When the curvature of space is greater than zero, the universe is infinite. From a four-dimensional point of view, the universe is a sphere with a certain size, but it can't reach the edge on the sphere.

When the curvature of the universe =0, the universe is flat and infinite. From a four-dimensional point of view, the universe is a big plane without sides.

When the curvature of the universe

In fact, people live in time and space, without which they can never exist, just as creatures living in a two-dimensional plane (assuming there are two-dimensional creatures) can never jump into a three-dimensional space. What's the point of having endless edges?