You’ve probably heard about the Mayan carvings that predict the year 2012 will be our last. Supposedly, the war and creation god Bolon Yokte will return, bringing with him certain doom. Scholars have been trying to tamp down those claims, saying that’s an erroneous interpretation of the Mayan calendar, but it hasn’t silenced the Chicken Littles.

The end of the world isn’t really news anymore. Last year California pastor Harold Camping predicted that the world would end May 21. When the rapture didn’t come, he revised his doomsday prophecy to Oct. 21. That day also came and went without even a hint of Armageddon.

Religious fanatics consider the beginning and end of the world to be their exclusive domain, which endlessly frustrates secularists and some scientists. When someone suggested to British evolutionary biologist and strident atheist Richard Dawkins that he pose questions about the big bang to a chaplain, Dawkins responded, “Why not the gardener or the chef?”

Despite Dawkins’ implication that fundamental questions about our existence have more to do with science than religion, many scientists have been reluctant to speculate about the timing and manner of our demise. A few, however, have taken the leap, including Arizona State University astronomer Chris Impey, whose 2010 book “How It Ends: From You to the Universe” addresses this frightening and fascinating issue.

Impey points out that the human race, the Earth and the universe will all probably end at different times and in different ways. Our first and most immediate threat, according to Impey, is ourselves.

“We are a tribal people covered with a thin veneer of arts and culture,” he says. “Fifty years ago the greatest threat would have been thermonuclear war. Today, it’s likely some future weapon we haven’t imagined yet.”

Not everyone agrees on this point. Harvard psychologist Steven Pinker argued in his recent book, “The Better Angels of Our Nature: Why Violence Has Declined,” that humanity is becoming more peaceful.

If we don’t destroy ourselves, either through war or the destruction of our environment, Impey believes that unicellular and other exceedingly simple organisms are our next-greatest threat.

“The Earth has been dominated by microbes for billions of years,” he noted. “Having mammals and other large animals with brains is a recent occurrence. Maybe we’re slightly anomalous.”

Microbes have a tremendous advantage over us: They evolve a million times faster than humans. There are more generations of bacteria every 10 years than human generations since our species diverged from our nearest primate cousins, according to Impey. That makes them more adaptable to a changing environment, especially as global warming accelerates that change.

To understand why microbes are likely to destroy us, consider tuberculosis. The disease has plagued mankind for thousands of years and killed untold millions. It has achieved this even though we identified the pathogen that causes it in 1882 and have been desperately trying to destroy it ever since. Now think about all of the pathogens we don’t yet know about and those that haven’t yet evolved. It’s entirely possible that some bacterium will figure out how to destroy us before we destroy it.

No matter how our species ends, it’s statistically likely to happen in the next 800,000 years. The average mammalian species has spent around a million years on the planet. We’re about 200,000 years into that allotment.

That doesn’t exhaust the doomsday scenarios in which humans die independent of any damage to the Earth, but let’s move to our big blue rock. Many of the simpler cosmic threats to our planet are well known. An asteroid larger than a kilometer (about half a mile) across has struck Earth on average about every 500,000 years, and faster-moving comets collide with the planet every 30 million years. Even if we avoid such disasters, our sun has a limited life span.

“The sun will expire in about 5 billion years,” says Impey. “But the end of life on Earth will come before that, because the sun will begin to heat up and slowly toast the biosphere in 500 to 700 million years.”

While humans won’t be around to see it, scientists say the universe itself also has an expiration date. Some astrophysicists believe that in 20 billion years, a form of dark energy will literally tear the universe apart in an event known as the big rip. First galaxies would be torn, then the Earth, then atoms themselves will lose their coherence. If the big rip doesn’t happen, electrons, protons and neutrons are likely to decay, slowly returning the universe to its most fundamental building blocks in 10 to the 98th power years, give or take a few.

While those who believe the Mayans predicted the end of the world in 2012 — and believe it may happen — are easy to mock (and probably deserve it), even serious scientists have offered some science-fictional doomsday theories.

In 2010, eminent physicist Stephen Hawking warned against looking for alien life. His point was that we are pretty much bound to the Earth and its immediate surroundings.

If we make direct contact with aliens in the near term, it’s probably they who will have come to us. That means they would have technology far exceeding our own and may be on the hunt for resources. Hawking and some other scientists believe that seeking such contact risks our very existence.

Then there’s the possibility that we don’t really exist in the first place. It’s possible for computers to become so sophisticated and computing resources so inexpensive that one could build silicon-based worlds in which the simulated people “think” they really exist. Maybe this has already happened. If it has, assuming that we’re the simulators rather than the simulated starts to seem like an extreme form of anthropocentrism.

“Once you have the resources to construct a simulated world, it becomes easy to build many of them,” says Impey. “So many, in fact, that the simulations vastly outnumber the real biological entities.”

In that scenario, the end is rather simple: Someone or something will simply turn us off.

Brian Palmer writes for Slate and The Washington Post.

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