Numberphile
2 HN recommenders · recommended in 4 months, 2020–2025
10:33 · 768K views · Sep 18, 2017
Matt Parker on Numberphile explains the strange properties of spheres in higher dimensions, such as how they poke out of their bounding boxes. It uses Pythagoras to build intuition for 4D and beyond.
Recommended whenever the counterintuitive geometry of high-dimensional spheres comes up, including in vector embedding discussions.
4 comments from Hacker News
Generalizations to higher dimensions[1] also have some fun properties. For one, the volume of a n-dimensional sphere (ball) goes to zero as n goes to infinity. But not in a trivial way: given a radius r, you can find the number of dimensions n that maximizes the volume of the n-sphere. For r=1 it's 5 dimensions, but for r=3 it's 55 dimensions. Numberphile[2] has a video on higher dimensional spheres which talks about this weirdness. [1]: [LINK] [2]: this video
There is a good numberphile video about that this video It contains also a hilarious reference to the "parker circle:.
Also not a topologist, but thought it was interesting after watching the video from the current top comment, this video , where if you look at the size of the "contained sphere", 4D is the only place where the contained sphere is exactly tangent to the containing box. Lower than that, and it's easy to visualize how the contained sphere is smaller, higher than that, the contained sphere is always bigger. So seems like it might be a natural consequence that techniques that work at higher or lower dimensions don't work for the case in 4D where the sphere is exactly tangent.
Oh they are very spike-y, well, my point in the above post is to just solve the eq but easier 'visualization' would be [0] By the way, this is a similar phenomena to the 'curse of dimensionality' [1] [0] this video [1] [LINK]