(Before we go any further, be warned there are spoilers below. Casual spoilers for Interstellar, Contagion, World War Z, and for Back to the Future. I respect your time. It can be hard to get to the movies, but sometimes you have to just say a thing in order to talk about a thing.)

Interstellar’s director is Christopher Nolan, best known for the Dark Knight trilogy. He also wrote and directed Inception in 2010, which is about the decidedly non-scientific idea of stepping into someone else’s dream. But discussing “The Metaphysics of Interstellar” with Wired, Nolan said “Inception had a lot of science in it: A rigid set of rules, mathematical and geometrical in their nature, define that script. That took a very long time to work out. They’re not real science, but they have that quality. You always have to cheat in cinematic narrative, but you try to do it as little as possible and in a way that doesn’t violate the pact with the audience. In Inception, the geometry’s pretty solid.”

Which is to say, Inception establishes the laws of its fake science, and it abides by them. A rigid set of rules.

There are two recent science fiction movies that have similar premises that explore science (and relationships) in different ways: Contagion (released in 2011, directed by Steven Soderbergh and written by Scott Z. Burns) and World War Z (released in 2013, directed by Marc Forster, written by … well, written by a whole lot of people, frankly, and based on the book by Max Brooks).

Contagion’s trailer begins with relationships, and then it starts to look like an action-thriller. And I call it science fiction because, in the simplest sense, it is. Not to go all term paper on you, but Webster’s says sci-fi is a story “about how people and societies are affected by imaginary scientific developments in the future.” Contagion is a day-after-tomorrow kind of future, but a 21^st century global pandemic remains (thankfully) science fiction.

World War Z’s trailer plays out similarly, with a family in their SUV playing 20 questions (and Brad Pitt is there playing himself? Because what other dad has hair like that), but it quickly turns into…

…yup, an action-thriller. Both Contagion and World War Z are movies about global pandemics and a virus spread through basic human contact. WWZ’s virus is anthropomorphized as actual zombies coming to get you, but the social unrest that ensues is similar. Governments go into lockdown and teams of scientists race to find a cure or a vaccine.

But the science of the movies are very different. WWZ’s zombie virus transforms victims in twelve seconds exactly, and late in the film our heroes discover that an injectable vaccine-of-sorts will trick the zombies into thinking you’re already infected, making them ignore you. The question of how the zombies -- or more specifically, the virus that has taken over the human bodies -- can tell if someone has been infected or not is unclear.

There’s a lot of sniffing. A little minor jaw snapping. There is not a lot of expository dialogue, except for the incredibly unhelpful, “He just walked right past him!” Over at Vulture, biophysicist and post-doctoral fellow Scott Forth offers a quick fact-checking of the science of World War Z, saying, “It’s completely unclear how they are able to sense an individual that is infected with some sort of illness. Smell? We see the zombie sniffing intensely at Brad Pitt, but the human olfactory system isn’t terribly sensitive. Maybe the zombies have rapidly developed super-smell abilities? Any other form of sensing the presence of infected prey, unless they just kind of know it preternaturally or something, would require methods we're not currently aware of.”

The science of Contagion got a warmer reception because it was closer to actual science. Yes, there is a scene where a researcher tries out a potential vaccine on herself, but the context is very different, and the film itself is concerned with how actual viruses travel the globe, how they are found and researched by the scientific community, and how the scientific process is the best (and maybe only) hope for stopping a future pandemic. Screenwriter Burns worked with Dr. Ian Lipkin, a professor of epidemiology, neurology, and pathology, to consider how that process could contribute to plot, as opposed to how an action/adventure plot might work a little science into it.

Contagion isn’t very action-based at all, but boy, it is absolutely terrifying. Every hand that lingers on a metal surface transferring possible germs, every cough and sneeze, is scarier than any of the snorting zombies chasing Brad Pitt.

How each movie treats relationships is different too. In WWZ, the only relationship that really matters is between Brad Pitt and his family -- he, too, promises to return to them -- and solving the worldwide zombie war is simply the thing he has to do before getting back to his wife and kids. There are plenty of other characters in the movie, including a young soldier who plays the role of surrogate daughter for the movie’s middle act (also Doctor Who’s Peter Capaldi, playing a W.H.O. Doctor … !), but they barely have names, much less motivations beyond don’t become a zombie. The stakes are high in Contagion, but, with fully realized characters like these, it would be just as interesting to watch what happens to them one year (or one decade) before or after the virus spreads.

Interstellar comes from a similar place. Theoretical physicist Kip Thorne has been interviewed and mentioned nearly as much as Christopher Nolan and co-screenwriter Jonathan Nolan when it comes to the movie, and with good reason. As Dr. Lipkin helped shape Contagion, so did Dr. Thorne help shape Interstellar, if not moreso. Thorne worked with Jonathan Nolan on the screenplay for several years before Christopher came on to direct, and he was on set to discuss the science with actors Matthew McConaughey, Anne Hathaway, and Michael Caine.

In the same Wired article mentioned above, Christopher Nolan related that his brother “says that through working with Kip, he finally grasped relativity for a couple of weeks, and then the writers’ strike happened and he had to stop writing, and it was gone. I know exactly what he means. It’s like a little window opening up. That’s why the relationship between storytelling and the scientific method fascinates me. It wasn’t really about an intellectual understanding. It was a feeling of grasping something.”

A feeling of grasping something. That’s what it is. Good science -- operating within the realm of what we understand, consistent logic and rules -- engaging relationships, good storytelling. More than convey truth or an accurate understanding of physics, good science allows the audience to feel like they’ve grasped something, even if it slips away after. Jaws isn’t great because sharks are terrifying. Jaws is great because sometimes you’re out in the ocean before you realize, We’re gonna need a bigger boat.

Cooper tries to tell himself to stay both early and late in Interstellar’s story, and it’s consistent with how the movie presents time travel. When Marty McFly starts to fade away in Back to the Future, it’s not good science -- not even in a time travel movie. But the moment when George dances with Lorraine and Marty springs back to existence? That’s a feeling of grasping something.

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