Goemon wrote:YOU are "space-like separated from Sol", technically speaking - by about eight light minutes. Does this mean you can't measure Sol's motion? (Hint: you can).
I can measure Sol's motion eight minutes ago, certainly. For a period of eight minutes we can realistically model Sol with only small unexpected and unobservable variations. If you were 8 billion light years out instead of eight minutes, so that nothing we recognize as "Sol" is in your past light cone, would you be able to describe it's motion now? Would you even have a non trivial chance of being able to ask what "Sol" 's frame was, being as it's future matter was mixed with other future star's in the interstellar medium?
Goemon wrote:The point is that a "frame" is an imaginary construct; a reference system that doesn't have to be tied to any physical object that you can see. If Xytzil the alien can figure out his distance and relative direction from Sol BY ANY MEANS, then he can measure his motion or that of anything else relative to Sol's frame.
The referent (the platonic frame) doesn't physically exits, but the reference (the information) does, as is limited by the speed of light. The bucket brigade won't be able to get the information to Alice any faster than light. Even if they could, Alice simply asking for the information per-supposes faster than light communication because she knows Sol exists in the first place.
And even if everyone had tachyon telephones, there would still be a time in all (non-looping) time frames when Sol didn't exist yet.