Special relativity is good enough for most purposes, which means that (a time slice of) the real universe is very nearly Euclidean. So if you are going to explain the geometry of the universe to someone, you might as well just say “very nearly Euclidean, except near objects with very high gravity such as stars and black holes”.
I don’t think it’s helpful to compare with Euclid’s postulates, they reflect a very different way of thinking about geometry than modern differential geometry.
Special relativity is good enough for most purposes, which means that (a time slice of) the real universe is very nearly Euclidean. So if you are going to explain the geometry of the universe to someone, you might as well just say “very nearly Euclidean, except near objects with very high gravity such as stars and black holes”.
I don’t think it’s helpful to compare with Euclid’s postulates, they reflect a very different way of thinking about geometry than modern differential geometry.