For our second argument in favor of God’s existence, we’ll need to lay some mathematical and scientific groundwork. Bear with me – this argument is quantifiably powerful in a really unique way, so I promise the numbers pay off.

Most of us probably learned the equation for gravity in high school:

In that equation, F is the force of gravity, and are the masses of the two objects on which gravity is acting, and r is the distance between the masses. G, though, is just a number – 6.67408 × 10^-11 m³ kg^-1 s^-2, to be exact. And G isn’t alone – we find constants like this throughout the most foundational equations in physics. These constants don’t seem to be determined by the laws themselves or (generally) by one another – mathematically, many combinations of values for these constants would produce a consistent description of a universe.

It was typically assumed that the values of these constants could have fallen anywhere within a wide range of possibilities without any substantial consequences for the universe; this idea is now near-universally rejected by theoretical physicists. It turns out that an inconceivably small number of the possible combinations of these values produce a universe permitting life – physicists call this phenomenon “fine-tuning.” There are many examples of fine-tuning, but to examine one of the more understandable ones, let’s think about stars. We take it for granted that the universe is filled with interesting elements from which life is made – oxygen, carbon, iron, nitrogen, and so on. But immediately after the Big Bang, the universe contained only hydrogen, helium, and trace amounts of lithium and beryllium; those ingredients aren’t sufficient to produce the chemical complexity needed for life of any kind. Heavier elements had to be formed through billions of years of nuclear fusion in stars – but what if stars didn’t exist? As outlandish as that may sound, stars depend on a delicate balance of gravity and the strong nuclear force to sustain themselves – in fact, if you were to pick a random gravitational constant and coupling constant (which determines the strength of the strong nuclear force), the odds that you’d pick one that permits stars is just 1 out of 10³⁵! Without stable stars there’s no way of producing heavier elements and hence the chemical complexity needed for life to exist. (This example was selected for clarity rather than strength; for any sciency readers wanting more data, you can check out the work of Luke Barnes in his book “A Fortunate Universe: Life in a Finely Tuned Cosmos” or his research papers such as this one: https://arxiv.org/abs/1112.4647.)

The question, then, is how are we to explain this fine-tuning? We can divide explanations of the fine-tuning of the universe into three basic categories:

1. Fine-tuning is the result of design.
2. Fine-tuning is the result of necessity.
3. Fine-tuning is the result of chance.

I define these terms so as to make the groupings exhaustive: “design” means that the fine-tuning of the universe was purposefully causally influenced by a personal being, “necessity” means that the universe wasn’t designed and could not have different from the way it is, and “chance” means that the universe wasn’t designed and could have been different, i.e. it just happened to be the way that it is.

How do these explanations fare? Design does pretty well – if there were a transcendent person, it’s pretty plausible (or at least not wildly implausible) that they’d be interested in creating a universe in which other persons could come to exist. Let’s turn to the other two.

The explanation of physical necessity proposes that our marvel at fine-tuning is like a 2-D creature marveling at the fact that the angles of the triangle in which he lives add up to exactly 180 degrees – but of course it shouldn’t be that surprising, since the angles of a triangle must add up to 180. But the proposal that, like the triangle, our universe had to be this way is worse than speculative – a wide range of constants do appear to be compatible with the laws of our universe, and far from having evidence to overwhelm this appearance, the variability of constants is implied by the Standard Model as well as even its more speculative competitors (including String Theory). There’s just no good reason to believe that the values of the constants are necessary – it’s sheer wishful thinking.

The “explanation” of chance simply acknowledges fine-tuning and asserts that we got really really (really really really) lucky. And while this is certainly possible, rational thinkers seek to avoid excessive improbability. If a bank robber entered the 12-digit vault code in a single try, it’s possible that he guessed it, but overwhelmingly more likely that he already knew it (e.g. from a corrupt bank employee) – any good detective would move forward with the latter as their working theory over the former. So unless we have prior evidence making the design hypothesis as unlikely as fine-tuning by chance (on the order of 10^-35 from just my one example), design is the way we ought to go.

As with all our arguments, the Fine-Tuning Argument doesn’t produce certainty in its conclusion that a cosmic designer exists, just rational confidence. Furthermore, the Fine-Tuning Argument in isolation doesn’t even tell us that the designer is God – for instance, the theory that our universe is a computer simulation could also explain the fine-tuning via a design hypothesis. But just as learning that someone is at the door makes it more likely that any particular person is, our confidence in there being some cosmic designer should likewise make it more plausible that a particular cosmic designer (God) exists.