Here's a rundown of the seven most likely ways our world could crumble right on schedule.
What did for the dinosaurs could do for us, too. Objects fall to Earth from space every day, but most of them are small enough to burn up on entry to the atmosphere or fall where nobody is around to notice. An asteroid big enough to wipe out civilization on Earth, experts agree, would need to be at least a mile across—and that kind of impact only happens once every 10 million years or less.
For what it's worth, it's thought the dinosaurs were wiped out by an asteroid six miles across. On the off-chance that NASA's failed to spot a rock that size hurtling towards the planet, physcists have worked out that it would be impossible to nuke an Earth-killing asteroid—so it really would be curtains.
People seem to have forgotten about the nuclear threat since the end of the Cold War—but the risk remains. In 2008, Physics Today published an article that explained the consequences of nuclear war. It concluded that 100 nuclear bombs would bring about a "nuclear winter" featuring the lowest temperatures in 1,000 years, while 1,000 of things would "likely eliminate the majority of the human population."
Now might be good time to point out that more countries than ever have nuclear weapons at their disposal: currently, nine countries are known to have nuclear capabilities, but only five of them are members of the safeguarding Nuclear Non-Proliferation Treaty. With North Korea throwing rockets into the air like confetti, the nuclear threat is as present as ever.
If you thought the 2010 eruptions of Eyjafjallajökull in Iceland caused problems, think again. Over two million years ago, a massive volcanic eruption—which happened where Yellowstone National Park now stands—produced 600 cubic miles of dust and ash. For some perspective, that's 10,000 times worse than Eyjafjallajökull. All it would take to bring the planet to its knees would be a couple of such eruptions in close succession. And the next Yellowstone super eruption is closer than you think.
It might sound like something straight outta Hollywood, but biological warfare poses a very real and dangerous threat. Anthrax may have been wildly hyped in the past, but in reality it remains an effective means of taking out large swathes of the population. Weaponized in the form of aerosol particles of 1.5 to 5 microns, it could cause fatalities in 90 percent of the population. Things don't stop at toxins like anthrax, either; bear in mind that—even though it might take more than a day—an engineered avian flu could kill half the world's humans. A cursory glance at a list of—officially recognised—institutions involved in biological warfare research suggests that this is something that we should definitely be worried about.
Solar storms happen all the time: the sun sends wave upon wave of charged particles through space, and they whizz through our atmosphere at 4 million mph. Large storms result in particularly amazing light shows, comparable to the Northern lights. However, the Earth hasn't experienced a major solar storm since 1859. Then, the storm was intense enough to instantaneously set fire to telegraph lines—but that was before the days of the electricity grid, power in homes and the slew of technology that we all depend on each and every day. These days, a storm like that—or worse—could wreak untold havoc.
Ever since the first atomic bomb was developed back in 1945, scientists have wondered whether the raw power of some of the reactions they set in motion could end up causing catastrophic problems. The worry hasn't faded. When Brookhaven National Laboratory prepared to fire up its Relativistic Heavy Ion Collider, speculation circulated that the experiments at the facility could create a black hole which would then consume Earth. When the LHC was first switched on, the same rumors resurfaced. Many physicists dismiss the threat offhand—but nobody's really, really sure that it couldn't happen.
Perhaps the most creative explanation of how the world could end tomorrow is that we might just be living in a gigantic computer simulation that happens to get switched off. It might sound ridiculous, but scientists still haven't settled, once and for all, whether we're living a life made of code. Sure, people have recently suggested how we could tell if everything around is happening on a sliver of silicon in a giant server room in the sky—but nobody's yet tested the theory. Let's hope nobody hits ESC.