It's really just a phrase used nearly-rhetorically in order to convey the vast scope of a thing. Everyone understands that the number of atoms in the universe i

It's really just a phrase used nearly-rhetorically in order to convey the vast scope of a thing. Everyone understands that the number of atoms in the universe is a huge number, so it's a good benchmark. When people use this phrase they're not trying to claim that the number of atoms in the universe is directly related to the problem at hand; they're just trying to convey scale.