4 ms·
Heard a mathematician friend call this the “hairy sphere theorem” once. At first I thought he was being a prude, but now I appreciate that the theorem is about
by orlandpm 1y ago
Heard a mathematician friend call this the “hairy sphere theorem” once. At first I thought he was being a prude, but now I appreciate that the theorem is about spheres, as opposed to balls.
- IAmBroom 1y agoIt's not. It's about closed surfaces, which include the surface of spheres, oblate spheres, footballs, pencils, and airplanes.
- orlandpm 1y agoWell, all these closed surfaces you mention are (topologically) spheres. The theorem doesn’t apply to some other closed surfaces, like the torus, which does admit a continuous non-vanishing vector field.