Earlier quoted context omitted.
It is because in both cases, you can work out that you'll never make an observation that really proves it one way or the other, but you might come up with some laws of physics that are more conveniently expressed in one way than another. They're both ultimately questions about your coordinate system, and in fact it is easier to invert time than it is to work out how everything's supposed to function in a rotating+sun…
If we reverse time and this implies running everything backwards in physics, do we include gravity in the set of things that are reversed? Then everything would fly off the face of the earth in reverse-time.
Imagine a ball being thrown up and then falling down, in a parabola. Reversing a video of that still gives you a video of a ball in a normal parabola trajectory.