Some readers may recall E A Abbott's book Flatland - A Romance in Two Dimensions. Flatlanders lived in a flat two-dimensional world and could not imagine "up" and "down", but only the points of the compass in their world. However, what if their flat world was the surface of a large sphere? Such a surface would not have a "middle", though it could have expanded from a point, rather like a balloon being blown up. A Flatlander anywhere on this expanding surface would observe objects in his universe to be receding, and would perceive himself to be in the "middle". Thanks to relativity, we now have to accept that our simple three-dimensional space is similarly curved, and it no longer makes sense to talk about a middle.
I still find it baffling myself, though!
Dr R S Lowrie