If an alien civilization is 1 billion light years from us in one direction (and it is highest distance for contact), it implies that median distances between civilizations is 1 billion ly, and there are 5 others: in opposite direction, as well as up, down, right and left direction. So it is 1 civ or at least 7 including ours, based on some symmetry considerations. Two civs seems unlikely.
If an alien civilization is 1 billion light years from us in one direction (and it is highest distance for contact), it implies that median distances between civilizations is 1 billion ly, and there are 5 others: in opposite direction, as well as up, down, right and left direction. So it is 1 civ or at least 7 including ours, based on some symmetry considerations. Two civs seems unlikely.
The idea about prevention s-risks via acausal trade is discussed by me here: https://forum.effectivealtruism.org/posts/3jgpAjRoP6FbeESxg/curing-past-sufferings-and-preventing-s-risks-via-indexical