If nothing is eternal then all is temporal. If all is temporal then all had a beginning. If all had a beginning then something came from nothing. Since something can't come from nothing the opposite must be true: at least something is eternal. We call it "God" but "God" as a word holds as much meaning as "dark matter", it's a placeholder variable, nothing more.
How about a proof of existence by contradiction?
If nothing is eternal then all is temporal. If all is temporal then all had a beginning. If all had a beginning then something came from nothing. Since something can't come from nothing the opposite must be true: at least something is eternal. We call it "God" but "God" as a word holds as much meaning as "dark matter", it's a placeholder variable, nothing more.