"It is believed there are more possible game variations than atoms in the visible universe."
I personally don't like this kind of comparisons. Why? Because two things are not on the same world of perception/organization of things.
One can compare number of ants to number of bees, or weight of a car to weight of an elephant. But not number of neural connections to number of atoms in a glass of water. Attaining numbers to things doesn't make them comparable, I believe.