The evidence that the universe emerged 14 billion years ago from an event called ‘the big bang’ is overwhelming. Yet the cause of this event remains deeply mysterious. In the conventional picture, the ‘initial singularity’ is unexplained. It is simply assumed that the universe somehow sprang into existence full of ‘inflationary’ energy, blowing up the universe into the large, smooth state we observe today. While this picture is in excellent agreement with current observations, it is both contrived and incomplete, leading us to suspect that it is not the final word. In this lecture, the standard inflationary picture will be contrasted with a new view of the initial singularity suggested by string and M-theory, in which the bang is a far more normal, albeit violent, event which occurred in a pre-existing universe. According to the new picture, a cyclical model of the universe becomes feasible in which one bang is followed by another, in a potentially endless series of cosmic cycles. The presentation will also review exciting recent theoretical developments and forthcoming observational tests which could distinguish between the rival inflationary and cyclical hypotheses.
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