Outside In

ssgelm · 11.7M views · 2011-04-23 · 21:25

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Overview

A 21-minute animation showing how a sphere can be turned inside out without creases or tears, known as sphere eversion.

On Hacker News

Linked as a classic visualization when sphere eversion or counterintuitive mathematics comes up.

Discussed on HN; no positive recommendation is recorded in this export · HN mentions 2021–2025

Topics

Pure mathematics Recreational & visual math

What people said

gosub100 · 2025-01 · Reference
Sort of a tangent, but here's a 20m video explaining how to invert a sphere without tearing it: [VIDEO]
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ykonstant · 2022-04 · Reference
Here are two classic youtube videos on the topic of sphere eversion; they mostly overlap, but I am posting both for double the hilarity in the comment sections :) (the full 21 minute one) [VIDEO] (the first 10 minutes) [LINK] If I remember correctly, I think the 10 minute one has the more hilarious comment section.
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st_goliath · 2021-10 · Reference
> 19. Given a solid ball in 3‑dimensional space, there exists a decomposition of the ball into a finite number of disjoint subsets, which can then be put back together in a different way to yield two identical copies of the original ball. While you're at it, you can completely turn that sphere inside out without creating any holes or creases[1]. [1] [VIDEO]
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Sources

Video by ssgelm, played through YouTube.

HN Library · Source license

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