when Altares is caught in the pull of a black hole. Although the ship cannot reach the faster-than-light speeds needed to break free, Anna believes that the hole may lead to another universe and urges her companions not to give up hope. Crossing the event horizon, the travellers experience mind-bending space-time distortions. They emerge on the other side of the hole safe and well, albeit unable to return home. As Altares approaches an unknown planet, the narrator concludes: "One thing is sure – this is not the final word. Not the end, but the beginning. A new universe, a new hope? Only time will tell." Production After filming on the first series of Space: 1999 came to an end in the spring of 1975, producer Gerry Anderson was contacted by NBC executive George Heinemann with an idea for an educational science-fiction TV series. This would comprise seven one-hour episodes designed to teach children science in the form of an action-adventure. NBC intended to promote the series by distributing information leaflets to schools. To launch the series, Heinemann commissioned Anderson to produce an episode about 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 moving. By 1975, Anderson's production company, Group Three, had received no assurance from distributor ITC Entertainment that it would order a second series of Space: 1999. Faced with the prospect of cancellation, Anderson and Space: 1999 story editor Johnny Byrne conceived Heinemann's episode, which they had named "Into Infinity", as a pilot for a new series, provisionally titled The Day After Tomorrow. Anderson was ultimately unable to secure the funding needed to make further episodes, leaving "Into Infinity" – now more commonly known by the series title – as a one-off special. Writing Anderson prepared for the production by researching Einstein's work; he later said that he had not understood any of the theories and suggested that some of Einstein's ideas are essentially impossible to demonstrate on TV. Byrne wrote the script, which instructed that the equation – Einstein's formula relating mass to energy – should appear on screen at intervals. According to Anderson, the writing process was "extremely difficult" as it was a challenge to "get over in a few words the problems of time changes that affect long-distance travel. You also have to do it in a language that