Season 17, Episode 25: The “Dark Forest” and Scary Solutions to the Fermi Paradox

Hey StarTalkians! Season 17, episode 25 saw Neil, Paul and astrophysicist Charles Liu answer a whole bunch of alien-themed cosmic queries, inspired by Neil’s upcoming book Take Me to Your Leader. Among many interesting queries, the end of the show discussed the Fermi paradox:

Cosmic Queries – Take Me To Your Leader

(from 51:36)

In particular, they cover a relativity well-known idea, the “dark forest” hypothesis. But is it realistic? Should we be worried?

The Fermi Paradox: Light-Speed Summary

The Fermi paradox is simple: Since we have billions of stars in the Milky Way, there are billions of planets too, and there probably will be tons of intelligent extraterrestrial life forms in the galaxy. So where are they? Why haven’t we met them yet?

This is the Fermi paradox.

The Dark Forest Hypothesis

The “dark forest” hypothesis is named after Liu Cixin’s novel, which posits that the reason for the Fermi paradox is the same as the reason that you would stay quiet in a dark forest frequented by hunters. If you make a noise, they will come and snuff you out.

In the context of the galaxy, the “noise” would be a transmission, such as a radio transmission, and the “hunters” could be alien life forms or violent autonomous probes. So far, our signals reach out 200 light years, which is huge by our standards but pretty small on cosmic scales.

The Beserker Hypothesis

The even scarier “Beserker” hypothesis posits that some such autonomous probes could be created by a xenophobic extra-terrestrial species, loaded up with bombs and tasked to replicate and attack any signs of life they encounter.

In a famous paper David Brin writes, “It need only happen once for the results of this scenario to become the equilibrium condition in the Galaxy.”

How Likely Are These Scenarios?

These and other “scary solutions” to the Fermi hypothesis are gripping, but seem unlikely. As Brin points out in the paper, Beserker-style self-replicating probes may eventually become a threat to the creator species, so even xenophobic species may be wary of ever creating them.

We can also invert the above quote from Brin to tackle the dark forest: it only takes one species to ignore this risk – or not know about it – for signals to exist anyway. We are one example of such a species.