Since W.J. van Stockum, K. Gödel and F.J. Tipler proposed their solution to the Einsteinian field equations and de Felice et al. discussed Kerr's ones, the time-machines have turned from fiction to physical objects. Immediately, philosophers of science, such as Earman (1972), Malament (1985) and Horwich (1987), began to analyse them on account of the several paradoxes implied by backward causation.