What is going to happen on December 21, 2012?

I don't really think anything will happen. Of course, some people believe the world will end because that is the last day of the Mayan calendar (they were pretty good astronomers so many take this topic seriously). The thing is, the Sun will align with the center of the galaxy (which the Mayans called the Sacred Tree) which some say may cause doom. The Mayans divided the the Long Count into several cycles where something horrible occurs at the end of each cycle. The Mayans also believed that there is no end, and that there may be peace and happiness spread in the world.