1. The problem statement, all variables and given/known data No math required, mostly just a conceptual question. Consider two points at direct opposite sides of the expanding visible universe. Could these two points ever been in causal contact? 2. Relevant equations 3. The attempt at a solution I take causal contact to mean that a photon, without encountering any medium that could cause it to take a less than perfect path, could have been exchanged by the two points. To me, all points (including non-visible) should have been in causal contact at some point directly after the big bang. Unless expansion has always been greater than the speed of light? But, I know that right now that these two points, according to us, are moving away from each other at a speed greater than the speed of light due to expansion. Meaning they could not possibly have had any causal contact. So, I guess it comes down to how quickly the universe was expanding at it's lowest expansion velocity. We haven't discussed expansion in that much detail so perhaps I'm thinking of this wrong. Thanks for the help!