Bitcoin is a “social movement” and an “epidemic of enthusiasm,” according to Robert Shiller, Sterling Professor of Economics at Yale University.

Shiller appeared on “Bloomberg Surveillance” on Tuesday to share his explanation for how and why investors are attracted to the cryptocurrency, specifically, which factors he believes can be attributed to the digital currency’s success in gaining considerable traction.

“It’s generational and geographic,” he said, and added that “the east coast is less into it than the west coast—Silicon Valley is really into it. This to me shows that this is not a rational response to new information.”

Although Shiller stated that bitcoin is a “speculative bubble,” he refused to rule out a hopeless future for the currency.

“Speculative bubbles recur,” he said. “We had a bubble in bitcoin in 2013, and it looked like it was done… but now look, it comes back.”

Related: Goldman Sachs CEO Lloyd Blankfein: Bitcoin ‘Not for Me’

Whether or not Shiller’s comments are true, it comes without question that cryptocurrencies have achieved remarkable worldwide attention over the years. In December 2017, the global volume in cryptocurrency markets passed $50 billion, close to the average turnover on the New York Stock Exchange, proving just how popular digital currencies have become.

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