Twin Paradox, Lorentz Transformation, Relativity.
known result dt_1 = γ^(-1)(t)*dt, and this is true since v(t) = v_1 (t_1) and γ (t)=γ (t_1). Since dt_1 < dt, proceeding to integrate we also obtain t_1 < t. (the body in motion is “younger” than all the other stationary bodies in the frame S) dx_1 is less than dx, also x_1(t_1) < x(t) and this is