• Mark A. Peterson, Dante and the 3-sphere, American Journal of Physics 47 (1979), 1031-1035. https://physicsgg.me/wp-content/uploads/2021/04/dante-and-the-3-sphere.pdf
"In the Paradiso Dante describes his ascent sphere by sphere through the Aristotelian universe to the Primum Mobile. Beyond this is the Empyrean, the abode of God and the angels. The conventional picture of the Empyrean seems to have been rather vague, geometrically speaking. In diagrams of the universe, for example, it was represented by the border area, outside the Primum Mobile, often richly populated with angelic beings. Dante, however, endows the Empyrean with a detailed and precise geometric structure. This structure is described in Canto 28, as if seen from the Primum Mobile, as a bright Point representing God, surrounded by nine concentric spheres representing the various angelic orders. The details which follow leave the almost inescapable impression that he conceives of these nine angelic spheres as forming one hemisphere of the entire universe and the usual Aristotelian universe up to the Primum
Mobile as the other hemisphere, while he is standing more or less on the equator between them, as if at the point P in Fig. 7 (see also Fig. 6). Taken all together, then, his universe is a 3-sphere.
Dante himself believed he was expressing something entirely new at this juncture.
Dante’s elation with this idea—a feeling we may readily share—has traditionally left readers somewhat puzzled. That is just another way of saying that if this passage is not taken as a description of the organization of 2-spheres into a 3-sphere, then it is hard to see what the point of it is."
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