that it lies flat everywhere along the surface. If the ball were a donut, or it existed in

two dimensions, this would be easy! But in three dimensions? Well, you're going to run

into trouble. A lot of trouble. A big hairy ball of trouble.

That's because of a theorem in algebraic topology called the "Hairy Ball Theorem" (and yes,

that's it's real name) which unequivocally proves that at some point, the hair must stick

up. Now don't go wasting your time playing around with a hairy ball trying to prove the

theorem wrong - this is math we're talking about. It's proven - done - QED!

Technically speaking, what the Hairy Ball theorem says is that a continuous vector field

tangent to a sphere must have at least one point where the vector is zero.

So what does this have to do with reality apart from uncombable hairy balls? Well, the

velocity of wind along the surface of the earth is a vector field, so the Hairy Ball

Theorem guarantees that there's always at least one point on earth where the wind isn't

blowing.

And it doesn't really matter that the object in question is ball-shaped. As long as it

can be smoothly deformed into a ball without cutting or sewing edges together, the theorem

still holds. So the next time a mathematician gives you trouble, ask them if they can comb

a hairy banana.