 Thomson’s violinist showed that abortion could be morally permissible even when the fetus has a right to life. Similarly, Einstein’s elevator showed that light will bend in a gravitational field, because according to the principle of equivalence, there is no difference between such a frame of reference and one that is accelerating in free space; the laws of physics are the same in all. Suppose then, an observer is inside an elevator sealed off from the outside so that the observer cannot tell whether he is in a gravitational field or accelerating. If it were accelerating, and if a light beam were to enter one side, then, due to the elevator’s motion, the beam would appear to drop or curve down as it crossed the elevator. Consequently, it would have to do the same thing if the elevator was in a gravitational field. Therefore, gravity ‘bends’ light.