I was asked to the following question: "If you were in a debate with an atheist and he asked you to give empirical evidence for God, what would you say?"
To which I answered:
I’d make a couple of preliminary observations before I tried to answer that question:
1.We need to clarify our expectations, and have reasonable expectations. It might obvious to some that if God exists, then his existence should be easy to prove. After all, if he exists, then shouldn’t that be fairly evident or conspicuous? He’s the source of everything else. The biggest fact of all.
However, there’s a paradox in proving God’s existence. Normally, when we try to prove that something exists, we use one thing to prove another. We take for granted the existence of something else, something related, and use that as a launch pad.
For example, we use time and consciousness as background conditions to prove other things. If, however, you were asked to prove the existence of time or consciousness itself, you might be stumped. It’s hard to come up with a non-circular argument for the existence of a background condition. Precisely because time and consciousness are so fundamental, they are resistant to direct demonstration. It’s hard to get “behind” them.
Because we see with our eyes, we never see our eyes. Not directly.
2.The answer to your question also turns, in part, on the precise form of the question or the implied audience. Is the question what empirical evidence would you cite to undergird your own belief in God? Or is it what empirical evidence would you cite for the benefit of someone who is not already a believer?
If, for example, you’re speaking for yourself, then depending the specifics of your religious experience, certain empirical evidence might dovetail with the argument from religious experience. For example, the argument from miracles could also count as empirical evidence in case you or someone you trusted had had a fairly unmistakable experience of God’s miraculous involvement in your life or his.
If, on the other hand, the answer is directed at outsiders, you might appeal to something more public.
3.Depending on how you define empirical evidence:
i) Among formal theistic proofs, I think the teleological argument has the most general appeal. And, as you know, there are different versions.
ii) If you regard testimonial evidence as an oblique form of empirical evidence (i.e. testimony to an empirical event), then the argument from miracles is also in play (although it needs to be carefully qualified).
iii) The argument from religious experience can also have a lot of popular appeal.