Let's take a look back to the Ancient mayan civilizations. As most of us already know, the mayans created the world's most exact calendar ever invented, is even more exact than our own calendar.They were amazingly skilled astronomers, who were able to predict every solar and lunar eclipse until this day, natural disasters, and even the fall of their own empire! (I am trying to make this as short as possible, so feel free to look up info on the many accurate predictions they made =D) They do not state that their calendar, or the world end on December, 21, 2012. However, it does say that it will be a period of judgement, and a new world begins, they stated that an apocalypse would occur, this will start at exacly 11;00 AM. Scientist have proved, that on that exact date, the sun will align with the center of the milky way galaxy. Is said that the center of the milky way is the gate to H***(sorry i hate the name, but you know, where da D**** lives). So now, hold on to those thoughts and take a look at this next piece of info....
The mayans described their god to have a long shaped skull, which is why mothers began disforming thier children's skulls shortly after birth, by applyind devices like, splints, cradleboard, or tightly wound cloth. They said that their god descended from the sky, and the day of departure promised to come back on the date marked in the calendar as 2012. I believe that this god which they spoke of was really aliens, take a look at pictures of the skulls for yourself. This would also explain how they were so extremly advanced in Astronomy. This alien beings gave them the knowledge they had to be able to make such great predictions. And you wanna know the creepy side to this? The mayans made human sacrifices to offer their gods! Do you know what this meant? They want blood! They are planning a return, and soon!
Now, lets take a short peek into the bible. The bible also mentions an apocalyse, during this time, demons are supposd to break out of the gates of H****(which in this case would be the center of the milky way) and come into our world (do you see where i am going?) It says after this period, there will be a new beggining. And god will come. I am sure you know the rest, take some time and think about it.
Now, put everything i've told you together, and see how it fits like the pieces of a puzzle? These aliens are coming on 2012 to attack our planet, why, and what is going to happend i don't know. But i put together all this things and came to that conclusion.