What is 5D chess?

I interpreted the description as normal chess board = 2 dimensions. time = third dimension. moving on the x axis in the multiverse as 4th dimension and moving on the y axis in the multiverse as 5th dimension. So yes, in this wacky world a standard game of chess in progress is 3D.

Hmm, fractal dimensional chess could perhaps be implemented as having subboards within each tile of a standard chessboard. Completely spitballing over lunch, I propose the following rule set:

* Every square of a chessboard is itself a chessboard. This applies recursively. The top-level chessboard is named "Prime". All other chessboards are named according to the subdivision of Prime where they are located. So, the board located one level deep at F3 is called "Prime-F3". The board located two levels deep at A7 of Prime-F3 is called Prime-F3-A7.

* All infinite chessboards start in the standard board starting position.

* Black and white alternate making moves. Each move consists of moving a single piece within a single chessboard, following standard chess rules.

* The game is won when a player does not have a King located in Prime.

So far, this only introduces additional moves that can be made, which have no impact on the Prime board. Apart from being harder to force a draw, the subboards have no impact. Next up, adding rules to allow boards to influence the boards above/below them.

* If player X has a piece on board Z in location Y, then all pieces belonging to player X in board Z-Y may, in addition to their normal move, also move like the piece in board Z. For example, at the start of the game, white has a queen on Prime at location D1. Therefore, in board Prime-D1 may move like a queen, in addition to their normal movement.

* If player X does not have a King in board Z-Y, then their opponent may, as their move, move any piece from board Z-Y to board Z in location Y. For example, if Black has captured White's King on board Prime-D8, then Black may move any piece on Prime-D8 to the Prime board at location D8.

Now, there is an incentive to playing on the lower level boards. Play here goes much faster, by virtue of having more moves available. By investing time into the subboards, you can gain additional pieces on the main board. If a subboard is being used to funnel more pieces in, then it may be worth investing in a subsubboard, in order to pull a king in from the subsubboard to the subboard.

I count it thusly: Ordinary chess is 2D. Adding in the ability to bifurcate the timeline and play distinct possibilities in parallel is 3D since it is a distinct degree of freedom. Adding in the ability to go back and forth along a timeline is 4D. Adding in the ability to also jump back and forth to ANY timeline (sideways rather than strictly back and forth) requires a fifth degree of freedom. So it's 5D as far as I'm concerned.

> So checkmate in any one timeline counts?

Yes. ( https://news.ycombinator.com/item?id=24065059 )

> You couldn’t do all timelines.

How do you reckon that? I mean, it makes sense on an intuitive level; however, since now we're not talking about Conor Petersen's 5D chess, but the vast space of possible multiverse time travel chess variants, it's not obvious how one could prove this to be impossible in a somewhat rigorous way. For example, what if time-lines end when a king is mated (or wioll fore-when haven been mote [0]), but you only lose when you can't make a valid move in any time-line?

[0] http://pages.cs.wisc.edu/~param/quotes/guide.html

> 3d chess is another popular variant: https://wikipedia.org/wiki/Three-dimensional_chess

I was crazy enough as a high-schooler to actually build (with the help of my father) a 3D chess "board". It was mostly plywood, with eight 8x8 boards stacked vertically. I had previously gotten a "3D" chess board which was just three 8x8 boards. They weren't making Star Trek tri-dimensional chess sets back then.

With the 8x8x8 3D board, movement rules for 2D chess have a "natural" expansion to 3D, with only a few corner cases. White player's non-pawn pieces start out on the bottom board, with the pawns on the next board up.

In practice, it was hard to visualize how the game was going in general. We were constantly standing up and crouching to see. Only one of my friends wanted to play, and he only lasted about half a game. :-(

With the failure to interest my friends, I had intended to write my own chess program to play it. I had started out with the 2D version, and was then intending to expand it later. The original was written in BASIC... and that did not go too well.