So none of you think that there is possibly a red-dwarf star? And that the star is on an oval orbit that brings it within range to screw with the earths gravitation every 5000 years or so. And by doing that it sets off earthquakes, floods, fires, and general catastrophic crap.
It's possible, but one of the things about pseudoscience that pisses me off the most is they glom on to
anything within the scientific realm that even vaguely supports their bullshit, and claim it as evidence, even if there's a mountain of contradictory evidence or logical flaws in the idea.
From that article you linked, it sounds like the best scientific evidence is that there
may be something or other beyond the Kuiper Belt, but there's no hard evidence that it exists, or of what it might be, or what its orbital path is. And they suggest that if it exists, it may help explain periodic extinctions on Earth, but not every 5,000 years - every 25 million. And they don't suggest it'd directly affect Earth, just disturb the Kuiper Belt enough to send an abnormal number of comets hurtling towards the Sun.
Suppose we assume there's something else with a 5,000 year orbital period. For the Mayans to have known that period in order to base their calendar around it, they would have had to witness at least two of its approaches, each one 5,000 years apart, and record the date of each, with enough accuracy to predict the exact date of the next one.
Then, you run into the problem that if this pile of bad shit happens exactly every 5,125 years, there should be cave paintings or some other artifacts somewhere else in the world depicting it too, which could be carbon dated to show that it coincides with the Mayan calendar.
There's also the fact that for this hypothetical comet or asteroid or whatever to be able to affect the Earth just by passing us, it'd need to be pretty goddamn big. Many times the size of the moon, because for a predictable 5,000 year cycle it would need to be able to wreak havoc on the Earth from farther away than the moon is (otherwise for most of its approaches it would harmlessly pass us). Something with that much gravitional pull would also fuck with all the other bodies in the solar system it passed, not just Earth. If it did this every 5,000 years, it would leave noticable orbital irregularities, like with our moon, or Mars' two peanuts, Phobos and Deimos.
tl;dr - Every last bit of this 2012 crap is 200 proof pseudoscientific bullshit.