Time dilation was used in the Doctor Who episodes " World Enough and Time " and " The Doctor Falls ", which take place on a spaceship in the vicinity of a black hole. Due to the immense gravitational pull of the black hole and the ship's length (400 miles), time moves faster at one end than the other. When The Doctor's companion, Bill, gets taken away to the other end of the ship, she waits years for him to rescue her; in his time, only minutes pass. Furthermore, the dilation allows the Cybermen to evolve at a "faster" rate than previously seen in the show.