You just completely missed my point. GR and curved space time again isn’t an issue as long as everyone knows what space time looks like. Mission Control on ea

You just completely missed my point. GR and curved space time again isn’t an issue as long as everyone knows what space time looks like. Mission Control on earth, a moon base, and mars would all experiencing time at a different rate and those rates would vary based on the orbits of each body. However assuming we needed extreme precision, such as telescope interferometry, people can pick one of them arbitrarily or perhaps due to politics some arbitrary 4th option. Whatever their choice everyone’s timelines based on that choice end up being absolutely identical. The math simply works without any ambiguity. So because there’s an obvious choice based on the actual universe we live in, ie maximum amount of time since the Big Bang, then in theory trillions of civilizations across many different galaxies might all use the exact same reference even if no particle experienced it. Edit: Well not exactly the same there’s uncertainty for such calculations but effectively the same.