2001: A Space Odyssey remains one of the most scientifically grounded films of all time, despite the trippy ending. But originally, it would have featured a prologue in which 20 real-life astronomers talked about the possibility of encountering alien life.
According to the Guardian, director Stanley Kubrick felt such a debt to the scientists of the late 1960s, he wanted to feature them talking about their work in the film:
The creator of the Jodrell Bank Observatory, Bernard Lovell, influenced the director Stanley Kubrick's conception of the film. Kubrick wanted the movie grounded in fact and originally planned for it to have a prologue in which Lovell and 20 other scientists would discuss their thoughts about aliens, evolution and space travel. But 2001: A Space Odyssey turned out to be an unusually long film, even without the prologue, and so the 1966 footage was never used and is now lost. Fortunately, the transcript has survived and makes fascinating reading.
And apparently, in the prologue, Lovell says that the Search for Extraterrestrial Intelligence (SETI) should not be allowed to distract us from the real task of astronomy — something it's fascinating to imagine scientists debating in a science fiction movie in 1968.
Also in the Guardian's article: Lovell's weird account of the Russians trying to give him radiation poisoning by using a telescope to bombard him with possibly lethal radiation, when he was spying on their Sputnik satellite. And also, their supposed attempt to erase his mind after he visited their space communications center. [The Guardian]