Wasn't it Clarke who said that any technology sufficiently advanced, would be indistinguishable from magic? As has been stated in another thread, anyone of us, travelling back in time with a trunk (we're using a DeLorian, of course) full of battery-powered gadgets and weapons could convince any cave man that we were, in fact, all-powerful. It's hard to be a critical thinker when somebody displays unfathomable power in certain areas, even if they display no unusual power in other areas. Aren't there som OT passages where God is shown as less-than-omnipotent, along the lines of being unable to smite some warriors because they possessed chariots and spears of metal?
Anyway, I'm firm in my belief that if time travel were indeed possible, we'd have encountered time travellers long ago