ELON MUSK, in his telling, is a modern-day Cassandra—better than most at predicting the future, but doomed to be disbelieved. “People don’t realise that what I’m saying will come to pass,” he tells The Economist in a 90-minute interview for The Insider , held at a giant Tesla factory in Texas where electric cars drive themselves off the assembly line. That may be because his future-gazing ranges from the unsettling to the downright weird. Mr Musk predicts that, within five years, artificial-intelligence systems may surpass the sum of all human intelligence. Within ten years, robots in the workplace will help...