Atomic chess

Atomic chess is a chess variant. Standard rules of chess apply, but all captures result in an "explosion" through which all surrounding white and black pieces other than pawns are removed from play. Some variations additionally remove rules concerning check such that the king may be able to move into or remain in check.

A capture in atomic chess. Nxg7 causes an "explosion" in which the capturing knight, captured pawn, and adjacent black rook and bishop are removed from play. Adjacent pawns are unaffected.

History

In 1995 the German Internet Chess Server (GICS) introduced the game, based on rules one of its users collected from friends who played offline.[1][2][3] It was soon after incorporated into the Middle East Wild Internet Server (MEWIS) and other smaller servers before being implemented at Chess Live and Internet Chess Club in 2000, Free Internet Chess Server in 2003 and Lichess in 2015.[4][5]

Rules and variations

Rules of atomic chess are the same as standard chess with a few important differences concerning capturing, check, and winning conditions.

Capturing

In standard chess, the captured piece is removed from the board and the capturing piece takes its place. In atomic chess, a capture causes an "explosion" through which both pieces are removed from the board as well as all non-pawn pieces in the eight squares immediately surrounding the capture. Pawns are removed only when capturing, captured directly, or promoted. In case of en passant, the capture is considered to take place on the sixth rank square where the capturing pawn would have landed. Captures that result in the explosion of a player's own king are illegal, and therefore a king can never capture any other piece.[6][7]

Check
Black to move: Win or stalemate?
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With Black to move, this position would be a stalemate in variations of atomic chess that do not allow a king to move into check, but a win for White in variations that do not enforce the rules of check. In no version of the game would it be legal for the king to take the rook.

Threats to the king can be direct or indirect. Putting a king in check is a direct attack and is sometimes called "atomic check".[8] An indirect threat occurs when a player threatens to explode the king by capturing an adjacent piece. In most variations of atomic chess, players must respond to being checked in a similar way they would in traditional chess—by moving the king out of check, blocking the check, or removing the checking piece—but an exception exists when the checked player can win the game by exploding the checking player's king.

As the king cannot take another piece, it is possible to move the kings next to each other without a check occurring or to escape check. A losing player will often aim to position his king next to his opponent's in an endgame, as this is almost always a draw. If a piece or pawn can be blown up next to one king (without the other blowing up), or if one player can occupy the squares next to his king with pieces (or pawns) forcing the opposing king away, it is a win.

The variant of atomic chess played at the Internet Chess Club is one that does not enforce check at all, making legal any move, even one leaving the king to be captured directly in the next move.[7][9]

Winning conditions

In all variations of atomic chess, a player wins by exploding the king of the opposite color without exploding their own king. This is usually done by capturing a piece on a square adjacent to the opponent's king or putting a queen next to the king which results in checkmate since a king can not take any piece.

In variations that require a response to being checked, it is possible to checkmate an opponent to win the game, creating a situation in which a king is directly threatened and cannot make a legal move. This is sometimes called "atomic checkmate".[8] It is likewise possible for the game to end in stalemate if a king is not directly threatened and no legal moves are possible.

When typical rules of check are not enforced, victory is only attained via the explosion of the enemy king. In these variations without check, the king may be forced into check and thus capture through zugzwang.

Strategy

The first-move advantage enjoyed by White is much greater in this game than in standard chess. Hence, it is a game imbalanced against Black. Although the advantage is significant, no attempts to prove a win for White have been successful.

Material sacrifices are more common in atomic chess than in chess. In the opening and middle-game it is common to offer a piece in order to seize an initiative enabled by the newly opened spaces captures create.[7]

Opening
A common opening trap
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A common response to 1.Nf3 in chess is 1...d5. In atomic chess this leads to a forced loss after 2.Ne5!!, threatening Nxf7. After either 2...f6 or 2...f5 White can play 3.Nd7!!. White's knight cannot be taken by any piece because of its proximity to Black's king, and Black cannot stop 4.Nxf8.

White has the initiative in atomic chess, and many openings begin with a quick attempt to explode Black's d-, e-, or f-pawns in front of the black king.[10] For this reason atomic openings are fraught with traps and Black may have to respond precisely to defend. Several common traps begin with 1.Nf3 followed by Ng5 or Ne5, forcing Black to start with 1..f6 to maintain rough equality.[2] Games between experienced players follow more traditional opening principles such as piece development, controlling space, and winning material.[10]

Endgame
An endgame position
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Black has connected kings and become immune to check. However, White can win by forcing the black king to be adjacent to the black pawn, then capturing the pawn.
1.Kc4 Kd4 2.Kb5+ Kc5 3.Ka6+ Kb5 4.Ka7+ Ka6 5.Qxa5

Black is forced to retain the connection, or the queen will chase the king and deliver mate.

As with atomic opening theory, a small amount of endgame theory and analyses have been published online by strong players.[11]

A common scenario in atomic endgames is to have two kings on adjacent squares. As a player cannot intentionally blow up his or her own king, a king can never capture another piece, including another king. Similarly, because a capture affects all adjacent squares, one king cannot be captured directly if it means destruction of the other. Moving one king towards the other is thus a strategy to achieve a draw. The player with the advantage must then maneuver into a position where a non-king piece can be captured that is adjacent to one king but not the other. If there is no piece that can be captured, the player with the advantage can promote two queens and force the opponent into zugzwang and therefore forcing the opponent's king away from his king. Creative use of zugzwang is a common tactic to force a win in these situations.[12]

The Internet Chess Club variation of atomic chess ignores check completely, and thus leads to different outcomes in certain situations. For example, a king and rook vs. king endgame that would be a draw under normal circumstances can become a forced win on ICC.

gollark: Δy/Δx, if you prefer.
gollark: The slope of the line.
gollark: Ah, so if two adjacent things are the same and both extrema it wants the midpoint?
gollark: If they mean approximately the same things as in the calculus I did, then if the gradient was positive/negative on one side and the same sign on the other it would not be a maximum/minimum but just an inflection point. But if the gradient changes sign, then it can be, and this probably requires a different value to on either side. But I don't really get what they're saying either.
gollark: I think to be a valid maximum/minimum it has to be >/< but *not* equal?

See also

Other chess variants based on explosions

References
  1. Knopper, Klaus (27 November 1995). "Atomic Chess Rules". GICS. Retrieved 24 May 2014.
  2. "Vlasov's Atomic-Chess Homepage". Retrieved 24 May 2014.
  3. Long, Nick. "Atomic Chess". Chronatog.com. Retrieved 12 June 2020.
  4. "Atomic Chess! And more". lichess.org. Retrieved 2017-11-08.
  5. "Atomic rules". Free Internet Chess Server website. freechess.org. 27 February 2008. Retrieved 24 May 2014.
  6. Seymour, Tim (2009). "Atomic Chess: Rules". Atomic Chess (archived copy). Chronatog.com. Retrieved 12 June 2020.
  7. Blackburn, Leonard. "The Rules of Atomic Chess" (PDF). Parkland College. Archived from the original (PDF) on 25 May 2014. Retrieved 25 May 2014.
  8. "ICC Help: atomic". chessclub.com. The Internet Chess Club. Retrieved 24 May 2014.
  9. Krakov, Sergey. "Atomic chess openings". Siggemannen's Atomic Chess Page (archived copy). chronatog.com. Retrieved 12 June 2020.
  10. "Atomic Land". 2005. Retrieved 24 May 2014.
  11. "On Joined Kings". Atomic Land. 2005. Retrieved 24 May 2014.
  • Vlasov's Atomic Chess Homepage - Homepage created in the mid-1990s by a player involved with atomic's earliest implementation at GICS. Its most prominent feature is its attempt an opening book that covers many of the most common openings and traps. However, several of the ideas have been improved upon or refuted in the years since publication.
  • Molten Thinker Atomic Page - Covers some tactical and endgame theory, including diagrams and puzzles.
  • Nick Long's Atomic Page - Covers the game's variations, its role on different chess servers, lists of strong players, and other historical information.
  • Leonard Blackburn - Several documents and videos on the rules of atomic, openings, sample games, and a detailed paper on endgames.
  • - The atomic rule page on Lichess.
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