Recently I was reading an article titled When Facebook Knows You Better Than You Know Yourself which talks about all of the ways Facebook could predict our behavior thanks to to all of the information we have shared with the site with our likes, shared links and the various websites & apps we use that are connected to Facebook. This article then links off to Why Does Facebook Keep Suggesting You Friend Your Tinder Matches? which seems to present a conundrum

Maria Ledbetter has noticed six people she has met on Tinder in her Facebook suggested friends within the last few months, including one match who showed up so late to their date that she left. She said the suggested friends from Tinder often pop up within a week of getting her number, usually in cases where she hasn’t spoken with them since.

“It’s always people I don’t even talk to, have deleted their number, and have no friends in common,” she said. “It’s really frustrating.”

Emilio Ferrara, a data science and machine learning professor at Indiana University who studies social networks said the most obvious answer would be that these apps are collecting and sharing your information.

“It is likely that these social network companies are buying data from one another, which means that Facebook can acquire some information on user activity from other platforms,” he said.“If that’s the case, it would be very easy to cross match.”

“It could also be a coincidence,” he added. “But I don't believe very much in coincidences.”

The article goes on with a number of theories and quotes from other experts trying to understand the magic behind how Facebook seems to know who you’re talking to in dating apps when you’ve not added them as a contact on your phone nor have any friends in common. The answer is actually quite simple; your Tinder/OKCupid/Grindr dates have your phone number.

A long standing capability of Facebook is that it creates shadow profiles of its users. For example, if my email address known to Facebook was dare@example.com and phone number 555-1212 then when someone joins Facebook with that email address or phone number as a contact then Facebook knows that they know me. So Facebook has a “shadow” friend list of people who have my email address and phone number even if I haven’t added them as a friend nor have mutual friends in common with them.  Since there are lots of people who sync their phone contacts with Facebook there are likely dozens of people that Facebook knows you know even if you’ve not added them as friends.

Mystery solved. 

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