"Border Guards" is a science-fiction novelette by Australian writer Greg Egan, first published in Interzone 148 in October 1999.
[1][2][3] In the city of Noether in a 3-toroidal universe, Jamal and Margit play a game of quantum soccer, where the field is replaced by a potential well with infinitely high walls, the ball is replaced by a wave function and the players have to exchange energies between the modes with different frequencies to increase the wave function in the goal of the opposite team.
Jamal at first suspects Margit to actually be Ndoli, the Nigerian neurologist who invented the jewel, a device capable to map a brain and hence eroding the border between life and death, or having worked with him.
The novelette was translated into Japanese by Makoto Yamagishi (2001), Italian by Roberto Marini (2002), Dutch (2006), Polish by Iwona Michalowska-Gabrych (2007), French (2009) and Chinese (2024).
Karen Burnham writes in Greg Egan (Masters of Science Fiction), that the novelette "has more to do with humanity’s dislocation in becoming immortal, as well as the lasting effects of trauma."