Joshua was already in the Void beyond Stellaris when he opened his eyes.
Stellairs was a special superworld. In theory, it should have been enlarging endlessly with time like the infinite singular universe—perhaps, given that it was constantly absorbing mass from galaxies beyond, it could have well been the shape of an infinite realm on a totally different definition if the Initial Flame had never presented anomalies.
Nevertheless, the battle waged millions of years ago between the Wise One of the Arcane and the Masterminds—the existence which created the Evil Gods—had caused all manners of variations in the Multiverse. During that period, Stellaris ceased expanding and remained in its present size, but even so, it was already outstandingly massive and its World Barrier so strong that not even Joshua could break it open at once.