The more digital our daily lives become, the more perplexing the questions seem. Will the growth of social media destroy our notions of privacy? Is democracy helped or harmed by the cacophony of opinions online? And perhaps most confounding: Why does that guy I barely know from the 10th grade keep showing up in my Facebook feed?

If you've ever spent time on Facebook, you've probably pondered that last one. The social-networking giant promises to keep us connected with our friends in exchange for pumping a steady diet of advertising at us—but the algorithms Facebook uses to decide what news to pass along can seem capricious or altogether impenetrable.