Concerns about robots taking jobs are not just confined to low-wage workers, who are seen as more at risk to trends of automation, but also on the minds of some of the most noted thinkers about the economy.

Robert Shiller, the Nobel-Prize winning economist who is the Sterling Professor of Economics at Yale University, said that automation and artificial intelligence are the trends that most concern him about the economy’s prospects going forward.

“A.I. is a deeply challenging thing,” he said. “People who are growing up today don’t know if they’re preparing for the right career, and challenges associated with that could lead to secular stagnation.”

Shiller said that even he wasn’t immune to this threat, noting how videos of his lectures at Yale could be accessed free online. “If you can do that, then what’s the additional value of attending [in person]? Sometimes it makes me feel like I’ve outmoded myself.”

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Concerns over automation and artificial intelligence have existed for years, but talk over them has accelerated amid new technologies—such as driverless cars and “bot” programs that can mimic human speech patterns—that threaten to disrupt ever-larger segments of the economy. According to recent research, every industrial robot takes up to six jobs, meaning that up to 6 million jobs could be lost to automation over the coming decade.

Last year, the White House’s annual economic report of the president (under President Barack Obama) forecast an 83% chance that automation will take a job with an hourly wage below $20, a 31% chance automation will take a job with an hourly wage between $20 and $40, and just a 4% chance automation will take a job with an hourly wage above $40.

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“All this looks like it’s happening very fast, but it may not happen quickly,” Shiller conceded, noting how history was rife with eras when “Luddites”—who destroyed machinery out of concerns that their jobs were threatened—fretted about technological upheavals that changed the economy but didn’t result in widespread unemployment.

“This could be a 23rd-century problem,” he admitted.

Shiller gave his comments as part of a broader lecture on what he called “Narrative Economics,” or the theory that “stories going viral is a major driver of economic events,” as he described it. “Stories drive perspective, and economic fluctuations are caused by narratives going viral.”

As an example, he speculated that the Depression of 1920—when consumer prices fell by 16% in a single year, still a record in U.S. history—was caused by widespread media reporting about “profiteers,” which in turn caused people to boycott such vendors, leading to a recession.

He pointed to President Donald Trump and the idea of “fake news” as a narrative that could have economic ramifications.

“Trump is a genius at narrative, and his stories don’t have to be true to go viral.” Shiller referenced how Trump, when he announced his candidacy, said that Mexico was “sending” rapists and criminals to the United States, even though data show immigrants are less likely to commit crimes.

“It’s very hard to come up with a counternarrative for something like that, which Trump knows very well. I don’t think Donald Trump really cares about truth, he just looks at the response he gets.”