I scheduled a Q&A after Aristotle's first proof for the existence of God.
1. A couple of commenters clearly believe the cultural myth that religion is completely against science. This is true of some religions, not all of them. The only one that comes to my mind right now are the Jehovah's Witnesses (who wrongly believe that the Bible is a science textbook).
History lesson: the modern version of the Big Bang Theory was developed by a Catholic priest. His thought process was something like, "We Catholics have known the world started at a specific point, for almost two thousand years now. Let's use science to prove this." So he went ahead and did it, and it was awesome.
...Scientists never give the Catholic Church any credit for this. I think they're still mad because the Catholic Church banned that one book Galileo wrote. Guys, it was 500 years ago. Get over it. Besides, that book was banned because G-dizzles used it to launch personal attacks against the Pope, not because of scientific reasons.
And of course, that book shouldn't be confused with G-dizzles' book which was shut down for scientific reasons (namely, lack of proof), by a completely different group.
2. It bears repeating that Aristotle was Greek who lived 300-400 years before the birth of Jesus. He believed in the Greek gods (Zeus, Hera, Athena and the like). This is less a proof for the existence of capital-G God, and more a proof for the existence of lower-g gods. I forget the exact number, but his astronomy text calculates something like 44-70 gods.
And, of course, this is over 2000 years before the Big Bang Theory was developed, so he didn't take that into account.
3. Let's take another look at things. Is Aristotle being intellectually lazy and using "God did it" as a convenient excuse to explain how physics works? "Motion can only be transferred, not generated. So, in order for motion to exist in the first place, there must be a god who generates movement."
I think Aristotle's saving grace (pardon the pun) here is that he specifically avoids using the word "god". He uses the term "immobile mover", something which generates movement without itself being moved. He applies absolutely no qualities or properties to this thing, besides for the two that it logically must have, in order to account from the generation of movement.
So really, it could be that the "immobile mover" is just a large lava lamp, not a god. Aristotle would be 100% cool with that.
4. Would it be legitimate to apply Aristotle's ideas of motion to something else? Modern physics teaches that "energy cannot be created or destroyed, only changed". Therefore, I conclude that, in order for energy to exist, there must be something like "an uncreated creator".
Actually...where does energy come from, if it can't be created? I don't know. I never took physics in high school.
Also, I hear people say "mass cannot be created or destroyed, only changed". So maybe I can apply Aristotle's theories to the existence of mass. Mass exists, because God exists, and people go to mass every Sunday because of God! This is a great proof.
5. I didn't realize it until just now, but the Christian version of Aristotle's argument is, um...different. I guess that means I'll have to make a separate section for Aristotle's proof, and the Christian version of it. You readers don't mind, right?