> if I jump out of an aeroplane, I don't accelerate towards the ground? Not in your rest frame. In your rest frame, the ground accelerates towards you. Howeve

> if I jump out of an aeroplane, I don't accelerate towards the ground? Not in your rest frame. In your rest frame, the ground accelerates towards you. However, the acceleration described in both frames (yours and the Earth's) is coordinate acceleration, which is frame-dependent, and in relativity frame-dependent quantities don't have any direct physical meaning. The quantity that has physical meaning in terms of acceleration is proper acceleration--what an accelerometer strapped to you would read--and in free fall that is zero.