Author:
Andrew Snyder-Beattie
University
of Oxford
NASA Ames/SETI Institute/JPL-CalTech
Last week, scientists announced the discovery of
Kepler-186f, a planet 492 light years away in the Cygnus constellation.
Kepler-186f is special because it marks the first planet almost exactly the
same size as Earth orbiting in the “habitable zone” – the distance from a star
in which we might expect liquid water, and perhaps life.
What did not make the news, however, is that this
discovery also slightly increases how much credence we give to the possibility
of near-term human extinction. This is because of a concept known as the Great
Filter.
The Great Filter is an argument that attempts to
resolve the Fermi Paradox: why have we not found aliens, despite the existence
of hundreds of billions of solar systems in our galactic neighbourhood in which
life might evolve? As the namesake physicist Enrico Fermi noted, it seems
rather extraordinary that not a single extraterrestrial signal or engineering
project has been detected (UFO conspiracy theorists notwithstanding).
This apparent absence of thriving extraterrestrial
civilisations suggests that at least one of the steps from humble planet to
interstellar civilisation is exceedingly unlikely. The absence could be caused
because either intelligent life is extremely rare or intelligent life has a
tendency to go extinct. This bottleneck for the emergence of alien
civilisations from any one of the many billions of planets is referred to as
the Great Filter.
Are we alone?
What exactly is causing this bottleneck has been
the subject of debate for more than 50 years. Explanations could include a
paucity of Earth-like planets or self-replicating molecules. Other
possibilities could be an improbable jump from simple prokaryotic life (cells
without specialised parts) to more complex eukaryotic life – after all, this
transition took well over a billion years on Earth.
Proponents of this “Rare Earth” hypothesis also
argue that the evolution of complex life requires an exceedingly large number
of perfect conditions. In addition to Earth being in the habitable zone of the
sun, our star must be far enough away from the galactic centre to avoid
destructive radiation, our gas giants must be massive enough to sweep asteroids
from Earth’s trajectory, and our unusually large moon stabilises the axial tilt
that gives us different seasons.
These are just a few prerequisites for complex
life. The emergence of symbolic language, tools and intelligence could require
other such “perfect conditions” as well.
Or is the filter ahead
of us?
While emergence of intelligent life could be rare,
the silence could also be the result of intelligent life emerging frequently
but subsequently failing to survive for long. Might every sufficiently advanced
civilisation stumble across a suicidal technology or unsustainable trajectory?
We know that a Great Filter prevents the emergence of prosperous interstellar
civilisations, but we don’t know whether or not it lies in humanity’s past or
awaits us in the future.
For 200,000 years humanity has survived
supervolcanoes, asteroid impacts, and naturally occurring pandemics. But our
track record of survival is limited to just a few decades in the presence of
nuclear weaponry. And we have no track record at all of surviving many of the
radically novel technologies that are likely to arrive this century.
Esteemed scientists such as Astronomer Royal Martin
Rees at the Cambridge Centre for the Study of Existential Risk point to
advances in biotechnology as being potentially catastrophic. Others such as
Stephen Hawking, Max Tegmark and Stuart Russell, also with the Cambridge
Centre, have expressed serious concern about the exotic but understudied
possibility of machine superintelligence.
Let’s hope Kepler-186f
is barren
When the Fermi Paradox was initially proposed, it
was thought that planets themselves were rare. Since then, however, the tools
of astronomy have revealed the existence of hundreds of exoplanets. That just
seems to be the tip of the iceberg.
But each new discovery of an Earth-like planet in
the habitable zone, such as Kepler-186f, makes it less plausible that there are
simply no planets aside from Earth that might support life. The Great Filter is
thus more likely to be lurking in the path between habitable planet and
flourishing civilisation.
If Kepler-186f is teeming with intelligent life,
then that would be really bad news for humanity. For that fact would push back
the Great Filter’s position further into the technological stages of a
civilisation’s development. We might then expect that catastrophe awaits both
our extraterrestrial companions and ourselves.
In the case of Kepler-186f, we still have many
reasons to think intelligent life might not emerge. The atmosphere might be too
thin to prevent freezing, or the planet might be tidally locked, causing a
relatively static environment. Discovery of these hostile conditions should be
cause for celebration. As philosopher Nick Bostrom once said:
The
silence of the night sky is golden … in the search for extraterrestrial life,
no news is good news. It promises a potentially great future for humanity.
Note: This article was originally published on The Conversation.com
