One of the key challenges in creating The Theory of Everythingthe biopic about physicist Stephen Hawking and his wife, was figuring out how to accurately portray the effects of the neurodegenerative disease that Hawking contracts as a young man, and continues to live with even today, says the film’s director James Marsh in the video interview above.

The key was “figuring out the physicality of the foreground tragedy of the film,” Marsh tells Deadline’s Dominic Patten during a Q&A from last night.

Hawking suffers from a variant form of amyotrophic lateral sclerosis. The film tracks his life over decades, and star Eddie Redmayne had to show the disease’s impacts over those years, beginning with a first day of shooting that involved showing Hawking at several progressively worse stages of the disease’s impact.