# Quantum tic-tac-toe — marks in two places at once

- From: Quantum tic-tac-toe, by Allan Goff
- Players: 2 players
- Time: 10–15 min
- Made by: Allan Goff, 2002, made to teach quantum physics

Made with boardgameBuilder 0.14.4. To design from it, open boardgameBuilder and choose Open game: its blocks go on the canvas, and the feelings are left for you to pick.

Each move puts your mark in two squares at once, and only later does it settle in one. When the marks form a loop, the other player chooses how it collapses. Tic-tac-toe becomes a game of decisions you don't control.

## What it shows a designer

Each move is uncertain until a later moment decides it, and the decision is handed to the opponent. It shows how a game can be built to teach an idea from science, with delayed effects as its main mechanism.

## What you need

- paper with a 3 by 3 grid, squares numbered 1 to 9
- a pen

## How to play

1. **A move.** X goes first. On move 1 write X1 small in two different empty squares; on move 2, O writes O2 in two squares; and so on. A square can hold several small marks.
2. **Loops.** Think of each move as a line between its two squares. When a move closes a loop of these lines, the loop must collapse.
3. **Collapse.** The player who did not close the loop picks one move in the loop and chooses which of its two squares it settles in. That fixes the others: each move in the loop, and any move tied to it, settles in its other square. Settled marks are written large and never move.
4. **Last square.** When only one empty square is left, the last move puts both halves in it.
5. **Win.** Three settled marks of yours in a line wins. If both players get a line in the same collapse, the line whose highest move number is lower scores 1 and the other 1/2. A full board with no line is a draw.

## After playing, talk about

- When did you place a mark to force a loop?
- How did it feel when the other player chose your collapse?
- Did the rules make sense of entanglement for you?

## Where the rules are written down

- http://www.cel.edu/Quantum/Tic-Tac-Toe/
- https://doi.org/10.1119/1.2213635

## Its blocks

- Core mechanic: pattern building
- Player interaction: direct confrontation
- Chance or skill: mostly skill
- Theme: educational
- Timing: take turns
- Simulation: delayed effects

## Saved state

boardgameBuilder reads this part back when the file is opened.

```json
{"mechanics": {"core-mechanic": ["pattern-building"], "player-interaction": "direct-confrontation", "chance-skill": "mostly-skill", "theme": "educational", "timing": ["take-turns"], "simulation": ["delayed-effects"]}, "chosenFeelings": [], "previousMechanics": {}, "previousFeelings": [], "turnNumber": 0, "locked": false, "turnHistory": [], "answers": {}, "tests": {}}
```