| I'm not talking about our own light cone. I'm talking about https://en.wikipedia.org/wiki/Shape_of_the_universe Basically, ignoring wormholes and black holes and assuming that spacetime is locally flat everywhere and it's mathematically a manifold, my question is: what's the shape of the (global) universe? Global as opposed to observable. So we might have a hard time answering that question. How would you be able to distinguish between the (n-dimensional equivalent of) a torus vs a flat infinite space, if you can't see the repetition? You'd even have a hard time distinguishing a hypersphere from a flat infinite space, if the hypesphere was big enough so that we can't tell it's curvature apart from no curvature. Or the universe might be weirdly shaped, and we just happen to live in the flat part. So I guess the question comes down to: * assuming no edges
* assume Copernicus at least for space (we might have a special position in time)
* What's the simplest theory about the shape of the global universe that satisfies our observations? I suspect general relativity toys around with such questions, because I know that they sometimes look at cosmological (toy) models for the whole universe, and not just what's in the light cone of one particular observer. |