How the world could end

Later this year the world will come to an end – that is, if you believe what some are saying about an old Mayan calendar. They named 21 December as the day when all hell is due to break loose, in case you'd like to circle it in red. On the other hand, better not blow all your savings on one last outrageous Armageddon party. While it's true there is such a thing as the Mesoamerican Long Count calendar, which clicks over to its next 5,000-and-odd-year cycle this December, there's nothing in the archaeological records to suggest the Mayans linked such an event with anything catastrophic.

The simple fact is we love tales of doom and disaster, especially if we don't have to take them too seriously, for the same reason we enjoy scary movies: they help us escape for a while from the daily routine. Remember Elenin? Last year, if you bought into the rumours, a comet as big as a planet was going to crash into us or pass so close that it would cause mayhem. The whole saga kicked off when some folk mistook the size of the comet's coma – the big, bright, but almost vacuum-thin fuzzy glow around Elenin – for that of the rock-ice nucleus. In fact, as astronomers knew all along, Elenin had a pretty small nucleus, only a couple of kilometres across, and it was never going to come any closer to us than 90 times the distance of the Moon. So wimpish did it prove in the event that it crumbled apart into dust as it warmed up in the Sun's rays.

People with only a tenuous grasp on science have been inventing end-of-the-world tales for centuries, and it seems we fall for them every time. Occasionally, the consequences can be tragic. Back in 1997, members of the San Diego-based Heaven’s Gate cult were persuaded that a UFO trailing behind comet Hale-Bopp would save their souls from the impending destruction of the world. The daft idea started when amateur astronomer Chuck Shramek mistook a star for what he thought was a “Saturn-like object” following the comet. Internet gossip ballooned the story to ludicrous proportions. There was no UFO (surprise!) and Hale-Bopp never came close to colliding with the Earth. But 39 members of the cult committed suicide in the belief that their souls would be among the few to be rescued.

What gives these crazy notions a bit of traction is that life on our planet really is under permanent threat from destructive forces, both natural and, these days, of our own making. Giant rocks from space do sometimes careen into us. One that struck about 65 million years ago was at least partly to blame for a mass extinction in which all the remaining dinosaurs, and many other groups of animals and plants, were wiped out. As recently as 1908 a mighty explosion in the atmosphere over Siberia flattened hundreds of square kilometres of forest. Had it happened over a major city, the body count doesn't bear thinking about. The intruder was most likely a fragment of a comet or possibly a small asteroid. And there's plenty more where these cosmic missiles came from. Thankfully, astronomers are starting to get a handle on the many thousands of “near-Earth objects” that threaten to use our world as a coconut shy. At least if we have some advance warning about what might be heading our way we might be able to do something about it, either by diverting or destroying the incomer.

Other potential megacatastrophes wouldn't be so easy to stop. How could we possibly put the lid on a super-volcano, for instance? These vast eruptions, which dwarf ordinary volcanoes, pump out so much molten lava and dust that they can blanket most of a continent, making life there almost impossible. The thousand cubic kilometres or more of debris they pump into the atmosphere can trigger deep volcanic winters, lasting years, which seriously inconvenience the entire globe. Maybe the super-volcano that lies dormant beneath Yellowstone National Park won't erupt this year or the next, or in our children's children's lifetimes, but at some point, like other sleeping giants of its kind, it will blow – and the Earth will be changed, not for the better, because of it.

Ice ages, Snowball Earth episodes (when virtually the whole planet becomes frozen over), reversals of the magnetic poles, and nearby exploding stars, are among the other apocalyptic phenomena which have happened in the past and will happen again. None are likely to overwhelm us in the next few centuries or so, but we can't even be sure of that because our knowledge of these events, and our ability to predict them, is so sketchy.

On top of this we now have to worry about a whole slew of disaster scenarios of our own making, even leaving aside the usual suspects of global warming, nuclear warfare, and general vandalism of the Earth's ecosystem. Some of these human-inspired concerns are a bit far-fetched, such as the suggestion that the Large Hadron Collider on the Franco-Swiss border might be able to spawn black holes capable of devouring the Earth or even open up some kind of rift in the fabric of spacetime into which our entire universe could plunge.

Others seem too close to home to shrug off so easily. New technologies are developing at such a pace that we can't be sure of their side-effects. Computers and artificial intelligence could very easily eclipse our biological brains in the decades ahead. And what then? Will we somehow merge with our machine inventions or become subservient to them? Neither option seems very appealing.

Nanotechnology offers the promise of new materials and devices manufactured at the molecular level. But it might also spin out of control, converting everything to a dreaded “grey goo” or, perhaps more realistically, exposing us all to a new breed of insidious toxins.

For much of history, people have speculated, often wildly, about how the world might end. Now we have science – and a new selection of much more realistic catastrophes to choose from.

Megacatastrophes by David Darling and Dirk Schulze-Makuch is published by Oneworld on 1st April.