Advocates of intelligent cosmological design often rely heavily on the embattled fine-tuning argument to prop up their theistic beliefs. But, even if the argument were to come up trumps, there would still be a gaping chasm between so-called fine-tuning and a Christian God.
Design arguments for God’s existence come in two colours: biological and cosmological. The biological design argument has been floundering ever since Darwin pulled the rug out from under it, but its cosmological cousin–often called the “fine-tuning argument”–has not yet suffered the same decisive fate. Even today, it’s not entirely unrespectable in scientific circles to argue that certain features of our life-permitting universe are suggestive of deliberate fine-tuning in the universe’s distant past.
Now, I happen to believe that the fine-tuning argument is far stronger than it’s commonly given credit for–but that it ultimately fails, both philosophically and scientifically. Nonetheless, for now, I want to set these considerations aside and suppose exactly the opposite.
Imagine that a future development of the argument succeeds in overcoming its difficulties and turns out to be broadly successful. We would then have a general consensus in favour of the view that our universe was deliberately fine-tuned for life. My new question is: would this hypothetical consensus lend any weight to religious claims–such as the assertion that, for instance, the Christian God exists?
It was David Hume who pointed out that any argument, no matter how successful, must not be taken to demonstrate anything more than is licensed by its conclusion. The conclusion of the fine-tuning argument is that the universe was fine-tuned, but not that the Fine-Tuner was anything in particular. At first glance, then, there’s no automatic link between the Fine-Tuner and the God of any particular religion.
In fact, we could come up with many different hypotheses, all consistent with the basic idea that someone or something fine-tuned the universe. For instance:
The Brahmins assert, that the world arose from an infinite spider, who spun this whole complicated mass from his bowels, and annihilates afterwards the whole or any part of it, by absorbing it again, and resolving it into his own essence. 
It would be entirely consistent for someone to accept the conclusion of the fine-tuning argument and remain an atheist or agnostic. To hold this position would be to say something along the lines of, “I can see that the universe must have had a Fine-Tuner, but I’ve seen no reason to think that this Fine-Tuner had the characteristics of any particular god, so this doesn’t help me in deciding whether to accept theism.”
After a while, though, wouldn’t this position begin to look a little awkward? Consider an analogy:
The Mysterious Footprints. An explorer sets up camp in a previously uncharted area of the Arctic. His mission is to find out whether there are any other humans living in that area. One morning, he awakens to find a trail of human-sized footprints in the snow near his tent.
After consideration, he forms the following opinion: ‘I can see that these footprints were made by something, but I’ve seen no reason to think that this footprint-maker had the characteristics of a human, so this doesn’t count as evidence that there are other humans around.’
Clearly, the explorer is making a mistake. At the very least, the sight of fresh human-sized footprints should have increased his estimate of the probability that a human is in the area.
Or should he? Isn’t he just following Hume’s wise advice and not drawing any conclusions other than those which are strictly justified by the evidence?
Suppose we challenge the explorer’s conclusion, asking, “Well then, what do you think made the footprints?” He might reply as follows:
I don’t know. I accept that it might have been a human, but it might also have been any other creature, or perhaps a natural phenomenon. Perhaps it was an ostrich in a man’s shoes, or a superintelligent polar bear trying to trick me by deliberately leaving human-sized prints, or a previously unencountered species of giant penguin with feet the same size and shape as a man’s boots. Or perhaps these apparent footprints are actually just the way the snow chanced to fall last night. There’s any number of possible theories and no way to choose between them.
Well, in a peculiar way, this is right. The existence of the footprints, strictly speaking, is only evidence for the existence of something with footprint-making characteristics–and this is Hume’s point about the universe and the infinite spider.
But it’s that kind of shameless hair-splitting that gives philosophers a bad name. After all, the explorer’s evidence surely throws up a further question, namely: “And what might that something be?” And his mistake was to think that he could only take into account the evidence before his eyes when considering that further question.
That’s dead wrong. In fact, he was entitled to take into account all his background knowledge of the world and use that to break the deadlock between the various competing theories. In other words, his reasoning should have been something like this:
From the limited evidence right here, it seems that any one of many different phenomena could have made those footprints. But I know from experience that one possibility stands out among the others–the possibility that it was a human. Experience gives me excellent reason to believe that humans actually exist, and they do frequently go around leaving footprints; but experience gives me no reason at all to believe that any particular rival hypothesis, such as ostriches in shoes or devious polar bears, might actually be true. Therefore, drawing on my experience in conjunction with the evidence before me, I conclude that these footprints were almost certainly made by a human.
Notice that this conclusion is only almost certain. Human-sized footprints aren’t a proof that a human has been nearby, because there’s always a chance, albeit an incredibly small one, that they were left by ostriches in shoes or devious polar bears after all. Nevertheless, it’s clear that the explorer can draw very strong conclusions–if not absolutely decisive ones–after he takes into account his own experiences of what kinds of things exist in general. These considerations point to the conclusion that a human was very probably responsible for the footprints.
This moral can be applied to the fine-tuning argument. We’re supposing, remember, that the argument is successful and the universe really was fine-tuned for life. The next question is: fine-tuned by what, or by whom?
We’d be making the same mistake as the explorer if we thought that the only thing we could say about the Fine-Tuner is that it’s something with universe-fine-tuning characteristics. Instead, we ought to draw on other considerations, such as what kinds of things we have reason to think exist.
This is where it gets difficult, because we run into the question: Do we have any independent reasons for thinking that something like a god–any god–exists? If we have, then the success of the fine-tuning argument provides support for the god’s existence, and the stronger our reasons for believing that a god exists, the more useful the fine-tuning evidence will be. But if we haven’t, as seems more likely, then we’re left in the same position as the bamboozled explorer: we have evidence for the existence of something with universe-fine-tuning characteristics, but we don’t really know what. It might be a god; then again, it might be an infinite spider, or a very devious polar bear indeed.
The fine-tuning argument is not a self-supporting religious argument, even if it’s ultimately successful in its own terms. If we want to say who or what it was that fine-tuned the universe, we have to draw on independent evidence to break the deadlock between competing possibilities. Such evidence must, of course, come from outside the fine-tuning argument itself.
So those people who put their faith in the fine-tuning argument to justify their religious beliefs would be well advised to think again. Even if their argument eventually comes up trumps, they’ll still have a hell of a lot of work to do.
 Hume, David, 1779: Dialogues concerning Natural Religion.