From Wikipedia:
Just Imagine is a humorous science-fiction movie musical presented by 20th Century Fox in 1930, directed by David Butler, to console audiences distressed by the Great Depression.
The film was set in the year 1980, and it depicted the conventional expectations of technological progress associated with that "distant future" date. A large dirigible hangar was used to house a huge, detailed, large-scale model of a modern city, complete with suspension bridges between towering skyscrapers, multi-lane elevated roadways, and a flock of flying machines flitting around above the city as another level of traffic. To modern viewers, the city resembles an implausibly exaggerated version of 1930s New York City.
The plot involves a man from 1930, who is experimentally revived from the dead by a team of physicians who have no interest whatsoever in him after he awakens. Two young men who have observed the process as guests of one of the nurses kindly take him in hand and show him (and the audience) the wonders of 1980. He also gets to travel to Mars, which turns out to be inhabited by friendly humans, each of whom has an evil, otherwise-identical twin.
The man from 1930 is played by El Brendel, an ethnic vaudeville comedian of a forgotten type: the Swedish immigrant. The citizens of 1980 are now identified only by an alphanumeric code (the hero is "J21," and the El Brendel character is quickly dubbed "Single Zero," pronounced "Single Oh."). Instead of a sexual revolution, there is rigid government control of relationships between the sexes; marriage partners are chosen or approved by judges of an official marriage tribunal, while the only legal babies come from vending machines. J21's trip to Mars is motivated by the fact that he needs to make a spectacular contribution to society in order to be allowed to wed the high-status female of his choice, LN18. One detail interesting to modern viewers is the huge change depicted in the style of men's suits, a change that in reality has never taken place. There is also a running gag concerning homosexuality, a reminder that this film predates the infamous Production Code.