8.16 O Arjuna, all the lokah, worlds; abrahma-bhuvanat, together with the world of Brahma-bhuvana is that (place) in which creatures are born, and brahma-bhuvana means the world of Brahma; punah avartinah, are subject to return, are by nature liable to come again; Tu, but; kaunteya, O son of Kunti, na vidyate, there is no; punarjanma, rirth; upetya, after reaching; mam, Me alone.
Why are all the worlds together with the realm of Brahma subject to return? Becuase they are limited by time. How?