The fine-tuning argument to the existence of a god, however you define him/her/it, is in reality just another god of the gaps argument. ‘God of the gaps’ is a phrase used to indicate a particular type of argument employed by those who want to show the existence of a god by reasonable means. Such people acknowledge the achievements of science and agree with its findings, but point to where scientific knowledge is lacking, say “you’ll never figure this out!” and consequently claim that a divine being of some sort is necessary to complete the explanation. In conversational terms, their god is hiding in the gaps of scientific knowledge. This type of argument has gone out of fashion a little, since it appears the gaps where a god can hide are getting smaller and smaller. Indeed, there’s no reason to think there’s going to be any gaps left eventually. Or otherwise, the gaps that are going to be left will not be sufficient to hide a god in.
Fine-tuning is a peculiar feature of our universe that was discovered some time ago by theoretical physicists. Scientific understanding is always based on models, usually in the form of a set of equations of some sort. These models almost always contain what we call empirical constants, numbers that have to be measured in the real world by experimental physicists. A small set of these constants, seven or so, has the honorary title of being fundamental. This just means scientists think that some forces, and their respective constants, cannot be explained in terms of other forces.
The job of theoretical physicists is, to put it a bit bluntly, to try and play around with the models to get a better understanding of them. And so they discovered that the fundamental constants are, in fact, highly sensitive to tampering. The universe as we know it wouldn’t exist if the constant were only different in the slightest. In a word, the fundamental constants seem to be fine-tuned to result in our universe.
This is a great source of joy for those who like to argue the existence of a god. “See,” they say, “we knew it! This means there must be a god who created this universe solely to result in our existence!” Indeed, changing any of the fundamental constants slightly will probably result in a universe devoid of life. Sometimes there’s no matter, sometimes there is but it can’t form complex molecules needed for life (incidentally, almost anything in our universe is about just as sensitive to fine-tuning, so maybe their god really likes black holes or lampposts or vaseline).
However, it seems to me that they’re conveniently forgetting something. In the history of science, many constants were usually of the empirical kind until better models came along. To give an example, experimental physicists measured the vacuum permeability, the vacuum permittivity and the speed of light separately, just thinking these were completely unrelated. A better model, famously discovered by Maxwell, stunningly resulted in a deep intertwined relation between these three formerly deemed fundamental constants. According to Maxwell, you only needed to measure two of them, while the third one was fixed by a mathematical relation!
Mind the gap
Of course, the first problem of the fine-tuning argument is the multiverse. It used to be a bit of a joke, but the idea of a multiverse is rapidly gaining popularity and stature. The multiverse completely shatters the fine-tuning argument, of course. If there’s many, possibly even infinitely many, universes that all have different fundamental constants, then we just happen to be living inside one that has them just right. How do we know? Here we are, alive and well. Although, it would be funny if someone went one step further than Bishop Berkely and denied our own existence in favour of the existence of a god. Cue Descartes.
Regardless, even if you dismiss the multiverse, the story above about Maxwell’s discovery means that the fine-tuning argument faces a very real problem. A possibility adherents are very happy to ignore, and moreover, a possibility that scientists are very apprehensive to point out. Why? Because they seem reasonably sure that this is it. Similarly to roughly 120 years ago, many scientists sort of believe that physics is almost complete. Nobody will tell you like people did back then, for instance when Max Planck was told not to bother studying physics.
If you know what to look for, however, you’ll see the signs. In a way, the last great problem of physics is thought to be the unification of quantum theory and general relativity, resulting in the grand unifying theory, more colloquially known as the theory of everything. Even the name itself is kind of a giveaway that physicists believe this is the last hurdle. But even if it is, like Maxwell’s discovery it could reasonably result in fewer fundamental constants, or even none. The point is, we just don’t know. Yet again, god is claimed to be hiding in the gaps of scientific knowledge.