The Deceptively Asymmetric Unit Sphere

by ThatGeoGuyon 11/22/24, 4:00 PMwith 30 comments
by ssivarkon 11/22/24, 5:01 PM

Very nice "visual" introduction a topic that's usually treated very abstractly in math textbooks! If you'd like more of such a visual perspective on differential geometry, I recommend Tristan Needham's book [1].

[1]: https://press.princeton.edu/books/paperback/9780691203706/vi...

by bryan0on 11/23/24, 1:20 AM

I'm not sure if this is the main point of the article (but it does at least mention it), a good intuitive visualization of how the sphere can be thought of as asymmetric is the Hairy Ball Theorem[0], which basically states: "you can't comb a hairy ball flat without creating a cowlick"

[0]: https://en.wikipedia.org/wiki/Hairy_ball_theorem

by ykonstanton 11/23/24, 10:50 AM

Something that may be of interest to CS people and reveals the complexity of the unit sphere is the following problem:

Find an efficient (class of) algorithm(s) to select a large number N of uniformly distributed points on S^2, where "uniformly distributed" is given in a more flexible sense than the usual one. For instance, you may want to minimize the Weyl discrepancy between average and integral, or you may want to focus more on minimizing the number of ε-clusters of distances.

One of the most elegant approaches to this problem is the classic work of Lubotzky, Phillips and Sarnak: Hecke Operators and Distributing Points on the Sphere I and II. They translate the problem to one of generating good sequences of elements of SO(3), which they attack with a combination of harmonic analysis on the semisimple groups, homogeneous dynamics and number theory with Hecke operators as their central tool.

by red_trumpeton 11/22/24, 11:52 PM

Were does the notation T^2 for oriented real projective space come from? That's just bad, because it is not a torus but a sphere, and the two are topologically very different!

by Animatson 11/22/24, 6:55 PM

No mention of quaternions and SLERP?

by wcrossbowon 11/23/24, 6:59 AM

Great example of a corporate blog! My immediate reaction is I want to work in this team.

by hammockon 11/22/24, 6:55 PM

Another awesome mathematics article that loses me about 10-15% of the way in do to my own technical limitations. Any tips from HN on how to improve my ability to get thru, say, 45-50% of these types of articles?? Generally speaking, not specific to the math in OP article