ok so u have two twins, both have clocks set to zero. One of them takes off at close to the speed of light. That twins clock would run slow. However If the twin were to reset both clocks and take of at the same speed in the opposite direction for the same distance. would the clocks be off by the same amount? The stationary twin can only be stationary compared to another object. So how do we know that he is not flying through spacetime making the two flights time dilate at different rates?