Relativity, Twin Paradox, Time Dilation, Lenghts Contraction, Lorentz Transformation.
the distance is shorter (d/γ < d). In this case, in the frame of the Earth S, the twin on Earth is the same age as the astronaut twin. In my article “TEMPORAL DILATATION (IF THE SPEED IS CONSTANT)” I have already introduced the alter ego of the astronaut twin (when I gave the example of a spaceship