The Theory of Everything (2014)

Stephen Hawking: I will write a book.
Jane Hawking: About what?
Stephen Hawking: Time.
Jane Hawking: Time?
Stephen Hawking: What is the nature of time? Will it ever come to an end? Can we go back in time? Some day these answers may seem as obvious to us as the Earth orbiting the sun, or perhaps as ridiculous as a tower of tortoises. Only time, that’s what we say.

Movie site: http://www.imdb.com/title/tt2980516/