In a small bubble surrounded by nothing (or not surrounded by anything), no matter which way you looked you would see the back of your head. If you threw something away from you, it would hit you in the back.
He brings the example of a spaceship flying into space and asks what would happen if it went on and on. Is there an end point or does one eventually loop back to the starting point? These possibilities seem rather implausible. — spirit-salamander
If there is nothing beyond, why wouldn't it come back to its beginning?
If the universe has actually expanded from a point with itself being the center, then the center has become the whole universe. The center is everywhere.