I had been informed that for objects in free fall orbit no proper acceleration would be measured. https://www.physicsforums.com/threads/stationary-frames-of-reference.899195/page-2#post-5658771 But I also understood it that for objects in free fall orbit gravity time dilation would be observed. https://www.physicsforums.com/threa...vitational-time-dilation.563173/#post-3685830 . So I am not sure how proper acceleration and gravity are equivalent, as in the example given in the last thread referenced, each time B comes back to A the difference between the clocks would show an affect of gravity, and the affect could be dismissed as being an affect of proper acceleration, as no proper acceleration would have been measured by A or B. So can someone explain why proper acceleration and gravity are equivalent in this example? With two satellites, going at the same velocity, in free fall orbit around a massive body at different altitudes for a few thousand years, as I understand it the clock on the one much closer to the massive body would run slower than the one in a higher free fall orbit so that if they were both quickly brought together and compared the clock that was in lower orbit would have measured less time passing. Would the comparison be significantly different if one of the satellites was in free fall orbit at a much greater velocity than the other? If so, what type of difference would it make compared to if they were going at the same velocity? If the bringing the together (presumably a constant affect) were to influence the outcome, perhaps it could be explained how the difference (if there would be one) would vary dependent on how long they had been orbiting for, once the gravitational affect had been taken into account.