Einstein's GENERAL theory of relativity says that there is no experiment that can distinguish between uniform acceleration and uniform gravitation. So if the FE community want to say that there is uniform acceleration - rather than uniform gravitation - that doesn't change the results of any experiments.
The problem for FET is that gravity isn't uniform...things weigh different amounts in different places - and that can't be explained by acceleration without some parts of the Earth accelerating faster than others...with obvious unfortunate consequences. So universal acceleration alone can't explain all of the facts that are plainly out there.
I'm glad you added "uniform" to both acceleration and gravitation, to make it technically correct. The best kind of correct. Because in practical reality, specially on earth, you can tell. You can weigh yourself in Badwater Basin, then again at the top of Mt. Whitney. Or with experiments like this.
http://physics.ucr.edu/~wudka/Physics7/Notes_www/node87.htmlIn fact, it would be hard to imagine a scenario where you could not distinguish between gravity and acceleration. Given enough precise technology and some freedom to move.
That has been a headscratcher for me, as I grew up accepting that equality assertion. I reasoned that since they are identical, they must somehow be the same thing. At some deep fundamental level. Maybe everything is expanding at a rate proportional to it's mass. Maybe all the subatomic particles are expanding. But somehow maintaining proportional attributes, fields, etc. That could explain some things, say, the force of gravity on the Earth's surface, kind of like the UA. But I don't think that could explain the inverse square law. How would galaxies work, and the attraction between two of them. How would orbits work.
Anyway, at some point I figured that maybe they aren't the same fundamental thing. And maybe the claim that there is no experiment that can tell them apart, is flawed. Because is really no such thing as uniform gravitation. There is always a gradient. For something like the largest black hole known that has an event horizon about the equivalent of Pluto's orbit, and standing on a platform 10 times again as far, the gradient might be essentially practically immeasurable with any conceivable technology over the span of a few meters. (Given the inverse square law.) But if the distance between measurements is large enough, you'll find the gradient.
And yet, as you also pointed out, I don't think it would be possible for a gradient to form with acceleration.
Or would it? Nothing can travel faster than the speed of light. Not gravitation, and presumably not acceleration. We've never tried to accelerate a mountain, let alone long enough to measure G-force at top and bottom. If the velocity can only increase at on quantized planck time boundaries, and can propagate from bottom to top no faster than the speed of light light, and only in planck time increments, then the top will always be a bit behind the velocity of the bottom, thus you'd always weigh less at the top than the bottom. I know that seems illogical, but so does photons traversing the universe instantly while we see them as slow as molasses, until you understand General Relativity. Maybe there's a deeper underlying truth that unites both phenomenon.
So maybe gravitation and acceleration could be the same fundamental thing after all. Not just indistinguishable.
In other words, we just assume that UA would not produce the same weight measurments at sea level vs. mountain top. Certainly makes sense. But maybe it's not that simple, and it really would be indistinguishable. (And therefore we wouldn't need the "uniform" qualifier on gravitation and acceleration to make the equivalency still valid.)
My head hurts. I hope I didn't just give ammunition the the flat-earth UA model. Like, enough plausible-sounding babble to run with.