No.
Scientists don't expect anything out of the ordinary to happen in the year 2012, or specifically on the date December 21, other than the solstice, which happens every year.
None of the "predicted" happenings for 2012 hold up under close scrutiny. "Planet X" and "Nibiru" simply don't exist. The Mayan calendar ends a cycle, but there were no predictions of the end of the world. The Sun doesn't line up with the galactic centre; it's 6 degrees off. No asteroids or comets are actually predicted to hit Earth.
All of this stuff was put together by crackpots in order to promote their books and TV shows, and shamelessly promoted by the History Channel. Don't take any of it seriously!
