Why Elon Musk fears artificial intelligence

Elon Musk is usually far from a technological pessimist. From electric cars to Mars colonies, he's made his name by insisting that the future can get here faster. But when it comes to artificial intelligence, he sounds very different. Speaking at MIT in 2014, he called AI humanity's "biggest existential threat" and compared it to "summoning the demon." He reiterated those fears in an interview published Friday with Recode's Kara Swisher, though with a little less apocalyptic rhetoric.