5D en passant

[Koros Antavo]

So, all pieces in this game move the same way they do in regular chess, generalized to 2 extra dimensions. I got curious if it was possible to perform an en passant move onto a neighbouring timeline. Turns out it isn't - you can only do it on a single board.

The problem lies in how 5D chess treats pawns in general. The pawn is really the only piece that breaks the otherwise incredibly strict consistnecy of this game's rules. Unlike literally any other piece, if a pawn moves in board-space, it can only move in board-space; if a pawn moves in time-space; it can only move in time-space.

What I mean by that is best illustrated with an example. Say you want to move your knight. Knight moves in a pattern (2a, 1b), where "a" and "b" are stand-ins for the game's dimensions: two space dimensions - x and y, and two time dimensions - t and w. Both a and b can be any of the four available dimensions. So you can move a knight on a single board, or one move into past and two moves on the past board, or two moves across timelines and one move on that board, or any other combination.

All pieces can move freely across any combination of space and time dimensions, except pawns. If a pawn moves forward across the board, it cannot threaten pieces diagonally through time; if a pawn moves forward through time onto another board, it cannot threaten pieces on that board diagonal to itself. A pawn can only take a piece diagonally exclusively on the board - the plane of board-space, or exclusively through time - the plane of time-space. Imagine if the knight were unable to move in a (2x, -1t) kind of way - move one square into the past and two on the board. Imagine if a and b could only BOTH be space dimensions or BOTH time dimensions, never the mix of the two. That is exactly how a pawn moves.

And I am fine with that. I suppose this is a balancing issue, since if the pawn's movement were completely consistent, making alternate timelines and leading armies of pawns that raze everything on their way might've been a fairly overpowered strategy. Still, I am not sure it would've actually been the case, and I would love to play this variant of the game at some point.

But even within the current set of pawn movement rules there is a possibility for time-space en passant. The situation is extremely difficult to set up, but it is very much worth exploring. So first you need at least three concurrent timelines. Your pawn on the nearest timeline shoud be right before the opponent's pawn line - row 6 basically. At least one of the spaces diagonal to the pawn should be open. On the opponent's turn their pawn swoops in onto that open spot from two timelines back - the furthest timeleine, making it a move of two squares and the pawn eligible for en passant. In order for the two-square move to be possible, this same open square must also be open on the middle board. On your turn you take the newly arrived pawn and take its place. Now everything is ready for the en passant.

Once the opponent's next turn is over, you find yourself in a peculiar situation: your pawn is on the opponent's pawn line and one turn in the past that same space is occupied with an enemy pawn that has just made a two-square move. So there is a pawn next to yours in time-space that has made a two-square leap in time-space, which is why you should be able to perform en passant in time-space, right?

Well, unfortunately, no. The game doesn't allow that. Probably because it is an absurd sitation to begin with. Probably because it would necessitate creation of two new timelines in a single move - one timeline with the enemy pawn taken and one with your pawn on that spot right behind it across timeline axis. It is such a shame that this isn't a thing. Shouldn't such a rare occurrence be honored? I believe it should.

[Rayalot72]

I'd love to see en passant translated to 5D, and maybe even castling if it can be interpreted that way.

I'm not sure about your thoughts about the pawn operations.

The pawn gets to move one square in one dimension "forward" (either forward horizontally on the board or into a universe further towards the universes created by your opponent). Other dimensions are excluded (horizontal movement on the board and time travel). When attacking, pawns can only assault by combining one move "forward" with one move in a corresponding perpendicular dimension.

In-game, this means the pawn can either move diagonally forward to attack or into the next universe one turn prior. The horizontal and vertical axis on the board are taken to be a pairing with universes and time being interpreted as another pairing.

A change I could see is interpreting any pairing of forward and sideways movement as valid, which would allow pawns to attack by: moving forward and back in time; into the next universe and horizontally.

Theoretically, all other dimensions are perpendicular to forward movement, so pawns could also be allowed to move: into the next universe and vertically; forward and into the next or previous universe.

These would definitely be quite scary pawns, but I also think it would be neat to try out (and have pawn lines between universes).

[Twelvefield]

The King suffers from a similar issue, which is why you need to capture any time-travelling piece that puts the King in check. Since the King can move one space in 5D, it could be possible to use time to create a stalemate, if he were allowed to simply run away from temporal check.

Time travelling pieces ought to be able to move more than one square 5D in order for time travel to be effective, otherwise the loops become too tight.

In that vein, a pawn in its opening could be allowed to move a square up and a square back in time: that would be interesting as well. John Connor would not save Sarah, instead a board full of duplicate Reese's would. Or to finesse the analogy, Edward Furlong- John Connor's zit-faced friend would go back in time a bunch of times and save the world just by filling it with duplicates of himself. It would be hard to kill the Queen if she and the King hid behind two full ranks of time-travelling pawns.

[Ja-senpai]

uhm.. rook, bishop, queen, unicorn and dragon can move infinite spaces as long as it's the allowed dimension and nothing is blocking them, so i don't know what you mean with
"Time travelling pieces ought to be able to move more than one square 5D in order for time travel to be effective, otherwise the loops become too tight."
if you can create a stalemate with time travel, then your attack wasn't perfect. It's not really an issue of the game, it's just a rookie mistake

[Twelvefield]

Pawns and the King almost always are restricted to being able to move only one square. That's what I meant. The other pieces can move more, so their time travel abilities are greater. Pieces that can only move one square have very limited time travel, and the 5D game rules seem to acknowledge this shortcoming. That's why you need to capture a time-travelling piece that puts your King in check. If your King could time travel to avoid a time travel check, that's stalemate in 5D: you'd just keep adding timelines into infinity.

[Rayalot72]

Originally posted by Twelvefield:

Pawns and the King almost always are restricted to being able to move only one square. That's what I meant. The other pieces can move more, so their time travel abilities are greater. Pieces that can only move one square have very limited time travel, and the 5D game rules seem to acknowledge this shortcoming. That's why you need to capture a time-travelling piece that puts your King in check. If your King could time travel to avoid a time travel check, that's stalemate in 5D: you'd just keep adding timelines into infinity.

This isn't true. The king can move back in time to get out of check. It's just that a king in the past has no available moves (since that board has been played) and sometimes progressing a turn will put that board into check from the future.

You cannot stalemate by making infinite timelines. If one player makes too many timelines, the other player is no longer obligated to play those boards until they make their own timelines, so you can effectively checkmate in one timeline, and then survive (while preventing ways of taking your checkmating piece across universes) until your opponent has opened too many timelines to be able to escape (forcing them to play the checkmated board).

Allowing the pawn or king to move multiple squares in different dimensions would break the rules of chess in general. Neither can move more than one square in any dimension to begin with (excluding pawn first move and castling, of course).