Marsh had studied archival images to give the film its authenticity, stating, "When we had photographs and documentary footage of Stephen that related to our story, we tried to reproduce them as best we could". Redmayne met with Hawking himself, commenting, "Even now, when he's unable to move, you can still see such effervescence in his eyes". He described portraying Hawking on-screen as a "hefty" challenge, adding that, "The real problem with making a film is of course you don't shoot chronologically. So it was about having to really try and chart his physical deterioration [so] you can jump into it day-to-day, whilst at the same time keeping this spark and wit and humour that he has".