Bracketing agent-causation, there are only three types of things that govern the universe: constants, quantities, and laws.
By “constants” I just mean phenomena that are universal in nature and unchanging in value. For example the speed of light in a vacuum, the Gravitational Constant, the elementary charge, etc. We can include the rate of entropy in this category if you want (and if you think it is stable).
By “quantities” I mostly just mean the amount of matter and dark matter that exist, and the amount of energy that exists (and the amount of dark energy, if any exists). Theoretically those quantities should remain constant, but if they have changed (or can), then just take their initial values. We can include the amount of entropy in this category if you want, or rather the initial amount of entropy (or zero if there was none).
By “laws” I mean things like gravity (or, more accurately, Relativity), electromagnetism, etc. Keep in mind that most of the laws listed in that link are laws describing the behavior of high-order phenomena like buoyancy and thermodynamics and others that operate on matter at a high level of description like planetary bodies, chemicals, etc. Theoretically all of these logically supervene on lower-level phenomena like the nuclear forces, that operate on matter at a low level of description like subatomic particles. Ultimately it’s probably all governed by just a few fundamental interactions (and maybe even just one), operating on just a few fundamental particles like quarks or maybe strings.
So get this though. It turns out that the values of these constants, quantities, and laws could have been anything. There is nothing about the gravitational constant that makes it logically necessary. It could have been a totally different value altogether. It seems somewhat arbitrary that it is dialed to the value that it is. There is no explanation for it. And the same goes for the amounts of the stuff in the universe, and the laws governing it all—why is energy equal to mass times the square of the speed of light? It could have been the cube of the speed of light, and the speed of light could have been different, or the phenomena could have behaved according to different rules relative to different phenomena altogether.
The possibilities are, logically, infinite.
But it gets weirder. If the values of any one of these things had been different by even a hair’s breadth, the universe wouldn’t have been life-permitting. Planetary bodies couldn’t have formed, space couldn’t have expanded or would have expanded too quickly, etc. The logically possible scenarios according to which the universe could have existed such that it could not have been able to sustain life are infinite, while the life-permitting scenarios are extremely few.
To conceptualize the situation, I like to picture a number line for each value that requires fine-tuning—so there is a number line for the Gravitational Constant, and the value for the GC could have been anything on that infinitely long line, but it needs to fall within an infinitesimal range to play its role in a life-permitting universe, the boundaries for which are marked in red on the line. Then I picture another number line below that with Planck’s Constant, with the markings, and so on. There are a quite a few of these number lines (some lists are longer than others), but even if there were only one, the possibility is equivalent to one in infinity.
Then I like to imagine a lottery, the results from which determine the values for each thing. The lottery is run once to determine each value, and there are an infinite number of possible outcomes each time. This helps me wrap my mind around how improbable a life-permitting universe is. And it doesn’t even touch on the fact that a life-permitting universe alone doesn’t necessarily yield life. You have to somehow get life into it (a topic for another post), and then you need a planet within the universe that can support the life (the specific requirements of which I’ll leave for another post as well).
And yet, here we are.
It’s obvious to me that cosmic fine-tuning cannot be due to necessity, and I explained why earlier. But by now it should be almost as obvious that it is not likely to have occurred by chance either. Like literally, mathematically, it is unlikely. So the question you have to ask yourself at this point is:
How plausible is it that this fine-tuning is due to Design?