Einstein Chess is a fairy variant of chess inspired (loosely) from Einstein's relativity theory where mass is energy and vice versa. The genre was invented by Roméo Bédoni and Jean Zeller in 1981.
In Einstein chess, every time a piece moves (without capturing), it "loses energy" and transforms itself (= "is demoted") into a smaller unit, one step down the ladder from Queen to Rook to Bishop to Knight to Pawn. Every time a piece captures, it gains energy and transforms itself (= "is promoted") into the next bigger unit.
Kings do not transform. A capturing Queen-move or a non-capturing Pawn-move does not lead to any transformation.
There are no promotions. So that you can have pawns on the 8-th rank (where they are stuck). You can also have pawns on the 1st-rank (after a non-capturing Knight move): these pawns can make a single, double or triple step forward. After a double or triple step, they can be captured en-passant by an enemy pawn on the 3rd or 4th rank. After a triple step, en-passant capture can take place on two different squares!
Clearly, Einstein Chess in retros will give rise to interesting inventory and balance problems, where time (i.e. number of moves) will interfere with balance.
[Q] What happens with castling? This is still debated. Is the Rook demoted? (Castling counts as a King move!) Also, can you castle with a demoted Queen or a promoted Bishop who never moved as a Rook? (This would be weirder.)
3242 - Thierry Le Gleuher
diagrammes 112, 01/1995
15+13. Position after Wh. 18th move. Game score? (Einstein chess)
1. d4 Nf6=P 2. d5 f5 3. d6 f4 4. dxe=N f3 5. Ng8=P Ke7 6. Qd4=R Kf6 7. Rh4=B+ Kg6 8. g4 h6 9. Bf4=N+ Kh7 10. e3 a6 11. Bxa6=R Rxg8=Q 12. Rg6=B+ Kh8 13. Bh7=N Ra4=B 14. Ng6=P Bb3=N 15. axb=N Bd6=N 16. Ra3=B Ne8=P 17. Bd6=N e7 18. Ne8=P Qf8=R.