In his book The Goldilocks Enigma: Why Is the Universe Just Right for Life? (2006) physicist Paul Davies discusses the options for those trying to explain why the universe is so finely-tuned for life. That is, why are the forces, constants, and parameters that underlie the physical world "just right" to allow life to exist? The enigma is that it's incomprehensibly improbable that such a universe, a "Goldilocks" universe, exists by chance.
An obvious reply, perhaps, is that it doesn't exist by chance, that the universe is the intentional creation of an intelligent agent. This explanation doesn't sit well with many scientists, however, in whose ranks there are many metaphysical naturalists who are ill-disposed to countenance any explanation that involves non-natural causes.
Many scientific naturalists simply say that the universe just is, it's a brute fact, and we can't explain why it is the way it is nor should we even worry about it. The problem with this is that once scientists give up trying to discover why things are the way they are then science comes to a screeching halt..
Another possibility that's gaining in popularity is one version or another of the many-worlds hypothesis or the multiverse hypothesis. These are really two different theories, but we may consider them together for the purpose of our discussion. They both hold that there are in fact innumerable other universes, perhaps an infinity of other worlds, inaccessible to, and different from, ours.
If this is so then the laws of probability require that, if there are indeed enough worlds, and if they are all different in terms of their laws and properties, then, as improbable as our world seems to be, at least one world like ours must exist. To see this consider that the odds of getting a head on a coin flip are 1 in 2. If you flip a coin ten times you should expect on average to get five heads.. If the odds of an event are 1 in 100 then you would expect that out of a thousand trials it would occur ten times on average. Likewise, an event whose likelihood is 1 in a trillion should occur at least once in a trillion chances and in an infinity of chances everything which is possible, no matter how improbable, should happen.
Thus, if there are an infinity of different worlds then our world, as incredible as it is, must exist and we need not posit intelligent designers to explain it.
So, there are two live options on the table for those who want an explanation, the multiverse and intelligent design. Many non-theists choose the multiverse and conclude that there's no need for a designer, but actually the existence of a multiverse, so far from being a defeater for ID, actually makes intelligent design more likely to be true – for a number of reasons. Here are two:
In The Goldilocks Enigma Davies explains that in an infinite number of worlds it's probable that some of them would be inhabited by beings advanced enough to create simulated universes. The sims, for reasons Davies explains, would probably far exceed the number of real universes. Thus, any world that exists is more likely to be a designed simulation than not and our universe is therefore more likely than not to be such a “Matrix” world, designed by a superintellect, in which case intelligent design is true.
A second reason is that if there are an infinity of different worlds then every possible world would be actualized. Since a world that is the product of a designer is a possible world then such a world must exist somewhere.
Whether ours is that world or not, it must still be true to say that there is an intelligent designer that has designed at least one world (actually, it would be a near infinity of them) in the multiverse. The question then becomes, “Are there any good reasons to think that ours is or is not one of them?" There are no good reasons to think our universe is not designed (given the existence of a designer and numerous designed worlds) and many good reasons to think it is. Therefore, since we should believe what we have good reasons to believe we should believe that our world is probably one of the worlds designed by the intelligent designer.
Davies himself doesn't like the metaphysical implications of designed universes. If the universe is designed then it would seem that there is something like God out there and Davies balks at this conclusion. But what else is there?
Surprisingly, perhaps, Davies opts for a fourth possibility. Circulating among some physicists is the bizarre notion that as the universe unfolds it evolves ever greater forms of intelligence until at some point superminds are produced which have the power to actually cause events in the distant past. One of the events that these superminds cause is the origin of the universe itself. In other words, the universe was brought into being by minds that didn't exist until the universe was many billions of years old. The universe is thus like a loop which in some fashion manages to create itself.
This seems to me to be an act of metaphysical desperation, but it shows the lengths that some will go to in order to avoid having to agree with the psalmist who said that "the heavens declare the glory of God and the firmament shows forth the work of His hands."
Even though Davies himself ultimately rejects intelligent design, almost every chapter in The Goldilocks Enigma contains something that points to the fact that the universe is underwritten by an intelligence, a mind, that has structured it so as to support living things. It's a very interesting and readable book for anyone interested in the interface of cosmology, philosophy, and religion.