Mass distorts spacetime, which to an outside observer appears to change the direction light travels. The light travels in a straight line.
Gravity doesn't alter the particle's trajectory (or ours, for that matter). The warping of spacetime from Earth's mass causes our movement through space to accelerate "down" at ~9.8 m/s^2
So the ghosts are in the center of the Earth, in nearly literal hell.
They would fall through the center of the earth, continue back up through the mantle, pop up momentarily to spook someone on the opposite hemisphere, then repeat the whole trip in reverse with a period of about 40 minutes.
Hm.. actually are they incorporeal AND massless, or just incorporeal?
If just incorporeal, you're right of course that initially after death they'd be falling back and forth, but over time through uneven gravity/curvature and through heat loss (stretching of unequal acceleration applied across the ghost essence, potential energy conversion, yadda), they should generally settle to the center after some time, unless there's a maximum natural pressure of ghosts at whatever temperatures they have, so they may spread out somewhere within the crust if there are enough of them.
If they're incorporeal AND massless, then I totally F'd up and they'd fire off at light speed as soon as they shed their mortal coil.
If the spacetime is distorted, and the light no longer appears to travel in a straight line, does that not mean that spacetime itself and the light that travels in are no longer straight?
How can a straight thing be distorted but still be straight?
Is this 2D-3D comparison supposed to be like a human-understandable analogy for a 3D-4D relationship?
I saw an explanation once about how time is the 4th dimension. They drew a line on the edge of a book. From the perspective of a single page (2D) it just looks like a dot, but because we can see many instances of that 2D representation it appears to us as a line. An individual page represents how we experience time.
Is your ball example supposed to be kind of like that because I just can't imagine how spacetime could be a 2D thing in a 3D universe.
I think a better way of explaining it is with the idea of a shortest path, and not nessesarily a straight line. With two points in space the shortest path between them will be a straight line. If there’s a large amount of gravity tugging on space time the shortest path will be curved.
That's called General Relativity and Reference Frames.
Start watching PBS Spacetime if you actually want to get into it.
You're also entirely missing the point of the comment that was a joke entirely re-explaining the "reason" for ghosts ending up at the center of the Earth, which is implied by the original comment.
I really hate that people just accept these advanced theories as objective truth. It's just the best theory we have right now, that doesn't mean that's how it actually works. It's good enough that we can almost always just use the theory and get good results, but then people get all pissy when you point out that it's still just a theory and is not without its flaws.