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.