October 9th, 2024

An n-ball Between n-balls

The article explores a geometric thought experiment illustrating high-dimensional spaces, focusing on the behavior and volume relationships of n-balls and n-cubes as dimensions increase, revealing counterintuitive results.

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An n-ball Between n-balls

The article discusses a geometric thought experiment that illustrates the complexities of high-dimensional spaces through an interactive visual model. It begins with a 4x4 square containing four blue circles at each corner and a central red circle, which is maximized without overlapping the blue circles. As the model transitions to three dimensions, the circles become spheres, and the red sphere grows larger while new spheres are introduced. The article defines an n-dimensional construct as an n-cube with n-balls positioned between its vertices and the center. It explores the behavior of these shapes as dimensions increase, noting that the red ball can extend beyond the confines of the enclosing box in higher dimensions, a counterintuitive result. The article also discusses the volume relationships between n-balls and n-cubes, highlighting that while the volume of the n-ball decreases as dimensions increase, the surrounding space grows, leading to the perception of the n-ball being "spiky." The mathematical implications of these constructs are examined, including volume calculations for various dimensions, revealing that at certain dimensions, the volume of the n-ball can exceed that of the enclosing box significantly.

- The thought experiment illustrates the counterintuitive nature of high-dimensional geometry.

- The model transitions from 2D to 3D, showing how shapes evolve with added dimensions.

- In higher dimensions, the central n-ball can extend beyond the enclosing n-cube.

- Volume relationships between n-balls and n-cubes change as dimensions increase.

- The article emphasizes the mathematical complexities and visualizations of high-dimensional constructs.

AI: What people are saying
The comments on the article about high-dimensional spaces and n-balls reveal several key themes and points of discussion.
  • There is confusion and debate over the distinction between "ball" and "sphere" in mathematical terminology.
  • Many commenters express fascination with the concept of the curse of dimensionality and its implications.
  • Visual aids and animations are highly appreciated, with several users noting their impact on understanding the concepts.
  • Some users reference additional resources, such as videos and previous articles, to further explore the topic.
  • There is a sense of wonder and challenge in grasping the complexities of high-dimensional geometry.
Link Icon 15 comments
By @Sharlin - 7 months
A good way to conceptualize what’s going on is not the idea that balls become "spiky" in high dimensions – like the article says, balls are always perfectly symmetrical by definition. But it’s the box becoming spiky, "caltrop-shaped", its vertices reaching farther and farther out from the origin as the square root of dimension, while the centers of its sides remain at exactly +-1. And the 2^N surrounding balls are also getting farther from the origin, while their radius remains 1/2. Now it should be quite easy to imagine how the center ball gets more and more room until it grows out of the spiky box.
By @steventhedev - 7 months
This is a really good demonstration of the curse of dimensionality[0]

[0]: https://en.m.wikipedia.org/wiki/Curse_of_dimensionality

By @drdeca - 7 months
Why did I imagine that this would be about two shapes that are merely topologically n-balls, each having part of their boundary be incident with one of the two hemi(n-1)-spheres of the boundary of an n-ball (and otherwise not intersecting it)? (So like, in 3D, if you took some ball and two lumps of clay of different colors, and smooshed each piece of clay over half of the surface of the ball, with each of the two lumps of clay remaining topologically a 3-ball.)

I don’t know that there would even be anything interesting to say about that.

By @robwwilliams - 7 months
Impressive, helpful, and now time to rebuild my own embeddings so I can grasp that red n-ball with my new n-D hands.
By @ColinWright - 7 months
For other HN discussions of this phenomenon you can see some previous submissions of another article on it.

That article doesn't have the nice animations, but it is from 14 years ago ...

https://news.ycombinator.com/item?id=12998899

https://news.ycombinator.com/item?id=3995615

And from October 29, 2010:

https://news.ycombinator.com/item?id=1846682

By @bt1a - 7 months
I am struggling to juggle the balls in my mind. Are there any stepping-stone visual pieces like this to hopefully get me there? Very neat write-up, but I can't wait to share the realized absurdity of the red ball's green box eclipsing in our 3D intersection of the fully diagonalized 10D construct
By @Imustaskforhelp - 7 months
Can I just say how my mind is utterly blown by the animations
By @chadhutchins10 - 7 months
Anyone else click just to slide some animations?
By @mbowcut2 - 7 months
Numberphile did a video on this a while back. https://youtu.be/mceaM2_zQd8?si=0xcOAoF-Bn1Z8nrO
By @joaquincabezas - 7 months
wow discovering Hamming’s lecture was enough for me! so good
By @WhitneyLand - 7 months
Both ChatGpt 4.o and Claude failed to answer

“…At what dimension would the red ball extend outside the box?”

If anyone has o1-preview it’d be interesting to hear how well it does on this.

By @Asraelite - 7 months
I never understood the need to distinguish between "ball" and "sphere" in maths. Sure, one is solid and the other hollow, but why is that fact so important that you need to use a completely different word? As I understand it, you could replace every instance of "ball" in this article with "sphere" and it would still be correct.

We don't have special words for the voluminous versions of other 3D shapes, so why do spheres need one?

By @beretguy - 7 months
I… can’t.
By @eniwnenahg - 7 months
Matlock, is that you?