Changing the past?

By reading the novel it becomes evident that the author chooses to share the story in a unique way. He jumps around to different points in time, as he says early on that he is writing as the events or "memories" come to him. The main character, Billy Pilgrim, skips around in time. It is possible that the authors choice of skipping around is justified when he shows that Billy literally skips around through time. When he skips to times in the past, he knows almost exactly what is going to occur during that time.

If Billy knows the turn out of the events in the past when he jumps back to them, why in the beginning of chapter four does he still go to the place outside where the Tralfamadorians "abduct" him? The narrator states on page 72, "Billy now shuffles down his upstairs hallway, knowing he was about to be kidnapped by a flying saucer." (p.72)

If Billy knew he was going to be kidnapped as the narrator states, then why didn't he stay in bed with his wife instead of going downstairs and outside to where he knew that he would be kidnapped? Could it be that Billy thinks he cannot change the past so he simply goes along with what already happened? It could be thought of as a memory or a dream instead of him actually traveling back in time. It could be referring to Billy's PTSD that he has on the event that occurred long ago. Maybe this is the narrators way of telling the reader that Billy is re-living the abduction and it all seems so real that he actually thinks he is truly traveling through time experiencing this event once again.