You can have expansion with no center. For a 2D model, consider only the surface of a balloon. As the balloon expands, each point on the surface increases in d

You can have expansion with no center. For a 2D model, consider only the surface of a balloon. As the balloon expands, each point on the surface increases in distance from every other point, but there is no center of the surface. Be sure to consider only the surface, not the 3D embedding your (flawed) intuition wants to inject. You can do the same thing in 1D with a circle. This works in any dimension, including the 3+1 spacetime manifold.