As we discover numerous habitable planets around other stars in the Milky Way galaxy, including the nearest star, Proxima Centauri, one cannot help but wonder why we have not yet detected evidence for an alien civilization. As the physicist Enrico Fermi asked, “Where is everybody?” Even though the first interstellar object to be discovered in the solar system, ‘Oumuamua, had an unusually elongated shape as might be expected from an alien probe, it does not appear to maneuver and is radio-quiet below the level of a single cell phone.
True, a signal from an alien civilization might be subtle or sophisticated, but the disappointing silence of the sky may also indicate that long-lasting extrastellar civilizations do not use technologies that would make them visible to our telescopes.
Based on our own experience, we expect that civilizations much older than ours will be scientifically savvy and hence technologically advanced. But it is also possible that a simpler lifestyle rather than scientific prosperity has dominated the political landscape on other planets, leading to old civilizations that are nevertheless technologically primitive.
Could exoplanet politics explain Fermi’s paradox?
Human history allows us to imagine the possibility that under a different political scenario, our planet could have remained dominated by the anti-scientific mindsets of the middle ages. Such a scenario is imaginable over the timescale of thousands of years, although the likelihood that it would prevail over millions or billions of years is unclear. Perhaps Earth was lucky to see technology arise (in the spirit of the novel Origin by Dan Brown). Environmental or political disasters could have easily reset the evolutionary clock.
Or perhaps the ultimate lifetime of civilization on Earth will turn out to be shorter than it would have been if humans remained technologically primitive. Technology poses long-term risks to our future in the form of climate change and nonconventional (nuclear, biological or chemical) wars. In this case, the surfaces of other planets will show either relics of technologically advanced civilizations that destroyed themselves in self-inflicted catastrophes or living civilizations that are technologically primitive.
We could search for the remnants of technological civilizations from afar. But if we detect nothing through our telescopes, the only way to find out whether long-lived civilizations are technologically primitive is to visit their planets. Astrosociology could become a particularly exciting frontier of exploration as we venture into space.
Traditional astronomers would argue that it is much less expensive to remotely observe distant planets than to launch a probe that will visit them. But remote observing can only detect civilizations that transmit electromagnetic signals, change the planet’s atmosphere through industrial pollution, or leave artifacts on the planet’s surface such as photovoltaic cells, industrial infrastructure, artificial heating or artificial illumination. If the aliens do not dramatically modify their natural habitat or transmit artificial signals, we will be forced to visit their home planets in order to uncover their existence.
Civilizations on other worlds might mesh seamlessly with their natural environment for a variety of reasons. At a minimum, camouflage is a natural survival tactic, so alien civilizations might prefer to appear indistinguishable from other forms of life, such as vegetation. One could also imagine a civilization so intelligent that it deliberately keeps a low-key technological profile to sustain its biosphere, maintaining a lifestyle reminiscent of Henry Thoreau on Walden Pond. The only way to find these extraterrestrials would be to send probes that visit their planets and report back.
The first significantly funded project to visit another planetary system, Breakthrough Starshot, was inaugurated in 2016. Starshot aims to reach the nearest stars within a couple of decades. Since even Proxima Centauri is 4.24 light years away, this necessitates a technology capable of accelerating a spacecraft to at least a fifth of the speed of light. The only suitable concept involves a lightweight sail (to which the payload is attached) pushed by a powerful beam of light. The downside of reaching such a high speed with this design is that braking near the target planet is not feasible without a similar light-beamer there.
Visiting the surface of another planet therefore requires slower speeds and longer travel times. For example, conventional rockets would bring us to the nearest stars within hundreds of thousands of years. This might still be appealing from a theoretical perspective, since this timescale is tens of thousands times shorter than the age of the Universe. Over the billions of years available to our technological civilization to explore the Milky Way, we could compile a sociological census of billions of exoplanets. And even if we find mostly faith-based alien cultures instead of advanced infrastructure that would accelerate our own technological development, it would be fascinating to explore the diversity of galactic interpretations of the concept of God.