Redmayne spent four months preparing for the role. First, he thoroughly researched Hawking himself, studying videos and documentaries about him and reading his books. The latter proved challenging as Redmayne did not have a background in physics, but he felt it was important to understand Hawking’s work. Redmayne ultimately had a physics teacher at Imperial College London explain much of Hawkings writings to him in layman’s terms. Then to mimic Hawking’s movements, he worked extensively with a choreographer, Alexandra Reynolds. This work depended on his visits to a neurology clinic in London, where he was able to interview patients in different stages of ALS. This was important as he had to depict Hawking in different stages of the disease as well, a task that was especially challenging since the film wasn’t going to be shot chronologically. According to Redmayne, he wound up carrying around a sheet of paper summarizing all of his research as a guide for his performance. Finally, Redmayne met with Hawking days before shooting, which helped him fine tune his performance even more. For example, Redmayne discovered that right before Hawking relied on his voice machine to communicate, his voice had become very slurred. Redmayne also observed that Hawking had “one of the most expressive faces…The irony I found was that everything you’ve been taught about film acting is to reduce. The weird thing here is you are doing the absolute opposite. Your face is in these huge extreme positions and expressions.”

In depicting Hawking’s later years, when he became thinner and smaller, the make-up artist actually used prosthetic ears to create that illusion. According to writer/producer Anthony McCarten, “you make the ears bigger and the whole body seems smaller.”

When Hawking viewed an early cut of the film, he was so pleased with Redmayne’s performance that he gave the filmmakers permission to use his own distinctive computerized voice in the film rather than the re-creation they used and wound up discarding. According to McCarten, much time and money had been spent re-creating Hawking’s computerized voice, but they were never able to replicate it accurately.