As a cosmology layman, I have a hard time grappling with this notion. On the one hand, I could understand that all galaxies would lie on the surface of an expanding cosmic bubble. This would satisfy me as a reason for each galaxy moving away from each other at an increasing speed. But what about the interior of the bubble. Could it be empty? On the other hand, if matter and galaxies are evenly distributed in the volume of the universe and that it all started from a speck location somewhere, this location should be centrally located vis-à-vis the current universe volume, and, on the average, galaxies should be moving away from that location and it should be possible to measure the direction to it. I could even imagine that there could be multiple expanding and co-centric bubbles.

This is actually a scenario I have a hard time to understand. Let’s consider the case used in this section’s problems where the lengths at rest are 10 feet for the barn and 15 feet for the pole and the relative speed 12/13 the speed of light. Each team arrives at a different conclusion as to whether the pole fits or not in the barn. However, as they must agree on events occurring or not, explosion or no explosion, how can they reconcile? Is it that each team has to compute a correction to consider what happens when both the barn and the pole are at rest? But then, each team must be living in a transformed world and must always make corrections to find what the motionless world is. Patrick