Who created God?
When theists ask "Who created the universe? It must have been God", asking "Who created God?" is a way of turning the original question back on itself. This is the most concise answer to the first-cause argument. This leads to an infinite regress, known as Ad infinitum.
Asking about God's creator is a way of drawing attention to the fact that inventing a god is not an explanation for the existence of the universe, or of unexplained features within the universe. On the contrary, it fails as an explanation because it does nothing more than push the question of origin up a level, and on this new level the same problem exists. Many theists also them use the special pleading fallacy to justify their beliefs.
In a more general way, this is a template for the technique of turning theistic questions about the world around on the God that they use to explain it. It can also be used as a response to arguments such as:
- The natural-law argument ("If the order of natural laws can only be explained by a creator, then what explains the order of the creator?")
- Irreducible complexity ("If complexity can only be explained by an intelligent designer, then how do you explain the complexity of the designer?")
- Morality, as in the Euthyphro dilemma ("If God is needed to tell us what is right and wrong, then on what basis does God decide what is right and wrong?")
- Cosmological argument ("If the universe had to have God as a cause, what caused God?")
The argument that stipulating a cause for a phenomenon which requires a cause simply "pushes the question of origin up a level" fails to address that if -- on one level -- a certain observable set of rules is in effect, that other level is required to circumvent these rules and therefore is a necessary addition to the theory.
The objection could therefore also be applied to physics where the behaviour of particles is explained by its structure of its subparticles. According to the objection one could simply ask "And what accounts for the behaviour of the subparticles?". The theory of subparticles only "pushes the question of the origin of the particles behaviour up one level".
However, just as the existence of subparticles is the only explanation for the different behaviours of the particles, the only explanation for the existence of a universe in which it is an observable rule that nothing can come from nothing is the stipulation of something outside of this universe that has the capacity to create something without itself needing to be created. This of course does not necessarily have to be what we call "god." However, it is some sort of argument which counters the "lack of evidence" claim.
Another common theistic response is that God is specially exempt from the rules they (the Apologists) have invented, because he exists "outside of time" and so is not subject to rules such as "everything requires a creator." (See also Kalam.)
This argument is ultimately self-defeating. If there exist things which are not subject to the rules, then the rules are not really rules, but more like guidelines. If theists grant that some things do not need a creator, then we may as well simplify and say that it is the universe, or some other ungodlike entity, that requires no creator.