1- It's not a theory
2- Satan is in the ground? What made you come up with that? Asume there God and Satan exist. I can't recall any part of the bible saying that Satan is inside our planet (y'know, people thought the world was flat in those days, so down would still be in the heavens or as we call it: outer space).
Where do you think Hell is(assuming you believed in Hell)? How would down be considered up if the Earth was flat???
Yeah, I didn't get that one either.