Twin Paradox, Lorentz Transformation, Relativity.
Lorentz factors γ(t) and γ(t_1) coincide. From the Lorentz transformation x_1 = γ*(x -v*t), for x_1=0 as the body is positioned in the origin of the frame S_1, we obtain x -v*t=0, from which x=v*t. Turning to the differentials we obtain the relation dx = v(t)*dt. From the other Lorentz