How do you think it possible for the ancients to be satisfied with the concept of FINITE SPACE, with "fixed stars" at its limits? To our minds, the idea of infinite extension comes so naturally, without the slightest effort, even for the mathematically unsophisticated. So what is really hiding here?
Who believed in a closed world? The fathers of science, the Old Greek, did not.
Anaxagoras 499-428 BC knew: Of the great there is no greatest but there is always a greater.
Anaximander of Milet 611-547 BC already said: The infinite (apeiron) is not exhaustible. Wherever the warrior stays, he can stretch out his spear farther.