-Under Construction-The Apocalypse is the end of the world itself, as predicted by various respectable religions, fully provable science, and also some complete crackpots who heard it from the little radio in their head.
Religions may have figured it out first, but modern science does not deny that the universe itself, as we know it, is finite.
On a large, large scale, entropy itself is slowly dissipating the existing energy in the universe. The best physicists seem to agree that this process is inevitable. Not only are we all going to die...everything is going to die.
Technically speaking, you don't have to worry too much about the universe being expended though. You'll be dead way before that. Even if you could be cryogenically frozen today, you'll STILL be dead before the universe is.
The problem for us on this planet is that the sun itself will eventually have burned up all of it's gases. When it goes dark, it maybe collapses or something. Who cares at that point? If the sun goes dark, every living plant, animal, and human will be dead.
All life on planet Earth extinguished? As far as we are concerned, that pretty much qualifies as an Apocalypse.
So, what can you do to prevent this from happening?
Not unless you are an astrophysicist who has quietly been advancing the field by a few hundred years. Right now, not a damn thing we know of will keep the sun going, and srewing with it is probably a bad idea (ie, more likely to speed up a disaster than slow one down). It won't go out for hundreds of thousands of years anyway, so try not to worry about it too much. If people are ever going to find any solution to this one, they do have time to figure it out.
Most people expect that humanity will actually leave the Earth long before this happens, so it may ultimately not be an issue for the species directly. Still, the fact is that life on earth seems to be a strictly finite phenomenon, and indeed there can one day come a "final day" for all living things here.
Do you like horror stories?
Whether you want to believe in this one or not, there is no denying that it fucking owns. Starting from the first couple of signs of disaster, there is more terrifying stuff written here than in the entire careers of Stephen King and Clive Barker put together.
Christianity wasn't the first religion to talk about the end of the world, but they hit the ground running with it, and gave it some highly interesting details. "Revelation", the entire last book of the bible, is devoted completely to explaining what happens when our age comes to a close.
As with many other Apocalypses, the final war between good and evil figures highly in the story.
No one seems to be enjoying it very much, but it's probably too late to complain...
The Norse version of the end of the world is just as badass as the Christian one, except it's even more metal.
This one has gods, vikings, giants, dwarves, wolves, and a big fucking serpent...which makes it the equivalent of 3 Narnias.
First they gave it the most hardcore sounding name they could come up with: "Ragnarök". It means "final destiny of the gods", so you can see the justifiable need to throw a metal umlaut in there.
OH SHIT!!! THERE ARE ONLY TWO YEARS LEFT UNTIL 2012!!!
WHAT ARE YOU GOING TO DO???
Just...buy a new calendar. The Mayans didn't actually think the world was going to stop existing at all. This whole 2012 business is more like the Y2K bug; just a hardware limitation that someone could have worked around.
Their current calendar only went as far as 2012, but the Mayans themselves were wiped out before that date even got close. Otherwise, someone there would no doubt be carving a new disk-shaped calendar, which would start in the year 2013. Then someone on the internet could start shitting a brick about how that one also seems to end.
The Aztecs, on the other hand, believed that when the sun went out, everyone would die. Maybe it was a lucky guess. Maybe they were just really smart.
They did claim that there would be a succession of five suns though. Each one would light to replace the old one, and each have a new Earth to shine on. Once the fifth sun goes out though, there won't be any more, and the planet will rip itself apart in the biggest earthquake ever.
Whatever. You're going to be freezing to death by that point, so what do you care?
The ancient Egyptians invented a lot of things, and certainly some of Judaism, Christian, and Muslim beliefs were drawn from the ancient Kemet beliefs. However, they had no single definitive end of the world scenario.
Instead, they believe that the gods and goddesses of balance and nature were in an ongoing struggle to stop the forces of chaos and corruption from destroying everything. So instead of a single war of good vs evil, they had many conflicts between balance and chaos. Balance was known as "Ma'at" and chaos was known as "Isfet". They didn't translate into exact western ethical ideas though. For example, the god of night, Set, was quite evil and vicious; yet he was still considered one of the "good guys" in some way, because he stood with the others in protecting the land and sky. It seemed not to matter that he battled with the more clearly good gods. He was just a family member they didn't get along with, but still part of the family.
In terms of the most fierce battles between balance and chaos, the Egyptians believed that every night the sun would have to be safely piloted across the dark part of the sky so it could return. In their minds, it was a giant boat, and therefore had to be sailed through the sky. The problem was that chaos would send out it's forces to try to destroy it before it's journey could be completed. One of the principal assailants was Apep, a ferocious serpent born of chaos itself.
According to Hindu beliefs, we are now living in the 4th and final era of our planet's current age. When this one ends, there's going to be a big sweeping change. The god Vishnu will then take on his 10th incarnation, Kalki.
Basically, Kalki is like a Hindu superhero who uses his mighty powers to defeat all of the forces of evil and wickedness. After everything is pretty well wrecked, Kalki will start to drop science and reveal mind-blowing truths and philosophies which answer everything and make everyone enlightened. Yay!
This is the Goddess Kali. She's scary, but not a demon.
Finally, Kalki will go to fight and slay Kali, a huge demon. This isn't the same Kali who has all the arms though. That is a Goddess, and this Kali is a nasty monster who just happens to have the same name. So, Kalki will kill Kali, finally turn back into Vishnu, and return to heaven. The end.
And then the next age will begin!
In fact, the earth and the universe will just keep rebooting every time they are finished! This has to be the most awesome kind of Apocalypse, because no matter how bad it gets, nothing is really over. There were other people before us, and there will be other after us. It's never done; always in motion.
So...let's just end this on a happy note.