How did Earth and all the planets and stars and galaxies form? How old is our universe? What "banged" at the moment of the big bang? We have a remarkably successful model of cosmology, but theorists are still asking these questions. We just don't know how the universe emerged from a cosmic singularity – the assumed starting point of the big bang. Today, scientists are exploring several possibilities for the origins of our universe. Neil Turok wonders if the big bang singularity was not the beginning of time, but a gateway to a pre-big bang universe. Theory and observation are tackling the big bang of our past, and they will determine whether it was really the beginning of everything, or merely the latest in a series of bangs, each of which produced a universe like ours.