Common sense told humanity that the universe had no edge. The widely accepted Big Bang theory on the Earth of Su Ming's previous life held that the universe had continuously expanded outward from a central point.
The foundation of the Marvel Universe was also the "exploding egg" theory. It had been an egg formed after the Sixth Firmament collapsed, and when it burst open, it formed the present Seventh Firmament—the universe of today.
However, this universe had boundaries.
Though the physical distance was "infinitely" far away, one could still reach that infinite distance after mastering certain special methods.
There were quite a few such methods. For example, the Time Shuttle Su Ming had snatched from Kang directly exploited the mechanism by which time created Parallel Worlds, sending people into the multiverse's "selection interface" on a conceptual level.
Most Mages could also get here through teleportation, taking shortcuts through the dimensions of demon gods.
Then there was Thanos's technology. His ship happened to be one of the few special vessels capable of jumping to the edge of the universe.
Not even the ships of the Three Great Empires could do that. Yet the Universal Truth Church's ships, which used living people as fuel, could unexpectedly reach this place through their "Idealistic Engines."
Of course, those who had reached a certain level of power could fly here themselves, such as Carol in Binary Form, Phoenix after being completely Darkened, Wanda after fully mastering her abilities, and Spider-Man after becoming Captain Universe.
After all, this was a universe where fists did the talking. If you were strong enough, you could do whatever you wanted.
Aside from those cases, there was another sort of person: lunatics and madmen. As long as they were crazy enough, even the universe's boundary could not stop their thoughts.