How should one respond to the old schoolboy retort, “If everything needs a cause, who caused God?”
First, philosophers and theologians do not maintain that whatever exists needs a cause. Instead, they propose that certain things need causes, such as things that have a beginning or things that 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 perceive 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. Each could not exist. Therefore, we need an explanation for why each 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?”
You might be surprised, as I was, that in his book The God Delusion, prominent atheist Richard Dawkins rehashes this line of argumentation, calling it “the central argument of my book.” “If the argument of this chapter is accepted,” writes Dawkins, “the factual premise of religion—the God Hypothesis—is untenable. God almost certainly does not exist" (pp. 188-189).
Here's a summary of his argument:
1. One of the greatest challenges to the human intellect has been to explain the complex, improbable appearance of design in the universe.
2. The natural temptation is to attribute the appearance of design to actual design itself.
3. The temptation is a false one because the designer hypothesis immediately raises the larger problem of who designed the designer.
4. The most ingenious and powerful explanation is Darwinian evolution by natural selection.
5. We don’t have an equivalent explanation for physics.
6. We should not give up the hope of a better explanation arising in physics, something as powerful as Darwinism is for biology.
Therefore, God almost certainly does not exist.
Well, you don't need a PhD in philosophy to see that his conclusion, "Therefore, God almost certainly does not exist," in no way follows from his premises (even if his premises were true).
This is one of the reasons philosopher William Lane Craig writes of Dawkins' argument:
Several years ago my atheist colleague Quentin Smith unceremoniously crowned Stephen Hawking’s argument against God in A Brief History of Time as ‘the worst atheistic argument in the history of Western thought.’ With the advent of The God Delusion the time has come, I think, to relieve Hawking of this weighty crown and to recognize Richard Dawkins’ ascension to the throne.