The job of science fiction is to push boundaries. Indeed, the very description of science fiction suggests going a bit further than established fact. Science fiction is supposed to build on the known world around us. It is supposed to explore the unknown. When science fiction is at its best, this exploration is being fueled by our own human condition. The reason we are exploring outward is because there is an uncertainty inside. We feel incomplete in some regard, and the answers might be out there.
Science fiction films that can best communicate the relationship between the universe and our own minds tend to be the films that leave a lasting impression. This is my pick for the 20 films that do the best job of this.