This might require a science fiction historian to answer. I'm watching "Mirror, Mirror" again and started wondering about the terminology of 'parallel universe' in regards to motion pictures and radio & television programs. I'm sure the term previously appeared in written fiction or scientific non-fiction, but what about in audio or visual presentation? I usually pin down the time that I was turning into a science fiction fan as 1959, when I was 8. I'm sure I might have seen Adventures of Superman before then, as we first got a TV around 1955. And I had dreams about dinosaurs walking around, so I might have seen 1933's King Kong too. I remember having wind-up and battery powered toy robots. I remember shows like Science Fiction Theater, Men Into Space, and The Twilight Zone by 1959. In 1963, Fireball XL5 and The Outer Limits appeared on two different networks in America. The terminology in those shows seemed to usually refer to other dimensions, with dimensions as the key word. Was Star Trek the first radio/tv program or film to refer to these as a parallel universe, which seemed to culturally evolve into alternate universe?