There is an elevator in an office block in Manchester. If you enter this elevator from the twentieth floor, at the exact time you were born, and enter your date of birth into the floor number buttons, the elevator will start to move upwards, and will stop once, twenty floors up. One person will enter the elevator, you, twenty years from the future. He will tell you how you will die, and that he is due to die this way in 10 more years. But what if you go down to the ground floor, and a you twenty years younger enters? What will you say?