Big Ideas presents Sean M. Carroll of CalTech discussing how the direction of the arrow of time was defined by the Big Bang. He also speculates about what might have come before the Big Bang. The lecture is entitled The Origin of the Universe & the Arrow of Time. 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.