Putnam. Oscar Smith steps into a machine in 2024. From  his point of view, things proceed much as in Doctor : time  seems to Oscar Smith to pass for a while; then he steps out in  1984. For observers outside the machine, things proceed  differently. Observers of Oscar’s arrival in the past see a  time machine suddenly appear out of nowhere and immediately divide  into two copies of itself: Oscar Smith steps out of one; and (through  the window) they see inside the other something that looks just like  what they would see if a film of Oscar Smith were played backwards  (his hair gets shorter; food comes out of his mouth and goes back  into his lunch box in a pristine, uneaten state; etc.). Observers of  Oscar’s departure from the future do not simply see his time  machine disappear after he gets into it: they see it collide with the  apparently backwards-running machine just described, in such a way  that both are simultaneously  annihilated.[4]