I thought that the FoR was obvious from the discussion of an accelerating Earth.
Oh, thank the Lord! You wouldn't believe how often people get these completely wr-
One observer on Earth looking outward from horizon to zenith. The observer is accelerating at 9.81 m/s2 by virtue of being pushed along by the accelerating Earth as per UA. The observer is accelerating relative to the background starfield with both observer and starfield at v = 0 at t0. tnow being no less than 100 years after t0, the observer's vnow relative to the starfield should be "approaching relativistic velocities". Somewhere north of 0.999 c by my back of the envelope calcs.
Oh. Oh dear.
So, this is why reading about UA would have been helpful. Sure, hypothetically, an observer that's somehow not subject to UA would see the Earth zoom away at ludicrous speeds after a year of somehow not being affected by UA. However, the "U" in "UA" is a bit of an issue there.
You can feasibly have an observer that's in relative proximity to the Earth, in which case they'll observe the Earth accelerating towards them together with the atmolayer until they reach terminal velocity. This will also not last anywhere near
a year 100 years(?!), because falling is usually a rather temporary affair.
You can also have an observer that's outside of the Earth's area of influence, and thus affected by UA. From their perspective, the Earth is not accelerating.
Your hypothetical does make sense from a physics standpoint (a breath of fresh air, honestly), but it simply isn't very relevant to what's being discussed. It's like saying that if I somehow managed to propel myself to relativistic speeds relative to the Round Earth, I'd observe time dilation. Sure, I would. So what?
What saddens me particularly about your contribution here is that we just finished talking about why your observer isn't relevant. You said you've done your reading, but this turns out to have been untrue. You should have done so much better.
Honestly Pete, this is so basic I shouldn't have to explain.
I agree, and I was honestly excited when you seemed to know your stuff, but, alas, you managed to cock it up.
The background starfield begins as stationary relative to us
This incorrect assumption is at the core of your misunderstanding. There is no magical "background" that's unaffected by UA; Universal Acceleration is... universal. So, for your FoR to make sense, you have to introduce a hypothetical observer. One that, from an Earthly perspective, has unprecedented energy that somehow allows it to defy the nature of our universe. You will have to prove the existence of such an object before we can discuss its relevancy, but if such an object exists and you can slap a time-measuring device on it, then, by all means, I agree, you'd measure significant time dilation there.