What do you think makes things fall?
And what is the mechanism behind it?
In your own time.
Since Action80 won’t take you up on your challenge, I’ll take a shot and see if he has a response.
Let’s consider an apple on the branch of a tree. What causes it to fall? While the apple is still on the tree, we could consider the tree/apple being accelerated up by UA or at rest in a gravitational field. Either works right up until the apple falls. After it separates from the tree, UA can again explain its motion, but it doesn’t explain why it separated from the tree in the first place.
GR does explain it. In GR, the tree and apple, while at rest in a gravitational field, are traveling along a geodesic. The stem is holding the apple to the tree, so it is following the geodesic of the tree, not its own geodesic. As the apple ripens the stem weakens and eventually breaks. When the stem breaks, the apples is no longer prevented from traveling along its own geodesic and beings to travel independently along its own geodesic.
One could argue that when the stem breaks, the apple just stops accelerating up with the tree and waits patiently while the earth rises up. This is not a valid argument because according to Newton’s first law, if the apple was traveling in uniform motion while it was attached to the tree, it would continue with that uniform motion whether it was attached to the tree or not. IOW, the apple would continue its acceleration upwards at 9.81 m/s2. “Stopping” is a change in velocity and a change in velocity is acceleration. UA offers no explanation for that acceleration. This is the fatal flaw of UA. It rises and falls (pun intended) on the EP, but the EP doesn’t apply to accelerated motion.
Even if, by some miracle FE could come up with some explanation for how the UA force works, or even what it is, they still could not be able to account for why things fall.