We have you: the player.
We also have: the server and other players.
now, lets put this in perspective;
you are a god.
the server is your personal world.
other players are other gods, logged into your server.
however, because of this small limitation, the other players must die in the server, before they can join another one, thus meaning an infinite possible servers, limited to what gods joined what.
e.g. this world could be the author's world.
however, this is strictly not the point.
children created by a god a limited to that world (until they reproduce and die), much like a child entity in a programming environment, continue that world.
if there are no more players in the the world for x (unknown defined god time) the world deletes and starts a-fresh. however, the owner cannot re-join even if he dies from the world.