Several months ago I began a project called "Mapping the Fine-Tuning Argument". I started off with a lot of dedication, but gradually I forgot about it and the result is that I haven't posted anything about it in months, in spite of the fact that I had not yet examined all of the premises of the argument. Anyway, here is the argument as I stated it, here are the posts I made on the argument so far. I'm now going to attempt to do a hasty and sloppy wrap-up to this project (It's better than nothing, right?). So, here are my closing points:
1. I blogged that I did not believe there was any reason for God to create a physical universe. On closer inspection, I think this is false. "Physical" and "Natural" things are basically just things that can't think (objects, if you will). I don't think it's a big stretch to imagine God creating a universe with physical (or unthinking) things for sentient creatures like us to interact with. So God might create a physical universe.
2. Even if the universe is fine-tuned for life and God explains this perfectly, we are still left wondering whether God is the best explanation for our life-friendly universe. Here are some considerations against the God hypothesis:
A. Every mind we have any experience of is a physical mind which has a body. We have all known thousands of minds, but each and every one has a body, which implies that all minds probably have bodies. God is a spirit, which means that he is a disembodied mind. The strong inductive evidence we have against disembodied minds also counts strongly against God.
B. The God hypothesis postulates not just a new entity, but a new type of entity, a supernatural being. Remember Ockham's razor (aka The Principle of Parsimony): Do not multiply entities beyond necessity, the simplest explanation is most probably correct? Philosophers now distinguish between quantitative and qualitative parsimony: Quantitative parsimony concerns the number of entities you postulate, qualitative parsimony concerns how many types of entity you postulate. In both cases, fewer is better: a smaller number of starting assumptions increases the odds that the explanation is right.
As I said: The God hypothesis postulates not just a new entity, but a new type of entity, a supernatural being. And this means that other explanations, such as the multiverse theory, which invent no new types of entities, may be seen as superior to supernatural explanations, because (amongst other things) they invoke no new types of entities.
C. Supernatural explanations (like the God hypothesis) are further degraded by the fact that they have a bad track record. In this book review I wrote, I explain why.
D. If God wanted the universe to be friendly to life, it is very difficult to explain why most of the universe is not able to support life. From the radiation filled vacuum of space, to the super-chilled astronomical bodies so far away from stars that they are nothing but icy deserts, to the feverish bodies that are too hot to be anything except living hell, the universe seems to be anything but designed for life. Sure, the laws of physics may seem 'rigged' to support life, but other aspects of the universe, like those just mentioned, are not.
The fact that I have just mentioned weighs in on this debate for three reasons:
Because the God hypothesis cannot explain the hostility to life in the universe whereas essentially any atheistic explanation could (the universe not being designed for life entails that it could be hostile to life in some ways) which gives atheistic explanations more explanatory scope.
Because the life-hostility is evidence against God which decreases the probability that the God hypothesis is correct. Think about it: if life-friendliness is evidence for God, then life-hostility must be evidence against God.
Because the life hostility alerts us to the anthropic principle: Since we exist, we can expect to find ourselves on one of those rare islands of life, and we can expect the rare islands of life to exist because the universe is vast (100 billion galaxies) and is highly variable in its conditions from planet to planet. This explanation has proven itself correct and adequate to explain why a life-friendly planet exists, and therefore it has a weighty precedent which suggest it be given more weight as a possible explanation for the life-friendly laws of physics.
E. No other explanation for the fine-tuning of the universe suffers from the problem of evil or any other consideration that usually weighs against God. Other than the problem of evil, there is at least one other extremely powerful, knockout argument against God that comes close to disproving God's existence, called the Ultimate 747 Gambit.
With all of this in mind, my judgement is that the fine-tuning can be explained by (1) postulating a large number of universes (called the 'Multiverse) (2) Postulating some variation in the physical constants of these universes and (3) Invoking the anthropic principle: we exist in one of those few universe capable of supporting life because we could not find ourselves (as living beings) in a typical barren universe.
On various multiverse theories:
David Darling's article
Lee Smolin explains Cosmological Natural Selection in Two Minutes
The Life of the Cosmos by Lee Smolin
Pages 141-150 of Dawkins, The God Delusion