One common argument that apologists use to justify belief in God is called the cosmological argument, one form of which runs as follows:
1. Everything that begins to exist has a cause.
2. The universe began to exist.
3. Therefore, the universe must have a cause.
Apologists argue, naturally, that the cause of the universe can't be a part of the universe itself; therefore, only God can cause a universe to begin. Since we know the universe exists, therefore we know God exists.
However, this argument fails on several levels, but the biggest failure in my view is that it conflates the components of the universe with the universe itself. While it can be argued that every 'thing' in the universe, every component--from human beings to stars to galaxy clusters--were caused to exist, it does not follow that the universe itself must also share the same characteristic--namely, being caused to exist.
The universe is not a 'thing' in the same manner that an apple or a planetary nebula can be called a thing. The universe is the sum of all things in space and time. The difference between the universe and the components of the universe is a difference of kind, not one of degree. Here's an example to highlight the difference:
1. All novels are written by an author.
2. The category of Literature is composed of novels.
According to the apologists' argument, we must therefore conclude that:
3. Literature was written by an author.
But that wouldn't make sense. What's the author of Literature's name? When did the author write Literature? All novels share other characteristics, such as a publishing date, and a first word, and a last word. So what is Literature's publishing date? What is Literature's first word, or last word? Of course, these are meaningless questions that can't be answered, because Literature is not just one giant novel; it is a different class altogether. For the same reason, the Universe is not just one giant thing that must share the characteristics of the components of itself.
What's more, if, as the apologists assert, the universe must have a cause just like everything else does, then the universe should also share other characteristics with everything else. One characteristic that all components of the universe exhibit is that they inhabit a place in space and time. Here's how that would work, according to the apologist:
1. Every thing inhabits a place in space and time.
2. The universe is a thing.
3. Therefore, the universe inhabits a place in space and time.
While at first glance this might seem to be logically sound, in reality it fails. If your definition of 'universe' is 'something that inhabits a place in space and time,' then your definition of 'universe' is not big enough. The universe can't be everything if that everything also inhabits space and time. The universe would have to also include that additional space and time as well in order for us to declare it to be everything.
The classic response to the cosmological argument is that if everything has a creator, then who created God? One objection that apologists raise is that God is exempt from the necessity for a creator because God is outside of space and time. Of course, apologists provide no evidence for this claim--nor could they--except for the fact that it solves a logical problem--but its a problem of their own making. Whenever someone declares that God is exempt from argument because he's outside time, I have two questions for him:
1. What time did God create the universe?
2. Where in the world did he put it?
If the apologist has an answer for these questions, then he's having God create space-time inside space-time, a logical contradiction. It's as though the universe sits inside a 'room' somewhere, but that room is not a part of the universe. If the apologist is not able to answer the two questions, then he is declaring that the universe is also outside of space and time.
So apologists are trapped either way. If they declare that the universe is not outside of space and time, then they aren't talking about the universe, but only a component of it--that portion that is inside of space and time. But if they concede that the universe is also outside of space and time, then the universe is as exempt from the same objections that they want God to be. "Who created the universe?" becomes as meaningless and unanswerable as "Who created God?"
In the end, the universe is what philosophers call a "Brute Fact," something that exists in and of its own right and does not require a beginning or a creator. Apologists can't object to this idea because they also believe in a Brute Fact. Naturalists call their Brute Fact, the Universe; Theists call theirs, God. However, the Naturalist can point to the Universe. Can the Theist point to God?