I would probably have to re-read this again, but having read it and reviewed a few points you make I still can't seem to figure out why they would have to age at different rates, I get stuck at "perceived" mostly, because then when we align their perception once they are back on earth time is equal again and then no time difference should exist.

Thank you for all the sources because as you can see from the above I can do with the reading and your introduction to it will help me make sense of it.

I am looking forward to more of these kinds of daily doses and think it will also help a person discover interesting things easier. Not knowing what to search for can make a person either go down a rabbit hole with no exit or jump on the wrong train.