Originally shot as a pilot for a series "The Day After Tomorrow", it was screened with the opening title removed, as a one-off film.
On the original and subsequent NBC airings, a simple card was flashed briefly on screen before going to commercial breaks reading simply "E=MC²" - Einstein's formula relating energy, mass and the speed of light. This was obviously intended to pique the interest of children watching and push them into learning what the strange equation meant, quite a task in a pre-Internet world.
When originally aired, a slide with Einstein's relativity equation (e = mc^2) was shown whenever NBC broke to a commercial.
In the spring of 1975, after filming on "Year One" of Space: 1999 had been completed, NBC agent George Heinemann contacted Group Three producer Gerry Anderson with an idea for a new science-fiction TV series. This would comprise seven one-hour episodes designed to teach children about scientific subjects in the format of an entertaining action-adventure. To publicise the series, NBC undertook to distribute information leaflets to schools. Heinemann hired Anderson to produce a TV special that would discuss, as its main topic, the physicist Albert Einstein's theory of special relativity, which holds that the speed of light cannot be exceeded and remains constant whether an object is still or in motion.
Principal photography was conducted over ten days in July 1975 at Pinewood Studios in Buckinghamshire on a budget of £105,000. The special effects sequences required a further six weeks' filming at Bray Studios in Berkshire; production ended in September.