Market volatility is near a five-decade low, despite elevated geopolitical concerns. And there isn’t much of a consensus on why this is so.

Yale professor and economist Robert Shiller explained there is a risk of confusing tranquility with safety.

“In 1929, the markets weren’t volatile until October or around that time,” Shiller said of the 1929 market crash. “Volatility tends to jump up when there’s some unusual news regarding the stock market and [there’s] a big drop in the market. and we haven’t seen it.”

“The unusual news might be Donald Trump,” Shiller said.

“But volatility has not gone down since he was elected,” Siegel chimed in, adding that there may actually be less underlying uncertainty in the market.

“One hypothesis is that there is actually less real uncertainty, particularly financial,” Siegel said. “Never before has the financial system in the US been as well financed and banks as well protected as now. The amount of reserves [and] of safe capital, if you go back historically, is just enormous. If we think financial instability is a source there, maybe safety of the banks is leading to less volatility.”

For more from Shiller and Siegel:

Robert Shiller and Jeremy Siegel tell us what they think of each other’s market forecasts
Jeremy Siegel: ‘On the whole, we have nothing replicating 1999’
Siegel: If Trump doesn’t bring reform we could have trouble in the markets
Jeremy Siegel and Robert Shiller tell us what’s next for the economy
Robert Shiller and Jeremy Siegel face off and answer 7 key questions

Nicole Sinclair is markets correspondent at Yahoo Finance