How A Threesphere Would "Look" or Work? I have been trying to understand threespheres (4D spheres) for a while and I just can't understand it. First off is the 4th dimension time (it progressing in time is what makes it 4D)? Or does this sphere involve 4 spatial dimensions and one time dimensions (thus 5D)? Or is time not used? How can it involve 4 spatial dimensions when we can only imagine 3? You can supposedly "construct" a threesphere according to the wiki article; http://en.wikipedia.org/wiki/3-sphere This article tries to demonstrate how to make it but I don't get it; http://www.dpmms.cam.ac.uk/~etc21/hexlet/hexlet3.html [Broken] When I pressed "Animate" I still couldn't get it. What do a few balls rotating under and above two balls inside a bigger ball have to do with when you go in one direction in the universe that you will eventually come back to the point you started from (in a assumed finite universe)? This site explains it a bit better; http://www.math.union.edu/~dpvc/math/4D/stereo-projection/welcome.html Ok that does make more sense of the universe was like a donut shape. And I can see how a sphere can be rotated to a torus (well sort of). But even in this case there a surface you can go outside of! So in order for a threesphere to work does it have to constantly "move" in order to catch up with the point traveling at the "edge" of its shape before going around? Furthermore if the "outer space line" moves at a further distance from the point would it not violate what makes a sphere or circle a, well, sphere or circle (not at an equal distance from the origin)?