AES256 already has more possible keys than exist atoms in the visible universe and that’s a pretty mundane thing. If you wanted to store all those keys, that’s even large. # of atoms in the universe turns into a very small very quickly when talking about permutations and permutations come up all the time (mathematical simulations, probability computations, etc).

I really don’t understand what point you’re trying to make saying “pick the largest possible number relevant” as that number varies. Also, that’s just the rational numbers. There’s plenty of digits of precision needed for trajectories over galactic distances and the more precision you try to give irrational numbers, the larger your magical “largest number” needs to grow again.

Also, we don’t know how big the “non observable universe” is and it’s beyond the scope of science. It very well could be an infinite number of atoms and then what?