One of the world's top thinkers on artificial intelligence, tells us why we should be cautious but not terrified at the prospect of computers that can outsmart us. Professor Stuart Russell of the University of California, Berkeley, tells Ed Butler where he thinks we are going wrong in setting objectives for existing artificial intelligence systems, and the risk of unintended consequences. Plus IBM fellow and computer engineer John Cohn talks about blockchain, deep neural networks and symbolic reasoning. (Picture: Ponderous robot; Credit: PhonlamaiPhoto/Getty Images)