Just a couple of questions:(adsbygoogle = window.adsbygoogle || []).push({});

1. If we imagine space to be curved over a sphere is it possible to travel in one direction and eventually end up where you started, assuming that the sphere it self is not expanding.

2. What's the difference between a two sphere and a three sphere? I find it hard to grasp the idea of a three sphere, because if there is now a radial or z coordinate then it's not really a sphere is it?

Thanks

Raj

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# Two spheres and three spheres

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