
The Longest Possible Chess Game - monort
https://www.chess.com/blog/kurtgodden/the-longest-possible-chess-game
======
tromp
The article itself doesn't arrive at the correct number of 5898 moves, but
some of the commenters do. At my own page
[http://tromp.github.io/chess/longest.html](http://tromp.github.io/chess/longest.html)
you can play through a 3-moves-shorter game.

~~~
ramshorns
It seems like the alternating of irreversible moves makes the 5870 shorter
than it could be. The pattern of (49.5 + b) + (49 + w) + (49.5 + w) + (49 + b)
+ … could be replaced with several moves in a row by black, then several in a
row by white, allowing some of the 49s to be 49.5 instead. Is that where the
discrepancy comes from?

~~~
tromp
Yes, that would explain most if not all of the 56-ply discrepancy. In the game
on my page you can indeed see black making irreversible moves on move
50,100,150, ... 450 and white's first irreversible moves comes only at move
500.

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schoen
A user who is banned asked in this thread why you can't have an unlimited-
length game where kings just move back and forth. The answer is

[https://en.wikipedia.org/wiki/Fifty-
move_rule](https://en.wikipedia.org/wiki/Fifty-move_rule)

[https://en.wikipedia.org/wiki/Threefold_repetition](https://en.wikipedia.org/wiki/Threefold_repetition)

~~~
dfan
All that the 50-move and threefold repetition rules do is permit one player to
claim a draw; the game may continue if both players wish to play on. (It has
happened, particularly threefold repetition where the repetitions are spaced
far apart and the players don't have much time.)

There are actually new FIDE rules as of 2014 or so, where after 75 moves, or a
fivefold repetition, the game is immediately declared drawn without the need
for a player to take action.

~~~
schoen
This is a good point in that it means players could have collaborated to
deliberately achieve an arbitrarily long game (and indeed, in some of the long
reported games it looks like nobody chose to claim a draw for a while). I
guess such collaboration isn't sportsmanlike in a competitive setting, but it
wouldn't have been precluded by the rules.

Thanks for that clarification.

~~~
sanderjd
At the highest levels it probably does imply collaboration, but where I play
at (much) lower levels, I might very reasonably choose not to take a draw
because I think my opponent is likely to make a mistake that will result in a
win for me. My opponent may reasonably think the same about me.

------
Someone
I thought the 50 move rule has been lifted for a few cases where a position is
known to require more moves to win.

However, [http://www.fide.com/component/content/article/1-fide-
news/10...](http://www.fide.com/component/content/article/1-fide-
news/10115-fide-laws-of-chess.html) doesn't mention that, and even has the in
some sense stronger _" a game is drawn if any series of at least 75 moves have
been made by each player without the movement of any pawn and without any
capture."_, which doesn't require either player to claim the draw, and, thus,
cannot be avoided.

So, even if the players wanted it, a game can't be longer than somewhere
around 96*75 or 7200 moves.

~~~
bluGill
It was up to 75 for a while, and then someone worked out a winning sequence
that required more than 75 moves, and there is every reason to believe longer
sequences are possible - to work them out is a brute force problem (chess is
not mathematically solved)

Note that by winning sequence I mean perfect play on both sides - there are
lots of sequences to allow to allow the game to continue longer than it has
to.

~~~
schoen
In fact, there are already solved positions that are known to require over 500
moves to mate:

[https://en.wikipedia.org/wiki/Endgame_tablebase#Tables](https://en.wikipedia.org/wiki/Endgame_tablebase#Tables)

It seems like different parts of the chess world are a little bit divided
about the best way to integrate this knowledge into the game.

------
mikeash
From 2007, for whatever that's worth. I only noticed because the sudden
mention of a "PDA" made me think, "what year is it?!"

------
schoen
One thing that I wondered about when looking at the longest recorded
professional games that occurred in real play was at what point they reached a
position that is actually solved in a tablebase. In particular, chess endgames
involving only 7 pieces were explicitly solved by computer search in 2012.
(But I also wonder if bringing those solutions to bear in a real game would
involve ignoring the 50-move rule, since tablebase solution for these
positions may often require more than 50 moves to complete.)

On tablebase-informed endgame theory, some of the professionals in these
ultra-long games should probably have resigned long before the actual end of
the games, except that they can also assume that their opponents don't know
the full solutions.

~~~
Someone
Professionals may try to get a draw by getting their opponent to make an error
under time pressure, even if they know their position theoretically is a lost
one.

That even happened back in the time when games got adjourned after x moves
(sort of an example: [https://www.chess.com/blog/NimzoRoy/a-famous-bishop-vs-
knigh...](https://www.chess.com/blog/NimzoRoy/a-famous-bishop-vs-knight-
ending-or-smyslov-blows-botvinnik-off-the-board3)), so should be more popular
nowadays, if the losing party has more time on the clock, or thinks to know
the particular endgame better.

------
ouid
>Otherwise, we have nothing further to discuss here regarding the longest
possible game.

The 50 move rule is there to ensure that the players don't have to occupy
every possible position twice before making progress, but it is not the only
possible way to put an upper bound on the game's length. Since the position
will eventually repeat, and the three repititions rule can be invoked.

