I will prove to you that God exists

[Sheldon]

(Bold mine)

I disagree. I have no doubt that gods do not exist. I may be wrong, but I’m not uncertain.

Boru

I'm a theist but I'm not 100% sure. How can anyone be certain how a universe that caused intelligent life to exist was caused inadvertently by mindless natural forces? Do we 'know' such forces alone could do that? Do we know they did do that? Where does your certainty come from?

That's an argumentum ad ignorantiam fallacy, it is fallacious to argue that anything is true because we lack an alternative explanation. It is also an objective fact the the universe and natural processes exist, but there is no objective evidence any deity or anything supernatural exists, or that they're even possible.