This TEDEd video works through the thought experiment, with messages sent from each twin to the other at 1-year interval (in the sender's frame of reference).

This TEDEd video works through the thought experiment, with messages sent from each twin to the other at 1-year interval (in the sender's frame of reference). https://www.youtube.com/watch?v=h8GqaAp3cGs https://www.youtube.com/watch?v=h8GqaAp3cGs