The standard FLRW metric[1] that's used to model the universe is "not necessarily simply connected," which means it allows for shapes such as toruses, multiple

The standard FLRW metric[1] that's used to model the universe is "not necessarily simply connected," which means it allows for shapes such as toruses, multiple connected toruses, and so on. There's one proposal for something called the Poincaré dodecahedral space - see "Is the universe a dodecahedron?"[2] But a sphere, or rather, a higher-dimensional hyperspherical equivalent, is the simplest possibility for that kind of scenario, and the FLRW metric allows that. This article, "The Shapes of Space", has some nice explanations: http://www.ic.uff.br/~aconci/poincare.pdf http://www.ic.uff.br/~aconci/poincare.pdf [1] https://en.wikipedia.org/wiki/Friedmann%E2%80%93Lema%C3%AEtre%E2%80%93Robertson%E2%80%93Walker_metric https://en.wikipedia.org/wiki/Friedmann%E2%80%93Lema%C3%AEtr... [2] https://physicsworld.com/a/is-the-universe-a-dodecahedron/ https://physicsworld.com/a/is-the-universe-a-dodecahedron/