In real life, in the natural course of conversation, it is not uncommon to talk about a person you may know. You meet someone and say, “I’m from Sarasota,” and they say, “Oh, I have a grandparent in Sarasota,” and they tell you where they live and their name, and you may or may not recognize them.
You might assume Facebook’s friend recommendations would work the same way: You tell the social network who you are, and it tells you who you might know in the online world. But Facebook’s machinery operates on a scale far beyond normal human interactions. And the results of its People You May Know algorithm are anything but obvious. In the months I’ve been writing about PYMK, as Facebook calls it, I’ve heard more than a hundred bewildering anecdotes:
- A man who years ago donated sperm to a couple, secretly, so they could have a child—only to have Facebook recommend the child as a person he should know. He still knows the couple but is not friends with them on Facebook.
- A social worker whose client called her by her nickname on their second visit, because she’d shown up in his People You May Know, despite their not having exchanged contact information.
- A woman whose father left her family when she was six years old—and saw his then-mistress suggested to her as a Facebook friend 40 years later.
- An attorney who wrote: “I deleted Facebook after it recommended as PYMK a man who was defense counsel on one of my cases. We had only communicated through my work email, which is not connected to my Facebook, which convinced me Facebook was scanning my work email.”
Connections like these seem inexplicable if you assume Facebook only knows what you’ve told it about yourself. They’re less mysterious if you know about the other file Facebook keeps on you—one that you can’t see or control.
Behind the Facebook profile you’ve built for yourself is another one, a shadow profile, built from the inboxes and smartphones of other Facebook users. Contact information you’ve never given the network gets associated with your account, making it easier for Facebook to more completely map your social connections.