The theory of relativity explained in 1923

This educational documentary is marvelous. It explains the theory of relativity in a time when cinema was still in its infancy (there is not even music in the film). Just eight years after Einstein formulated the general relativity, this video shows all key concepts of the theory. The movie talks about the speed of light, the effect of gravity, that time is relative, and even about time travel! Enjoy, it is definitely worth watching!