Relativity, Twin Paradox, Time Dilation, Lenghts Contraction, Lorentz Transformation.
the alter ego of the Earth. If the alter ego of the Earth moves in the frame of spaceship S_1, he’s younger than the alter ego of the astronaut twin (t < t_1, in the frame of the spaceship S_1 the tail has no length d/γ, the tail has length d.). The Earth-planet distance is the tail of the