Relativity, Twin Paradox, Time Dilation, Lenghts Contraction, Lorentz Transformation.
x = v*t then t = d/v (we know that x = d) and, considering the two Lorentz transformations x_1 = γ*(x -v*t) and x = γ*(x_1 + v*t_1) (from which the others are also obtained), we necessarily obtain x_1 = 0 and t_1 = (1/γ)*t. By symmetry (the Lorentz transformations are symmetrical), we can imagine