©Illustration: Science Photo Library/Mikkel Juul Jensen
Did our universe arise from the collapse of an earlier one?
Alexander Friedmann once said: "My job is to solve equations. It's up to the physicists to decide what the solutions mean.” The mathematician meant this half-deprecatingly, because he spent most of his time dealing with quite mundane problems: from flows in liquids to turbulence in the earth's atmosphere to the development of the entire universe. The equations he derived from the General Theory of Relativity in 1922 are still up to date - and what their solutions mean has remained a topic of cosmology to this day....
