To hear science fiction tell it, all human life or even the planet Earth itself can be destroyed a dozen times over before breakfast. Apocalyptic events have long been a favorite topic for sci-fi writers, and, indeed, some consider the Book of Revelation and other works of religion and myth early speculative fiction. Still, some armageddons are more plausible than others. On one end of the scale, it’s unlikely that we’ll be visited by a warrior culture of extraterrestrials with faster-than-light drives and other unsurpassable technology (no Vogon highway projects or Death Star superlasers to worry about), or that any virus could reanimate living tissue, the recent popularity of zombies notwithstanding. On the other, there are also a fistful of doomsday scenarios that have at least some sound scientific basis. Here are five apocalypses we just might have cause to worry about:
The Nemesis Hypothesis
What if we could never see the end of the world coming but it was literally right out of the corner of our eye this whole time? That is, essentially, the logic of the Nemesis hypothesis, which states a very small star, possibly a red dwarf, is orbiting the sun just beyond the Oort cloud a light year and a half away from Earth. Most of the time, Nemesis is undetectable because it’s, well, directly on the opposite side of the Sun. But occasionally, the star’s orbital period will bring it in sync with Earth’s orbit, and it’ll collide with us, burning the very atmosphere and causing mass extinction. Paleontologists David Raup and Jack Sepkoski came up with the idea in the 1980s to explain the apparent regularity of worldwide extinction-level events, but more recent science has allowed for infrared scans of the Milky Way as far as 10 light years from the sun and found no such star like Nemesis. For all the evidence against it, though, the idea seems to make intuitive sense, and it’s captured a lot of imaginations–British horror writer Ramsey Campbell once wrote a Cthulhu mythos horror story in which Nemesis is actually the god Ghroth, which periodically destroys Earth by awakening ancient evils with its passing.
The latest MacGuffin-du-jour in science fiction is nanomachines. Many a spacefaring hero in books, video games, and films nowadays wears an armored suit with nanotechnology that progressively repairs injuries and enables other amazing feats. We definitely haven’t reached that stage in current nano-development yet, but one of the most exciting concepts in nanotechnology is the potential for self-replication. It’s precisely the fact that nanomachines are so small and can hence theoretically assemble copies of themselves from stray matter they consume that makes the so-called gray goo apocalypse possible. Scientist Eric Drexler coined the term to describe a malfunctioning colony of nanobots that begins to consume all matter and add to the swarm rather than ceasing at a prescribed time, eventually destroying all life in the universe. Such a worst-case scenario requires a lot of things to fall into place, of course–there has to be nanotechnology sophisticated enough to transmute any kind of matter into more nanobots, for one–but however far-fetched, it’s a potent reminder of the dangers of letting technology get out of human control.
It would be a fitting irony if life on Earth were wiped out as a consequence of one of the most seemingly prosaic forces in nature, one that we encounter every day–magnetism. It’s commonly known that the geographic and magnetic north and south poles are not in precisely the same place. This is because the magnetic poles are subject to polar wander, in which the Earth tips along its own spin axis but its core does not, bringing the two slightly out of alignment. Polar wander is a very gradual occurrence and on its own is not known to cause catastrophes, but a complete and sudden geomagnetic reversal would be a different story. The geologic record shows that the poles have swapped in the past, as the magnetic field warps ferromagnetic minerals in a particular way. No complete polar shift has happened in human history, and coinciding events in prehistory can only be seen as correlated to, not caused by, the polar anomalies. Thus, there are a variety of theories on the damage a polar reversal could cause, some more plausible than others. If the Earth’s magnetic field is completely disrupted, which may happen, the momentary disappearance of the magnetosphere might be enough time for the planet to be bombarded with the intense infrared and ultraviolet rays of solar wind, causing climactic disaster. Less founded in fact is the idea that polar shifts are linked to massive tectonic and volcanic activity, and the supposed lost continent of Atlantis was sunk deep beneath the ocean by a polar shift-related earthquake.
The beloved French science fiction author Jules Verne is responsible for inspiring a number of contributions to real science, and has the honor of having a catastrophic type of theoretical volcanic eruption named after him. Mass extinction events that coincide in rock strata with flood basalts and iridium deposits are typically chalked up to asteroid impacts, such as the famous Chicxulub meteor that likely finished off the dinosaurs. However, an alternative explanation is one hundred percent terrestrial: A verneshot is a volcanic eruption caused by superheated gas building up in the interior of a tectonic plate. The resulting blast could launch parts of the crust and mantle into a low-Earth orbit, like the ballistic orbital launch that Verne described in From Earth to the Moon. The rock column would fall back to Earth, resulting in a similar impact to a large meteor and all of the attending floods and atmospheric debris coverage.
Anyone with a rudimentary knowledge of astronomy knows that a supernova represents a colossal release of energy. When a dying star goes supernova, its entire mass is blasted out at ten percent of the speed of light, briefly appearing as brighter than entire galaxies in the night sky. A hypernova is the one kind of astronomical event that’s more energetic than that. Unlike many of the other entries on this list, hypernovae are observable rather than just theoretical, and they are one of the causes of gamma-ray bursts in outer space. The radiation from a single gamma-ray burst from a nearby-enough source would be enough to penetrate every layer of the atmosphere and kill everything living on Earth. The key words here are “nearby-enough;” there is no known star large enough to even produce a hypernova within the Earth’s galactic neighborhood–yet.