The difference between "number of atoms in the universe" and "number of possible states of a system" are vastly different. The latter is a combinatorial problem, and if you're trying to to track the possible combinations of 100 variables that can take on 10 states each, you've got 10^100 combinations and are already beyond atoms in the universe (10^80). You can never enumerate them all, but the ability to work on large subspaces would be a help.