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# Many Worlds Chess

Many Worlds Chess is a chess variant, or something like a chess variant, invented by Adrian King in 1999.

Many Worlds Chess was inspired, in part, by the "many worlds" interpretation of quantum mechanics. Michael Clive Price has prepared a very nice although rather technical FAQ on this topic. Basically, the idea is that where an event whose outcome we would call "random" can occur, all possible outcomes actually do occur -- the universe effectively splits into a multitude of parallel universes, each representing one possible outcome of the event. The parallel universes do not communicate with each other further, which is why we aren't aware of having multiple selves.

I am entirely unqualified to evaluate any aspect of quantum mechanical theory, so I can't tell you just how plausible or useful the "many worlds" interpretation is. However, you have to admit it is an intriguing idea. Furthermore, if you are willing to relax a bit the restriction that there is no further communication between worlds once they split, there is a possible application of the idea to gameplay.

## The Rules

The rules of Many Worlds Chess are those of FIDE Chess, except as described below. The game starts out with a single 8 x 8 board set up as for FIDE Chess, but the rules require the addition of other 8 x 8 boards as the game goes on.

On each turn, a player may do one of two things:

• Choose one of the boards in the game and make two different legal moves from the current position on that board. This results in a splitting of the board into two boards, each containing the result of one of the two moves made. The original board (containing the starting position for the two moves) disappears from the game.

If either resulting board is identical to an existing board, the identical boards merge into a single board, so that the game never contains two identical boards.

Boards do not remember which player moved last; there is no rule preventing you from making a move on a given board even if you were the player whose move created the board.

Note that if there is a board on which you have only one legal move, you cannot make this type of move on it; this type of move requires that you make exactly two different legal moves from a given position.

• Transfer any friendly man except a King from one board to the same location on any other board, provided that the destination space is empty.

The goal of the game is to capture, not checkmate, an opposing King on any board.

It is legal to move a King into check (although it's hardly a good idea). This, combined with making capture rather checkmate the object of the game, sidesteps the thorny question of how to deal with the case where a King is stalemated on one board, or has only one legal move to get out of checkmate on one board.

Note that it is possible to block a check with a "transfer" move.

In the extremely unlikely case that it is your turn, but no transfer move is available, and there is no board on which you can make two different moves, you lose immediately.

## Notation

I'll use the following notational conventions:

• A semicolon separates White's and Black's halfmoves for clarity.

• Boards are numbered with Roman numerals, except that the initial board is numbered 0. A newly created board gets the next available board number.

• A "splitting" move is preceded by the parenthesized number of the board from which the move occurs and is written as two distinct moves, each followed by an equals sign and the number of the resulting board in parentheses; for example, `6. (VII) Nxe4 (=XII) Bd2 (=XV)`. This means that White's sixth move split board VII by moving `Nxe4` from the position on board VII, resulting in board XII; from the same starting position on board VII, White also moved `Bd2`, resulting in board XV. Since the numbers XII and XV are not consecutive, XII is presumably a board already in the game; XV might also be an existing board, or it might be a new board created by this move. Board VII is no longer in the game.

• A "transfer" move is written with the abbreviation and position of the piece transferred followed by the source and destination boards, separated by a dash; for example, `5. ...; Nc6 IV-VII`. This means that Black's fifth move was to transfer the Black Knight at c6 on board IV to c6 on board VII. The changed boards IV and VII are still called IV and VII, even though they don't contain the positions they originally did.

## Sample Opening Moves

A game might open something like:
``` 1. (0) e4 (=I) d4 (=II); (I) Nf6 (=III) e5 (=IV) 2. (II) Nf3 (=V) e4 (=VI); Nf6 III-IV ```

After move 1, the boards in the game are II, III, and IV (0 disappears after White makes a splitting from it; I disappears when Black makes a splitting move from it). After move 2, the boards in the game are III, IV, V, and VI, and Black has three Knights on board IV as a result of the transfer move.

Note that a transfer move is not possible on White's or Black's first turn, because there aren't any locations where there is a friendly piece on one board but an empty space on another board.

## Strategy

No way I'd play this game! However, if anyone is actually crazy enough to try to play it, let me know how it comes out.

There might be some benefit to trying to make splitting moves on boards where you have a material advantage, or trying to create such boards by transferring a lot of pieces there.

I'd recommend writing a computer program to manage all the different boards, and also keeping a plentiful supply of aspirin on hand.

## Closing Remarks

Obviously, the Many Worlds concept is not specific to Orthochess. Many Worlds Shatranj/Checkers/Shogi/Go, anyone?