Cosomological horizon and absolute time

[Quizatzhaderac]

eta oin shrdlu, thank you: thanks does clear a few things up. I looked closer at the definitions of preferred frames with respect relativity to relativity and, sure enough, relativity's claims were only for local events. Is there a term for relativity in an open room? Because that's what I believed before I started this thread, with a suspicion that the horizon wasn't as invariant as is believed.

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?

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.

[eSOANEM]

eta oin shrdlu, thank you: thanks does clear a few things up. I looked closer at the definitions of preferred frames with respect relativity to relativity and, sure enough, relativity's claims were only for local events. Is there a term for relativity in an open room? Because that's what I believed before I started this thread, with a suspicion that the horizon wasn't as invariant as is believed.

Locality is one of the defining features of relativity. IIRC throwing that out allows FTL transfer of information and introduces a load of other problems.

[eta oin shrdlu]

eta oin shrdlu, thank you: thanks does clear a few things up. I looked closer at the definitions of preferred frames with respect relativity to relativity and, sure enough, relativity's claims were only for local events.

I'm still not sure what you're trying to do here. From your original post it looked like you thought you'd found a problem with relativity, in terms of a preferred time coordinate. But that was a misunderstanding of the terminology; the time coordinate you define is not "preferred" in the relativistic sense, and it can't be used to settle any disputes about who's "really" moving in the sense meant in relativity.

So you've rediscovered the use of the CMB temperature and dipole moments -- I think, though I'm measuring this or similar early-universe radiation is what you mean when you talk about measuring the horizon; the horizon itself is not directly measurable -- as measures of (or at least correlated with) the age of the universe and the peculiar velocity of the measuring device. But this is nothing special or nonlocal; you are just using the plasma radiation in your past light cone to estimate a local observable-universe rest frame. Someone in a galaxy near the boundary of your observable universe would observe a different CMB emitted from a different blob of plasma, and it's only the assumed homogeneity of the early universe that means you and he will get similar behaviors of time coordinate.

Note too that there are other ways of estimating the age of the universe; one can observe stellar populations with different metallicities to count stellar generations, look at the dynamics of galaxies and clusters, and so on. These also let you estimate a cosmological time coordinate, and there's nothing really different in principle between these methods and the one you're proposing.

Is there a term for relativity in an open room? Because that's what I believed before I started this thread, with a suspicion that the horizon wasn't as invariant as is believed.

I'm not sure I understand this part of your post. For "relativity in an open room" I might jokingly suggest "cosmology" but I'm not sure what you're getting at. There's nothing nonrelativistic about the ability of Alice and Bob to agree on an event in the intersection of their past light cones as a velocity reference, which is what you're really doing.

[Quizatzhaderac]

I'm still not sure what you're trying to do here. From your original post it looked like you thought you'd found a problem with relativity, in terms of a preferred time coordinate. But that was a misunderstanding of the terminology;

That's essentially what I was trying to do, just with more suspicion on the cosmology than relativity.

I'm not sure I understand this part of your post. For "relativity in an open room" I might jokingly suggest "cosmology" but I'm not sure what you're getting at. There's nothing nonrelativistic about the ability of Alice and Bob to agree on an event in the intersection of their past light cones as a velocity reference, which is what you're really doing.

Since there's nothing about the ACs that contradicts "relativity", so I was defining "relativity in an open room" as a framework that disallows building an effective AC. Or more exactly, special relativity plus the inability to establish a reference frame based upon a universal invariant.

[eta oin shrdlu]

I'm still not sure what you're trying to do here. From your original post it looked like you thought you'd found a problem with relativity, in terms of a preferred time coordinate. But that was a misunderstanding of the terminology;

That's essentially what I was trying to do, just with more suspicion on the cosmology than relativity.

I'm not sure I understand this part of your post. For "relativity in an open room" I might jokingly suggest "cosmology" but I'm not sure what you're getting at. There's nothing nonrelativistic about the ability of Alice and Bob to agree on an event in the intersection of their past light cones as a velocity reference, which is what you're really doing.

Since there's nothing about the ACs that contradicts "relativity", so I was defining "relativity in an open room" as a framework that disallows building an effective AC. Or more exactly, special relativity plus the inability to establish a reference frame based upon a universal invariant.

Ah, so if I understand you right, you're worried about the fact that cosmological observations apparently allow you to define this universal frame beyond the light cone. This is indeed a puzzle. More precisely, the question is why observations of, e.g., the CMB at widely separated locations in the universe should show such similarities. This is known in cosmology as the horizon problem. It's the problem that the inflationary-epoch hypothesis was designed to solve, and testing predictions of inflation was one of the goals of the high-resolution satellite measurements of the CMB over the past 15 years or so.