One could say: "The boundary condition of the universe is that it has no boundary. " The universe would be completely self-contained and not affected by anything outside itself. It would neither be created nor destroyed. It would just BE.
Scilurus on his death-bed, being about to leave four-score sons surviving, offered a bundle of darts to each of them, and bade them break them. When all refused, drawing out one by one, he easily broke them, thus teaching them that if they held together, they would continue strong; but if they fell out and were divided, they would become weak.