What could cause a predictable apocalypse? [closed]

Question

A common theme among many of earth's cultures is a belief in an apocalypse. In general, these beliefs take the form of predictions that a certain sequence of events will happen at a certain time, usually finishing with some sort of rapture or rebirth of the world. Apocalyptic events, such as volcanoes, tsunamis, and asteroid impacts, most definitely do happen. They're also predictable, but often only in the few minutes/seconds you have to watch a giant fireball plummet through the sky before it vaporizes you. Plenty of time to wonder, "Is this Odin's way of saying I shouldn't have eaten the last cookie," but not enough time to write down the great prophecy of the last cookie in a book and tell all of your friends.

I want my people to be able to predict their demise. Not merely a prediction of 'Some time in the next 800 years a major earthquake will wreck San Francisco,' but a full fledged set of prophecies describing where and when what will happen leading up to the inevitable end. What sort of an apocalypse could feasibly happen and be predictable enough to create accurate prophecy around?

Answer 1

Two ideas: asteroid collision and solar system/galaxy collision.

Asteroids

It's entirely plausible that we could know about an asteroid collision years in advance. If there was an asteroid on an orbit that came closer and closer to Earth every 100 years, it wouldn't be too hard to figure out that after another, say, 5 orbits it's going to run into Earth. That gives you 500 years advance warning of an asteroid impact. Once people have figured that out, it won't be long at all before they've spent enough time to figure out all the effects that impact will have.

Solar system and/or galaxy collision

We know that galaxies collide. The Andromeda galaxy is going to collide with the Milky Way in around 4 billion years. If we could tell that a red giant was on a collision course with our solar system it wouldn't be too hard to plot its trajectory and figure out what would happen to our solar system and the Earth in particular. This is something that would would be able to see coming for centuries, if not millenia.

Answer 2

There are a number of things.

Things you mentioned: Volcanoes - It may not currently be within our capabilities to predict volcanic eruptions with any degree of real certainty, but in principle with advances of predictive models and technology it could be possible to predict these with great accuracy. But if you want it down to the day or second, that might not be possible.

Asteroids - You discount these, but it's already possible for us to spot an asteroid and extrapolate its trajectory for dozens of years into the future. In fact, we've already found, extrapolated, and cataloged thousands of Near Earth Objects that live in the neighborhood of Earth's orbit. And while none of the one's we've found are likely to hit us, it's entirely possible we find a new one tomorrow that has a 99.99% chance of hitting us on a particular day dozens of years in the future.

Other celestial bodies:

Rogue Planets and Comets - Either of these could be theoretically detected and predicted to hit earth up to a few hundred years out with pretty good certainty. We could spot one incoming that doesn't hit us on this orbit but extrapolating we find that the next time around (perhaps in a few hundred or even a couple thousand years) will likely impact Earth, again we could have this prediction down to within a few days.

Stars - If there was a star on course to hit Earth, we could potentially see this coming millions of years in advance. Millions of years out it would probably be narrowed down to only within a few dozen or hundred years, but as it got closer, the predictions could be refined. And by the time it was only a few hundred years away, it would appear as though we had a dimmer second sun and the prediction would be narrowed down to the day.

Our Sun - We already know that our star is going to grow and consume the Earth in roughly 5 billion years. However, all people living on Earth will likely be killed long before that. Long before that, the atmosphere and all of the water on the planet will have blown away from the Earth by the solar wind, and the planet will become baked like Mercury. Long before that temperature increases will lead to mass famine. It won't be fast. It won't be all at once. But it is predictable and certain.

The Heat Death of the Universe - Eventually all stars will go out, everything will spread out away from everything else, and the universe will become a scattering of distant lonely particles separated from each other at thermal equilibrium. It will take trillions of years. And it won't happen all at once, but according to our current understanding of physics, it is inevitable.

Answer 3

Fimbulvinter followed by Ragnarök

As global climate change progresses, our temperature models get more and more accurate, allowing scientists to predict the tipping point with high accuracy.
Fresh water from the polar caps disrupts the ocean currents, causing massive amounts of flooding, and causing warm water currents from the equator to stop flowing toward the far norther/southern hemispheres.
Water also has a higher albedo than land, and since more of the surface is water, more sunlight is reflected away.
Between these two there is massive cooling, and before things can correct naturally an ice age begins. Glaciers form over much of the northern and southern hemispheres, merging with the expanding polar caps and reflecting even more solar insolation. Any population that can migrates toward the equator, but between the flooding and the cold casualties are in the billions.

There are several years without summer, as things get colder and colder.
The glaciers get as far south as Nevada in the United States, and the ice over Yellowstone National Park in Wyoming is about a half mile thick. All that weight causes a lot of pressure on the fault there, which causes the supervolcano in the Yellowstone Caldera to finally erupt, sending ash and soot around the globe, along with a massive amount of CO2 into the atmosphere.
Between the soot covered snow reflecting less sunlight and the greenhouse gasses in the atmosphere, the earth begins to warm and the glaciers retreat.

Slowly the environment begins to correct itself, and the ice to recedes faster.
The survivors slowly migrate back out from the equator, finding scattered settlements where people were able to tough it out on the ice.

Answer 4

I'm definitely going to go with Asteroid/Planetoid Impacts. We have the technology in this day and age to calculate the orbital rotations of a variety of identified objects, tens or hundreds of years in the future, with potential collisions often narrowed down to the specific date.

Melancholia was a pretty good recent film involving such a scenario.