Predestination may be the most mind-bending time travel movie I’ve ever seen…and I’ve seen them all. It’s not the best time travel movie. I still prefer Primer, Looper, and of course Back to the Future. But Predestination is the ultimate exploration of the paradoxes involved in time travel.

The film, written and directed by the Spierig Brothers, is an adaption of Robert A. Heinlein’s “—All You Zombies—” which is probably the ultimate time travel short story. SPOILER ALERT! Both the short story and movie is about an intersex human who goes back in time as a man to impregnate himself as a younger woman, and that child grows up to be him/herself. It’s a causal loop. The ultimate paradox. Where does he/she come from? It’s an extreme version of the question, “What came first, the chicken or the egg?”

My mind was blown as I tried to think of how the events in Predestination could be possible. The only conclusion I could come up with is this: time travel to the past is physically impossible. If it were, then the predestination paradox could occur. But the predestination paradox can’t occur. Therefore going back in time is impossible.

Time travel to the future is theoretically possible. That makes sense. (I’m currently working on a project that explores that very topic.)

Admittedly, I’m no physicist, but logically speaking, the closest thing to time travel to the past that I could conceive being possible is time dilation, like the kind seen in Interstellar. Person A can travel through time slower than Person B, so that one year for A may be one-hundred years for B. But Person A is not actually going back in time 99 years—time is just relative between Person A and B.

The way I see it, you cannot go backward in time past a point in which you’ve already existed. Time travel to the past is simply impossible. The only person who can convince me otherwise is myself from the future coming back in time to slap me in the face and tell me what an idiot I am. Meaning the grandfather paradox and the bootstrap paradox and the predestination paradox cannot occur. Yet I still love time travel movies. Impossible as its events may be, Predestination is nevertheless a fun movie. It really makes you think.

If you’re a fan of time travel stories, check my short story, “TimeMail: Time Travel Email.”