Think of it like an inflating balloon(or a balloon that is inflated but is assumed to be expanding further). In the center of that balloon, you will have a point that is coordinately the center. If the balloon expands further, you can expand the grid in that direction, likewise if it shrinks, all the while leaving your origin in a single spatial location.-If the balloon is moving in space, its center is moving. Your theory works if you use the Earth, its whole volume, or its surfaace, but not space.