List of Ends of the World

The following is a non-comprehensive list of purported “End of the World” scenarios, in which the arrival of the final moments of mankind, consciousness, the universe, and/or reality will arrive in a specific manner at some point in the future (or have already arrived at some point in the past!). The End of the World, such as it is, is the centerpiece of study of eschatology and the crux of several belief systems, both theological and otherwise. For reasons not fully elucidated (perhaps yet another Shii tradition), it's also a topic explored by a handful of personal wikis.

Origin: Extraterrestrial.

Description: Gamma-ray Bursts are the result of very energetic explosions coming from either the collapse of a nova into a neutron star or black hole, or during the merge of binary stars. The massive release of energy is released in a “flash” of Gamma rays, usually tightly packed in a laser-like pulse (collimated within a cone of usually no more than 2º wide) originating from both poles of the stellar object in question.

If one of these explosions were to take place close enough to Earth (5-8 kilolight-years) and aligned in such a way that the gamma-ray beam impacts the Earth full-on, it could cause cataclysmic effects on the ecosystem: while the gamma-ray burst itself wouldn't probably cause much immediate damage (only a temporary increase in ultraviolet radiation), its effects on the atmosphere include the ionization of Nitrogen and Oxygen, causing ozone depletion (increasing for several years the influx of solar-based UV radiation) and the generation of Nitrogen oxides (NO, NO2) which may block out sunlight and cause a sort of cosmic winter with various detrimental effects to the global biosphere. These nitrogen oxides are eventually purged from the atmosphere in the form of Nitric acid, precipitated in global acid rains¹⁾.

While no climate model of the ozone and sunlight reduction has been developed at the time of this writing, it is quite possible for it to not only cause a mass extinction event, but also alter the biosphere in more subtle ways such as the destruction of worldwide crops leading to a global civilization collapse. After a Gamma-ray burst, more long-lasting exposure to radiation in other areas of the electromagnetic spectrum can reach the Earth as well, worsening the preexisting conditions over time.

It's theorized that a GRB was the leading cause in at least one major extinction event 450 million years ago, as it seems that the marine animals closer to the bottom of the ocean (i.e., farther from UV radiation exposure) seemed to have fared better than its more surface-level counterparts.

Estimated date: Unknown. Statistically calculated to take place every 5 million years, but doesn't account for the probability of GRBs with high enough energy to cause the world to end.

Early warning signs: None. As gamma rays travel at the speed of light, its arrival would come at the same moment it's observed.

Likelihood: Negligible. GRBs in the Milky Way can take place anywhere between once every 10,000 to 1,000,000 years. Then, it has to be within at least 8000 light years to cause any discernible effect. And then, the Earth has to be precisely aligned with the source's pole so as to fall within the extremely tight 2º cone. Sure, it probably happened before, but I wouldn't bet on it.

Origin: Extraterrestrial.

Description: Including famous examples such as asteroids or comets, a Near-Earth Object (NEO) is any small celestial object that passes through the solar system sufficiently near the Earth's orbit. Some of these, whether by orbital intersection of Earth's gravitational influence over the NEO, may cause the latter to collide against the former. This happens often for NEOs of negligible size, which is usually enough for the atmosphere's friction to cause them to burn up. However, a NEO that is sufficiently large and/or travels at sufficiently large speed may have enough kinetic energy to survive atmospheric entry and collide against the Earth.

While it may also be influenced by other factors (such as where precisely does the NEO impact, such as an ocean impact and a subsequent tsunami), the severity of the damage caused by the collission will be a result of its kinetic energy, i.e. size (mass) and speed. With most solar system asteroids stemming from the Kuiper belt which has an average speed of, give or take, 20km/s, an iron asteroid 100m in length is enough to vaporize most of Paris, a 500m one is enough to devastate a continent, and 1000-5000m asteroids are thus more than enough to cause sufficient environmental damage to significantly threaten human life on Earth. Anything beyond the 5000m mark may just be enough to provoke swift and near total extinction of life on Earth.

Estimated date: Within 100-200k years. Impacts with localized destruction happen roughly once every a few thousand years, impacts with regional destruction and widespread social-biological effects are expected to occur every twenty or thirty thousand years. Finally, impacts with prompt terminal effects against (human) life on Earth happen, give or take, every hundred thousand years.

Early warning signs: Space agencies around the world have been tracking NEOs for a few decades, and as NEO surveys continue to be more detailed and comprehensive, it's expected that an eventual collision will be calculated within a timeframe of decades²⁾. This provides a significant window of opportunity to come up with and execute countermeasures to avoid asteroid impact, given that NASA predicts that planning, preparation and execution of an asteroid avoidance mission³⁾ would take roughly five years. However, some objects such as ice comets or other NEOs that may be coming in too fast or at too eccentric an angle, may approach Earth undetected⁴⁾ and significantly shorten this 25 year window.

Likelihood: Eventually certain, but all signs point to humanity having sufficiently advanced technology to be able to avoid or at least mitigate catastrophic damage by the time one occurs.

Origin: Terrestrial

Description: While statistically random, the Earth's magnetic poles flip every 450000 years or so, with a period of roughly 6 to 7 thousand years to complete the flip. While it's expected that this happens spontaneously by the chaotic convective patterns of the planet's core, it may also be that the flip can be triggered by external factors such as asteroid impacts.

It's not precisely known what the relationship between the reversal of Earth's poles and extinction level events may be, it's believed that the flip may weaken the magnetic field enough for high-energy particles to hit the Earth, causing radiation buildup. If the magnetic field were to disappear completely, merely the solar winds may be enough to cause irreparable damage to the biosphere. An association between pole reversal and increased volcanic activity is currently hypothesized.

Estimated date: Within the next 500k years.

Early warning signs: None at first glance, but the event itself takes several millennia to actually take place.

Likelihood: Certain, but of unknown repercussions. It's very hard to set up a proper correlation between geomagnetic reversals and end-of-the-world scenarios⁵⁾, therefore any link between one and the other are ultimately tenuous. The long period of time for the flip to occur may just offer mankind several generations to come up with a good mitigation strategy in case it indeed facilitates a mass extinction event.

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