What is the shortest game with the largest material imbalance? This of course means that one side will have 9 queens, 2 rooks, 2 bishops, 2 knights, and a king, and a bare king on the other side. From some experimenting, I got this:

[FEN ""]

1.h4 g5 2.hxg5 h6 3.gxh6 Rh7 4.g4 Rg7 5.h7 Rg6 6.h8=Q Bh6 7.g5 f5 8.f4 e6 9.e4 d5 10.d4 c5 11.c4 b5 12.b4 a5 13.a4 Qe7 14.exf5 Bb7 15.fxe6 Bc6 16.cxd5 Bb7 17.bxc5 Bc8 18.axb5 Bb7 19.c6 Bc8 20.Rxa5 Ra7 21.b6 Rd7 22.Qe5 Nf6 23.b7 Kf8 24.c7 Rd6 25.f5 Kg8 26.Nc3 Bd7 27.c8=Q+ Kh7 28.Qc4 Nc6 29.b8=Q Be8 30.Bd2 Qf8 31.e7 Qg7 32.Bg2 Bf7 33.e8=Q Re6 34.dxe6 Bg8 35.d5 Nb4 36.d6 Nc6 37.d7 Nb4 38.d8=Q Nc6 39.e7 Nb4 40.Qdd7 Na6 41.Qed8 Nc5 42.e8=Q Nd3+ 43.Qcxd3 Ng4 44.f6 Ne3 45.f7 Nf5 46.f8=Q Qf7 47.Qfb4 Rg7 48.g6+ Kh8 49.gxf7 Ne7 50.Q3d6 Kh7 51.Q6xe7 Kh8 52.f8=Q Kh7 53.Qed5 Rf7 54.Bh3 Kh8 55.Q7xf7 Bg7 56.Ke2 Kh7 57.Ke3 Kh6 58.Kf4 Kh7 59.Q8xg8+ Kh6 60.Qgxg7#  0-1

This can of course be improved though, as I was essentially moving pieces around randomly.

  • Well, 48 moves is the absolute theoretical minimum. What needs to be done is to see whether it's possible to get this material imbalance with white only making pawn moves. – Scounged Feb 16 '18 at 23:00
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    @Scounged Problem is taking all the pieces right away leaves the enemy king vulnerable to stalemate or checkmate. – ericw31415 Feb 16 '18 at 23:10
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    @Scounged How do you come up with the number 48? – user1583209 Feb 16 '18 at 23:15
  • @user1583209 Sorry, I was probably being unclear, we have a lower theoretical limit in that white has to make at least 48 (8*6) moves (since all eight white pawns need to promote, and thus each white pawn needs to make at least 6 moves). I should have made it more clear that this is only a lower limit, and that it may not be possible to achieve this lower limit. – Scounged Feb 16 '18 at 23:37
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    Ok, so I just miscalculated totally and forgot that the white pawns begin on the second rank. Of course the lower limit is 40 moves (8*5 pawn moves). – Scounged Feb 17 '18 at 0:43

I got this, which is much shorter:

[FEN ""]
1. a4 a5 2. b4 b5 3. c4 c5 4. d4 d5
5. e4 e5 6. f4 f5 7. g4 g5 8. h4 h5
9. bxa5 Bd6 10. axb5 Be6 11. dxc5 Nf6 12. cxd5 O-O
13. fxe5 Rf7 14. exf5 Ra6 15. gxh5 Rb7 16. hxg5 Rbb6
17. bxa6 Nc6 18. axb6 Qe7 19. dxc6 Kh8 20. cxd6 Ng8
21. a7 Qf6 22. gxf6 Ne7 23. b7 Bd7 24. e6 Ng8
25. c7 Kh7 26. f7 Kg7 27. e7 Kf6 28. h6 Ke5
29. f6 Kf5 30. a8=Q Kg6 31. b8=Q Ba4 32. c8=Q Bb5
33. f8=Q Bc4 34. d7 Bd5 35. d8=Q Be4 36. f7 Bf5
37. e8=Q Bd7 38. h7 Bc6 39. h8=Q Bb7 40. Qcxb7 Kf5
41. fxg8=Q#

It's one move above the lower bound, but I feel that this is optimal.

It is optimal. See proof in comments.

  • After some thinking I'm more or less convinced that the 40 move solution cannot exist; that would require that at one point 7 white queens would be standing on the 8th rank while there would only be one uncaptured black piece besides the king itself (say, after move 39 by white). But this would be a contradiction since the black king would then lack shelter anywhere on the board. So I think that this solution is at most 2 moves from an optimal one. – Scounged Feb 17 '18 at 0:56
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    @Scounged It is possible to set up a position with 7 white queens and 1 black piece on the 8th rank, one white pawn on the 7th rank and the king not in check. For instance: black king on g6, white pawn on f7, black knight on g8, white queens on all remaining squares on the 8th rank. I am not claiming it is possible to achieve this setup, just saying that more careful analysis is needed.. – user1583209 Feb 17 '18 at 1:09
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    @Scounged I shaved off one more move and got 42. – orlp Feb 17 '18 at 1:16
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    @Scounged Are there any other 'safe squares' than b6 and g6 for the black king that need to be investigated? I don't see any. I don't see any either. Only b6 and g6 are safe and only in a setup with a white pawn on c7 (f7) and a black piece on b8 (g8). – user1583209 Feb 17 '18 at 2:07
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    @user1583209 Neat parity argument, but you mean files, not ranks. – Rosie F Feb 17 '18 at 9:09

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