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 1098 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.”
Inthat scenario, the end is rather simple: Someone or something will simply turn us off.
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