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Strange Spheres in Higher Dimensions - Numberphile

30 videos recommended on HN
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2 HN users recommended this explainer2 months2020–2025 score 2
Years with an HN recommendation, 2007–2026

Recommended whenever the counterintuitive geometry of high-dimensional spheres comes up, including in vector embedding discussions.

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.

“Numberphile[2] has a video on higher dimensional spheres which talks about this weirdness.” (HN, 2020)

2 recommendations · 2 citations · Explainers

4 Hacker News comments

From the HN archive; up to 20 kept per video, favoring different commenters. Recommendations first.

@magicalhippo Feb 2020 Recommends
on HN thread Volume of a Sphere
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]
Numberphile on strange higher-dimensional sphere properties.

Citations, criticism and jokes

@ithinkso Sep 2021 Cites it
on HN thread A mathematician's guided tour through higher dimensions
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]
Easier visualization of spiky high-dimensional spheres.
@hn_throwaway_99 Oct 2021 Cites it
on HN thread Tadayuki Watanabe disproved a major conjecture about spheres
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.
Shows 4D sphere exactly tangent to its containing box.

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