Machines could put more than half the world's population out of a job in the next 30 years, according to a computer scientist who said on Saturday that artificial intelligence's threat to the economy should not be understated. Vardi, a professor at Rice University and Guggenheim fellow, said that technology presents a more subtle threat than the masterless drones that some activists fear. He suggested AI could drive global unemployment to 50%, wiping out middle-class jobs and exacerbating inequality. "Humanity is about to face perhaps its greatest challenge ever, which is finding meaning in life after the end of 'in the sweat of thy face shalt thou eat bread'," he said. "We need to rise to the occasion and meet this challenge."