality drives the whole demonstrative process that establishes the truth of the Earth’s annual revolution and reveals the planetary order. This outcome, which necessarily implies the Earth’s daily rotation, both deprives the starry sphere of the very reason for its existence, traditionally grounded on its rotation, and validates the arguments by which Copernicus and Galileo had shown that in matters such as the limits and shape of the universe neither intellect nor the senses can produce any unassailable proofs.
Keywords: Galileo, Copernicus, three-dimensionality of the universe, modern cosmology, order of the universe, motions and bodies in a three-dimensional universe