The Mayan calendar:

The Long Count Calendar was used by the Mayans as a regular calendar, but it also extended many hundreds of years into the future. The calendar ends after 13 b’ak’tuns (about 5200 years), which would be on Friday, Dec. 21. Many people think that the world will end on this day due to the “world ages” myth. According to this legend, the world has ended and restarted four times. The last time it did this was supposedly at the end of another 13 b’ak’tun cycle.

There are a number of other theories as to how and why the Long Count Calendar predicts the end of the world. However, there is no evidence that the Mayans thought the world would end on this date.

Nuclear war:

Another theory for the end of the world is a nuclear war that would likely obliterate everything, making the Earth uninhabitable. Some people fear that, due to rising tensions around the world, a war of this type will be happening soon.

While wide-scale war is a legitimate concern, it is unlikely that nuclear weapons will be used to fight it. These weapons are designed simply for destruction and aren’t really practical in any sort of extended warfare. Also, there have been strict bans on the production and stockpiling of nuclear weaponry since 1963. The countries that have been most vocal about threatening nuclear warfare are also the countries with the least amount of nuclear weapons, so their threats aren’t too serious.

 Electromagnetic shift:

This theory claims that the Earth’s north and south magnetic poles will suddenly switch places. On it’s own, this wouldn’t be too terrible, but believers of this theory proclaim that this switch will coincide with a series of strong solar flares. These two things combined would crash satellites around Earth and expose the surface to harmful radiation.

Although this one sounds scary, it’s really not. The north and south poles can and do switch places, due to the shifting of the Earth’s core. However, this process takes thousands of years and doesn’t weaken the magnetic field in any way. Also, solar flares happen all the time and most of them aren’t harmful because of the magnetic field.