LOS ANGELES — There are years that are remembered for changing the course of human history: 1492. 1776. 1945.Then there are years that were predicted to change the course of history. 1844, when Judgment Day didn’t materialize. 1910, when Halley’s Comet didn’t wipe out humanity. And remember Y2K?But rarely does a year arrive with such a mixture of anticipation and dread as 2012.We speak not of the presidential campaign but of the Maya calendar, and the projection that it — or, more accurately, a cycle within it — will end on Dec. 21, 2012. That date has kicked up a swirl of anticipation, based on science, pseudoscience, hucksterism and spiritual belief. The idea is that 2012 will be a game-changer, the last year of civilization as we know it.The predictions range from the benign — that this will be a year of spiritual breakthrough, the beginning of a new era of nonviolence and sustainability — to the worst sort of disaster movie cataclysm. And the Maya calendar is just the start. A hodgepodge of other theories has sprung up around the same date.There are groups who claim that an uncharted, unseen planet called Nibiru will strike Earth or nearly miss it; that the Earth’s polarity will reverse (so that north is south and south is north), wreaking widespread havoc; or that solar storms will destroy civilization by disrupting power grids. Most of the predictions are timed to coincide with the “end” of the Maya calendar on Dec. 21, the winter solstice.Although scientists and many Maya scholars insist that there is nothing to most of the predictions, the idea of 2012 as a watershed year “has gotten great traction,” said John Hall, a sociologist at the University of California, Davis who specializes in apocalyptic movements. Hall said he expects the frenzy will only grow over the next 12 months.