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[escepticos] 20 Ways the World Could End

    Un poco de catastrofismo.




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DISCOVER Vol. 21 No. 10 (October 2000)
Table of Contents

20 Ways the World Could End

Swept away.

By Corey S. Powell

We've had a good run of it. In the 500,000 years Homo sapiens has
roamed the land we've built cities, created complex languages, and
sent robotic scouts to other planets. It's difficult to imagine it all
coming to an end. Yet 99 percent of all species that ever lived have
gone extinct, including every one of our hominid ancestors. In 1983,
British cosmologist Brandon Carter framed the "Doomsday argument," a
statistical way to judge when we might join them. If humans were to
survive a long time and spread through the galaxy, then the total
number of people who will ever live might number in the trillions. By
pure odds, it's unlikely that we would be among the very first
hundredth of a percent of all those people. Or turn the argument
around: How likely is it that this generation will be the one unlucky
one? Something like one fifth of all the people who have ever lived
are alive today. The odds of being one of the people to witness
doomsday are highest when there is the largest number of witnesses
around- so now is not such an improbable time.

Human activity is severely disrupting almost all life on the planet,
which surely doesn't help matters. The current rate of extinctions is,
by some estimates, 10,000 times the average in the fossil record. At
present, we may worry about snail darters and red squirrels in
abstract terms. But the next statistic on the list could be us.

                  Natural Disasters

1 Asteroid impact

Once a disaster scenario gets the cheesy Hollywood treatment, it's
hard to take it seriously. But there is no question that a cosmic
interloper will hit Earth, and we won't have to wait millions of years
for it to happen. In 1908 a 200-foot-wide comet fragment slammed into
the atmosphere and exploded over the Tunguska region in Siberia,
Russia, with nearly 1,000 times the energy of the atomic bomb dropped
on Hiroshima. Astronomers estimate similar-sized events occur every
one to three centuries. Benny Peiser, an anthropologist-cum-pessimist
at Liverpool John Moores University in England, claims that impacts
have repeatedly disrupted human civilization. As an example, he says
one killed 10,000 people in the Chinese city of Chi'ing-yang in 1490.
Many scientists question his interpretations: Impacts are most likely
to occur over the ocean, and small ones that happen over land are most
likely to affect unpopulated areas. But with big asteroids, it doesn't
matter much where they land. Objects more than a half-mile wide- which
strike Earth every 250,000 years or so- would touch off firestorms
followed by global cooling from dust kicked up by the impact. Humans
would likely survive, but civilization might not. An asteroid five
miles wide would cause major extinctions, like the one that may have
marked the end of the age of dinosaurs. For a real chill, look to the
Kuiper belt, a zone just beyond Neptune that contains roughly 100,000
ice-balls more than 50 miles in diameter. The Kuiper belt sends a
steady rain of small comets earthward. If one of the big ones headed
right for us, that would be it for pretty much all higher forms of
life, even cockroaches.

2 Gamma-ray burst

If you could watch the sky with gamma-ray vision, you might think you
were being stalked by cosmic paparazzi. Once a day or so, you would
see a bright flash appear, briefly outshine everything else, then
vanish. These gamma-ray bursts, astrophysicists recently learned,
originate in distant galaxies and are unfathomably powerful- as much
as 10 quadrillion (a one followed by 16 zeros) times as energetic as
the sun. The bursts probably result from the merging of two collapsed
stars. Before the cataclysmal event, such a double star might be
almost completely undetectable, so we'd likely have no advance notice
if one is lurking nearby. Once the burst begins, however, there would
be no missing its fury. At a distance of 1,000 light-years- farther
than most of the stars you can see on a clear night- it would appear
about as bright as the sun. Earth's atmosphere would initially protect
us from most of the burst's deadly X rays and gamma rays, but at a
cost.  The potent radiation would cook the atmosphere, creating
nitrogen oxides that would destroy the ozone layer. Without the ozone
layer, ultraviolet rays from the sun would reach the surface at nearly
full force, causing skin cancer and, more seriously, killing off the
tiny photosynthetic plankton in the ocean that provide oxygen to the
atmosphere and bolster the bottom of the food chain. All the gamma-ray
bursts observed so far have been extremely distant, which implies the
events are rare. Scientists understand so little about these
explosions, however, that it's difficult to estimate the likelihood of
one detonating in our galactic neighborhood.

3 Collapse of the vacuum

In the book Cat's Cradle, Kurt Vonnegut popularized the idea of
"ice-nine," a form of water that is far more stable than the ordinary
kind, so it is solid at room temperature. Unleash a bit of it, and
suddenly all water on Earth transforms to ice-nine and freezes
solid. Ice-nine was a satirical invention, but an abrupt, disastrous
phase transition is a possibility. Very early in the history of the
universe, according to a leading cosmological model, empty space was
full of energy.  This state of affairs, called a false vacuum, was
highly precarious. A new, more stable kind of vacuum appeared and,
like ice-nine, it quickly took over. This transition unleashed a
tremendous amount of energy and caused a brief runaway expansion of
the cosmos. It is possible that another, even more stable kind of
vacuum exists, however. As the universe expands and cools, tiny
bubbles of this new kind of vacuum might appear and spread at nearly
the speed of light. The laws of physics would change in their wake,
and a blast of energy would dash everything to bits. "It makes for a
beautiful story, but it's not very likely," says Piet Hut of the
Institute for Advanced Studies in Princeton, New Jersey. He says he
worries more about threats that scientists are more certain of- such
as rogue black holes.

4 Rogue black holes

Our galaxy is full of black holes, collapsed stellar corpses just a
dozen miles wide. How full? Tough question. After all, they're called
black holes for a reason. Their gravity is so strong they swallow
everything, even the light that might betray their presence. David
Bennett of Notre Dame University in Indiana managed to spot two black
holes recently by the way they distorted and amplified the light of
ordinary, more distant stars. Based on such observations, and even
more on theoretical arguments, researchers guesstimate there are about
10 million black holes in the Milky Way. These objects orbit just like
other stars, meaning that it is not terribly likely that one is headed
our way. But if a normal star were moving toward us, we'd know
it. With a black hole there is little warning. A few decades before a
close encounter, at most, astronomers would observe a strange
perturbation in the orbits of the outer planets. As the effect grew
larger, it would be possible to make increasingly precise estimates of
the location and mass of the interloper. The black hole wouldn't have
to come all that close to Earth to bring ruin; just passing through
the solar system would distort all of the planets' orbits. Earth might
get drawn into an elliptical path that would cause extreme climate
swings, or it might be ejected from the solar system and go hurtling
to a frigid fate in deep space.

5 Giant solar flares

Solar flares- more properly known as coronal mass ejections- are
enormous magnetic outbursts on the sun that bombard Earth with a
torrent of high-speed subatomic particles. Earth's atmosphere and
magnetic field negate the potentially lethal effects of ordinary
flares. But while looking through old astronomical records, Bradley
Schaefer of Yale University found evidence that some perfectly
normal-looking, sunlike stars can brighten briefly by up to a factor
of 20. Schaefer believes these stellar flickers are caused by
superflares, millions of times more powerful than their common
cousins. Within a few hours, a superflare on the sun could fry Earth
and begin disintegrating the ozone layer (see #2). Although there is
persuasive evidence that our sun doesn't engage in such excess,
scientists don't know why superflares happen at all, or whether our
sun could exhibit milder but still disruptive behavior. And while too
much solar activity could be deadly, too little of it is problematic
as well. Sallie Baliunas at the Harvard-Smithsonian Center for
Astrophysics says many solar-type stars pass through extended
quiescent periods, during which they become nearly 1 percent
dimmer. That might not sound like much, but a similar downturn in the
sun could send us into another ice age. Baliunas cites evidence that
decreased solar activity contributed to 17 of the 19 major cold
episodes on Earth in the last 10,000 years.

6 Reversal of Earth's magnetic field

Every few hundred thousand years Earth's magnetic field dwindles
almost to nothing for perhaps a century, then gradually reappears with
the north and south poles flipped. The last such reversal was 780,000
years ago, so we may be overdue. Worse, the strength of our magnetic
field has decreased about 5 percent in the past century. Why worry in
an age when GPS has made compasses obsolete? Well, the magnetic field
deflects particle storms and cosmic rays from the sun, as well as even
more energetic subatomic particles from deep space. Without magnetic
protection, these particles would strike Earth's atmosphere, eroding
the already beleaguered ozone layer (see #5). Also, many creatures
navigate by magnetic reckoning. A magnetic reversal might cause
serious ecological mischief. One big caveat: "There are no
identifiable fossil effects from previous flips," says Sten Odenwald
of the NASA Goddard Space Flight Center. "This is most curious."
Still, a disaster that kills a quarter of the population, like the
Black Plague in Europe, would hardly register as a blip in fossil

7 Flood-basalt volcanism

In 1783, the Laki volcano in Iceland erupted, spitting out three cubic
miles of lava. Floods, ash, and fumes wiped out 9,000 people and 80
percent of the livestock.  The ensuing starvation killed a quarter of
Iceland's population.  Atmospheric dust caused winter temperatures to
plunge by 9 degrees in the newly independent United States. And that
was just a baby's burp compared with what the Earth can do.
Sixty-five million years ago, a plume of hot rock from the mantle
burst through the crust in what is now India. Eruptions raged century
after century, ultimately unleashing a quarter-million cubic miles of
lava- the Laki eruption 100,000 times over. Some scientists still
blame the Indian outburst, not an asteroid, for the death of the
dinosaurs. An earlier, even larger event in Siberia occurred just
about the time of the Permian-Triassic extinction, the most thorough
extermination known to paleontology. At that time 95 percent of all
species were wiped out.

Sulfurous volcanic gases produce acid rains. Chlorine-bearing
compounds present yet another threat to the fragile ozone layer- a
noxious brew all around. While they are causing short-term
destruction, volcanoes also release carbon dioxide that yields
long-term greenhouse-effect warming.The last big pulse of flood-basalt
volcanism built the Columbia River plateau about 17 million years
ago. We're ripe for another.

8 Global epidemics

If Earth doesn't do us in, our fellow organisms might be up to the
task. Germs and people have always coexisted, but occasionally the
balance gets out of whack. The Black Plague killed one European in
four during the 14th century; influenza took at least 20 million lives
between 1918 and 1919; the AIDS epidemic has produced a similar death
toll and is still going strong. From 1980 to 1992, reports the Centers
for Disease Control and Prevention, mortality from infectious disease
in the United States rose 58 percent. Old diseases such as cholera and
measles have developed new resistance to antibiotics. Intensive
agriculture and land development is bringing humans closer to animal
pathogens.  International travel means diseases can spread faster than
ever.  Michael Osterholm, an infectious disease expert who recently
left the Minnesota Department of Health, described the situation as
"like trying to swim against the current of a raging river." The
grimmest possibility would be the emergence of a strain that spreads
so fast we are caught off guard or that resists all chemical means of
control, perhaps as a result of our stirring of the ecological
pot. About 12,000 years ago, a sudden wave of mammal extinctions swept
through the Americas. Ross MacPhee of the American Museum of Natural
History argues the culprit was extremely virulent disease, which
humans helped transport as they migrated into the New World.

             Human-Triggered Disasters

9 Global warming

The Earth is getting warmer, and scientists mostly agree that humans
bear some blame. It's easy to see how global warming could flood
cities and ruin harvests. More recently, researchers like Paul Epstein
of Harvard Medical School have raised the alarm that a balmier planet
could also assist the spread of infectious disease by providing a more
suitable climate for parasites and spreading the range of tropical
pathogens (see #8). That could include crop diseases which, combined
with substantial climate shifts, might cause famine. Effects could be
even more dramatic. At present, atmospheric gases trap enough heat
close to the surface to keep things comfortable. Increase the global
temperature a bit, however, and there could be a bad feedback effect,
with water evaporating faster, freeing water vapor (a potent
greenhouse gas), which traps more heat, which drives carbon dioxide
from the rocks, which drives temperatures still higher. Earth could
end up much like Venus, where the high on a typical day is 900 degrees
Fahrenheit. It would probably take a lot of warming to initiate such a
runaway greenhouse effect, but scientists have no clue where exactly
the tipping point lies.

10 Ecosystem collapse

Images of slaughtered elephants and burning rain forests capture
people's attention, but the big problem- the overall loss of
biodiversity- is a lot less visible and a lot more serious. Billions
of years of evolution have produced a world in which every organism's
welfare is intertwined with that of countless other species. A recent
study of Isle Royale National Park in Lake Superior offers an
example. Snowy winters encourage wolves to hunt in larger packs, so
they kill more moose. The decline in moose population allows more
balsam fir saplings to live. The fir trees pull carbon dioxide out of
the atmosphere, which in turn influences the climate. It's all
connected. To meet the demands of the growing population, we are
clearing land for housing and agriculture, replacing diverse wild
plants with just a few varieties of crops, transporting plants and
animals, and introducing new chemicals into the environment. At least
30,000 species vanish every year from human activity, which means we
are living in the midst of one of the greatest mass extinctions in
Earth's history. Stephen Kellert, a social ecologist at Yale
University, sees a number of ways people might upset the delicate
checks and balances in the global ecology. New patterns of disease
might emerge (see #8), he says, or pollinating insects might become
extinct, leading to widespread crop failure. Or as with the wolves of
Isle Royale, the consequences might be something we'd never think of,
until it's too late.

11 Biotech disaster

While we are extinguishing natural species, we're also creating new
ones through genetic engineering.  Genetically modified crops can be
hardier, tastier, and more nutritious. Engineered microbes might ease
our health problems. And gene therapy offers an elusive promise of
fixing fundamental defects in our DNA. Then there are the possible
downsides. Although there is no evidence indicating genetically
modified foods are unsafe, there are signs that the genes from
modified plants can leak out and find their way into other
species. Engineered crops might also foster insecticide
resistance. Longtime skeptics like Jeremy Rifkin worry that the
resulting superweeds and superpests could further destabilize the
stressed global ecosystem (see #9). Altered microbes might prove to be
unexpectedly difficult to control. Scariest of all is the possibility
of the deliberate misuse of biotechnology. A terrorist group or rogue
nation might decide that anthrax isn't nasty enough and then try to
put together, say, an airborne version of the Ebola virus. Now there's
a showstopper.

12 Particle accelerator mishap

Theodore Kaczynski, better known as the Unabomber, raved that a
particle accelerator experiment could set off a chain reaction that
would destroy the world. Surprisingly, many sober-minded physicists
have had the same thought. Normally their anxieties come up during
private meetings, amidst much scribbling on the backs of used
envelopes. Recently the question went public when London's Sunday
Times reported that the Relativistic Heavy Ion Collider (RHIC) on Long
Island, New York, might create a subatomic black hole that would
slowly nibble away our planet.  Alternately, it might create exotic
bits of altered matter, called strangelets, that would obliterate
whatever ordinary matter they met. To assuage RHIC's jittery
neighbors, the lab's director convened a panel that rejected both
scenarios as pretty much impossible. Just for good measure, the panel
also dismissed the possibility that RHIC would trigger a phase
transition in the cosmic vacuum energy (see #3). These kinds of
reassurances follow the tradition of the 1942 "LA-602" report, a
once-classified document that explained why the detonation of the
first atomic bomb almost surely would not set the atmosphere on
fire. The RHIC physicists did not, however, reject the fundamental
possibility of the disasters. They argued that their machine isn't
nearly powerful enough to make a black hole or destabilize the
vacuum. Oh, well. We can always build a bigger accelerator.

13 Nanotechnology disaster

Before you've even gotten the keyboard dirty, your home computer is
obsolete, largely because of incredibly rapid progress in
miniaturizing circuits on silicon chips. Engineers are using the same
technology to build crude, atomic-scale machines, inventing a new
field as they go called nanotechnology. Within a few decades, maybe
sooner, it should be possible to build microscopic robots that can
assemble and replicate themselves. They might perform surgery from
inside a patient, build any desired product from simple raw materials,
or explore other worlds. All well and good if the technology works as
intended. Then again, consider what K. Eric Drexler of the Foresight
Institute calls the "grey goo problem" in his book Engines of
Creation, a cult favorite among the nanotech set.  After an industrial
accident, he writes, bacteria-sized machines, "could spread like
blowing pollen, replicate swiftly, and reduce the biosphere to dust in
a matter of days." And Drexler is actually a strong proponent of the
technology. More pessimistic souls, such as Bill Joy, a cofounder of
Sun Microsystems, envision nano-machines as the perfect precision
military or terrorist tools.

14 Environmental toxins

>From Donora, Pennsylvania, to Bhopal, India, modern history abounds
with frightening examples of the dangers of industrial pollutants. But
the poisoning continues. In major cities around the world, the air is
thick with diesel particulates, which the National Institutes of
Health now considers a carcinogen. Heavy metals from industrial
smokestacks circle the globe, even settling in the pristine snows of
Antarctica. Intensive use of pesticides in farming guarantees runoff
into rivers and lakes. In high doses, dioxins can disrupt fetal
development and impair reproductive function- and dioxins are
everywhere. Your house may contain polyvinyl chloride pipes,
wallpaper, and siding, which belch dioxins if they catch fire or are
incinerated. There are also the unknown risks to think about. Every
year NIH adds to its list of cancer-causing substances- the number is
up to 218. Theo Colburn of the World Wildlife Fund argues that dioxins
and other, similar chlorine-bearing compounds mimic the effects of
human hormones well enough that they could seriously reduce
fertility. Many other scientists dispute her evidence, but if she's
right, our chemical garbage could ultimately threaten our survival.

              Willful Self-Destruction

15 Global war

Together, the United States and Russia still have almost 19,000 active
nuclear warheads. Nuclear war seems unlikely today, but a dozen years
ago the demise of the Soviet Union also seemed rather
unlikely. Political situations evolve; the bombs remain deadly. There
is also the possibility of an accidental nuclear exchange. And a
ballistic missile defense system, given current technology, will catch
only a handful of stray missiles- assuming it works at all. Other
types of weaponry could have global effects as well. Japan began
experimenting with biological weapons after World War I, and both the
United States and the Soviet Union experimented with killer germs
during the cold war. Compared with atomic bombs, bioweapons are cheap,
simple to produce, and easy to conceal. They are also hard to control,
although that unpredictability could appeal to a terrorist
organization. John Leslie, a philosopher at the University of Guelph
in Ontario, points out that genetic engineering might permit the
creation of "ethnic" biological weapons that are tailored to attack
primarily one ethnic group (see #11).

16 Robots take over

People create smart robots, which turn against us and take over the
world. Yawn. We've seen this in movies, TV, and comic books for
decades. After all these years, look around and still- no smart
robots. Yet Hans Moravec, one of the founders of the robotics
department of Carnegie Mellon University, remains a believer. By 2040,
he predicts, machines will match human intelligence, and perhaps human
consciousness. Then they'll get even better. He envisions an eventual
symbiotic relationship between human and machine, with the two merging
into "postbiologicals" capable of vastly expanding their intellectual
power. Marvin Minsky, an artificial-intelligence expert at MIT,
foresees a similar future: People will download their brains into
computer-enhanced mechanical surrogates and log into nearly boundless
files of information and experience. Whether this counts as the end of
humanity or the next stage in evolution depends on your point of
view. Minsky's vision might sound vaguely familiar. After the first
virtual-reality machines hit the marketplace around 1989, feverish
journalists hailed them as electronic LSD, trippy illusion machines
that might entice the user in and then never let him out. Sociologists
fretted that our culture, maybe even our species, would whither
away. When the actual experience of virtual reality turned out to be
more like trying to play Pac-Man with a bowling ball taped to your
head, the talk died down. To his credit, Minsky recognizes that the
merger of human and machine lies quite a few years away.

17 Mass insanity

While physical health has improved in most parts of the world over the
past century, mental health is getting worse. The World Health
Organization estimates that 500 million people around the world suffer
from a psychological disorder. By 2020, depression will likely be the
second leading cause of death and lost productivity, right behind
cardiovascular disease. Increasing human life spans may actually
intensify the problem, because people have more years to experience
the loneliness and infirmity of old age.  Americans over 65 already
are disproportionately likely to commit suicide. Gregory Stock, a
biophysicist at the University of California at Los Angeles, believes
medical science will soon allow people to live to be 200 or older. If
such an extended life span becomes common, it will pose unfathomable
social and psychological challenges. Perhaps 200 years of accumulated
sensations will overload the human brain, leading to a new kind of
insanity or fostering the spread of doomsday cults, determined to
reclaim life's endpoint. Perhaps the current trends of depression and
suicide among the elderly will continue. One possible solution-
promoting a certain kind of mental well-being with psychoactive drugs
such as Prozac- heads into uncharted waters. Researchers have no good
data on the long-term effects of taking these medicines.

         A Greater Force Is Directed Against Us

18 Alien invasion

At the SETI Institute in Mountain View, California, a cadre of
dedicated scientists sifts through radio static in search of a
telltale signal from an alien civilization. So far, nothing. Now
suppose the long-sought message arrives.  Not only do the aliens
exist, they are about to stop by for a visit.  And then . . . any
science-fiction devotee can tell you what could go wrong. But the
history of human exploration and exploitation suggests the most likely
danger is not direct conflict. Aliens might want resources from our
solar system (Earth's oceans, perhaps, full of hydrogen for refilling
a fusion-powered spacecraft) and swat us aside if we get in the way,
as we might dismiss mosquitoes or beetles stirred up by the logging of
a rain forest. Aliens might unwittingly import pests with a taste for
human flesh, much as Dutch colonists reaching Mauritius brought cats,
rats, and pigs that quickly did away with the dodo. Or aliens might
accidentally upset our planet or solar system while carrying out some
grandiose interstellar construction project. The late physicist Gerard
O'Neill speculated that contact with extraterrestrial visitors could
also be socially disastrous. "Advanced western civilization has had a
destructive effect on all primitive civilizations it has come in
contact with, even in those cases where every attempt was made to
protect and guard the primitive civilization," he said in a 1979
interview. "I don't see any reason why the same thing would not happen
to us."

19 Divine intervention

Judaism has the Book of Daniel; Christianity has the Book of
Revelation; Islam has the coming of the Mahdi; Zoroastrianism has the
countdown to the arrival of the third son of Zoroaster. The stories
and their interpretations vary widely, but the underlying concept is
similar: God intervenes in the world, bringing history to an end and
ushering in a new moral order. Apocalyptic thinking runs at least back
to Egyptian mythology and right up to Heaven's Gate and Y2K
mania. More worrisome, to the nonbelievers at least, are the doomsday
cults that prefer to take holy retribution into their own hands. In
1995, members of the Aum Shinri Kyo sect unleashed sarin nerve gas in
a Tokyo subway station, killing 12 people and injuring more than
5,000. Had things gone as intended, the death toll would have been
hundreds of times greater. A more determined group armed with a more
lethal weapon- nuclear, biological, nanotechnological even- could have
done far more damage.

20 Someone wakes up and realizes it was all a dream

Are we living a shadow existence that only fools us into thinking it
is real? This age-old philosophical question still reverberates
through cultural thought, from the writings of William S.  Burrows to
the cinematic mind games of The Matrix. Hut of the Institute of
Advanced Studies sees an analogy to the danger of the collapse of the
vacuum. Just as our empty space might not be the true, most stable
form of the vacuum, what we call reality might not be the true, most
stable form of existence. In the fourth century B.C., Taoist
philosopher Chuang Tzu framed the question in more poetic terms. He
described a vivid dream.  In it, he was a butterfly who had no
awareness of his existence as a person. When he awoke, he asked:

"Was I before Chuang Tzu who dreamt about being a butterfly, or
am I now a butterfly who dreams about being Chuang Tzu?"

- with additional research by Diane Martindale


The folks at the Bulletin of Atomic Scientists maintain the
famed "Doomsday Clock at


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