In the genre of time travel, the Back to the Future trilogy stands as one of the best examples. But it still has its share of logical inconsistencies. The first movie stands pretty well on its own, but logic goes out the window at the beginning of the second movie.
A few times in the trilogy, Doc attempts to explain what’s happening by talking about multiple timelines. This is fine as far as it goes. The whole point of science is to attempt to explain the observed facts. They observe some rather strange facts and Doc attempts to explain them. But they skip the next part of the scientific method, which is to design an experiment which tests your explanation. I suppose we could excuse this because of Doc’s fear of destroying the space-time continuum. But this fear seems to be misguided. Doc says that knowing too much about your own destiny could endanger your own existence. This is a bizarre claim that seems to have no basis in the observed facts.
What threatens Marty’s existence isn’t knowledge of the future, but making changes to the past. Specifically, he prevents George from getting hit by the car, which he knows is the moment that causes Elaine to fall for George. This is an example of the classic Grandfather Paradox, which I discussed in my last post.
I say again, Doc is completely wrong when he says that Marty endangered his existence by knowing too much about his future. On the contrary, the more Marty knew about the future, the better equipped he was at trying to avoid damaging the fabric of the space-time continuum. Marty was able to repair the damage because he knew that his parents first kissed at the Enchantment Under the Sea Dance. If he’d had the presence of mind to remember the car accident story, he could have avoided the disruption in the first place. Knowledge of the future is helpful, not hurtful. Doc is wrong. However, BTTF would hardly be the first movie where a character reaches an incorrect conclusion. This is not my complaint.
Doc apparently changed his mind when he put on a bullet-proof vest after reading Marty’s letter. Perhaps he realized his previous mistake and figured out that the universe would sweep under the rug minor paradoxes. He went to a great deal of effort to make the smallest possible change. He didn’t seek an alternate source of Plutonium. He didn’t tell the police about the Libyans. He didn’t even try to jump into the DeLorean with Marty and escape before the Libyans arrived. He merely wore a bullet-proof vest under his radiation suit, allowing Marty to film a video which looks identical to the one he saw in 1955. Clearly, Doc still believes that big paradoxes are dangerous. He only permits himself the smallest possible paradox, and then only when his own life is in danger. Why would he throw caution to the wind, upon discovering that Marty Jr. goes to jail in 2015? Assuming that Doc wanted to repay Marty for saving his life, his logical course of action would be to kidnap Marty Jr. on that fateful day in 2015. Griff goes to Cafe Eighties and Marty Jr. simply isn’t there. Problem solved. Instead, Doc decides to go back in time to 1985 and kidnap Marty so that Marty can impersonate Marty Jr. It’s a reckless plan. This is not my complaint either.
My complaint is that BTTF2 doesn’t play by the same rules that BTTF did.
In the first movie, every time anyone jumps forward in time, the timeline continues on in their absence and they arrive to find everything is just as you would expect it to be, given the way things were before the jump. In other words, jumping backward in time creates a new timeline but jumping forward does not. It just continues the existing timeline. We see this three times: Einstein the dog jumps forward one minute in 1985, Marty jumps forward from 1955 to 1985, and Doc jumps forward from 1985 to 2015. The time traveler always arrives to find a world that follows logically from the one they left as it continued on without them. Einstein arrives to find Marty and Doc anxiously waiting for him, because they saw him disappear at 88 mph. Marty arrives in 1985 to find that the mall is called Lone Pine, because he ran over one of the pine trees in 1955. And Doc arrives in 2015 to find that Marty and Jennifer have kids, because they were teenagers in love back in 1985. All that is logical. Then the logic goes out the window at the beginning of BTTF2.
Doc goes back in time to 1985 and finds Marty talking to Jennifer. He convinces both of them to get into the DeLorean and travel to 2015. What will they find when they get there? By the rules of BTTF, they should find a 2015 where Marty Jr. does not exist because he had no parents. Marty and Jennifer were kidnapped in 1985 and were never seen or heard from again. This new timeline would be caused by Doc going back in time from 2015 and changing the past by kidnapping Marty and Jennifer.
Logically, they should arrive in 2015 and be unable to find Marty Jr. They should seek out George and Elaine, only to discover that George and Elaine haven’t seen Marty or Jennifer since 1985. George and Elaine think Biff killed Marty and Jennifer, then hid their bodies. After all, Biff was the last person to see them alive and his story is that he saw a flying DeLorean disappear in a fireball. Add to this the fact that George and Elaine remember that Biff tried to rape Elaine in 1955. But Marty and Jennifer’s bodies were never found and there wasn’t enough evidence to convict Biff. Doc should sheepishly admit that he made a huge mistake and return Marty and Jennifer to 1985 so they can stay there and get married and have kids. But that movie would stink. So the film makers changed the rules. That’s my complaint.
And then we see Biff create major paradoxes with no apparent bad consequences. He doesn’t erase himself from existence. The fabric of the space-time continuum doesn’t tear. It seems that Doc was completely wrong and the universe can tolerate quite a large amount of meddling. The writers seem to have gone back to option one regarding the Grandfather Paradox. Just accept the weirdness.
But it’s still a really good story, better than most time travel movies.