Edge of the universe

Daniel Boorstin, The Discoverers [dust-jacket illustration;
attributed to a 16th-century woodcut by the Bettmann Archive]

A Medieval science thought experiment...well, maybe not so Medieval:

"If you thrust your hand beyond the outermost sphere, would your hand be in a place?"--Aristotle

Or to put it another way..."What is outside of the universe?"

Aristotle replied:

"It is therefore evident that there is no place or void or time outside the heaven [i.e., the outermost sphere of fixed stars]. For in every place, body can be present; and void is said to be that in which the presence of body, though not actual, is possible; and time is the number of movement. But in the absence of natural body there is no movement, and outside the heaven, as we have shown, body neither exists nor can come to exist. It is clear then that there is neither place, nor void, nor time, outside the heaven. Hence whatever is there, is of such a nature as not to occupy any place, nor does time age it; nor is there any change in any of the things which lie beyond the outermost motion...."On the Heavens, Book I, Chapter 9.

Okay, from the Medieval perspective this was more of an issue for an argument for the "flat Earth" hypothesis and despite that stance it did provide fodder for analytical thought experiments. [As old as the Stoics the thought experiment is thus: What would happen if a man tried to extend his arm beyond the outermost sphere? (See the above woodcut)]. Clearly Aristotle advocated a "finite" universe where neither matter or time existed beyond the known universe and many Medieval theologians/philosophers saw an opportunity to place God and heaven in that realm. Guess what, we are still asking that question some 700 plus years beyond the Medievalists. The question is...is it still a relevant question despite our sophisticated technology to peer into the universe, the ability to mathematically extrapolate hypotheses, to find the nebulous question of our own existence, fragility, destiny? Is the question of finiteness-infiniteness of the universe a matter of science or philosophy--or both?