Why Facebook Thinks You Became Friends With People 46 Years Ago Today: The Unix Epoch

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Many people logging on to Facebook today have been greeted with a strange statistic: they’ve apparently known their friends for 46 years. “Friends on Facebook with Joe Schmo for 46 Years!” the service trumpets loudly, which is odd, because many of Facebook’s users are not 46 years old, and Facebook itself is certainly not 46 years old. Also not 46 years old: The web. Here’s what’s happening.

While you might be counting down to the New Year on Thursday night, computers everywhere will be celebrating a different — not better, just different — holiday: the 46th anniversary of the Unix epoch! If you ever received an email from December 31, 1969 — or been told by Facebook that you’re celebrating an anniversary from before its existence — you are familiar with the Unix epoch.

Basically, the Unix operating system — the basis of Mac OS X and used on servers around the globe — keeps time by counting up forever, in increments of one second, starting from zero — which is tied to January 1, 1970, at midnight Greenwich Mean Time. All dates are calculated relative to this one: The Unix epoch. January 2, 1970, at midnight, for instance, is 86,400 in Unix time, because there are that many seconds in a day.

When you receive phantom emails or notifications from 1969, it’s because there’s a bug in the way a computer — maybe yours, maybe your email providers, maybe Facebook’s — is calculating time. If the time has no value, or if the value has been reset, the computer assumes that it’s zero: midnight 1/1/1970 GMT. Once you roll that back for the United States, because GMT is five to eight hours ahead of the U.S., you land on December 31, 1969. This glitch is four and a half decades old.

Here is one idea for how to celebrate the anniversary of the Unix epoch: Explain all of this very loudly and aggressively at your New Year’s party.

Note: This post has been updated to include the extremely hilarious Facebook bug that popped up today.