Billy Pilgrim Goes Back to the Future

One of the biggest questions with Slaughterhouse-Five is: What is time in this book? or How does Billy's time traveling work? It's something I'm thinking about a lot as I read more and more of this book.

One comparison I can think of is, of course, Back to the Future. Time is a continuum, and as the Tralfamadorians say, everything that ever has happened, is happening, and will happen is going on simultaneously. That is why Marty and Doc (and Billy) are able to travel into the future and back to the past as many times as they do. But, in Back to the Future, if Marty runs into himself in the past/future, the whole fabric of the universe could be upset, which isn't the case for Billy.

Billy travels back and forth in time, but it doesn't seem to be that he disappears from one time or another. His mind simply seems to transport into the body of his past or future self. So, theoretically, he is simultaneously living all the moments of his life. My question about that is, since he is only aware of one moment at a time, does he remember his life in some sort of nonchronological order? He jumps in time to random ages, for example he might be 20 then 40, then 25. Being that Slaughterhouse is nonlinear, it seems that Billy's life is nonlinear as well.

He often seems to travel while sleeping as well, so I often wonder whether his time travel is just dreaming, memories, or simply a product of the insanity from PTSD and his head injury. However it works, Billy seems to travel back and forth to more significant moments in his life, moments he visits again and again, as if his life is one big Moebius strip in time. Slaughterhouse-Five definitely makes me look at time differently, as there doesn't seem to really be a past, present, or future Billy, because it all depends on what time he is in at any given moment.