A student once asked me the question that a lot of people wonder about: who made God? A few scriptures directly address this question, but I referenced Psalm 90:2 in my answer to the student and one might also consider 1 Timothy 1:17. Furthermore, I tried to reason with her concerning the difficulty of understanding how God could have always existed without being created by invoking concepts in physics that are hard to understand (i.e., they are comparable to understanding God's necessary existence). For example, most people do not comprehend the math for relativity theory. But two arguments for God's existence that seem compelling to me are (1) the argument from possibility and necessity or Aquinas' third way; (2) the need to avoid an infinite regress.
Regarding number (1), it seems reasonable to suppose that "if all things possibly fail to exist at some time then possibly there is a time when nothing exists" (Robert E. Maydole).
If it's logically possible that nothing finite once existed, then it is logically possible that if non-existent things did come to have actual existence instead of just potential existence, then a necessary being (one who exists without any other entity sustaining the being's existence) brought once non-existent things into existence. Nevertheless, I think Aquinas' third way (proof) only works if one modalizes it like Maydole does.
But my student objects that we can't see God or empirically detect him like we are capable of measuring or detecting physical entities (e.g. the wind, atoms, and gravity). While I grant this point, it does not seem that the objection is fatal to belief in God. Many things in physics are less than certain (to understate the matter) and science has even predicted the existence of some things that were not detected at the time, for instance, in chemistry, cosmology and with string theory. There are still some things that science has never detected but these things are widely thought to exist. Besides, to suppose that we must see/hear something (etc.) to believe it exists is a metaphysical position or an article of faith: the proposition itself is not a fact.
Quite frankly, it takes more faith to believe this universe arose from absolute nothingness without God than it does to believe in God, the ens realissimum and ens necessarius. Peter van Inwagen has a great point about the odds of the universe coming into existence from absolutely nothing, including no God. Try 0% on for size.
