The Rules of Time Travel

Back to the Future screenwriter says time travel has become “too convenient”

Co-writer Bob Gale explores Back To The Future’s massive influence on the time-travel genre.

Few movies have impacted the public’s perception of time travel more than Back to the Future.

Alongside co-writer and director Robert Zemeckis, Back to the Future co-writer Bob Gale crafted his vision of how time travel would actually function and what rules should apply — and those rules continue to impact our real-life understanding of time travel to this day. (Just ask Ant-Man!).

Gale tells Inverse when they set out to make Back to the Future, they deliberately wanted to make the rules of time travel clear to audiences… and to make time traveling seem difficult, keeping it from being the sole driver of the plot.

“We created a history of the McFly family that we then changed,” he explains, “but the rest of history stayed the same.”

And that, he says, is why audiences went along for the ride with them.

Back to the Future set the cinematic world on fire upon its release in 1985, grossing almost $400 million and sparking two almost-as-profitable sequels. Millions (if not billions) of people have spent time absorbing the trials and tribulations of Marty McFly and Doc Brown, along with considering the movie’s rules of time travel as real-life science.

More than three and half decades later, Inverse sat down with Gale to talk about everything he knows about the rules of time travel, Back to the Future’s impact, and our perceptions of how time travel works — even when, in his opinion, it doesn’t work as well in other films.

This interview has been edited and condensed for clarity.

The Rules of Time Travel is an Inverse special issue exploring the evolution of science fiction's most imaginative sub-genre. From Marty McFly to Avengers: Endgame.

Bob Gale sits inside the DeLorean at a "Back To The Future" event in 2016.Renard Garr/Getty Images Entertainment/Getty Images

Inverse: Many people’s ideas about the rules of time travel are shaped by fictional properties — including Back to the Future. Why do you think that is?

Bob Gale: Because nobody knows. It gives you a certain level of speculation.

In Back to the Future, we made the rules pretty clear — so clear, in fact, that Alan Silvestri (our composer who also scored the last two Avengers movies) told me that the reason that they have that scene [in Avengers: Endgame] where Ant-Man says, "So, Back to the Future's a bunch of bullshit?” was added afterward because they showed the movie to test audiences and they said, "Wait a minute. You can't do that because in Back to the Future, Marty..." So they realized they had to hit that nail right on the head.

We did too good of a job, I guess.

How did you establish your rules of time travel for Back to the Future?

One of the things we did in Back to the Future that turned out to be really smart, if I do say so myself, is that we created a history of the McFly family that we then changed, but the rest of history stayed the same. So when you went to see Back to the Future, Ronald Reagan was president of the United States when you went into the theater, and when you came out of the theater, he was still president of the United States.

We didn't change anything about the world of the audience. We only changed the world of our fictional characters, and the audience was totally cool with going along with that version.

“There isn’t a damn thing in Blade Runner that looks like Los Angeles.”

Whereas, if we got rid of Hitler, what would the world look like? Well, that's just total speculation. If you did something like that in a movie, it would have to turn out that, even though you thought you killed Hitler, he survived the assassination attempt, everything still remained the same, and the train still stayed on that immovable track, or you'd end up in a world so entirely different that it put off the audience.

We always would plot our movies with index cards, and sometimes we really had to depend on that stuff to keep in mind, "OK, wait a minute, he's going to do this, so we'd better set this up." It was really important for us: "How do we do it? How do we make the 1885 version of a Frisbee? What have we shown before that everybody understands?”

The hoverboard came about, obviously, because of the skateboard sequence.

In the Back to the Future mythology or universe, we were always trying to say, "Let's take this element and either project it into the future or put it back into the past." One of the most fun ways to do that was with the whole town because the town almost became a character. In 1985, the town square was a parking lot, but in 1955, it was a grassy area, and in 2015, they restored it. That stuff was all based around the story of towns.

You see so many movies that go into the future, and it looks like they tore everything down and started all over again. I love the original Blade Runner, I really do, but there isn't a damn thing in Blade Runner that looks like Los Angeles. But if you were to take somebody from New York in 1955 and bring him to New York today, they would know where all the streets were, they would know how to go to Central Park, and the subways are still going to the same places. Lots of stuff has been torn down and rebuilt, but the grid of the city is exactly the way it's been for over 150 years.

“Doctor Strange basically can do anything, and that's too convenient.”

Have other writers come to you for time travel tips?

In all the various interviews that I've given, the one element that I stress above all is a lesson that people don't seem to learn — you cannot use time travel as a plot device. You can't use it as a way to get yourself out of a plot. Somebody gets killed, "Oh, we'll just go back in time and stop the bullet from reaching his heart." That's lazy writing. It's too convenient that you happen to have the technology to solve a dramatic problem like that.

That's why, in Back to the Future, we made time travel really difficult to do. You had to go 88 miles an hour, and you had to have 1.21 gigawatts of electricity. It was tricky; you couldn't just cavort around time.

That's why a lot of time travel TV series are not that successful, because after a while, the audience just kind of shrugs and says, "OK, they can travel through time and do this because the writer or the director says they can," as opposed to feeling connected or that we're discovering something through the characters.

Think about a movie like Primer, one of the best time travel movies of the last 20 years, and it was made for no money. They were honest about the concept and true to what their rules were. Then look at a movie like Looper, which I know some people think is really good, but I had a lot of problems with Looper because the premise was that the only way you could get rid of undesirable people was to send them through time, as opposed to just dumping them in an incinerator?

I mean, Doctor Strange basically can do anything, and that's too convenient. Like, "OK, you can just do a time spell, and that solves all the problems of the last Spider-Man movie?" Doctor Strange makes a spell that doesn't work right the first time and then goes, "You know what, I can fix it." I felt like saying, "Why did I watch, then?" The two hours in between weren't necessary.

Where did you first learn about time travel?

My conception of time travel came from seeing the George Pal movie adaptation of [H.G. Wells'] The Time Machine back in 1960. I was nine years old, and I had read the comic book adaptation before I saw the movie. My mother wasn't sure I should be seeing a movie that had a picture of a green monster on the poster, but nevertheless, I managed to go, and it pretty much fried my mind.

Then, I read the actual book, and from there, I discovered various time-travel science fiction, notably Ray Bradbury and Robert Heinlein. When I got older, I read Robert Silverberg, who wrote some wonderful time travel novels. Of course, the Twilight Zone was also on TV at the time, and uncharacteristic of my mother, she loved the Twilight Zone, so I would watch that with her. They did a number of fascinating time travel episodes.

It just was a fascinating idea that there was a way that you could travel through time the same way that you could travel through three-dimensional space.

Ray Bradbury's great short story A Sound Of Thunder was another one that always stayed with me. I was probably in seventh or eighth grade the first time I read that, and the idea that just stepping on a butterfly could change the outcome of the whole political movement was a pretty cool concept.

And then, of course, there were the Twilight Zone episodes where somebody would go back in time and try to prevent some historic event from happening and fail. Those are all those kinds of questions that people wonder about.

The interior of the DeLorean DMC-12 from Back to the Future II.Steve Russell/Toronto Star/Getty Images

When we think of time travel, we think about going forward, but something you did with Back to the Future is that you went backward — at least initially. What intrigued you about going backward?

I remember reading DC Comics, and they had a series called The Legion Of Superheroes. They'd have stories in the 30th century, and Superboy would travel to various centuries and have all these adventures with the superheroes of that era. But I always had a problem with it because it was like, "That's what you think the 30th century is going to be like."

The idea of predestination also never sat well with me, either — the idea that, no matter what you do, you're powerless because you're stuck on a track that's always going to go this direction. That kind of defeats the whole purpose of life, if you will.

So, with the idea of going backward, it makes sense that where or when you're going, you'd have an idea of what that world is going to be like. And then, of course, the inevitable question is whether you could change anything.

Before the first Back to the Future movie came out, there were time-travel movies, but there were many more afterward. How do you think Back to the Future affected the sci-fi movie market?

Time-travel movies before Back to the Future were not successful at the box office, which was one of the reasons we had such a hard time getting it made. We'd pitch this idea to people, and they'd read the script and say, "It's a great script, but time travel movies don't make any money. Forget it."

Once we proved that the right kind of time-travel movie could make money, they started making them.

The devil's advocate argument is that maybe they didn't make money because the vast majority were poorly written or just plain bad.

Well, no. Take a movie like The Final Countdown, which was pretty good. To understand it, though, it requires you to have enough knowledge of what happened at Pearl Harbor to get it. But then viewers were also in a situation where they'd see it and say, "They can't prevent Pearl Harbor because we already know that it happened."

Michael J. Fox in Back to the Future.Universal Pictures

Did you hear anything anecdotally around the release of Back to the Future in terms of how your movie affected pitches coming into studios, movies being greenlit, or anything like that?

I'm not sure if I heard anybody specifically say that, but I would imagine that if Back to the Future hadn’t been a success, they would never have tried to make Bill & Ted.

They had a great idea with that movie because going in, you know it's a comedy about these two goofballs who don't know anything about history. So let's have a-rockin' good time with their ignorance. That worked because the audience said, "Okay, these guys are bozos, and we can get down with them."

Christopher Lloyd in Back to the Future.Universal Pictures

Would you travel through time?

There's a fun game you can play with people, and it's a good icebreaker if you're in a group of people at some event and you want to try to get to know something about them. You ask, "Say you have a time machine, and you get to take two trips. One of them is personal, and one of them is historic. Where do you go? What do you do?"

My mom was a musician. She played the violin, and in the 1940s, she had an act called Maxine and Her Men that played in various nightclubs in the St. Louis area. I would love to go back in time and catch her act. That would be a real trip to see my mom in her 20s as a virtuoso musician.

For the historic question, I used to say I want to go back to Dallas and the Kennedy assassination to find out if the shots really did come from the grassy knoll. Now, since Covid, I'd want to travel 20 years in the future and get my hands on a book about what happened in 2020. The other option is since Mark Twain is one of my literary heroes, I think it'd be cool to go back in time and catch a lecture by Mark Twain.

“People think going back in time would be so romantic, but it wouldn't be.”

People think going back in time would be so romantic, but it wouldn't be. We tried to give you a little flavor of that in the third Back to the Future because if you go back to the Old West, you can't take a hot shower. And every street would smell like horse shit. That's not really romantic.

We did the horse shit gag in Back to the Future 3, and Marty walked around the town and saw how bad the conditions were for the Chinese people, too. We wanted to put some of that reality in there.

One of the great things about Sergio Leone’s westerns is that he always shows amputees. It's like, "That's right! That's how crude medicine was." Somebody got a bullet in their forearm, so they'd just cut it off. You see that and say, "Maybe I don't want to go to a time when they don't have penicillin or indoor plumbing."

Why do you think people love the concept of time travel?

Lots of different reasons. First of all, we're always seeing history after it’s been revised. You're hearing stories about the thing that they said happened. "This happened this way. This is what could have happened to the dinosaurs. These maybe had feathers." There's a history detective aspect to it.

There's also the thing about traveling to the future where you're wondering, "If I take this job, is it going to be okay?" You want to take a peek behind the curtain to find out if you're making the right decision or not. Everybody thinks when they're lying in bed before they go to sleep, "Dammit, why didn't I do this instead of that? Why didn't I tell that guy to go fuck himself? If I had another chance at doing that, I think I would tell him to go fuck himself."

It's just a very human thing.