[Greystoke]

What's a 3-Sphere?

[ThePythonicCow]

A 3-sphere is a solid ball - or warped equivalent. In 4-dimensional space, the set of points one unit from the origin is one example of a 3-sphere, just as in our ordinary 3-dimensional space, the set of points one unit from some point is an example of a 2-sphere that is more commonly called a circle.