xkcd What-If

(via Boing Boing) xkcd has a cool new feature, called "what if?"  It's linked up at the top of the  main page, under the xkcd logo and right here.

The current one, about SAT guessing, explains, basically, what looks like the one sense in which the SAT is a good test -- it's practically impossible to cheat.

The one before that, though, called "Relativistic Baseball," is awesome.

The question is, "What would happen if you tried to hit a baseball pitched at 90% the speed of light?"

And the answer is, basically, everyone dies.

Suppose you’re watching from a hilltop outside the city. The first thing you see is a blinding light, far outshining the sun. This gradually fades over the course of a few seconds, and a growing fireball rises into a mushroom cloud. Then, with a great roar, the blast wave arrives, tearing up trees and shredding houses.