Back to the Future

Back to the Future is a popular 80s film

Martha Jones didn't see any threat from the Carrionites because she knew that the world didn't end in 1599 as she was living proof. However the Doctor referenced this movie when he told her about how Michael J. Fox travelled back in time, did something that almost erased him from existence in the past. (DW: The Shakespeare Code)

Behind the Scenes
Christopher Lloyd, who played time travelling Doctor Emmett Brown in the movie and its two sequels, was almost cast as the Master in the 1996 Doctor Who: TV Movie. However, Universal (the studio which was financing the movie and also financed the trilogy) baulked at the pay he was asking for.

While Steven Moffat claims the trilogy's executive producer, Steven Speilberg, merely knows and admires Doctor Who. George Lucas, who is a very good freind of Speilberg's, claims Speilberg merely knows and admires the 2005 series, Lucas also states Speilberg is a big fan of the original series and claims he (Speilberg) believes there are many things missing from the 2005 series that made the original series so great.