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Play Quantum tic tac toe free

Physicist Allan Goff built this in 2006 to teach superposition, and it works as a real game. Instead of one mark you place a pair, the same symbol in two squares, tagged with the move number. Nothing is settled until your marks form a loop. Then the loop gets measured, everything in it snaps to one square, and a board you thought you understood turns into something else.

Board
3x3
Board
Goal
Settle 3 in a row
Goal
Typical game
5 min
Typical game
Difficulty
Heavy
Difficulty
XO

Move 0

Loading the board

How to play

How to play Quantum

  1. 1

    On your turn pick two different empty squares. Your mark goes into both, tagged with the move number. It is in neither square yet, and in both.

  2. 2

    Squares and marks form a network. When your pair closes a loop in that network, the loop has to be measured.

  3. 3

    Your opponent does the measuring. They choose which of its two squares your looping mark takes, and every other mark in the loop is then forced into whatever square is left for it.

  4. 4

    Measured marks become real and their squares close for good. Three real marks in a row wins.

  5. 5

    If one measurement gives both players a line, the win goes to whoever’s line has the lower highest tag, meaning the one that settled first.

Strategy

What actually wins games

  • Closing a loop hands your opponent the choice of how it resolves. Only close one when both outcomes suit you.

  • A mark spread across two far apart squares is hard to pin down. Two marks sharing the same pair of squares are almost decided already.

  • Tags break ties, so an early mark inside a line is worth more than a late one.

  • Count the loop before you commit. One running through five squares rearranges far more of the board than one through two.

Can you win it?

Quantum tic tac toe was invented in 2006 by physicist Allan Goff as a teaching tool for superposition and entanglement. The rules are a working analogy rather than a loose metaphor.

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All twelve games