Jim enters the multiverse with Astronomer Royal Martin Rees. He's worked on the big bang, black holes and the formation of galaxies but what he would really like to know is if there is life elsewhere in the universe.
As an ex president of the Royal Society and a member of the House of Lords he is at the heart of science policy and worked with the G8 to put science on the international agenda. An atheist, he has attracted criticism from other scientists for his religious views.
He says we can now be fairly certain of what happened in the universe from a nanosecond after the big bang until today and is a supporter of the idea that there may have been many big bangs leading to many universes.
Producer: Geraldine Fitzgerald.