I am surprised this has apparently not been discussed here as such in this forum (nor anywhere else on the web). The point is that in the classical space-ship twin paradox, not only the traveling twin will be subject to a proper acceleration, but, according to Einstein's equivalence principle, also the twin staying on the earth, because of the gravitational field of the latter. If the space traveler is accelerated with 1g (assume he starts from an earth orbit), it should not be too difficult to construct a scenario where both the accelerometers on the space ship and the earth will measure exactly the same time dependence of the proper acceleration according to their respective clocks. Even the turnaround of the traveler could be replicated by the earth twin (by moving to the other side of the earth). On the basis of the accelerometer measurements, it should thus not be possible to single out on twin from the other because of the equivalence principle. Does this imply that for this scenario there would be no age difference when the traveling twin returns?