Journal Entry Second Chapter, Slaughterhouse-Five

This new chapter takes on a whole different trun than the first chapter. Here is where the story really begins. the previous chapter was sort of like an introduction, where the character gives a bit of background information about himself and what his purpose, be it as a goal or in his life as a whole, is. One thing that I noticed was the change in narrator from one chapter to the other. The first chapter is told in first person, where as the second chapter is told in third person, in which the narrator is omniscient.
The second chapter starts telling the actual story of Billy Pilgrim, his youth, his service in th emilitary, his life back home and his crazy stories about aliens who can see and travel through time at the same time. Throughout this chapter, the narrator mentions people whom Billy knew and connections of these people. Every paragraph with a description of a "flash-back" ends with the phrase "So it goes." What does the phrase mean? What is the author's purpose for using it? the only answer i could think of to this is that Billy thinks the way the aliens do, he "sees" through time, so he can see different stages of a person's life at the same time. He can visit any momente he wishes and he knows that you can't change anything. "So it goes" could make a reference to the fact that when a person dies, there's nothing you can do about it, just accept it and remember good moments of that person's life.
When Billy first "travels" through time, he is in the German woods during the Second World War, wlaking with the two scouts and with Weary. Did being alone and separated from everyone help him enter that trance-like state and travel through time? Was it being so far away from home that he was able to let go of all his thoughts and feel free, mentally? Maybe, these trip through time aren't really true, they just happen in Billy's head as a way of relaxing, or letting go of reality. He's in a tough situation, walking through the woods with a crazy teenager who is obsessed with torture, running away from the Germans, and having to stand really cold weather. Maybe he lets himself fly mentally, and just get away from everything.