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Every other Friday, the Outside/In team answers a listener question about the natural world. Got a question of your own? The Outside/In team is here to answer your questions. Call 844-GO-OTTER to leave us a message.

Outside/In[box]: What is the Dark Forest Theory?

The Green Bank telescope in the Allegheny Mountains in West Virginia. It is one of the radio telescopes used by the Breakthrough Listen project to search for alien communications.

Every other Friday on Morning Edition, the Outside/In team answers a question from a listener about the natural world.

This week, we encounter a question about space. Francisco Alexander Rodriguez on Instagram asked us to look into the Dark Forest Theory.

The Drake Equation

The Dark Forest Theory deals with the possibility of “intelligent life” beyond planet Earth. But how likely is it that other “advanced civilizations” exist in the universe?

Astrophysicist Frank Drake once wondered the same thing, and in 1961, he proposed a formula to estimate the odds.

N = R* · fP ·  Ne · fl · fi · fc · L

N = number of civilizations with which humans could communicate
R* = mean rate of star formation
fP = fraction of stars that have planets
Ne = mean number of planets that could support life per star with planets
fl = fraction of life-supporting planets that develop life
fi = fraction of planets with life where life develops intelligence
fc = fraction of intelligent civilizations that develop communication
L = mean length of time that civilizations can communicate

According to the Drake Equation, the odds that we are alone are vanishingly small. But a civilization with the capacity to communicate or travel across the somewhat inconceivable distances of space would necessarily be quite advanced. What would it mean if the Search for Extraterrestrial Intelligence (SETI) is someday successful?

The cover of The Golden Record, launched with the Voyager spacecraft in 1977. It includes recordings of sounds of Earth and instructions for use, should alien life find it.

The Dark Forest Theory  

According to the Dark Forest Theory, we should be very glad that we have not encountered alien life… because that encounter might not go so well for human civilization. The term comes from a series called The Three Body Problem by Chinese sci-fi author Liu Cixin.

“The universe is a dark forest. Every civilization is an armed hunter stalking through the trees like a ghost, gently pushing aside branches that block the path and trying to tread without sound. Even breathing is done with care. The hunter has to be careful, because everywhere in the forest are stealthy hunters like him. If he finds another life—another hunter, angel, or a demon, a delicate infant to tottering old man, a fairy or demigod—there’s only one thing he can do: open fire and eliminate them.”

From this perspective, anything in the “dark forest” – in space – is a threat. Many sci-fi conceptions of alien life ostensibly share this worldview.

In Alien (1979), director Ridley Scott depicts a species that implants its larvae into human bodies – which does not work out for the human host. In HG Wells’ classic novel War of the Worlds (1898), adapted for both radio and film, the Martian invaders are decidedly hostile. But in Steven Spielberg’s E.T. (1982), it’s actually humans whose behavior is the scariest, and E.T. is a rather gentle being.

Other depictions entertain the possibility that, even if we don’t intend to be threatening, alien life might perceive humans as dangerous. What might happen if an alien civilization intercepted a century-old radio signal announcing a declaration of war, for instance?

But any artist imagining intelligent life beyond this planet is also making assumptions about the human species, consciously or not. The Dark Forest Theory suggests that all the hunters in the forest should assume a degree of violence in each other.

But that’s a big assumption – and a tension in many works of science fiction, including the series The Expanse. 

Maybe it’s the nature of intelligent life to destroy itself,” one character says.

“Well, I prefer to think that intelligent life can choose not to,” replies another.

What do you prefer to think about intelligent life? If there is someone else out there, should we be looking for them? Or should we be trying to hide?

If you’ve got a question about the natural world, send it as a voice memo to outsidein@nhpr.org, leave a voicemail on our hotline at 1-844-GO-OTTER, or share it with us on Twitter or Instagram.

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