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Suppose there are 6 cars on a roller coaster and I synchronize 6 clocks at rest with respect to each other in a box with no wiggle room on the space station. The bottom of the box has the same shape as the curvature of the earth, and the box is always kept "top side up" with respect to the ground. Next I bring the 6 clocks down to Earth along with the next set of returning astronauts. I place the box next to the train and load the clocks, one per car, in such a way that each clock remains the same distance from the ground during the loading process. The train starts perfectly level in the sense that the track exactly follows the curvature of the earth (and in an idealization the earth is a perfect sphere as well). Once the clocks are loaded (none having changed elevation during the loading process), the rollercoaster accelerates, starts turning wildly and doing loop the loops, before returning to the "level" stretch of track. Next the clocks are carefully unloaded without changing their elevations, returned to the box, the box is kept right side up and returned to the space station on the next launch. In space, the box is opened and the clocks checked for synchronization. Are they still in sync?