The algorithm’s viral power has turned the media industry upside down, propelling startups like BuzzFeed and Vox to national prominence while 100-year-old newspapers wither and die. It fueled the stratospheric rise of billion-dollar companies like Zynga and LivingSocial—only to suck the helium from them a year or two later with a few adjustments to its code, leaving behind empty-pocketed investors and laid-off workers. Facebook’s news feed algorithm can be tweaked to make us happy or sad; it can expose us to new and challenging ideas or insulate us in ideological bubbles.

The algorithm’s viral power has turned the media industry upside down, propelling startups like BuzzFeed and Vox to national prominence while 100-year-old newspapers wither and die. It fueled the stratospheric rise of billion-dollar companies like Zynga and LivingSocial—only to suck the helium from them a year or two later with a few adjustments to its code, leaving behind empty-pocketed investors and laid-off workers.