GEORGE P. DVORSKY
P. Dvorsky is a Canadian bioethicist, transhumanist, futurist
and producer of the Sentient Developments blog and podcast.
He is also a contributing editor at io9.com
-- a journal of science and science fiction.
is difficult to not be pessimistic when considering humanity's
future prospects. Many people would agree that it is more likely
than not that we will eventually do ourselves in. And in fact,
some astrobiologists theorize that all advanced civilizations
hit the same insurmountable developmental wall we have. They
call it the Great Filter. It's a notion that's often invoked
to explain why we have never been visited by extraterrestrials.
there is another possible reason for the celestial silence.
Yes, the Great Filter exists, but we've already passed it. Here's
what this would mean.
we can get to the Great Filter hypothesis we have to appreciate
what the Fermi Paradox is telling us.
FERMI PARADOX AND THE GREAT SILENCE
so-called Great Silence is the contradictory and counter-intuitive
observation that we have yet to see any evidence for the existence
of aliens. The size and age of the Universe suggests that many
technologically advanced extraterrestrial intelligences (ETIs)
ought to exist -- but this hypothesis seems inconsistent with
the lack of observational evidence to support it.
much of what popular culture and sci-fi would lead us to believe,
the fact that we haven't been visited by ETIs is disturbing.
Our galaxy is so ancient that it could have been colonized hundreds,
if not thousands, of times over by now. Even the most conservative
estimates show that we should have already made contact either
directly or indirectly (such as from dormant Bracewell communication
skeptics dismiss the Fermi Paradox (FP) by suggesting that ETIs
have come and gone, or that they wouldn't find us interesting.
most solutions to the FP don't hold for a number of reasons,
including the realization that a colonization wave of superintelligent
aliens would likely rework the fabric of all life in the cosmos,
or that these solutions are sociological in nature (i.e. they
lack scientific rigor and don't necessarily apply to the actions
of all advanced civilizations; all it would take is just one
to think and behave differently -- what astrobiologists refer
to as the non-exclusivity problem).
have been many attempts to resolve the Fermi Paradox, including
the herculean attempt by Stephen Webb in his book, Fifty
Solutions to Fermi's Paradox and the Problem of Extraterrestrial
one solution stands out from the others, mostly on account of
its brute elegance: The Great Filter.
GREAT FILTER (GF)
in 1998 by Robin Hanson, the GF is the disturbing suggestion
that there is some kind of absurdly difficult step in the evolution
of life -- one that precludes it from becoming interstellar.
like the immutable laws of the universe, the GF is a stumbling
block that holds true across the board; if it applies here on
Earth, it applies everywhere.
look upon the GF as evidence that we'll destroy ourselves in
the future. The basic idea is that every civilization destroys
itself before developing space-faring technologies. Hence the
empty cosmos. Given our own trajectory and the ominous presence
of apocalyptic weapons, this scenario certainly seems plausible.
We're not even close to going interstellar, yet we're certainly
capable of self-annihilation.
that doesn't mean this interpretation of the GF is the correct
one. Rather, it is quite possible that human civilization has
already passed the Great Filter. Should this be the case, it
would be exceptionally good news. Assuming there's no other
filter awaiting us in the future, it means we might be the first
and only intelligent civilization in the Milky Way.
a possibility, however, that demands explanation. If the filter
is behind us, what was it? And how did we manage to get past
it? Interestingly, there are some excellent candidates.
and foremost there's the Rare Earth Hypothesis (REH), the suggestion
that the emergence of life was extremely improbable for a confluence
of reasons. The theory essentially suggests that we hit the
jackpot here on Earth.
argument, which was first articulated by geologist Peter Ward
and astrobiologist Donald E. Brownlee, turns the whole Copernican
Principle on its head. Instead of saying that we are nothing
special or unique, the REH implies the exact opposite -- that
we are freakishly special and unique. What we see here on Earth
in this solar system and in this part of the Galaxy may be a
remarkable convergence of highly unlikely factors -- factors
that have resulted in a perfect storm of conditions suitable
for the emergence of complex life.
important to note that Ward and Brownlee are not implying that
it's one or two conditions that can explain habitability, but
rather an entire array of happy accidents. For example, stars
might have to be of the right kind (including adequate metallicity
and safe distance from dangerous celestial objects), and planets
must be in a stable orbit with a large moon. Other factors include
the presence of gas giants, plate tectonics and many others.
even with all the right conditions, life was by no means guaranteed.
It is quite possible that the Great Filter involved the next
set of steps: the emergence of life and its ongoing evolution.
IMPROBABILITY OF LIFE
in addition to all the cosmological and chemical prerequisites
for life, there were at least three critical stages that could
all be considered candidates for the Great Filter: (1) the emergence
of reproductive molecules (abiogenesis and the emergence of
RNA), (2) simple single-celled life (prokaryotes), and (3) complex
single-celled life (eukaryotes).
and biologists are still not entirely sure how the first self-replicating
molecules came into existence. Unlike its big brother, DNA,
RNA is a single-stranded molecule that has a much shorter chain
of nucleotides. Moreover, it usually needs DNA to reproduce
itself -- which would have been a problem given the absence
of DNA in those early days.
said, scientists know that RNA is capable of reproducing through
autocatalysis. It does this by storing information similar to
DNA, which allows it to become its own catalyst (a ribosome).
This so-called RNA World Model suggests that RNA can function
as both a gene and an enzyme -- a pre-DNA configuration that
eventually became the basis for all life.
that we've never detected life elsewhere, it's difficult to
know how difficult this initial step was. But that said, this
form of life emerged super-early in the Earth's history -- about
a billion years after its formation, and immediately after the
cooling of rocks and the emergence of oceans.
what we do know is that the next few steps -- the leap from
single-celled life to complex single-celled life -- was exceedingly
difficult, if not highly improbable. The process of copying
a genetic molecule is extremely complex, involving the perfect
configuration of proteins and other cellular components.
how it likely happened: Once a self-replicating molecule emerged,
the presence of RNA allowed for the formation of protobionts,
a theoretic precursor to prokaryotic cells. These tightly bound
bundles of organic molecules contained RNA within their membranes
-- which could have evolved into proper prokaryotic cells.
here's where it gets interesting. After the formation of prokaryotes
-- about 3.5 billion years ago -- nothing changed in the biological
landscape for the next 1.8 billion years. Life in this primitive
form was completely stuck. Imagine that -- no evolution for
almost two billion years. It was only after the endosymbiosis
of multiple prokaryotes that complex single-cell life finally
emerged -- a change that was by no means guaranteed, and possibly
it's this highly improbable step, say some scientists, that's
the Great Filter. Everything that happened afterward is a complete
that said, there may have been other filters as well. These
could include the emergence of terrestrial organisms, hominids,
and various civilizational stages, like the transition from
stone age culture to agricultural to industrial. But unlike
the first primordial stages already discussed, these are porous
filters and not terribly unlikely.
if the GF is behind us, it would do much to explain the Fermi
Paradox and the absence of extraterrestrial influence on the
cosmos. Should that be the case, we may very well have a bright
future ahead of us. The Milky Way Galaxy is literally ours for
the taking, our future completely open-ended.
before we jump to conclusions, it's only fair to point out that
we're not out of the woods yet. There could very well be another
GF in the future -- one just as stingy as the filters of our
past. The universe, while giving the appearance of bio-friendliness,
may in reality be extremely hostile to intelligent life.