Predicting the future is a gamble; making it believable for two hours is an art. The greatest science fiction movies can make a conversation with a computer as unnerving as an alien loose on a spaceship—or leave you arguing over time travel long after the credits. Choosing just 50 means weighing spectacular worlds against ideas that work on a shoestring budget. These are our picks for the films that made those ambitions count, even when their version of the future is now technically the past.
