http://en.wikipedia.org/wiki/File:Tesseract.gif
This is a three dimensional perspective on a 4 dimensional shape. This is basically the theory on where our universe ends. When you reach where there is no more matter, time ceases to exist. You won't stop though you will still keep going in a straight path, but you will have actually gone back to where you started. Our human minds can't grasp our heads around this so don't bother overthinking it.
If anyone knows how to embed this, great. Otherwise ... /thread