With more board configurations than there are atoms in the universe, the ancient Chinese game of Go has long been considered a grand challenge for artificial intelligence.
I understand the 2nd part of the sentence. How about the first part?
I also understand the number of board configurations of the game of Go is more than the number of atoms in the universe.
I don't understand is why "there are ..." could be the object of "than". Could someone please give a hint about the rules/conventions of it? Thanks in advance.