AMA | October 2024

3946.511 - 3969.76 Sean Carroll

It's just a fact that in our universe, that's a pretty good approximation, especially when you look at very large scales and average out the number of galaxies and stuff like that. So once you've done that, it turns out that if the universe is homogeneous and isotropic, then at every moment of time you have three-dimensional space, and it's completely characterized by its overall curvature.