If you are on a sufficiently large planet the point will be far enough away that you can't detect the convergence.
Which is why I said “…if you have a sufficiently sensitive measuring instrument.” My understanding is that gravity operates as though the entire mass of the gravitating object were at its centre; so however large the planet, the marbles will still converge to as they near it.
The reason here is close to the same as for the first case. Since the force exerted on the marbles varies according to the inverse square law the force on the marbles is different based on the distance from the center of the planet.
Precisely: so you can still make the distinction.
If you were in free fall the marbles wouldn't move with respect to the box
They will not move vertically with respect to the box, but they will move horizontally with respect to the box.
GR/SR. I’m mildly dyslexic, sometimes I don’t watch closely enough.
