Form: the visible shape or configuration of something.
Shape: the external form, contours, or outline of someone or something.
Explanation:
In a one dimensional universe if space is straight then the universe is shaped like an infinitely long, one dimensional piece of spaghetti. In order to bring the ends together, we have to allow the space itself to become curved. How do we do this? We curve space by allowing the one dimensional straight line to curve into a (two dimensional) circle; it curves within a two dimensional space. This is the heart of the model, so think this part through carefully and make sure that you are comfortable with it.
Does this affect our friend the one dimensional ant? Not at all! Because the ant can only perceive his one dimension, he does not realize that his world is curved. From his point of view, space stretches out flat in front of him. Imagine that the one dimensional ants developed a great civilization, and became curious about the geometry of their universe. They built large telescopes, and invented rocket ships which flew very fast. If their telescopes were sensitive enough, and they peered far into the depths of the universe (looking around the circle formed by the rubber band), they would not find a brick wall marking the end of the universe, but instead might eventually look all the way around and see themselves (the backs of their heads)! If they set off in rocket ships, and traveled far around the rubber band, they might eventually end up at home again without ever having turned around! This might be quite confusing to the one dimensional ants, but for us three dimensional creatures the explanation is perfectly clear. But because the ants cannot get outside of the rubber band to see it, they don't understand how it can be circular in form.
In a two dimensional universe if space is straight then the universe is shaped like an infinitely long, two dimensional flat piece of paper. How do we curve this space? We curve space by allowing the two dimensional flat plane to curve into a (three dimensional) sphere; it curves within a three dimensional space (forming the surface of a sphere). Again, think this part through carefully and make sure that you are comfortable with it.
