Atheism is a
belief system, and not a system of knowledge. Nor is it scientific. As Goat and Ranger have explained, the existence of god(s) is not testable and therefore we can't
know whether any exist. Your belief (and that's what it is) that "there is a scientific answer to everything" is also unscientific. See, for example, Heisenberg's
uncertainty principle, which explains that even some things squarely in science's wheelhouse can't be known. Finally, your demand that theists prove the existence of God is incoherent. Of course they can't prove it, just as you can't disprove it.
The principled stance for someone who knows only what facts and reason can tell him is agnosticism, not atheism.