Editing Post-Apocalyptic (section)

===Cosmological events===
These are the more scientific version of The End Times since they are just as final to us if they hit - and one WILL happen eventually IRL due to the laws of physics. [[Grimdark|The Universe is a scary place, and not even it will be around forever]].

Subclasses include:
====Planet killers====
Humanity may survive on another world in the Solar System and/or beyond, but Earth is gone - either wiped sterile or no longer on the map at all.
*Gamma-Ray Bursts (GRBs) - basically, if a big star that's close enough dies when its magnetic poles are facing us, the resulting jet of radiation will destroy the Earth's ozone layer, making the Sun [[Meme|a deadly lazer]] once more. While it's possible to survive, given that one major extinction in Earth's past might have been caused by a weaker one, it's more likely to cook everything alive - either directly or indirectly depending on the distance.
*Solar luminosity - due to the way stars function, they get brighter and hotter as they get older. The Sun is no exception, and this is not a good thing. Eventually, in about 1 billion years or so, the Sun will be outputting too much energy for life on Earth to be viable anymore. While inevitable, we (or whatever comes after us) has a LONG time to prepare for the Great Exodus.
*Planetary collision - While ''extremely'' unlikely in the current state of the Solar System, it's still a possibility, and one scary enough for conspiracy theorists to fearmonger using. Any rocky body large enough for gravity to make spherical - be it a very large asteroid or comet, a moon, or another planet - ''will'' revert the Earth to a state similar to how it was when it formed if it smacks into it, or outright destroy it if massive enough. Usually the other planet won't fare much better, unless it's a gas giant that eats rocky planets for breakfast. The suspect to watch out for is rogue planets, though given enough time Mercury might become suicidal.
*Eaten by the Sun - either due to some freak gravitational disturbance or the Sun inevitably becoming a red giant (see 'death of the Sun'), there's a chance that the Sun will do what the Tyranids can't due to plot reasons and eat the Earth, melting it into a glob of plasma. It's iffy in the latter case since the Sun maxes out in size around the time it would eat Earth, becoming too big to hold onto all its gas. Not that it matters, as solar luminosity would have made it an unimportant magma ball by that time anyway.
*Yeeted into space - Gravitational disturbances - whether one big one or a series of smaller ones - could fling Earth out of its orbit and into interstellar space, likely killing all life since the big light in the sky is gone.
*Eaten by a black hole - if a black hole is big enough to start chowing down before it blows up due to Hawking radiation, but small enough not to throw a star system's gravity out of whack, it can easily replace the Earth with a black sphere of inescapable gravity.
====Star system killers====
For these, humanity has to have gone interstellar if it has any hope of not going extinct.
*Death of the Sun - Sun runs out of fuel and turns into a sad white ball unable to warm up anything, possibly eating the Earth in the process. Enough said.
*Supernova - Sure, the system it's in is going to be feeling most of the pain, but a close enough supernova doesn't even need to have its GRBs aimed at you to kill - the weaker radiation in all directions can do that too. Granted, it has to be VERY close for that to even be a threat, though candidates for such an event exist. You have even shittier luck if you're caught in a hypernova, which spreads radiation a fair bit farther. 
:*Gamma Ray Burst [[Meme|2: Electric Boogaloo]] - Speaking of GRBs, at certain distances one could wash over the entire solar system but still be lethal. More likely than a direct hit as described in the Planet Killer section, too, though technically weaker since they're less focused at the required distances. 
*Stellar collision - basically the only way the Sun can go boom like a supernova. White dwarf, main sequence, whatever - if it's big enough, a game of galaxy billiards can go horribly wrong. The chance it does is extremely low due to the distances involved, but it does happen - especially in denser regions of space.
*Black hole buffet - Large enough black hole to disrupt orbits? The entire system is either becoming a snack or getting torn apart, with nothing in between.

====The Big Ones====
No escape. No respite. Not even immortal beings can survive these. Worst of all, a few are inevitable, and the universe will never be the same. The existential dread is natural, but luckily most of these final doomsdays are so far off or so unlikely that humanity will likely have lived out its existence long beforehand. If not, we'd probably be so far along that we could just jump ship into another universe, either a natural one in a multiverse or an artificially created one. But adding 'post-' to these apocalypses is not really possible.
*Stellar decay - by the appropriately named "degenerate era", stars capable of supporting life will have burned out due to a lack of fuel, and no more will be made (if the universe is infinite, there may be infinite material for star formation but there's also an infinite amount of stars to use it up). Life developing as it did on Earth will be impossible, and unless humanity or some other advanced species has the means to keep the torch lit, life will cease to exist.
*Proton decay - unproven, but if it exists, there's a lifespan to solid matter that isn't part of a black hole. This would be a hard limit on life's possible existence with or without human intervention. If not, humanity may survive by leeching energy off black holes until the universe itself ends.
*Death of the universe - whether it crumples back into a point, rips itself apart, or becomes an empty, cold wasteland of nothingness, the universe WILL die, and there's nothing you can do about it. On obscene timescales even black holes disappear, which is the hardest of hard limits on existence. Past this point, time becomes meaningless, unless by some miracle an anomaly causes another Big Bang.
*Vacuum decay - helpfully described as "the universe's delete button" by a certain German duck, this is essentially what could happen if some of the universe suddenly received an update to its physics engine. Long story short, a sphere of nothingness expands at the speed of light, destroying everything and leaving behind a portion of spacetime where our laws of physics no longer apply. Given enough time, probability will spawn enough of these to clean up whatever remains of the universe after its death.
*The Off Switch - an ever-present threat if the simulation argument is true is that whoever made the simulation could get bored and just turn the 'game' off forever, or some accident happens in the real world that shuts it down. Temporarily turning it off isn't really a threat, for in all likelihood it would just resume where it left off, and we would be none the wiser. A meta version of post-apocalyptic fiction could be following the creators of a simulation after turning it off permanently, and how said simulation affected their society.

====Examples====
*[[Xeelee Sequence]] (Death of the universe)