The Universe Is Flat — Now What? Published: December 7, 2016

Flat as a (big) pancake

Remember that measuring the shape of the universe is a question for cosmology, the study of the entire universe. And in cosmology, nobody cares about you. Or me. Or solar systems. Or black holes. Or galaxies. In cosmology we care about the universe only at the very largest scales; small-scale bumps and wiggles are not important for this question.

The universe has all sorts of deformations in space-time where it varies from the perfectly flat. Any place where there’s mass or energy, there’s a corresponding bending of space-time — that’s General Relativity 101. So a couple light beams would naturally collide inside a wandering black hole, or bend along weird angles after encountering a galaxy or two.