Quantum Tic-Tac-Toe

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This Month’s Challenge: March 2004

Consider the situation shown in the figure below. X has just made a cyclic entanglement on move five in squares 7 & 8, consisting of only spooky Xs; no matter how O chooses the collapse, X will have a classical mark in both those squares. (The spooky marks forming the cyclic entanglement are underlined for clarity.) This gives him an open 2-row with one of his own spooky marks (move 1) in the open square (square 9). If O tries to collapse move 1 (squares 1 & 9), X gets to pick the collapse and will win on the bottom rank. If she doesn't try to collapse move 1, X will make the same move getting a win on the bottom rank anyway. O can't get a win in just one move, so no matter what she plays, X is going to get a 3-row on the bottom rank. It would seem that he has an unassailable position. However, since this is a quantum game, she can still win. Where must she move to defeat X?




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Last Month’s Answer: February 2004

One quantum fork is shown in the pdf file where X has set up a fork down the main diagonal (squares 1,5,9) and down the first column (squares 1,4,7). O has three possible responses: she can try to defend by playing both of her spooky marks within those five squares, she can ignore X's threat by playing both spooky marks in the other four squares (2,3,6,8), or she can place one spooky mark in each set.

If she chooses to defend, she has ten possible moves: four where one spooky mark is in the common square (square 1) and six where she does not play in square 1 at all. For every one of them, X also has ten possible responses within the same five squares, so there are 100 permutations. Let's explore them a bit.

There are six moves for O where neither spooky mark is in the common square; in all six, X wins on the next move (move 7) as long as he stays within those five squares (1, 4, 5, 7 and 9). In two of the six possibilities O makes a cyclic entanglement that X gets to collapse. But X makes another cycle on move 7, and even though O gets to collapse that one, it does her no good. For some permutations, regardless of O's choice, X actually gets his 3-row by move 5 of the classical game. One can think of this from the point of view of the classical game as if O played very badly and in trying to avoid the fork, missed a force that occurred prior to it.

There are four variations where O plays one spooky mark in the common square; in two of them she makes a cyclic entanglement, which X gets to collapse. He must force her out of the common square or he may lose. Having done that, X can make another cycle on move 7 and O gets to collapse it. If there was not a collapse on move 6, then X must play very carefully so that O's spooky mark is not on the cyclic part of the cyclic entanglement. He can always do this. However, since she placed one spooky mark in the common square, he cannot achieve a win by move 5 of the game unless O collapses the move 7 cyclic entanglement foolishly.

If O ignores his threat, X cannot get a collapse by move 7 since his moves form two entanglements, and it takes one move to merge them and another to make a cycle. However, O cannot get a cycle by move 8 without entangling with him, so she cannot prevent move 9 from happening by getting her own 3-row. If he now makes the move shown in this pdf file, she cannot stop him from getting a 3-row.

As before she has 10 possible moves, 4 with a spooky mark in the common square, and 6 with none, but now her move creates a cyclic entanglement so X gets to choose the collapse, so no way will she be able to block both 3-rows. She can, however, get a three row by move 8, earning half a point if she plays in squares 1 and 9. However, if neither spooky mark is in the common square, then X always has a collapse that lets him win on move 5.

Finally, if she plays one spooky mark in one of his 5 squares, and the other in one of the remaining 4 squares, there are 20 permutations and X has 10 responses for each. We believe that this situation works out essentially the same as for the case above, but given the 200 possibilities, it has not been exhaustively analyzed. Any takers?


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