On Saturday, at roughly 9 a.m. in Tehran, explosions lit up the Iranian capital. Wall Street didn’t wait for the morning shows. It didn’t wait for analysis. It didn’t even wait for traders to wake up.

Algorithms have taken on an almost mythical significance in the modern world. They determine what you see on social media and when browsing online, help form people’s belief systems, and impact the ...

Editor’s Note: If the market has felt harder to read lately, you’re not alone. The way stocks move has changed. Algorithms now account for a large share of daily trading, and major headlines can move ...