this post was submitted on 19 Apr 2025
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Today I Learned (TIL)

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submitted 1 month ago* (last edited 1 month ago) by [email protected] to c/[email protected]
 

The theorem has been expressed colloquially as "you can't comb a hairy ball flat without creating a cowlick" or "you can't comb the hair on a coconut".

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[–] [email protected] 47 points 1 month ago (2 children)

A hairy doughnut … on the other hand, is quite easily combable.

What gives someone the right to speak like this. You think this is the kind of factoid I can just forget?? No, this meme is going to jockey my brain until the day I die.

[–] [email protected] 6 points 1 month ago (1 children)
[–] [email protected] 6 points 1 month ago (1 children)

"CHICKEN JOCKEY!"

throws popcorn at phone screen

[–] [email protected] 3 points 1 month ago (1 children)

My nephews have been screaming this. I thought they were just insane, but apparently I've missed a meme!

[–] can 2 points 1 month ago
[–] [email protected] 4 points 1 month ago

I want to know more. Does this only work for donuts with 1 hole? Odd numbers of holes?

[–] [email protected] 20 points 1 month ago (2 children)
[–] [email protected] 4 points 1 month ago (1 children)

Why does Wikipedia do this?

[–] [email protected] 11 points 1 month ago (1 children)

Whoever posted the link was on mobile at the time and didn't feel like deleting the m. after copy pasting.

[–] [email protected] 9 points 1 month ago

Yeah ik. Just confused why Wikipedia itself does it

[–] [email protected] 3 points 1 month ago (1 children)

Thanks, I expected it would figure itself out. But I guess it only works in the desktop -> mobile direction, not the reverse.

[–] [email protected] 1 points 1 month ago

Totally, I don't understand why it doesn't work that way.

[–] [email protected] 18 points 1 month ago (1 children)
[–] [email protected] 3 points 1 month ago (1 children)

And where is the cowlick on there...

[–] funkless_eck 7 points 1 month ago (1 children)

buy it dinner and wherever you want

[–] [email protected] 1 points 1 month ago* (last edited 1 month ago)

With three extra stomachs, that'll cost ya!

[–] [email protected] 7 points 1 month ago (1 children)

Shave 'em. I don't want no cowlick near my balls

[–] [email protected] 7 points 1 month ago (1 children)

You haven't lived until a cow licks your balls.

[–] [email protected] 3 points 1 month ago (1 children)

I guess the closest I've gotten to that is to have a cow lick the "T" off of the "Passat" lettering on my trunk a couple years ago.

[–] [email protected] 1 points 1 month ago (1 children)

...where were your balls when that happened?

[–] [email protected] 1 points 1 month ago

nowhere near the trunk of the car, thankfully. :-)

[–] [email protected] 5 points 1 month ago (1 children)

For mathematicians in Germany, this is known as the "Hedgehog Theorem" ("Satz vom Igel", as in "you can't fully comb a hedgehog")

[–] [email protected] 3 points 1 month ago

I think it would be hard to find a hedgehog that would allow itself to be combed.

[–] [email protected] 4 points 1 month ago

I remember first hearing about the Hairy Ball Theorum when watching some of the extended features on our Monster's Inc DVD. One of the animators was talking about how they had to constantly be re-combing Sully's hair to make sure the cowlick was in an unseen location

I'll have to poke around at some point because there was a really neat video on that DVD as well that was talking about the origin of the Monsters Inc universe, and how the monsters both discovered the power of screams and built the doors/portals for reaching the human world and I remember it being super interesting and extremely fleshed out for something that literally never happen on screen and probably doesn't influence anything on-screen at all

[–] untakenusername 3 points 1 month ago (1 children)
[–] stevedice 2 points 1 month ago
[–] [email protected] 1 points 1 month ago

By moving the entire comb parallel, sure. But you can move one end slower than the other (i.e. as if you planted one end and pivoted it around, just with some speed, not stationary) and you can comb it without it.