How should one respond to the old school boy’s retort, “if everything needs a cause, who caused God?” Well, in the limited space I have available (due primarily to your attention span), here’s one way.
Firstly, believing philosophers and theologians do not maintain that whatever exists needs a cause. Instead, they propose that certain classes of things need causes, such as things which have a beginning or things which don’t have to exist.
If something came into existence at a certain point in time–that is, if it had a beginning–then there needs to be a cause, an explanation, for why it came to be. But if something exists outside of time–like God–then it does not need an explanation for its beginning because it does not have one.
In the same way, if something doesn’t have to exist then we need an explanation for why it does exist. But if something does have to exist–if it is a necessary being like God–then it does not need a further explanation.
The things we see around us in the universe, including space and time themselves, appear to have had a beginning, and so they need a cause–a reason why they began in the first place.
In the same way, each particular bit of matter in the universe doesn’t seem to be necessary. It could not exist. Therefore, we need an explanation for why it does exist.
Believing philosophers and theologians thus propose God as the ultimate explanation for these things. But since he is a necessary Being that exists outside of time, he needs no further explanation.
Indeed, the question, “Who created God?” is nonsensical, because it amounts to asking, “Who created an uncreated Being?”
PS Catholic Answers will host a 2 hour open forum just for atheists today from 3pm-5pm, Pacific. You can listen live here or if you’re reading this post after the show has aired you can download the podcast here.