Materialists generally aren't sure. Nor atheists. We're reasonably certain, and ask for proof, since the default assumption should be that the universe is what

Materialists generally aren't sure. Nor atheists. We're reasonably certain, and ask for proof, since the default assumption should be that the universe is what it seems. I should say that agnostics are pretty sure they don't know one way or the other, and some are sure the answer can't be known even in principle (I'm in that camp myself, in the sense that one can't logically prove a negative, and that absence of evidence is not evidence of absence). Most would still bet on materialism though, if they had to put money on it. The folks who are absolutely 100% sure are theists. Except they can't agree with one another, and their beliefs can't be reconciled, even superficially, except by the traditional means of exterminating believers. Which is probably why there aren't too many Zeus or Ra worshippers around.