“Since, in the long run, every planetary society will be endangered by impacts from space, every surviving civilization is obliged to become spacefaring — not because of exploratory or romantic zeal, but for the most practical reason imaginable: staying alive.”
It was not so long ago that the only explanations for what can be seen in the night sky were fictions produced for the sake of religious narrative. Some ancients were able to infer the Moon to be a distant sphere. Galileo studied the moons of Jupiter in some detail. Soon classical mechanics, a realm of physics that provides a basic understanding of everything from billiard balls to orbital trajectories, would unfold in part from the observations made through early telescopes.
Today no serious modern thinkers subordinate science to faith in the quest to understand the universe beyond our homeworld. We have found that the Sun is the most common sort of luminous object in this decidedly large galaxy. We know the Milky Way is bigger than average because we have come to photograph and study a diverse assortment of galaxies all around us. As it becomes evident that extrasolar planets are no freak occurrence, it also becomes evident that the cosmos features an unthinkable amount of real estate.
Pioneering nuclear physicist Enrico Fermi posed a question inspired by an understanding that our celestial home is not unique. If the universe contains countless worlds, a fraction of which may resemble our own, with a fraction of those producing life and a fraction of those leading to intelligence, then why has there not yet been any verifiable communications between an alien civilization and our own? Fermi’s thinking on the subject held that the lack of such encounters was a compelling argument against the existence of extraterrestrial intelligence.
Some scientists are quick to point out that “absence of evidence is not evidence of absence.” Though the argument has seen some application here, it takes a form Carl Sagan characterized as “appeal to ignorance” in his Baloney Detection Kit. Santa Claus, Invisible Pink Unicorns, Flying Spaghetti Monsters, etc. could all be defended based on the idea that a lack of reliable proof they exist does not provide any argument to believe they do not exist.
On the other hand, Sagan personally seems to have been strongly inclined toward the belief that other intelligences have evolved naturally in our universe. An appeal to ignorance should be disregarded on its own, but that does not justify disregarding other considerations. A North Pole compound where elves handcraft millions upon millions of toys seems unlikely because the Arctic has been extensively surveyed. By contrast, the capacity to survey worlds beyond our own solar system is still extremely limited.
Fermi had a point when it came to the fact that no overt relations have ever been established between humans and extraterrestrial beings. Yet does this point rest on entirely sound assumptions? When it comes to life from beyond our galaxy, physics poses some significant challenges to human contact. For one, galaxies themselves are so large, it is difficult to imagine a need that could only be fulfilled by reaching for a distant one. Then there is space itself. Not only are galaxies orders of magnitude farther apart than star systems, but the fabric of the universe constantly expands. On the scale of intergalactic travel, this creates an effect that makes a journey through space grow longer while it is underway.
Barring bold assumptions in the manner of “warp drive” or “hyperspace,” inhabitants of our galaxy may well be completely isolated from meaningful interaction with inhabitants of galaxies that are not cosmic neighbors to our own. On the other hand, our own galaxy is obviously not remote from itself. Interstellar distances are vast, but cosmological expansion has a trivial effect on the scale of journeys to and from millions of stars in the nearest 1% of our galaxy. Intergalactic civilizations require capabilities so far from current human understanding that meaningful speculation is difficult. Intragalactic civilizations are another matter.
One estimate, based on recently elevated energy prices, puts the price tag at $40 billion just to produce the power to propel an ark with a hundred colonists to a nearby star system. Actually constructing such a vessel and sustaining the lives of its crew is beyond the technology of today, but it is not so far beyond present limits that speculation is meaningless. Sagan is among many to have noted a remarkable coincidence. After billions of years of life on Earth, the rapid rise of intelligence and technology reveals the means to destroy our own habitat and the means to reach out to other worlds, with both prospects emerging in stunning historical proximity.
The ability to span interstellar distances is something of an awesome power. Is it really sound to assume that beings with such knowledge and means at their disposal would gain much from dealing directly with human beings? I’ve always thought it was a peculiar assumption, born of the jet age and the earliest space exploration efforts, to think that alien vessels would be prominent, or even visible, spectacles. Scientists headed into the bush to learn about the behavior of other species on our world will often use effective concealment, in order that their presence not change the behavior of subjects under observation. It would only take a fairly small technological edge to approach the study of humans in such a way as to leave no unambiguous evidence of the effort.
As the Sun is a common sort of star, systems with similar material composition are also likely to be common. Basic material needs may or may not ever be relevant in the context of interstellar shipping. If they are, surely it would be simpler and safer to harvest material from relatively inert orbs than one teaming with complex biology. Conspiracy theories and government secrecy leave the question of alien artifacts found on Earth so cloudy as to be best avoided in serious discussion. On the other hand, the extent of surveillance we conduct in our own solar system leaves all manner of prospective hiding places for listening posts or even traffic hubs. Pluto’s recent reclassification demonstrates the limits of what we actually know about celestial objects in our own proverbial backyard.
One exciting development in the field of astronomy involves interferometry. New technologies make it possible to deploy networks of telescopes that yield some visual details as if the network were a single lens with a diameter defined by the distance between those telescopes. With existing methods, it would be possible to deploy a space-based telescopic network with the capacity to directly image planets around other stars. So far study of extrasolar planets has been extremely limited — many discoveries do not go beyond observations of gravitational tug exerted by a star’s planetary companions, and the rest rarely go beyond analyzing the chemical composition of a planet as the smallest hints of reflected light are captured.
A global interferometer network, peering into the void with a virtual eye bigger than our own planet, could take clear pictures of these distant worlds. Would we find signs of biological activity (like the patterns of green evident on our own world?) Might we even find signs of technology (like the patterns of light evident in a night-side viewing of Earth?) These are questions that can be answered in the lifetime of most readers, provided there is political will to do it.
Until our understanding of distant worlds is improved in such a way, we remain in the dark about some details that might better frame Fermi’s paradox. Perhaps it is ultimately a question best answered with questions. Is it arrogant to think we are so accomplished or interesting that alien starships would have cause to make Earth a popular port of call? Might an existing interstellar authority maintain isolation for certain beings (or habitats) in the interest of allowing a natural rise from primitive biology to galactic citizenry? Could our lack of global political unity leave outsiders reluctant to risk actions that might contribute to such abominations as warfare?
As far as has been confirmed, we remain alone in the universe. Yet as far as we know, that seems an implausible guess. Given how common main sequence stars and extrasolar planets seem to be, it would be puzzling if none had given rise to a race of cosmic cohabitants. The fact that no credible individuals claim to possess E.T.’s phone number is a far cry from proof that there are no extraterrestrial civilizations.
We are only on the brink of looking deeply enough into space to lock down many crucial unknowns in speculation about the probability of such civilizations. Perhaps we are still a long way from looking deeply enough at our own political and social structures to be fit companions for a more enlightened form of life. Whatever the underlying reality may be, this is an area of contemplation that does much to put everything else in fresh perspective.