So worlds are related to each other by time and space, since they're all inside a universe, and other universes... aren't. I wonder if realms are sort of the same, but inside a world...

[he stares at Terezi's diagram for a disconcertingly long time. at least he didn't seem to have too much trouble following her explanation once he had a picture...]

--we don't know if we're in the same universe as the ones where we came from, then. Do we.