It’s a strange thing, admiring an actor’s ability to physically act out a part when the role in question has that actor almost entirely immobilized. And what Eddie Redmayne does in portraying Stephen Hawking in 'The Theory of Everything' is physical – what Redmayne conveys and accomplishes with basically just limited facial expressions is truly remarkable. But that’s the thing: who looks at Stephen Hawking and thinks to themselves, Yeah, I could successfully portray this man in a movie?

The way Redmayne describes getting the part puts it in terms that we can all understand: After convincing someone in a job interview that you’re just the perfect person for the job, that realization hits that you now actually have to do the job. It’s understandable why Redmayne might have felt that way at one time – and hearing that lets us relate to Redmayne in a “we’ve all been there” kind of way – but after seeing his performance in ‘The Theory of Everything,’ it’s not so easy anymore to relate to Eddie Redmayne … his performance is something not many human beings could do.

Eddie Redmayne is a charmer. Not overly fake in an off-putting, “what’s this guy’s angle?” sort of way, but more of a guy that would be fun to hang out with if he were a regular at your local pub. Redmayne seems genuinely thrilled at the reception so far for ‘The Theory of Everything’ (and the prognosticators are predicting he will do well this awards season), but he seems even more thrilled that he received accolades from Stephen Hawking himself … but Redmayne never did stop to think what would have happened if one of the smartest men of our time didn’t like Redmayne’s performance.

But, first, Redmayne seemed really concerned that my iPhone, which I use to record interviews, had stopped working (I had a backup).

Eddie Redmayne: Does it not work?

I spent an entire day at the Apple Store.

Are you kidding me? How can they not sort you out?

You play a man who overcame a crippling disease, yet we are lamenting over my broken phone. Woe is me.

[Laughs] I’m more frustrated with Apple. The injustice!

This is what Stephen Hawking and I have in common.

The struggle.

I’m going to make it through.

Damn right.

I read that you met Stephen Hawking and he gave you his blessing. What would you have done if he hadn’t?

That’s a very brilliant question and one that no one has asked. When I took on the part, I had been told it was Jane Hawking’s book and that Anthony [McCarten] had done an adaptation of it and that Jane had said that Stephen was OK with it. So, I went into it with that expectation. But, that didn’t mean that he was OK with me. And, to be honest, when I met him he was totally wonderful, but this is before we started filming and I desperately wanted his approval. But Stephen was never going to give me approval until he saw the film. He’s not a people pleaser by nature.

What do you mean by that he’s not a people pleaser?

He’s not someone that’s going to tell you, “I’m so thrilled you’re doing it.” He’s a straight shooter. And he’s incredibly funny and charismatic and warm, he has all of these amazing qualities, a razor wit – but, no, he speaks his mind as he’s done all his life. All I’m saying is that the stakes, it wasn’t just that I got his approval before we started shooting and I never expected to. It was only once he saw the film that he would judge what he thought.

And if that came and he didn’t like it … he just seems like a guy that people want his approval.

But across the board, once I was cast, I felt like the stakes were many. It was like, you have to be absolutely true to Jane, Stephen, their family, Jonathan. Then you have the science aspect of it. You have to depict the science truthfully. It’s not like Stephen invented the black hole – something that’s simple to depict on screen.

In the movie when you’re presenting his theories, how much of that do you understand?

Well, I spent a lot of time educating myself.

I suspect it’s harder to be the character if you don’t understand what the character is saying.

Totally. In the four months of prep, as well as doing the physical work, it was meeting one of his old students who is now a professor at Imperial College in London. So he was going into string theory and then he was talking about space-time and I’m like, “No, no, no. Imagine I’m seven.” I went from like hardcore analytic websites to websites for children like, “How to get away with your astronomy homework.”

Could you fake your way through a lecture right now?

A full lecture?

No questions, but Eddie Redmayne is going to teach us something about black holes.

How long would the lecture have to be?

Fifteen minutes.

Oof. [Laughs] Yeah. I think I probably could.

Oh, that’s impressive.

I would give myself six-and-a-half minutes, is probably as much as I can last.

But that’s still impressive. Most people could do zero.

What I love about it is the major thing that’s going on, the major thing you need to know is that in the world there is general relativity – which is Einstein’s thing – all about the big; then you have quantum, all about the small. And those are two concrete theories that seem to work, but the two don’t work together.

It would have been great if during your research you figured it all out.

[Laughs] “Wait a second!”

Smash cut to you winning a Nobel Prize.

Can you imagine if I won the Nobel Prize for physics? “That Redmayne was so method. He actually won the Nobel Prize that Stephen didn’t get.” Stephen would be livid.

You’d lose his approval.

I know. I know. When you play these characters, you do all the work and then a year later you’re promoting them. So, on the flight over, I was reminding myself of the physics. Of course it was absolutely fine in L.A., but it was when I arrived in San Francisco, where of course everyone is uber-tech savvy, and they were all going, “Define general relativity for me?” I’m like, “Really?”

Are you being serious?

Yeah. I was worried five minutes ago that you were going to ask me to give a 15-minute lecture.

No, I don’t want to attend it.

It would be really dull.

I was just curious if you could do it. I wouldn’t buy a ticket. Or if I did, it would just be to report if you did it or not. “Redmayne did it!”

“He lasted 15 minutes.”

When you first heard about this movie, how do you get it in your head that you can play this guy?

That’s the key thing: you never get it in your head.

But how do you know you can play this part? It seems like a specific skill set.

You don’t. Basically, I loved acting as a kid. I did plays. I found it fun. I never trained.

But everyone knows that you can act, this just seems like something completely different.

Well, you’re constantly waiting to be found out. Everything feels like a challenge, but, with this one, I wish I could say it was something that just arrived, “Will you play Stephen Hawking?” But it was not. It was me reading a script thinking it was going to be a biopic of Stephen Hawking.

You didn’t know it was more about his relationship with Jane?

I read the script and it totally subverted my expectations of what it was. And then asked to meet James Marsh. And I loved the idea that he was the director directing it … then I just really chased it down.

What’s that mean? Phone calls?

Trying to persuade people. So I had a phone call with James who was in Copenhagen, then he came to London and we went for a drink. We share a sensibility, I think, that fear drives us. But when you’re in that chasing phase trying to get a part, you’re never thinking about whether you can do it. Does that make sense?

No.

No, it doesn’t. You’re lying to people. You’re persuading people. It’s like having a job interview, you tell people how you’d go about it. And then what happens is you get the part and a moment of elation, like getting the job. And then you go, “Fuck, now I’ve actually got to do the thing.”

Did you really scream “fuck”?

No, I didn’t. I think it was [a phone call] from James and I was like, “This is extraordinary and wonderful and brilliant.” Then I put down the phone and screamed “fuck” very loudly. It lasted under a minute.

Mike Ryan has written for The Huffington Post, Wired, Vanity Fair and GQ. He is the senior editor of ScreenCrush. You can contact him directly on Twitter.