Of course there have beenplenty of incorrect predictions in the past, but this time people really, really, really mean it. The world is going to end on June 21. How do they know? Because the Mayans were not wrong but the Gregorian calendar being introduced in 1582 byPope Gregory XIIImade important changes that were used by the Julian calendar. The biggest thing here is that it removed 11 days from our year, to better reflect the time it takes the Earth to orbit around the Sun. Now, 11 days might not sound like much, but over 286 years that adds up. So much so that people on Twitter are now doing the math, saying that if we followed the Julian calendar as we should have, "we are technically in 2012 - which you may remember is when the Mayans said the world would end. So, according to the new math, December 21, 2012, = June 21, 2020.