Time Travel in Slaughterhouse 5

The main character, Billy Pilgrim, travels backwards and forwards in time depending on different variables that spark memories. After his capture by the Tralfamadorians, Billy becomes stuck and unstuck in time throughout the entire book.  Depending on the event he is experiencing in what time he thinks is the "present" is what triggers his time travel to another related period in his life. Whether or he moves forward or backward in time is totally undecided as well as when the time traveling takes place. I am not sure if the abducting is what triggered his time traveling or not, but regardless, it seems like he has been doing this for a long time. At first, i thought where he went in time was was unrelated as well, but after discussing it in class i have now been assured there is an emotional link to where he goes in time.