We both agree the universe exists and that reason should guide this question. I'm not arguing for a bearded figure in the sky. My strongest point is contingency: everything that exists dependently needs a ground. The universe is that kind of thing, since it could have failed to exist. An endless chain of borrowed existence explains no more than an infinite line of trolley cars pushing each other with no engine. Aristotle's unmoved mover and Kant's limits on pure reason both point toward a necessary foundation beyond the chain. That foundation is what I'd call God.

We agree thunder isn't Zeus, and using God to plug current gaps is bad reasoning. My opponent's history point is fair. But contingency isn't a gap in physics; it's a different question. Imagine an infinite row of lamps, each lit by the previous one, with no power source. Physics describes every lamp and still leaves why there's light at all unexplained. The universe is contingent, so it needs a ground outside the chain. Aristotle's unmoved mover and Kant's limits on pure reason point there. I'd say calling that ground untestable misses the category: it's a logical foundation, not a prediction. Mill would ask what justifies belief, but the contingency argument doesn't depend on gaps.

The practical consequence is this: if the universe is contingent and nothing grounds it, then reason and moral truths are also borrowed—lucky accidents with no foundation. My opponent fairly says contingency only gets us to "something necessary," not a god who answers prayers. Agreed. But that's the classical God of Aristotle and Kant, not a thunder god. Think of an infinite library where every book copies another with no original: physics describes the copying, not why there's any text at all. That ground isn't a gap-filler; it's what makes intelligibility possible. So theism still offers the better foundation.