After reaching records highs last year, the stock market went south in the final months of 2018. In the end, it was the worst year for markets since the 2008 crisis and the worst December since 1931.

And the tumult is carrying over into the first week of trading in 2019.  

What exactly is causing the turmoil? The government shutdown, rising interest rates, and unresolved trade tensions are all contributing to the ups and downs, but one reason for the triple point drops might have to do with how the market itself operates. 

This week on Money Talking, Charlie Herman speaks with Greg Zuckerman, special writer for the Wall Street Journal, about the increase in computerized trading, how it shapes the market's moves, and what it means for the average investor.