Special relativity to a first observer O, and frame S′ (pronounced "S prime") belongs to a second observer O′. Since there is no absolute reference frame in relativity theory, a concept of 'moving' doesn't strictly exist, as everything is always moving with respect to some other reference frame. Instead, any two frames that move at the same speed in the same direction are said to be "comoving". Therefore, "S" and "S"′ are not "comoving". The principle of relativity, which states that physical laws have the same form in each inertial reference frame, dates back to Galileo, and was incorporated into Newtonian physics.
The Einstein Theory of Relativity released their relativity film, produced in collaboration with popular science journalist Garrett P. Serviss to accompany his book on the same topic. Two versions of the Fleischer film are reported to exist – a shorter two-reel (20 minute) edit intended for general theater audiences, and a longer five-reel (50 minute) version intended for educational use. The Fleischers lifted footage from the German predecessor, "Die Grundlagen der Einsteinschen Relativitäts-Theorie", directed by Hanns-Walter Kornblum, for inclusion into their film. Presented here are images from the Fleischer film and German film. If actual footage was not recycled into "The Einstein Theory of Relativity",