December 21, 2012
The Mayan calendar ends on December 21, 2012... Too bad we don't have our own.
How do we know the world will end on the Winter Solstice of 2012? Simple. The ancient Mayan people developed an advanced calendar system some fifteen hundred years ago (or possibly 5,000 years ago; and it might have been given to them by the Atlanteans or spacemen, too -- no one is really quite sure). This calendar system consisted of several calendar rounds operating within each other. The shortest of these was the Tzolk'in which was based on the human gestation period lasting 260 days. They also had the Haab', which was a full solar year, lasting 365 days. They combined the Tzolk'in and the Haab' such that a full cycle of Tzolk'ins and Haab's came to a Calendar Round of 18,980 days, or 52 years. Within the Calendar Round they also had several very short periods called the trecena (13 days) and the veintena (20 days).
That was great on an everyday time scale, but to calculate dates far into the future they used the Long Count. Unlike our common base-10 mathematical system, the Mayans used a base-20 system for the Long Count. It works like this: the dawn of the first day of the first Long Count cycle begins at 0.0.0.0.1. The next day is 0.0.0.0.2. On the 19th day we'll have 0.0.0.0.19, but on the 20th day we jump to 0.0.0.1.0. This count continues such that 0.0.1.0.0 is the first year, 0.1.0.0.0 is the 20th year, and 184.108.40.206.0 is the about 400th year. Therefore, the Mayan date of 220.127.116.11.1 represents 1012 years, 7 months, 1 day. In our terms, the Mayan year 18.104.22.168.0 matches up with our June 15, 1224 CE, 22.214.171.124.0 is September 18, 1618 CE, and 126.96.36.199.0 is... Oh boy... December 21, 2012 CE.
Now, if you followed so far, you might be thinking "Shouldn't the world end on Mayan year 188.8.131.52.19?" Don't be silly! 184.108.40.206.19 is somewhere around the year 8000 CE, a date too far into the future for anyone to cash in on books, movies, or documentaries. Besides, the Long Count calendar only covers 5126 years, and it shows that the previous world (the world before our world) ended on 220.127.116.11.0 of the last Long Count, or August 11, 3114 BCE, at which point it cycled back to 0.0.0.0.1. If you do the calculations you'll discover that December 21, 2012 CE is exactly 5126 years after 3114 BCE, and thus when it hits 18.104.22.168.0, the current Long Count will END.
So you see, that is how we know the Mayans were able to calculate Doomsday with their Long Count calendar. When 22.214.171.124.0 comes around on December 21, 2012 CE, that's it. It's all over. No more world, no more people, no more McDonald's, no more reality TV shows, no more nothing.
What exactly will happen? How will the world end? No one can really agree on that either, but there sure are a lot of theories. Read here to learn more about all the different ways the world might end.