But it won't be from germ warfare, runaway nanobots, or shifting magnetic poles. A skeptical guide to Doomsday.

By Gregg Easterbrook

Omigod, Earth's core is about to explode, destroying the planet and everything on it! That is, unless a gigantic asteroid strikes first. Or an advanced physics experiment goes haywire, negating space-time in a runaway chain reaction. Or the sun's distant companion star, Nemesis, sends an untimely barrage of comets our way. Or ...

Not long ago, such cosmic thrills, chills, and spills were confined to comic books, sci-fi movies, and the Book of Revelation. Lately, though, they've seeped into a broader arena, filling not only late-night talk radio, where such topics don't seem particularly out of place, but also earnest TV documentaries, slick mass-market magazines, newspapers, and a growing number of purportedly nonfiction books. Everywhere you turn, pundits are predicting biblical-scale disaster. In many scenarios, mankind is the culprit, unleashing atmospheric carbon dioxide, genetically engineered organisms, or runaway nanobots to exact a bitter revenge for scientific meddling. But even if human deployment of technology proves benign, Mother Nature will assert her primacy through virulent pathogens, killer asteroids, marauding comets, exploding supernovas, and other such happenstances of mass destruction.

Fringe thinking? Hardly. Sober PhDs are behind these thoughts. Citing the hazard of genetically engineered viruses, eminent astrophysicist Stephen Hawking has said, "I don't think the human race will survive the next thousand years." Martin Rees, the knighted British astronomer, agrees; he gives us a 50-50 chance. Serious thinkers such as Pulitzer Prize winner Laurie Garrett, author of The Coming Plague, and Bill Joy, who wrote Wired's own 2000 article "Why the Future Doesn't Need Us," warn of techno-calamity. Stephen Petranek, editor in chief of the science monthly Discover, crisscrosses the world lecturing on "15 Major Risks to the World and Life as We Know It." University of Maryland arms-control scholar John Steinbruner is lobbying organizations like the American Association for the Advancement of Science and the World Medical Association to establish an international review board with the power to ban research into the Pandora's box of biomedicine.

If we're talking about doomsday - the end of human civilization - many scenarios simply don't measure up. A single nuclear bomb ignited by terrorists, for example, would be awful beyond words, but life would go on. People and machines might converge in ways that you and I would find ghastly, but from the standpoint of the future, they would probably represent an adaptation. Environmental collapse might make parts of the globe unpleasant, but considering that the biosphere has survived ice ages, it wouldn't be the final curtain. Depression, which has become 10 times more prevalent in Western nations in the postwar era, might grow so widespread that vast numbers of people would refuse to get out of bed, a possibility that Petranek suggested in a doomsday talk at the Technology Entertainment Design conference in 2002. But Marcel Proust, as miserable as he was, wrote Remembrance of Things Past while lying in bed.

Of course, some worries are truly worrisome. Nuclear war might extinguish humanity, or at least bring an end to industrial civilization. The fact that tensions among the US, Russia, and China are low right now is no guarantee they'll remain so. Beyond the superpowers, India and Pakistan have demonstrated nuclear capability; North Korea either has or soon will have it; Japan may go nuclear if North Korea does; Iran and other countries could join the club before long. Radiation-spewing bombs raining from the sky would, no doubt, be cataclysmic. If you're in the mood to keep yourself up at night, nuclear war remains a good subject to ponder. But reversal of the planet's magnetic field?

At a time of global unease, worst-case scenarios have a certain appeal, not unlike reality TV. And it's only natural to focus on danger; if nature hadn't programmed human beings to be wary, the species might not have gotten this far. But a little perspective is in order. Let's review the various doomsday theories, from least threatening to most. If the end is inevitable, at least there won't be any surprises.

1. Laws of probability!

Standing at the Berlin Wall in 1969, Princeton astrophysicist J. Richard Gott III used a statistical formula to predict that the barrier would last 2.66 to 24 more years. It lasted 20. Later, Gott applied the same equation to humanity and calculated, with 95 percent certainty, that it would last 205,000 to 8 million more years. His paper on the subject made it into the august British scientific journal Nature.

Basically, Gott's formula (you will be spared the details) combines a series of estimates, then treats the result as though it was precise. Speculations about the far future have about as much chance of being spot-on as next week's weather forecast. But Gott's academic reputation won't suffer; if humanity still exists in 8.1 million years, it will be a little late to revoke his tenure.

2. Chemical weapons!

Spooky-sounding, sure. And dangerous. But bombs and bullets are dangerous, too. In actual use, chemical weapons have proven no more deadly, pound for pound, than conventional explosives. In World War I, the British and German armies expended 1 ton of chemical agents per enemy fatality.

Are modern nerve agents like sarin superdeadly in a way World War I mustard gas was not? When the Aum Shinrikyo cult attacked Tokyo's subway system with that substance in 1995 - the subway being an enclosed area, ideal for chemicals - 12 people died. That was 12 too many, but a conventional bomb the same size as the cult's canisters, detonated on a packed subway, would have killed more.

During this winter's duct tape scare, I heard a Washington, DC, radio talk-show host sternly lecture listeners to flee if "a huge cloud of poison gas" were slowly floating across the city. Noxious clouds of death may float across movie screens, but no military in the real world can create them. Wind rapidly disperses nerve agents, and sunlight breaks them down. Outdoors, a severe chemical attack likely would be confined to a few city blocks.

Some chemical incidents have been horrifyingly deadly. In 1994, when a Union Carbide plant accidentally loosed a cloud of methyl isocyanate over Bhopal, India, 8,000 people died, some of them 20 miles from the site. But the source was an industrial complex, and it spewed gas for an extended period of time, something no bomb or aircraft could do. Another heinous event, Iraq's poison gas attack on the Kurdish town of Halabja in 1988, killed an estimated 5,000. However, the slaughter involved dozens of Iraqi aircraft flying repeated sorties over an undefended city. Had they dropped conventional bombs, the toll might have been equally high.

One reason US and Russian leaders agreed to destroy their stocks of battlefield chemicals was that generals on both sides realized conventional weapons were just as deadly and easier to control. You don't want to be near VX nerve gas, but then you don't want to be near a lunatic with a single-action Colt pistol, either.

3. Germ warfare!

Like chemical agents, biological weapons have never lived up to their billing in popular culture. Consider the 1995 medical thriller Outbreak, in which a highly contagious virus takes out entire towns. The reality is quite different. Weaponized smallpox escaped from a Soviet laboratory in Aralsk, Kazakhstan, in 1971; three people died, no epidemic followed. In 1979, weapons-grade anthrax got out of a Soviet facility in Sverdlovsk (now called Ekaterinburg); 68 died, no epidemic. The loss of life was tragic, but no greater than could have been caused by a single conventional bomb.

In 1989, workers at a US government facility near Washington were accidentally exposed to Ebola virus. They walked around the community and hung out with family and friends for several days before the mistake was discovered. No one died.

The fact is, evolution has spent millions of years conditioning mammals to resist germs. Consider the Black Plague. It was the worst known pathogen in history, loose in a Middle Ages society of poor public health, awful sanitation, and no antibiotics. Yet it didn't kill off humanity. Most people who were caught in the epidemic survived. Any superbug introduced into today's Western world would encounter top-notch public health, excellent sanitation, and an array of medicines specifically engineered to kill bioagents.

Perhaps one day some aspiring Dr. Evil will invent a bug that bypasses the immune system. Because it is possible some novel superdisease could be invented, or that existing pathogens like smallpox could be genetically altered to make them more virulent (two-thirds of those who contract natural smallpox survive), biological agents are a legitimate concern. They may turn increasingly troublesome as time passes and knowledge of biotechnology becomes harder to control, allowing individuals or small groups to cook up nasty germs as readily as they can buy guns today. But no superplague has ever come close to wiping out humanity before, and it seems unlikely to happen in the future.

4. Chain reactions!

The fear that scientists tinkering with the elementary components of matter might unleash disaster has a rich and distinguished history. Before the detonation of the first atomic bomb at Trinity Site in 1945, Robert Oppenheimer worried that the unprecedented heat might spark a fusion chain reaction in the atmosphere. Physicist Hans Bethe performed calculations proving the planet wouldn't ignite, and the test went ahead.

The possibility of runaway chain reactions reemerged when scientists began deploying advanced particle accelerators, like the Cosmotron built at Long Island's Brookhaven National Labs in 1952. Some scientists worried that slamming protons into antiprotons at extremely high velocities might generate an unnatural subatomic template to which other particles would bind, collapsing matter into a void, possibly for vast distances. Panels of earnest researchers met to discuss whether high-energy physics experiments might crush the planet out of existence. They decided the risk was insignificant, but their concern was reflected in Kurt Vonnegut's 1963 novel Cat's Cradle, in which a researcher inadvertently creates "ice-nine," a template molecule that turns water into a solid at room temperature. When a bit of the stuff falls into the sea, all water on Earth quickly solidifies, including the water in living things.

Martin Rees, who has taken part in panels evaluating the safety of particle accelerators, has revived the idea that high-energy physics could accidentally destroy the world. In his new book, Our Final Hour, Rees worries that power improvements in atom smashers like Brookhaven's new Relativistic Heavy Ion Collider might make these machines capable of creating a black hole that would scarf up the globe. Ever more powerful accelerators, he fears, might create a "strangelet" of ultracompressed quarks - the smallest known units of matter - that would serve as an ice-nine for the entire universe, causing all matter to bind to the strangelet and disappear. Since, fundamentally, matter seems to be made of very rapidly spinning nothingness, there may be no reason why it couldn't spontaneously return to nothing.

"The present vacuum could be fragile and unstable," Rees frets in his book. A particle accelerator might cause a tiny bit of space to undergo a "phase transition" back to the primordial not-anything condition that preceded the big bang. Nothingness would expand at the speed of light, deleting everything in its path. Owing to light speed, not even advanced aliens would see the mega-destructo wave front coming. In other words, a careless Brookhaven postdoc chopsticking Chinese takeout might inadvertently destroy the cosmos.

Can ordinary people evaluate the likelihood of such an event? Not without years of graduate-level study. The only options are to believe the doomsayers or regard them in light of the fact that, in the 15 billion years since the big bang, in a universe full of starry infernos and cosmic cataclysms, their nightmares haven't come to pass so far.

5. Runaway nanobots!

Eric Drexler, the father of nanotechnology, calls it "gray goo": the state of things in the wake of microscopic machines capable of breaking down matter and reassembling it into copies of themselves. Nanobots could swarm over Earth like intelligent locusts, Drexler fears, then buzz out into the cosmos devouring everything they encountered. Michael Crichton's latest novel, Prey, describes a last-ditch attempt by scientists to destroy such contraptions before they take over the world.

Set aside the fact that, for all the nanobot speculation you've seen (including in Wired), these creatures do not, technically speaking, exist. Suppose they did. As the visionary scientist Freeman Dyson pointed out in his New York Review of Books critique of Prey, not only wouldn't nanobots be able to swarm after helpless victims as they do in the novel, they'd barely be able to move at all. Laws of physics dictate that the smaller something is, the greater its drag when moving through water or air.

"The top speed of a swimmer or flyer is proportional to its length," Dyson notes. "A generous upper limit to the speed of a nanorobot flying through air or swimming through water would be a tenth of an inch per second, barely fast enough to chase a snail."

6. Voracious black holes!

A supermassive black hole roughly the weight of 3 million suns almost certainly occupies the center of the Milky Way. And smaller (actually, lighter) ones are probably wandering around in space.

If such a rogue black hole happened to find its way into the solar system, its gravitational influence would disrupt the orbits of all the planets and their moons. Earth might slingshot out of the temperate range it now occupies and into frigid reaches more familiar to Mars, or it might be pushed closer to the sun to be singed, charred, or vaporized. Worse, if a sufficiently large black hole were to pass through the globe, it might be lights-out in more ways than one. The planet would be sucked into a vortex of such intense gravity that nothing would escape. The atoms that once made up Earth would be crushed out of existence as it's currently understood.

An encounter between Earth and a black hole is astronomically, as it were, improbable. However, collisions with supermassive objects of any kind would not be survivable.

7. Shifting magnetic poles!

As Earth turns, spinning molten rock in its core generates a magnetic field that surrounds the planet. The magma hasn't stopped turning, as happens in the movie The Core. But magnetic effects preserved in Oregon lava flows show that the world's magnetic polarity swaps from time to time. Exactly what causes these reversals is unknown. The last one seems to have happened 16 million years ago, but some researchers speculate that Earth's polarity may change as often as every 10,000 years.

In the aftermath of such an event, a compass needle would point toward Antarctica - but it's the event itself that worries some scientists. As the magnetic poles lurch, charged bodies of lava would suddenly become repelled by areas that once attracted them, causing earthquakes and other seismic disturbances. All magnetic fields might collapse briefly, playing havoc with electronics. Earth's magnetic field repels some forms of solar and cosmic rays; if the field faltered, radiation would pound the planet's surface, possibly killing plants, animals, and people in significant numbers.

It's hard to know how scary polar shift really is, since the frequency of such events is unknown. Anyway, what can anyone do about it? Nada.

8. Supervolcanoes!

Pompeii (AD 79), Tambora (1815), Mount St. Helen's (1980): Be glad you weren't picnicking nearby. These exploding mountains obliterated the countryside for miles around. Anomalies in a geologically stable world, right? Wrong. The world's most storied eruptions - Krakatau in Indonesia, for example, which caused frigid winters in Europe after it blew in 1883 - were modest by the standards of volcanic history.

Much of India sits on a basalt formation geologists call the Deccan Traps. Hundreds or thousands of huge volcanoes are believed to have erupted in this region, the cataclysms lasting many millennia and covering much of the subcontinent with molten basalt to a depth of 1,000 feet. The Deccan Traps burst forth about 65 million years ago, coincident with the dinosaurian demise. Some researchers think the meteorite usually blamed for that event struck with such violence that it cracked tectonic plates, setting in motion unimaginable seismic upheaval. In addition to 100 percent destruction within the path of the 1,000-foot tidal wave of lava, the Deccan Traps eruptions would have caused an ice age, choking global megasmog, and acid rain from hell.

The Deccan Traps were a municipal fireworks display compared with a huge Siberian basalt formation called the Siberian Traps, the product of eruptions lasting 600,000 years. Those occurred about 250 million years ago, coincident with the Permian extinction - the worst mass extinction in the fossil record.

Then there are supervolcanoes, individual eruptors of extraordinary size and power, far more potent than Krakatau. Some are geologically recent. A supervolcano called Toba exploded near Sumatra 73,000 years ago. Toba pumped 5 billion tons of sulfuric acid into the atmosphere and spewed so much sun-blocking ash that global temperatures are believed to have fallen 9 degrees Fahrenheit for several years - the difference between current temperatures and those of the Pleistocene ice age. Remember the "out of Africa" theory that we're all descended from a small group of people who lived in Olduvai Gorge? They may have been the sole members of genus Homo to survive the supervolcano's global aftereffects.

Nobody knows what triggered the Toba eruption or how to estimate when the next supervolcano will detonate. Disturbing thought: According to the US Geologic Survey, a supervolcano in Yellowstone National Park may be ripe for explosion.

9. Sudden climate change!

The world has become 1 degree warmer in the past century. So far, that rise hasn't hurt anyone - in fact, it may have contributed to the ever-higher crop yields that have staved off predicted Malthusian famines - but it's reasonable to expect that global temperatures will get warmer, owing at least in part to artificial greenhouse gases. Eventually the extra warmth might cease to be benign.

A more pressing worry, increasingly entertained by researchers, is a sudden climate "flip." Scientists regard fossilized oxygen isotopes as proxy measures of past atmospheric temperatures. Based on isotope levels, Russell Graham of the Denver Museum of Nature and Science has identified at least 63 sudden flip-flops between cold and warm trends in the last 1.6 million years - a climate flip every two millennia, on average. Note that 10,000 years have passed since the current pleasantly temperate period began, so another sudden shift is overdue.

The notion that greenhouse gases could trigger such a rapid change keeps serious scientists up at night. Ocean currents, whose dynamics are poorly understood, appear to have been central to past climate shifts. What if they suddenly started changing? Western Europe - most of which lies to the north of Maine - is nicely habitable owing to the Gulf Stream, a conveyor belt of warm water that churns past England. If global warming somehow altered the Gulf Stream's course, the European Union might be plunged into a deep freeze even as world temperatures rise.

If the past is a guide, this could happen as rapidly as over the course of a few years. Yes, people would adapt, but their numbers might be much smaller by the time the adaptation was complete. And since scientists today have little understanding of past climate flips, it's impossible to say when the next one will start. So be prepared: Stock lots of sweaters and a few Hawaiian shirts. The weather can be tricky this time of year.

10. Killer asteroids!

A collision between Earth and the gargantuan Chicxulub meteorite, which left a 186-mile-long depression at the tip of Mexico's Yucatan Peninsula, probably killed off the dinosaurs. But that was 65 million years ago. It couldn't happen again. Could it?

You bet it could. Chicxulub was only one in a long line of interplanetary boulders, or near-Earth objects, that have struck the ground. And some have arrived quite recently.

In 1908, an object 250 feet across hit Tunguska, Siberia, flattening trees for 1,000 square miles and detonating with a force estimated at 10 megatons, or 700 times the power of the Hiroshima blast. Had the Tunguska rock hit Moscow or Tokyo, those cities might no longer exist. In AD 535, a swarm of meteorites kicked up enough debris to cause several years of cruel winters, possibly helping push Europe into the Dark Ages. Ten thousand years ago, something enormous struck the Argentine pampas, obliterating a significant chunk of the South American ecology with a force thought to be 18,000 times that of the Hiroshima bomb.

Estimates by Alan Harris of the Space Science Institute of Boulder, Colorado, suggest that 500,000 asteroids roughly the size of the Tunguska rock wander through Earth's orbit. Much spookier are asteroids big enough to cause a Chicxulub-class strike. At least 1,100 are believed to exist in Earth's general area, some capable of plunging the planet into a years-long freeze while showering the globe with doomsday rain as corrosive as battery acid. None of these killer rocks is known to be on a collision course with Earth - but then, the courses of hundreds have yet to be charted.

Can we stop an incoming asteroid? Not yet. NASA is trying to coordinate tracking of near-Earth objects but has no technology that could be used against them and no plan to build such technology. This may be unwise. As the former Microsoft technologist Nathan Myhrvold has written, "Most estimates of the mortality risk posed by asteroid impacts put it at about the same risk as flying on a commercial airliner. However, you have to remember that this is like the entire human race riding the plane."
 

And what if solar neutrinos reflecting off Jupiter cause runaway ionospheric decompensation?!

In 1972, John Maddox, editor emeritus of Nature, published a prescient book called The Doomsday Syndrome. In it, Maddox argues that most apocalyptic claims are dubious, inflated, or have such a low likelihood that rational people need not think about them. Worrying about nutty or improbable threats, he adds, only distracts the political system from dangers or problems that are entirely confirmed.

Thus Bill Clinton sat in the White House wringing his hands about the preposterous sci-fi thriller The Cobra Event, in which nearly everyone in New York City drops dead from an unstoppable supergerm, when he should have been worrying about al Qaeda, a confirmed threat to New York. Thus we fret about proliferating nanobots or instant cosmic doom when we ought to be devoting our time and energy to confirmed worries like 41 million Americans without health insurance. A high-calorie, low-exertion lifestyle is far more likely to harm you than a vagrant black hole.

The time and energy spent worrying would be more usefully applied to separating serious risks from long shots. For example, if there's a magnetic pole shift in Earth's near-term future, it's difficult to imagine what anyone might do about it. But an asteroid on an intercept course might be stopped. So perhaps NASA ought to take more seriously research into how to block a killer rock. The probability of one arriving soon might be small, but the calamity it caused would be terminal.

Yes, the world could end tomorrow. But if it doesn't, its problems will continue. It makes far more sense to focus on mundane troubles that are all too real.
 

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Gregg Easterbrook, a senior fellow at The New Republic, wrote about the convergence of science and religion in Wired 10.12.