At the start of a game of chess there are 20 possible moves for white. There are then 20 possible moves for black 20x20 = 400 possible permutations after one move each. Then there are 400 x 20 (or could be more with bishops/queen) = 8,000 for white. Then there are 8,000 x 20 = 160,000 for black, and so on. If you were to fully develop the entire tree for all possible chess moves, the total number of board positions is about 1,000,000,000,000,000,000,000,000,
000,000,000,000, or 10 to the power of 120, give or take a few. That's a very big number. For example, there have only been 10 to the power of 26 nanoseconds since the Big Bang. There are thought to be only 10 to the power of 75 atoms in the entire universe. When you consider that the Milky Way galaxy contains billions of suns, and there are billions of galaxies, you can see that that's a whole lot of atoms. That number is dwarfed by the number of possible chess moves!!!!!!