This question is representative of the type of paradoxes atheists use in attempts to prove that God cannot exist. It works like this. God is supposed to be omnipotent. If He is omnipotent, then He can create a rock so big that He can't pick it up. If He cannot make a rock like this, then He is not omnipotent. If He can make a rock so big He can't pick it up, then He isn't omnipotent either. Either way demonstrates that God cannot do something. Therefore God is not omnipotent. Therefore God does not exist.