I'm stumped on a question about symmetries: Imagine you and a friend are on two separate rocket ships. According to me - standing on spacestation Babylon 5 – the two of you are moving parallel to each other at a constant speed but in opposite directions. What test would you do to confirm that you were moving (besides looking at the speedometer, of course)? I'm kind of leaning towards there being no test to be done, but I'm not so sure. Thanks in advance.