The Tralfamadorians are an alien species that abduct Billy Pilgrim, keep him prisoner, and teach him their philosophy on life. They are green and resemble toilet plungers with eyes. The Tralfamadorians are fatalists – they believe that everything is predestined and that nothing can be done to change the course of the universe. They can time travel and do not view time linearly: “All moments, past, present and future, always have existed, always will exist.” Because of this, they know how and when the universe will end, but they accept this, as their worldview dictates that they have no power to change future events.

The Tralfamadorians teach Billy the phrase “so it goes,” which is a way to acknowledge the death of another living being while also remembering that death is simply a part of each being’s unchangeable destiny. And because all time exists at once, Tralfamadorians do not feel the need to excessively mourn over death, because the dead being is alive and well in other moments of time.

The Tralfamadorian philosophy actively challenges the belief systems that many “Earthlings” rely on. It is often pointedly in juxtaposition with Christianity: the aliens believe that life and the universe are ultimately purposeless, and they are more interested in Darwin than Christ. Billy, who like most Americans is mainly familiar with the Abrahamic worldview, is inspired by the Tralfamadorians’ absurdist philosophy. It allows him to let go of some of his guilt and trauma. However, while adopting a pre-determinist worldview helps Billy to cope with his PTSD, Slaughterhouse-Five does not make any claims that the Tralfamadorian belief system is necessarily right or good. The Tralfamadorians are simply a device through which Vonnegut grapples with the greater question: is there any life philosophy or belief system that can truly bring us peace or understanding in such a disturbed world?