Quantum tic-tac-toe

The game was invented by Allan Goff of Novatia Labs, who describes it as "a way of introducing quantum physics without mathematics", and offering "a conceptual foundation for understanding the meaning of quantum mechanics".

[1][2][3][4] The motivation to invent quantum tic-tac-toe was to explore what it means to be in two places at once.

For example, player 1's first move might be to place "X1" in both the upper left and lower right squares.

At the end of the turn on which the cyclic entanglement was created, the player whose turn it is not — that is, the player who did not create the cycle — chooses one of two ways to "measure" the cycle and thus cause all the entangled squares to "collapse" into classical tic-tac-toe moves.

The first player to achieve a tic-tac-toe (three in a row horizontally, vertically, or diagonally) consisting entirely of classical marks is declared the winner.

Since it is possible for a single measurement to collapse the entire board and give classical tic-tac-toes to both players simultaneously, the rules declare that the player whose tic-tac-toe has the lower maximum subscript (representing the first completed line in the collapsed timeline) earns one point, and the player whose tic-tac-toe has the higher maximum subscript earns only one-half point.

An animation of the game being played
The second player has just made move O 8 . The first player must now choose whether to collapse O 8 into the upper right square or the middle square. (Either way, O is going to get three-in-a-row.)
X has chosen to collapse O 8 into the middle square, which forces the rest of the entanglements to collapse. This gives X their own three-in-a-row, but since the maximum subscript of O 2 O 4 O 6 (namely, 6) is less than the maximum subscript of X 1 X 3 X 7 (namely, 7), O gets one point while X gets only one-half point. O still wins.