On New Year's Eve, Everyone Born In The 20th Century Will Be An Adult, According To This Viral Tweet — But People Are Debunking It

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There are many things that might tear people apart, but generally I don’t expect random little tidbits of trivia to be one of them. Clearly I need to reassess my expectations, however, because a fact about New Year’s Eve 2017 — or “fact,” as the case may be — that’s currently going viral has driven wedges between Twitter users, turning friend against friend and tearing them asunder. Is the “fact” true? Is it false? Is it somewhere in between? And why the heck does it seem to bother people so much, either way? Such drama! Let’s take a closer look, shall we? The fate of our planet might depend on it!

...Or not. Whatever — it's still interesting, so here's what's going on.

The tweet featuring the factoid that’s currently going viral was launched into the ether by Twitter user @WMcHBg on Dec. 27. “On Sunday 31st December 2017, all living adults will have been born in the 20th Century, while all living children will have been born in the 21st Century,” @WMcHBg’s tweet reads. “This is the only day in history where this will be the case.”

However, it’s worth noting that the piece of trivia the tweet contains has made the rounds before: Twitter user @_bethbethbeth_ tweeted it on Dec. 23. “My Dad’s just told me that on New Year’s Eve, every single adult in the world will have been born in the 20th century and every child will have been born in the 21st century, and that’s the only day that’s true for, and my mind is suitably BLOWN,” reads @_bethbethbeth_’s version.

For the sake of completion, here are both tweets in their original glory:

If you’re a little confused by what it all means, Indy 100 broke down @WMcHBg’s version into a few smaller bites that make it a bit easier to understand. Here’s what the tweet assumes to be the case (and yes, there is a reason I’ve positioned it as “assumes to be the case” — we’ll get to why that is in just a bit):

  • Everyone on the planet who was born on or before Dec. 31, 1999 will be 18 years old — which, in many countries, is the age at which a person is legally considered an adult — by Dec. 31, 2017.
  • However, everyone who was born on Jan. 1, 2000 or later will still be 17 or younger — that is, legally a child in many countries — on Dec.31, 2017
  • Also relevant: The oldest verified living person on the planet is currently Nabi Tajima, who was born on Aug. 4, 1900 — which, by this tweet’s logic, means that no one who is currently alive was born before the 20th century.

And, indeed, plenty of people responding to both @WMcHBg’sand @_bethbethbeth_’s tweets have reported experiencing similar states of exploded brains:

However, not everyone agrees that this fact is correct — and, indeed, the case is strong for the naysayers. The issue is this: It’s generally accepted that the 21st century began not on Jan. 1, 2000, but on Jan. 1, 2001. The reason? There was no year zero.

As Scientific American explained in 1999, the calendar we generally use today is the Gregorian calendar — and in the Gregorian calendar, years are counted beginning with the year A.D. 1. The year before A.D. 1, however, was not Year 0; it was B.C. 1. This means that the first century A.D. covers the years between A.D. 1 through A.D. 100, while the first millennium covers from A.D. 1 through A.D. 1000. (The second and third millenniums work similarly; they cover the years A.D. 1001 through A.D. 2000 and A.D. 2001 through A.D. 3000,respectively.) And if the first century covers between A.D. 1 through A.D. 100, then that means that the 20th century covers from A.D. 1901 though A.D. 2000, while the 21st century covers A.D. 2001 through A.D. 3000.

Also, this means that Oldest Verified Living Person On The Planet Nabi Tajima was actually born in the 19th century. If she was born in 1900, and the 20th century didn’t begin until Jan. 1, 1901… well, you get where I’m going with this one.

It’s OK, though; apparently, we’ve all been making the same mistake for years, so we're in good company. My favorite piece of evidence regarding the length of this prolonged error is an article by Jack Smith that was published in the Los Angeles Times in 1988 — nearly 30 years ago — titled, “For The 2,000th Time, The 21st [Century] Begins In 2001.” The salt is strong with this one, and I am very much here for it. The point is that, now that we know we've been wrong, we should correct ourselves and carry on.

HOWEVER. The plot thickens: There was also a version of this factloid that hit Twitter prior to both @WMcHBg’s and @_bethbethbeth_’s tweets — and it’s more on the mark, too. On Dec. 13, software engineer Cassidy Williams tweeted the following:

And that, according to the logic laid out by Indy 100’s explanation, is true — because referring to the 1900s and 2000s instead of the 20th and 21st centuries shifts the relevant timeframes to the years 1900 through 1999 and 2000 through 2099, rather than 1901 through 2000 and 2001 through 3000.

Of course, though, it also still assumes that 18 is the age at which people become adults, which isn’t the case everywhere in the world. Although 18 is the age of majority in a large number of countries, it might be as young as 15 in some countries and as old as 21 in others.

So, I guess the lesson we should really be taking away from this whole debate isn’t about a fixed fact; it’s about how things can change based on your perspective.

And also about how fact-checking is a good habit to get into.

Or… something.

Anyway.

Happy almost-New Year’s, regardless — no matter which centuryinto which you were born!