After winning an Oscar for his 2008 docu Man on Wire, about a daring and illegal tightrope stunt in 1974, and earning critical praise for 2011’s Project Nim, director James Marsh has moved back into the scripted realm with The Theory of Everything. The drama, starring Felicity Jones and Eddie Redmayne, is based on the 2007 memoir Travelling to Infinity: My Life with Stephen, which follows the marriage of Jane Hawking and her husband, the renowned astrophysicist Stephen Hawking. But the director says dramatizing a story based on the lives of real people doesn’t feel so different from docu work. “You need to be respectful and sensitive (to the subjects), but at the same time you are after something that feels truthful to you,” says Marsh, who also spoke about improvising on the set and some of the film’s shooting challenges.

You’re used to telling real-life stories from directing documentaries, but did you still have a strong sense of responsibility to these subjects?

There really is a bigger responsibility when doing a true story—particularly in this case, a true story about people who are still alive. Also, it’s a portrait of their marriage, which is about as intimate as it could be. And thirdly, you’re dealing with a public figure who is known for his brilliant scientific mind and also his illness and disability—that raises the stakes even further. Anthony McCarten’s script had already elegantly done this, so my job was to respect what Anthony had written and to elaborate upon it.

Did you do any work on the script once you signed on to the film?

Anthony’s script gave this surprising perspective on two characters. It’s about their emotional lives, not about Stephen’s career. That’s what drew me to it in the first place. As a director, you push at the script, and you interrogate it. You want to make it better. Once I cast Eddie and Felicity, I began to involve them in the script process, so they would have meetings with me and Anthony and explain and argue for some adjustments or additions or subtractions based on their research. These all ended up in the script. It’s a constantly evolving process. The actors would often spontaneously come up with a good addition to a scene, and we almost always embraced it. Some of the best lines in the film were improvised by them. But certainly the witty lines came from working with Anthony’s script—the wit was there already, and we just took it a bit further as we were shooting.

Were there technical challenges in shooting such a physical performance as Redmayne’s?

It was one of those films where every day there was some unusual technical complication, but in terms of Eddie’s performance, what we couldn’t do was shoot it in sequence. You just can’t do that with the resources of most films. The first week, where we’re shooting on location in Cambridge, he had to, in the morning, be able-bodied. After lunch he would be on two sticks. And then by tea time he’d be in the wheelchair. He had so mastered the stages of the illness that he could do this. We’d have people say, “Well, let’s give him half an hour to rest.” No, no, he never wanted it. Also, it is difficult to shoot wheelchairs, just as a technical issue because people are at a different level than people standing up. So we ended up choosing to shoot with an anamorphic format, which (worked) really well for the wheelchair and the domestic spaces of the film. There’s lots of domestic space, which can be really boring in a film if you feel like you’re just trapped in someone’s house all the time. These lenses allowed us to make those domestic interiors interesting in terms of the spatial relationships.

Were there any scenes that were particularly tough to shoot?

When we shot around a May Ball in Cambridge, we wanted to make it the kind of environment where the two characters literally fall in love across the course of this scene. But the technical terms of this were really difficult. It was a night shoot, so you basically start at 6 o’clock in the evening, and you go until the following morning. You have many extras to make it work. It’s cold, so you have to get those people warm. Some of the most difficult shots in the film are all in that sequence, and we had just two nights to shoot this 10-minute section of the film. But D.P. Beniot Delhomme, who has more experience than I do at bigger-budget films, was able to help us make that as beautiful as it turned out to be. There’s some very complicated lighting in that.

Emotionally, there’s the scene at the very end where the characters decide to separate. Stephen can’t speak at this point, so how do you tell your wife you’re leaving her when you can’t have a conversation? You can’t even touch her. It was one of those days when everyone knew we were doing something that felt pretty special. I don’t get emotional when I’m shooting a film—I can’t allow myself to—but I really felt things I was surprised at as I was shooting. And there were certain moments where I became emotional myself. There were people around the monitor, and they were all crying and really moved by what the actors were doing. It was a very intense day.

 James Marsh photographed by Mark Mann