Daily Archives: April 27, 2008

The Marty McFly Paradox

My friend Eric has written an awesome post about the massive holes in the Back to the Future trilogy’s time-travel logic. It’s too long to summarize, but here’s one choice riff:

But here’s the weird thing– when he returns to 1985, he goes back to the parking lot to find the scene from the beginning of the movie play out exactly as it did the first time (except of course that (MASSIVE SPOILER ALERT) the Doc is now wearing a bullet proof vest). Except the Marty who he watches go back in time had a COMPLETELY DIFFERENT SET OF LIFE EXPERIENCES. I’ll accept that to protect the space time continuum, Doc Brown made sure that he still became friends with Marty and he still sent him back to the past at the exact same moment as before (he had seen the video footage of same). But here’s what I’m wondering– and this would have been an interesting additional sequel. What exactly did the alternate, better-1985 version of Marty do when he went back in time.

While I haven’t read what are probably numerous hardcore, follow-the-premise-to-its-logical-conclusion sci-fi stories, my sense is there are two possible conclusions to a logically sound time travel story: infinite recursion on the one hand; the instant un-existing of the time traveling character (and anything else introduced in that character’s original moment in time) on the other.

I think Back to the Future is playing with the infinite recursion scenario when Marty returns to 1985 and sees himself drive off into the past. That is, Marty isn’t watching “the alternate, better-1985 version of Marty” (or “Marty 2,” as Eric calls him). It’s meant to be Marty literally watching himself re-enact the movie we just saw. Of course this makes no sense, since the revamped McFly clan was all changed thanks to Marty’s actions on his first trip back to 1955; Marty should be changed too, transformed into Eric’s Marty 2. But here the movie breaks from its already strained logic in order to toss out the cool, mind-bending idea of a single Marty McFly doomed to infinitely re-enact his time-traveling life.

This bad logic shows up again in Part II, when

Marty goes back to the past from the future (in order to get the sports almanac back from Biff). And he sees the exact version of himself that I was just talking about and, as he sees, that Marty does the EXACT SAME THING HE DOES IN THE FIRST MOVIE!! That’s weird!

Eric’s right that this should be Marty 1 watching Marty 2, but the movie instead walks away from its premise; it’s simply Marty 1 again watching himself. Which, again, makes no sense.

Anyway, if the first two BTTF movies blew your mind back in the 80s, go read Eric’s post and prepare to experience your own mental-infinite recursion. (Like contemplating infinity, ever-expanding space, and death, thinking about Back to the Future for too long makes my head hurt.)

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