Scientists
recently reported the discovery of Kepler 186f, an Earth-sized planet
in the habitable zone. In the past few days there was published an
opinion piece by Andrew Snyder-Beattie entitled Habitable Planets Are Bad News for Humanity. The essay made some very quirky
reasoning very similar to a much earlier essay
published on the web site of Nick Bostrom.
The
essay is based on the idea of Fermi's Paradox, and an idea called the Great Filter derived from Fermi's Paradox. Fermi's Paradox is the
“where is everybody?” mystery of why we have not yet observed
extraterrestrials, even though we live in a galaxy that seems to have
billions of planets on which life might have evolved. The concept of
the Great Filter is the idea that there is some tendency, process or
limitation that tends to prevent planets from producing
extraterrestrial civilizations that survive long enough
to spread throughout the galaxy.
The
very strained reasoning of Bostrom and Snyder-Beattie goes rather
like this:
- There must be some Great Filter which makes it very unlikely that planets produce civilizations that spread throughout the galaxy – something such as an unlikelihood of life originally appearing, an unlikelihood of intelligence ever appearing, or an unlikelihood of a civilization surviving for long.
- Such a Great Filter can either be in our past or our future (for example, if the Great Filter is the unlikelihood of life ever appearing on a planet, then the Great Filter is in our past, and we have already leaped over this hurdle).
- If the Great Filter is in our future, we should be very sad, because it will mean our civilization will probably not last very long.
- But if the Great Filter is in our past (some hurdle we have already jumped over), then we are in good shape, and our future is bright (the whole galaxy might be ours for the taking).
- If we discover life on another planet (or a habitable planet), it is evidence that life commonly evolves in our galaxy, and this shows that the Great Filter must be in our future, and that we won't last very long.
- Therefore, it is bad news if we discover any evidence that life commonly evolves in our galaxy.
This
reasoning fails to make any sense. The main fallacy in it is the
“single factor” fallacy of assuming that there is One Big Reason
why a habitable planet would not tend to produce a civilization that
would go on to spread throughout the galaxy. An additional fallacy
is the assumption that if a typical extraterrestrial civilization
does not go on to spread throughout the galaxy, then that tells us
something ominous about the lifespan of our civilization.
In
fact, there are many factors that might explain why a civilization
arising on another planet would not tend to spread throughout the
galaxy, and most don't suggest anything about the lifespan of our
civilization. The factors include the following:
The
slowness and difficulty of interstellar travel. The speed of
light is a physical speed barrier, and it takes years for light to
travel from one star to the nearest star of the same type. Contrary
to what you see in science fiction such as Star Wars and Star
Trek, travel between stars is probably very, very slow, even for
the most advanced civilization. There are engineering and physics
reasons for doubting that any civilization could produce a ship
capable of traveling more than about a fifth of the speed of light,
making travel from one star to a nearby star a matter of decades or
centuries. We have no reason to believe that warp drives or
instantaneous “star gates” are likely to be possible (either
would require that physics gives us a gigantic gift that we could
exploit, and such a gift is probably not waiting for us).
The
impracticality of long-distance control. Given the limit of the
speed of light, we have no reason to think that any civilization
could establish anything like an empire spanning a big fraction of
the galaxy. Even if it were to establish interstellar colonies around
neighboring stars, the communication lag between such colonies would
be many years, and the possibility of enforcing any control would be
minimal; the farther away the colony was, the smaller would be the
chance of controlling it. In fact, there is every reason to suspect
that the maximum radius for any type of interstellar empire is
very small, only about 20 to 50 light-years, as I explain in this blog post. This
is another reason why the whole “if they existed, they would have
spread throughout the galaxy” reasoning is very weak.
The
unlikelihood of ultra-expansionist extraterrestrials. Most
species on our planet (including almost all birds, fish, and insects)
are non-territorial, meaning they have no tendency to defend some
particular area, and regard it as belonging to them. Those species
that are territorial (such as dogs) are virtually never expansionist.
It is extremely rare to see any species having some organized
tendency to expand its control to a wider and wider area. Even among
the human species, ultra-expansionist tendencies are very rare. A few
short-lived regimes have been ultra-expansionist (such as the Nazis
and the Mongols), but almost all governments have not been highly
expansionist. Why, then, do we presume that extraterrestrial
civilizations would be ultra-expansionist, and that they would want
to spread their control over larger and larger sections of the
galaxy?
The
strong possibility that extraterrestrials might skip
astro-engineering and symbol propagation. We imagine
extraterrestrials as beings that might turn the galaxy upside down
with their engineering projects, or spread signs of their
civilization all over the place. But they might have no interest in
such activities. Extraterrestrials might have no interest in doing
things such as planting their symbols on other planets, in the way we
put a flag up on the moon. They may think such “we were here”
type of activities are vain and childish. Once a civilization gets
godlike powers over matter and energy, they might run wild for a few
centuries, doing all kinds of breathtaking engineering projects such
as building mile-high buildings or artificial rings around their
planets. But after a certain number of centuries of such activity,
they might get bored with that type of thing, and go back to a more
“low footprint” way of living. In the latter case, it would be
relatively unlikely that we would see any signs of them.
Any
combination of these factors might help to explain why we do not
currently observe extraterrestrials (and in fact, the non-observation
of extraterrestrials is debatable, giving things such as UFO
sightings, fast radio bursts, and the “Wow” signal). So we do
not have to make any gloomy assumption that a Great Filter and habitable planets implies
that man's future lifespan is limited.
In
short, there is no good reason to assume that a discovery of
extraterrestrial life (or habitable planets) tells us anything at all
about a future lifespan of our civilization. If you want to get
gloomy about man's future prospects, there are much more direct and
compelling ways of making that case, rather than the strained
reasoning advanced by Snyder-Beattie and Bostrom.
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