There Are More Possible Chess Games Than Atoms in the Observable Universe

In a landmark 1950 paper, Claude Shannon, the "father of information theory," was the first to seriously calculate the complexity of chess. He envisioned the game as a massive decision tree, where each move creates new branches of possibilities. Due to this exponential growth, known as a combinatorial explosion, he estimated the number of unique, sensible game pathways to be around 10 to the 120th power. This figure, now known as the Shannon number, represents a conservative lower bound for the game-tree complexity of chess.

To put this number into perspective, it utterly dwarfs other colossal figures. The estimated number of atoms in the entire observable universe is a comparatively tiny 10 to the 80th power. This means that if every single atom in our universe were its own separate universe, and you counted all the atoms in all those universes, you would still be nowhere near the number of possible chess games. This staggering scale is why chess remains unsolved. Even the most powerful supercomputers cannot use "brute force" to calculate every outcome; instead, modern chess engines use advanced AI and heuristics to intelligently prune the decision tree and find the best move within a sea of near-infinite possibilities.