Will the world end on dec. 21, 2012?

No. Christ will return before the world is destroyed. Jesus said that no one knows the day or hour of His return. The book of Revelation talks about a 7-year tribulation period that will also occur before the earth is destroyed. So if you want to look at it from a Biblical standpoint, your theory does not stand. Even if Jesus came back now, 2012 is only 3 years away. But we do not need to fear these things if we trust in Jesus to save us from our sins and from eternal punishment and hold to the hope that we can live forever with Him after we die.