But there's a hole in my model, I guess. Namely, what keeps us all from crashing into the Sun and Moon? Rats. I can't make sense of it.
Yep, this is what I'm asking about. According to UA, the sun and moon are also being accelerated, thus we don't crash into them. If all of these bodies are being accelerated, why isn't everything being accelerated? How does UA pick and choose?
in fairness, the same sort of question can be asked of contemporary physics: why does the gravitational force only act on mass? why not charges, too? how does gravity pick and choose?
To answer that question, Gravity does not pick and choose. Gravity affects everything with mass, just weaker on object with smaller mass and greater on object with bigger mass.
The reason Gravity act on mass is because the bending of space which cause pull between objects i caused by mass.
So yeah Gravity act on all object with mass but UA either does not work on Sun, Moon, and stars, or only affects us