Uncorrelated with their positions in three-dimensional space, Population I star systems are connected through etherstrands, a system of navigable pathways in the large extra dimension called the etherbrane, or etherspace. Conclusive evidence exists for a separate pathway system that connects Population II destinations, traversed by exoentities using non-technological means. The existence of a Population III pathway system is controversial.
While both human and artifact civilizations rely on the full range of chemical elements and thus can only arise in Population I star systems, exoentities seem to have only evolved across Population II space. As most Population II stars are billions of years older than most Population I stars, whenever exoentities breach the barrier, they are literally invading from the cosmic past.