They could just snapshot at important junctions of history and spawn parallel branches, one when a certain decision was made, the other where not. Or where a ce

They could just snapshot at important junctions of history and spawn parallel branches, one when a certain decision was made, the other where not. Or where a certain fraction won a decisive battle, or the other one etc. Even ancient philosophers played with that idea, treating time as a series of "pictures" and leaving to gods to decide if they add/remove somebody to/from a picture at a given moment. Pretty much primitive simulation stuff.