Everything you have heard about 2012 is full of half-truths and outright lies, with the following exceptions.
1. There will be an American presidential election in 2012.
2. The Summer Olympics will be in London in 2012.
3. The Planet Venus will transit the Sun in 2012. (The only effect of this will be that a small dot will be visible on the sun in telescopes that are adapted to look at the sun.)
4. There will be natural disasters, war, famine, plague, etc... but no more than in any other year.
That is all. Everything else is bull.
Nostradamus didn't predict anything for 2012.
Some people think the Mayans did, but they are wrong. The Mayan Calendar is just a very long calendar. It does NOT predict the end of the world. It just so happens that the Mayan version of "December 31, 1999" falls on what we would call "December 21, 2012." The Mayan calendar contains events that happen AFTER 2012, even after 4000 AD, so clearly the world will not "end" at this point.
(You'll remember that a lot of people also thought the world was going to end in 12-31-1999, but it didn't. Same deal. Many programmers expected a huge mess, but fortunately with a lot of hard work that didn't happen either, but nobody who actually knew anything expected the 'collapse of civilization' some nuts predicted.)
All the other predictions:
"pole shifts" (which take thousands of years to even start)
"galactic plane crossing" (a lie, we're far above the galactic plane and moving away from it)
"galactic alignment" (We don't even know exactly where the galaxy's center is - it's obscured by gas and dust and other stars - so we sure as hell can't predict an alignment with it with any accuracy)
"killer planet Nibiru" (physically impossible)
"antichrist" (no such animal. Christ's Apostles thought THEY were living in the 'end times,' too)
and everything else, are completely and totally made-up.
There are NO scientists who believe in this 2012 nonsense. If you see someone claiming "scientists" said so, ask for names and degrees, because they either don't exist, or got their "degree" from some mail-in fake "university of pulp paper." Degrees in theology don't count.
Here is one thing about 2012 that might actually be true... this answer will probably be thumbs-downed by wackjobs who are obsessed with 2012.