What causes thunder?

[Kinthalis]

Well, I know that lightning does. But how exactly? Right now it's majorly storming out there and the peals of thunder are defeaning. So how does lightning cause the booming sound?

[Bear_Nenno]

Because lightning is stupid hot!! It superheats the surrounding air causing all the air molecules to accelerate past the speed of sound - causing a sonic boom.

Don't worry. A smart person will be by shortly to give you a really good answer.

[Chefguy]

That's basically it. Air expansion along the path of a lightning bolt. Online dictionaries are your friend.

And you can win $78,000 in a bet, if you're lucky, but that was a different thread.

[Mangetout]

Oh yeah, that's one theory, but it's just a theory; there's no credible evidence to prove that it isn't actually the hammer of Thor.

[Kat]

My mother always told me it was angels bowling.

[Bear_Nenno]

Or Grandma moving furniture around up there.