Technology shows the way down. Investors had piled into these stocks, which opened Thursday with a year-to-date gain of more than 23% as software companies continue to monetize their artificial intelligence offerings and chipmakers see growing demand for their AI chips. Now some are taking their profits by selling.

Not helping is the fact that the 10-year Treasury yield has risen to 4.3%, almost a full percentage point from where it was about a month ago, as markets view the economy's recent strength as enough to contain some inflation and high interest rates maintain the picture.

The problem for tech companies is that higher long-term bond yields reduce the value of future earnings, and many tech companies are valued on the basis that much of their earnings will be many years in the future.