A lithe, red-haired Eddie Redmayne slips into the banquette in a restaurant in Toronto, takes one look at the table’s snack mix and pushes away the bowl. Shaking hands, he remembers that the last time we saw each other was in New York at a lunch for Les Misérables. We had discussed how he lied about his equestrian skills to get a role in Tom Hooper’s TV mini-series Elizabeth I, and his matriculation at Cambridge alongside Tom Hiddleston.

That elite university was also where Redmayne first spied Stephen Hawking, the genius cosmologist and amyotrophic lateral sclerosis (ALS) sufferer who Redmayne portrays in The Theory of Everything. The biopic delves into Hawking’s first marriage to wife Jane (Felicity Jones), as he suffers the effects of the neurodegenerative disorder that gradually robs him of muscle control. Redmayne and I spoke about meeting the real-life scientist, Redmayne’s terror at playing him onscreen, and the raves he’s earning at the Toronto International Film Festival for his immersive performance.

Had you known much about Hawking before you took the role?

I’d seen Stephen in his wheelchair from a distance at Cambridge. I’d studied history of art, and I just knew what I suppose most people know: the icon and the voice and something about black holes. Then I read this script and was embarrassed by how little I knew.

Did the role come easily to you?

There was a moment when I got the part where I felt a wonderful euphoria. It lasted about a second and a half. It’s been fear and trepidation ever since. The night before we started filming was the only night of my life that I did not sleep. It got to four in the morning, and I was being picked up at five, and I was like, ‘I haven’t slept. I can’t start this film without having had a minute’s sleep.’

Did it surprise you that Hawking was physically fit until he was an adult?

I didn’t know that much about him or ALS. I thought it was something that came on quite quickly. And in many cases, it does. But I found the love story aspect of it, this idea that there was this extraordinary woman named Jane, played by Felicity Jones, behind him completely riveting. I chased the role pretty hard, and I had a long conversation with [director] James Marsh. And I did that thing that actors do of pretending to sound really confident. I somehow managed to blag him into it.

What does ‘blag’ mean?

Blag means con him.

Well, maybe it wasn’t just blagging. You did an incredible job.

Thank you. My instinct had been that to approach a part like this, you needed to go back to an old school way of working. I felt that every single aspect of it would affect everything else. So the physical would affect the costume, would affect the makeup, would affect the voice. I worked with a dancer, an amazing woman called Alex Reynolds, and I spent a few months going to the London Motor Neuron Diseases Clinic to see how ALS manifests itself. It’s different in every single patient…. As the muscles stop working, you used other muscles. There are muscles here in our face that we never use, and [Hawking’s] mom and his wife Jane describe how he had incredibly expressive eyebrows. So it was trying to learn to isolate muscles, which meant a lot of time spent in front of a mirror with photos.

The movie frankly shows that Hawking remained sexually active post-diagnosis and fathered three children.

Completely. When you look at photos or hear about Stephen as a younger man, he was incredibly charismatic and flirtatious. The ladies loved him and still do…. It was absolutely apparent meeting him that he is a really strong, potent man in every sense of the word.

While a lot is made of the role’s physicality, the genius is that the illness never overcomes Hawking’s intellect or spirit.

The story of Stephen dwarfs the illness. For him, it is of no importance. He didn’t ever want to see a doctor again after he was diagnosed. He is someone that lives forward and lives optimistically. So, for me, what this film was about was an unconventional love story, a film about loving in all its guises. So, young love, passionate love, love of a subject, the tribulations of love, and the love of family.

With the current celebrity frenzy around the ALS Ice Bucket Challenge, it seems like a perfect storm for ALS awareness now.

For me, it’s a wonderful thing because as part of my research, I met 30 or 40 people suffering and their families. It’s a brutal, horrific disease. But because there is very little money invested in finding a cure, it’s been around for a long, long time, and they’re not much closer to finding one. I’m now a patron of the Motor Neuron Disease Association in London, and for them [the Ice Bucket Challenge] has been game changing.

Tell me about meeting Hawking.

It was five days before we started filming, which was not ideal. I’d spent all these months prepping, and I was a little worried: What if everything I had prepped was wrong? Our first half hour together was pretty hilarious in a kind of awful way. I basically just vomited forth information about Stephen Hawking to Stephen Hawking. But he was very generous…. Above and beyond the specifics I gleaned about how he slurred his words and such, was that he emanates this humor and wit. And that is what ended up being the most wonderful thing because it meant that I could start each scene — whatever obstacle’s been put in his way, he still finds humor and he still finds joy.

What’s your biggest takeaway from the whole experience?

The film quotes Hawking’s line: “Where there’s life, there’s hope.” I’m a massive culprit of all the foibles in your life taking all of that joy away. But, actually, when Stephen was given a death sentence at age 21, he committed to living each one of those moments fully.