The doomsday theory sprung from a Western idea, not a Mayan one. Mayans insisted that the world would not end in 2012. The Mayans had a talent for astronomy, and enthusiasts found a series of astronomical alignments they said coincided in 2012. Once every 640,000 years, the sun lines up with the center of the Milky Way galaxy on the winter solstice, the sun's lowest point in the horizon. The last time that happened was on December 21, 2012, the same day the Mayan calender expired. The modern doomsday myth was bolstered by several ostensibly scientific reasons for a disaster, including a pole shift, the "return" of Planet X or the Sun's sinister counterpart Nemesis, a galactic, planetary, or other celestial alignment, global warming, global cooling, a massive solar flare, or a new ice age. None had any basis in respected science. For example, the "galactic alignment" between the sun, Earth, and galactic center happens every December. The best alignment was reached in the 1990s, and was accompanied by its own set of doomsday theories. Alignments since then have been increasingly poor.
When Jackson goes to pick up the Russian oligarch's boys, the mansion he drives up to is the lavish Fleur de Lys estate in the Bel Air / Beverly Hills area. At $125 million, it was one of the most expensive real estate listings in the country .
Charlie Frost's animation about the end of the world heavily references the animated Internet meme, "The End of the World", which centers around the idea that humanity will kill itself as a whole before any natural disaster would ever have the time to destroy it.
Director Roland Emmerich wanted to show the destruction of the Kaaba in Mecca. Producer and co-writer Harald Kloser opposed the idea. He later stated he did not want radical Muslims to issue a fatwa against him.
The title refers to the end-date of the 13th b'ak'tun of the Long Count calendar, used by the Mayan Meso-American civilization. In their creation myth, we live in the fourth "attempt" at creating the world, while the third attempt was dismissed as a failure after its own 13th b'ak'tun. Though Mayan documents contain no such information, a popular myth stated that the calendar "ended" on that date, and certain religions predicted an apocalyptic event on that date. The Long Count calendar can express dates from about 3000 BC (their date for the creation of the world) to about 40 octillion years in the future. It's almost impossible to express that date in a mortally comprehensible fashion.
Dr. Charles Hapgood, spoken about in Charlie Frost's video, died on December 21, 1982. Despite what is said in the film, Hapgood is something of a fringe figure, and his views have been denounced as pseudoscience by his detractors.
In an interview by USA Today, Roland Emmerich said that this will be his final disaster film: "I said to myself that I'll do one more disaster movie, but it has to end all disaster movies. So I packed everything in." He ended up doing several more, including a sequel to Independence Day scheduled for release in summer 2016.
The trivia items below may give away important plot points.
The film contains various references to the Biblical flood. For example, Jackson's son is named Noah, the cruise ship where Adrian's father Harry performs is called Genesis (the book in the Bible in which the account appears), and humanity is saved by the use of "arks". At one point animals are lifted aboard the arks.
During the destruction of Los Angeles, Gordon's Porsche Cayman falls into the Earth after getting pushed by Jackson's limo upon fleeing from the Curtis residence. This foreshadows Gordon's own death, as he falls into the gears later in the film.
During the destruction of the Sistine Chapel, the cracks forming on the roof directly between God and Adam in the Creation of Adam symbolize two aspects related to the Bible: the transition between the first and second circles of life (specifically, breaking the connection between humans and God), and God's reversal of creation of humanity in Genesis 6-9.