Like most of us, they gave little thought to the connections they made. Mr. Young added friends he hadn’t spoken to in decades. When Ms. Pierce joined a nonprofit organization she accepted dozens of friend requests — some from people she’d met only in passing. “I meet people on airplanes all the time and we exchange Facebook handles,” she told me.
But as Facebook evolved, these weak connections became unlikely information nodes. Mr. Young and Ms. Pierce were now getting their commentary from people they hardly knew, whose politics had once been unknown or illegible.