"Hell is natively infinite vacuum which is not physically contiguous with - this." He waves, generally, at the entire mortal world. "Demons have added things to it; most of the civilization is on a gigantic tacky plane of solid gold. I am not a physicist, so I can't tell you much about whether any laws of physics are being broken apart from our ability to make stuff and be summoned, but when there is a source of gravity water flows downhill and my laptop works and stuff like that."