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3Blue1Brown mailing list · Jan 31, 2026

The Hairy Ball Theorem

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Grant Sanderson · 3Blue1Brown mailing list

What I love about the hairy ball theorem is that it shows how geometry enforces limits without dynamics. No matter how carefully you try to smooth things out locally, the global structure has the final word.

For black holes, we have the “no hair theorem,” but a quasar and the radiation emitted from an accretion disk eerily match the poles of the hairy ball theorem for a sphere rotating in one direction. Stars before they collapse into a black hole have spin angular momentum. Neutron stars are electrically neutral before the black hole forms. Where does the rest of the stars' information, the entropy, go?

Does it go out of the poles due to the hairy ball theorem?

Read the original on 3blue1brown.substack.com

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