The research was extensive. The actor spent time with Hawking's family. He also visited patients suffering from amyotrophic lateral sclerosis, and asked their families about coping with the disability. He watched footage of Hawking and read A Brief History of Time, without grasping all the intricacies of Hawking's classic 1988 text. Meeting the physicist was one of the last things Redmayne did before the shoot and he was worried the person he was about to meet was not the character he had prepared: "There were so many things in that first meeting, specific things that were so useful, such as he asked me if I was playing him before the voice machine.
Eddie Redmayne as Stephen Hawking in The Theory of Everything.
"He told me that his voice had been very slurry, but we hadn't taken that on board so much.
"We'd watched some of the documentary material where his voice was almost incomprehensible. So I could go back to the producers, and more importantly director James Marsh, and say we need to take this on board, but we still didn't go quite so far because they didn't want to use subtitles, but it did give me permission to really go and be pretty strong with that, because it was important for Stephen [Hawking] and screenwriter Anthony McCarten that we show the illness in full."
The other thing he noted, and something that is central to the love story that glues the movie together, is that Hawking is a very funny man. The actor points out: "Although he can move only a few muscles, he sort of emanates this vitality and humour, this wit and flirtatiousness."
The film is based on the book Travelling to Infinity - My Life with Stephen by Hawking's first wife, Jane, whom New Zealand writer McCarten convinced he could turn into a screenplay.
Redmayne says The Theory of Everything is also a love story.
She is played by Felicity Jones, an actress Redmayne has long respected.
It's almost par for the course that if an actor performs well essaying a character with a disability or someone famous, they'll be mentioned as an Oscar candidate. It's no different here, with Redmayne leading a British charge for Oscar glory.
Nonetheless, Redmayne avoided watching some of the great performances of actors playing people with disabilities: "You know what, I'd seen My Left Foot and I'd seen The Diving Bell and the Butterfly, which people talk about, and I'd watched them years ago, but I didn't watch them again. It's interesting because people talk about disability in film in such broad terms, but this is such a specific illness that what I did do was go and spend four or five months in a neurology clinic."
Yet there was also an acknowledgement that working on the film would have some career ramifications: "I fought hard to try and get it, so there must have been something in me that said this is a dream part. The second I got it, there was an instant euphoria, followed by, like, a punch in the stomach, a fear: it felt like a part that was such an amazing opportunity but could also cause so much offence."
It has been quite a year for the Londoner, who was in the same year at Eton as Prince William before going on to Cambridge to study art history.
He married his long-term partner Hannah Bagshawe on December 15 and cut short his honeymoon to pick up the Golden Globes in Los Angeles this week.
He does have a part in the space adventure Jupiter Ascending, directed by Andy and Lana Wachowski, but that film has been beset by production problems, reshoots, a long editing period and changes in release dates. As a result it will not be released until February, even though it was filmed before Redmayne took on Hawking.
His next film will be The Danish Girl by Tom Hooper who directed him in Les Miserables. It's an adaptation of Lucinda Coxon's novel inspired by the true story of the Danish painter Einar Wegener, who caused a storm when he became one of the first men to undergo a sex-change operation.
Lowdown:
Who:
Eddie Redmayne
What:
The Theory of Everything
When:
Opens February 5
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- Independent / TimeOut