More on time travel in Back to the Future

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So I was horrified and amused by this bit of perversity (the footnotes, not the main text), and I have to make a counterargument.

1. The Back to the Future timeline actually isn’t that sensitive to initial conditions. The proof lies in the ultimate chaotic system: weather. In the original timeline, lightning struck the clock tower at 10:04 p.m. In the altered timeline, after Marty has been hanging out for a whole week, breathing and running over trees and probably stepping on butterflies, lightning still strikes the clock tower at 10:04 p.m. Why?

Because the timeline is highly resistant to change. When Marty manages to change something, it’s because he interferes drastically. He doesn’t prevent his parents’ marriage by killing a butterfly—he does it by jumping in front of a car.

This also helps explain why Marty and his siblings snap back into existence so fast, instead of, say, getting replaced by a completely different set of kids conceived at slightly different times with slightly different genetics. The timeline wants to return to its original state (or as near as possible) and leaps at the first opportunity. Of course, it can’t restore itself entirely, because George can never go back to being a wimp and Old Man Peabody can’t be bothered to grow another pine tree.

2. Therefore, the second Marty probably does pretty much the same things the original Marty did. Why shouldn’t he? He has all the same problems and motivations. The one difference is that he doesn’t know about the original timeline with the car accident. As far as he knows, his parents got together when Lorraine was on a date with a mysterious stranger, who disappeared shortly after George punched Biff. Once Marty 2 realizes he is that stranger, he’ll try to do everything exactly the same way. Even if he does things a little differently, the timeline will resist any major changes.

Presumably, Marty 2 won’t find himself fading out of existence, because everything he does in 1955 conforms more or less to the timeline that produced his version of 1985. But Doc will figure out that Marty is part of a causal loop and make him understand the importance of fulfilling his role.

3. The obvious question remains. When Marty Prime returns home, he finds everything different from the way he remembers it. Doesn’t that imply that he and Marty 2 have two distinct sets of memories—in fact, that they are two distinct people?

Yes, but that doesn’t mean they’re going to remain distinct. Remember, it takes time (meta-time!) for alterations to ripple through the timeline. The changes have simply affected Marty’s family before they affect his mind, for reasons we can only speculate about. The point is, even if Marty’s memories eventually get overwritten entirely, the timeline will remain stable.

I would assume, though, that time travelers have the ability to retain two sets of memories side by side. Otherwise, they might eventually conclude that it’s impossible to change the past, because every “change” turns out to be foreordained. The mall has always been called Lone Pine. George always punched Biff.

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