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Comment by johnwatson11218 | Hacker News Reader

Not sure if it was in the article or not but I think the Hairy Ball theorem from Topology would be important. Since earth is a sphere the wind can't blow all in the same direction. Some currents must oppose others. In a torus the wind could start blowing in one direction and stay that way forever.

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That's not what the Hairy Ball Theorem (HBT) says, the HBT says that there must be a point on a sphere where a continuous vector field is zero. It doesn't say they can't be pointing in the same direction except that point.

this link http://uncyclopedia.wikia.com/wiki/Hairy_ball_theorem talks about the application to the torus. It states that it is possible to completely comb the hair on a doughnut. That is the point I was trying to make earlier. I think it does imply that the wind could start blowing in the same direction if we lived on a torus. I think it would be the same if we lived inside like in science fiction movies or if we lived on the surface with a normal atmosphere.

I can't tell if you're being sarcastic... but if not, this is the first legitimate use of uncyclopedia as a source I've seen.

In fact, it does -- to demonstrate, assume otherwise and use the definition of continuity.

sigh To quote because topology is a pain:

> "there is no nonvanishing continuous tangent vector field on even dimensional n-spheres. For the ordinary sphere, or 2‑sphere, if f is a continuous function that assigns a vector in R3 to every point p on a sphere such that f(p) is always tangent to the sphere at p, then there is at least one p such that f(p) = 0"

Which means they can all blow in a continuous path except for at least one point, so the wind at every point but 2 could be blowing east on a sphere.

http://en.wikipedia.org/wiki/Hairy_ball_theorem

Yes, but the velocity must go to zero as you approach the poles. I took the OP to mean "with the same velocity", not "in closed loops". Obviously wind must blow in closed loops, since there are no sources or sinks of air.

So to you, "pointing in the same direction" includes "pointing in exact opposite directions within an epsilon-ball for any epsilon"?

There's a whole continuum between "pointing in the same direction" and "pointing in exactly opposite directions".

Wind currents would be determined by convection and Coriolis effects, so it would always be going in different directions at different locations.

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