There are more possible iterations of chess games than there are atoms in the observable universe.

hasan.test

4, June, 19

INSPIRATION & LEARNING, STARTLING FACTS

This value, known as the Shannon Number, represents all of the possible move variations in the game of chess. It is estimated to be between 10^111 and 10^123. By comparison, there are 10^81 atoms that make up the known universe. 

Source: http://www.realclear.com/science/2013/07/08/astounding_facts_that_not_everybody_appreciates_2204.html