The details behind 21 December 2012 make no sense at all. The originator of the so-called prophecy studied at the University of Chicago in Arts more than 40 years ago. He was Jose Arguelles then. He now says time is faster than light (whatever that means) and that the way we measure time is harmful to all life on Earth (how does that work?).
He now calls himself Valum Voltan and says he is the re-incarnation of a Mayan priest and lives in New Zealand, last I heard. All this stuff was based on the fact that a Mayan count of days runs out of numbers on 21 or 23 December by our calendar. That has as much to do with the Mayan counting system as anything else. The Mayans counted by 20, then by 18s then by 20 again and so on.
The Mayans were pretty fair naked eye astronomers for a stone age people and had enough sense not to predict anything at all, except maybe party time. I reckon they were smarter than Arguelles.
But crazy as Arguelles ideas are, he did not say the world would end on 21 December 2012. All he said was that this would be the beginning of a new era. That was about 20 years ago.
Since then, people who are just as batty, but in a different way have grabbed his ideas and run away with them. Terence McKenna was an habitual user of mescalin, LSD or magic mushrooms and wrote down visions. He also produced a special (mis)interpretation of the I Ching, and when it didn’t quite fit 2012 he fudged it.
Another called Nancy Lieder claimed that aliens had abducted her about 1993 and told her that a planet called X would pass close to the Earth and cause a magnetic pole shift and other damage. That would be in 2003. Since it didn't come, she started making up stories of how it was a trial to test the governments of the world and that the planet would appear later. She usually says 2012 as far as I know.
Apart from Voltan, Mc Kenna and Lieder, others have jumped on the bandwagon and have predicted everything from bees dying to collisions with stray planets. There are supposed to be alignments with the other planets or the centre of the galaxy, a photon belt, crossings of the galactic central plane and on and on none of which will happen. And dear old Nostradamus and Edgar Cayce get quoted too, as if anyone believes that stuff.
The promoters of this, including the History Channel are vicious liars and only in it for the money. They are trying to sell "survival" supplies, shelters, books, videos and what all, but to do that you have to frighten people first.
http://2012hoax.wikidot.com/start
http://www.abhota.info/
http://eclectech.co.uk/mindcontrol.php