The Big Bang was not the beginning of time. Before the Big Bang, there was a tiny fraction of a second during which a process called inflation expanded a seed much smaller than the nucleus of an atom into a fireball the size of a basketball -- the Big Bang itself. From this fireball, the Universe as we know it developed. The origin of the seed from which the Universe began is not known with certainty, but as John Gribbin explains the most likely explanation is that it was a fluctuation of quantum energy in an eternal sea of cosmic energy. And that means that other seeds must surely have inflated to become other universes, bubbles in the cosmic sea. It is even possible that a collision between our universe and another bubble on the sea of eternity may have left an imprint on the cosmic background radiation, the echo of the Big Bang itself.

John Gribbin is an award winning science writer best known for his book In Search of Schrodinger's Cat. He studied astrophysics under Fred Hoyle in Cambridge, and is now a Visiting Fellow in Astronomy at the University of Sussex.