How does Facebook know who your friends are?

Facebook knows who your friends are, even better than you do?

The social media giant uses a mix of complex science and mathematics to narrow down on your friend’s list

Have you ever thought how Facebook exactly predicts your friends, sometimes even those whom you have long forgotten.

Last week, a Redditor named easyjet posted a thread on Reddit. He mentioned that he signed up with an email address he never, ever used. He even lied about all of his personal information. Yet Facebook was able to accurately predict and “recommend” a huge number of his real-life acquaintances including a women he had dated 19 years ago.

ELI5: Just signed up for Facebook with a rarely used email address. No phone number. They know all of my friends immediately.

submitted by easyjet

How does Facebook know who your friends are?  Irish Data Protection Commissioner decided to conduct a full-scale investigation in 2011, into the same to help us out. Four years later due lot of confusion and misinformation we still are back to square one asking how does FB know who our friends are?

Did it scrape your phone for names and numbers? Run a reverse-image search of your picture? Compile a “shadow” or “ghost” profile on you over a period of years, just waiting for you to log on and “confirm” its guesses?

No Facebook doesnt attempt any sneaky or malicious ways to find our friend. It uses a  pretty complex academic field called . . . network science.

In a nutshell, whenever you sign up for a Facebook account, it asks permission to look at your email contacts if you’re on a computer, or your phone contacts if you’re on a smartphone. When you grant the site permission, it searches your contacts for users already on the network, and it searches other users’ uploaded contacts for you.

That gives Facebook a basic idea of who you are, what your social circle is made of. This information is sometimes better than your memory.

Armed with basic idea of you, Facebook starts to refine your database by asking you more questions about yourself: where you went to school, when you were born, what city you live in.

Without your knowledge, each field you fill in your Facebook profile and each interaction you make through that profile actually doubles as a source of data for Facebook’s mapping algorithms.

Once Facebook knows the structure of your social network, it can analyze it to predict (with startling accuracy) not only the people you’re most likely to know now, but the people you’re most likely to know in the future. What FB does is not magic, its playing with permutations and combinations.

This is what another Redditor, Cayou suggested to jeteasy, and he was right

[–]Cayou 534 points

Nah, simpler than that. OP’s friends have let Facebook snoop through their phone or email contact list, and Facebook saw OP’s name in there. Nothing OP could have done about this. After snooping through these people’s contact lists, Facebook made a note that “OK, there’s this guy who doesn’t have an account yet, but he’s friends with these people”. Then, when OP finally created an account, Facebook had all those friendships ready to suggest.

So next time you find that Facebook has recommended you a long forgotten friend, dont be surprised, its the power of statistics.

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  1. The source isn’t just “Contacts” sharing: I used an email exclusive for fb signup and also had the same experience – without sharing Contacts, phone number or ever using fb on my phone.

    Is it possible fb is referencing other accounts signed-in on your browser?


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