The doctor travels through both time and space. He meets many alien races. For instance, he met an alien race of fish-vampires in Renaissance Venice. Now, I have been hypothesizing that most of these aliens don't have time travel. However, many of these alien races acknowledge the events in the Doctors life as having occurred in the past. The fish-vampire queen said that the Doctor belongs in a Museum, as the rest of his race were dead. Furthermore, when someone looks for him in the museums they only see one incarnation of him at a time. When Correy and Amy see him send messages from him, they only see the one incarnation of him that they knew. So the question is how are 1) Why are his past milestones always in the past, regardless of who is observing? In the episode where he meets the Christmas Shark, he has an old man interact with himself. I thought it was against the rules. So, 2) Under what conditions can a person interact with a past version of himself without the end of the universe? The milestones in his life occur in his subjective timeline in a certain order. What I don't understand is how other observers see the milestones in his life in the same order. Other observers should see the milestones in his life in a jumbled order.