I must admit, I'm impressed with the UA theory. There's some questions in my mind though... 1) Dark matter annihilates with matter upon contact, so why does it exist under our disk of matter, 2) Why would the dark matter accelerate with the earth if it is the main repelling force, and 3) If there is in fact material outside our bubble, what else is out there?
Story time: I live in Texas and had a friend from New York visit who has never seen cows. When he saw a feed lot, all the cows were black. Later, we went to my aunts' home and she had a brown cowhide rug. My friend was baffled because to him, he saw hundreds of black cows and no brown, white, or spotted cows and assumed black was the only variety of cow. Silly Northerners.
You are like my friend when you say "It seems flat, so that's the most likely conclusion". You don't need to understand reality for it to be real. I don't understand quantum mechanics, but thank goodness that it still works without my comprehension. You must rise to the level of comprehension required by reality. You can't change reality to match your comprehension. Tom hasn't made a conjecture like this in this thread, but I've seen it in other threads from him and others.