There have been so many predictions on the date at which the world would end, including:
-2800, -634, 1000, 1600, 1658, 1700, 1794, 1836, 1843, 1844, 1899, 1910, 1914, 1936, 1982, 1999, 2000, 2001, 2011, and now 2012 (C.G.P Grey).
And of course, everyone now believes that December 21, 2012 is the real deal...
Now, where did this date come from? This date came from the Mayan calendar, which recorded not only days and years, but cycles of about 5 millennia. And, the Mayans recording of thousands of years to the future happens to stop at the date of December 21, 2012. Now, can we assume that the end of a calendar is equal to the end of the world? Is it even logical to assume this?
Along with this, the end of the world means just the end of our planet Earth. What is the possibility that these unusual scientific phenomena (or at least as I have heard it) will occur solely onto our planet Earth? And most of all, how can anyone predict this in depth end to only our world, through scientific means? Actually, scratch that, how would the Mayans predict the end of the world through scientific means? I'm pretty sure we are making quite a large assumption that the Mayans would foresee and predict the end of the world, when they couldn't foresee and predict the Spanish crossing the atlantic.
There have been sayings: Alien invasions, a collision with the not even known Planet X, or even geomagnetic reversal, which occurs over a longer period of time than one day.
In fact, everyone has been asking so many questions about it, NASA wrote a question and answer page for everyone. Check it out. [link]
But of course, this time, theres gonna be some unusual and out of the ordinary happening. Just this time. Just because it is December 21st, 2012.
P.S. - There will be a winter solstice, so don't get freaked out about that.