The person who asserts that god exists must provide the proof of their claims. The person who asserts that god does not exist must also provide the proof of their claims.
For the scientist that uses the scientific method, and what scientist could be called a scientist that does not, that scientist must have something that is testable. It must be falsifiable.
The materialist who adopts the position that physical matter is all there is and that everything else is a manifestation of it must have proof of the metaphysical to accept its existence. That, I think, is an impossibility, that is, to prove something outside of what is, is. If something is outside of what is, it is not testable, hence not falsifiable (Except where the imagination is considered, it is illogical to think of anything outside of what is). The existence of the metaphysical cannot be proven. Manifestations of the metaphysical could simply be manifestations of the mind. If the metaphysical manifestations affect material, matter, then how could they not be physical? For the materialist, one that believes that matter is all there is, then the metaphysical is reduced to the imagination. For the materialist, if a god should exist, it would have to be made of matter. Such a god could not be all powerful as it would rely on matter and could not exist without it. If such a god was comprised of all matter, then everything is god, including us. If god is of matter, then that god had to appear at some point. A question arises, did that god create matter or merely rearrange it? Again, to substantiate that said god exists it would have to be testable. Matter is testable and thus far there has been no incidence where such a god has been detected. But, has all matter been tested? Can all matter be tested? There is no way to test all matter, at least at this point in our development. Again, god turns out to be non-falsifiable.
Ah ha, cries the theist. God exists!
The burden of proof lies with those making the assertion. No one can prove that something does not exist. Be it unicorn, leprechaun, or a teapot orbiting some distant orb, the non-provable may exist somewhere. The mighty Thor, despite our knowledge how such a story came to be, may exist somewhere in this vast cosmos.
Yet, for the materialist, the metaphysical, or anything outside of what is the material universe does not exist. So, the moment the theist makes claims that cannot be manifested, falsified, through the testing of matter, such claims can be dismissed. The claim that god is everywhere can be tested, has been tested repeatedly, and no such proof was found. That claim must fall. Omnipresence is out. What about Omniscience? To prove its existence would require a test subject. Refer to Omnipresence. The same goes with the claim of being all powerful.
Although the claim that no god exists could never be substantiated, since the christian bible claims that god is omnipresent, that god can be claimed to not exist, at least by the materialist.
1. Does materialism permit the existence of parallel universes?
2. Infinite parallel universes presenting every possibility would suggest that in one of those universes god exists. Perhaps this god created everything, including universes like ours where that god does not exist? Would there be any evidence?
3. Is that cat in the box really dead, or is that something else that I smell?