But what your teachers failed to explain is that “parallel lines never intersect” is only true in Euclidean geometry, which dates back to Euclid, a Greek mathematician living in Alexandria ...

This week on Spacetime, we take a detour into how geometry works in spacetime. Last time we talked about what curvature means, looked at geodesics, great circles on spheres, and tried to ...

You can find parallel lines all around you. Parallel lines can be straight lines, like the edges on this picture frame. They can also be curved lines, like these train tracks.

The illusion is that the two red lines appear curved, whereas they are actually parallel lines, like those on the right.

The curvature of the Earth itself caused these initially parallel lines to end up not-so-parallel. Ergo, the Earth is curved.

Instead, these researchers propose the universe may be ever so slightly "open," curved in such a way that parallel lines, which would never converge or diverge when running across a flat surface ...

You can find parallel lines all around you. Parallel lines can be straight lines, like the edges on this picture frame. They can also be curved lines, like these train tracks.