In an e-mail to director James Marsh about the portrayal by Eddie Redmayne, Stephen Hawking said there were certain points when he thought he was watching himself.
In addition to his copyrighted voice, Stephen Hawking also lent the filmmakers his Companion of Honour medal and his signed thesis to use as genuine props in the film.
Eddie Redmayne met with Stephen Hawking only once before filming. "In the three hours I spent with him, he said maybe eight sentences," recalls Redmayne. "I just didn't feel like I could ask him intimate things." Therefore, he found other ways to prepare for the role. He lost about fifteen pounds and trained for four months with a dancer to learn how to control his body. He met with forty MND patients, kept a chart tracking the order in which Hawking's muscles declined, and stood in front of a mirror for hours on end, contorting his face. Lastly, he remained motionless and hunched over between takes, so much so that an osteopath told him he had altered the alignment of his spine. "I fear I'm a bit of a control freak," Redmayne admits. "I was obsessive. I'm not sure it was healthy."
Stephen Hawking said that the film was "broadly true." He then went on to lend his voice for the final parts of the film.