Do we believe the universe has any extrinsic curvature at all? As far as I'm aware extrinsic curvature is only used in geometry/math to model the intrinsic curvature, correct?
From the answers to this question: How can we model intrinsic curvature?
Why do we still use Euclidean geometry instead of Riemannian geometry? And in what cases is one preferable over the other?