Nearly 2,500 years ago the Greek philosopher Metrodorus of Chios challenged his students with an analogy. He stated that, because it was unreasonable that in a large field only one shaft of wheat should grow, why then, in an infinite universe, should there be only one living world? Our understanding of how profligate and diverse life is on Earth and recent discoveries in astronomy point to tantalizing possibilities.
When speculating on the nature of advanced extraterrestrial life and a spacefaring extraterrestrial society, some authors go to great lengths to discuss such life forms’ behavior and how they might be disposed toward us, the lifespan of an advanced technological civilization, and so on. At this stage in our understanding, however, all bets are off. If we were to encounter an advanced spacefaring species, we would be confronted with an intelligence that we have never before encountered, one that may not even be possible for us to understand. We cannot assume that an alien species would be motivated as we are, or would share any universal system of values with us, or perhaps even recognize us. At the moment, our understanding of life is confined to its forms, plentiful and varied though they be, found only on our home planet. Assuming that life has arisen elsewhere in our cosmos, it is almost certain to be very different from anything we currently understand, and it would not have the humanoid structure routinely reported in the UFO community or in science fiction.
Biologists define life by four general processes: growth, reproduction, responsiveness, and metabolism. Scientists are in general agreement that if a collection of organic molecules increases in size, if it makes copies of itself, if it somehow responds to its environment, and if it somehow incorporates elements from outside its structure and converts them in a series of controlled internal chemical reactions to compounds needed to grow, reproduce, or physically respond to changes in its environment, it is alive.
In the early 1960s Frank Drake conducted the first search for radio wave signals from potential extraterrestrial civilizations at the National Radio Astronomy Observatory in Green Bank, West Virginia. This began the international effort in astronomy known today as the Search for Extraterrestrial Intelligence, or SETI. In 1961, when the National Academy of Sciences asked him to chair a meeting on the detection of extraterrestrial intelligence, Drake developed his famous equation designed to estimate the number of advanced technical civilizations in our galaxy. In 1980, Carl Sagan popularized this equation in his television series Cosmos to point out to viewers across the world that our own galaxy might well be teeming with not only life but also other advanced technological civilizations. Professor Drake persuaded astronomers and other interested researchers to think seriously about the possibility of other intelligent life in our galaxy, and Sagan persuaded the common man to think about that same possibility, including its implications for our own existence.
We may be assuming too much in thinking that we would be able to recognize an alien intelligence, civilization, or its artifacts. Without a better understanding of how and where life can arise and of what other forms an alien intelligence or civilization can take, any number concerning the Drake Equation is next to meaningless. However, what Professor Drake’s equation has done, even in the absence of hard data, is to stimulate thought and debate about the various factors necessary to predict the likelihood of extraterrestrial civilizations in our galaxy.
It is arguable that any organism possessing spacefaring technology, as we know it, would have had to develop a sophisticated understanding of physics and be able to comprehend mathematical concepts, thereby recognizing a basic order in the universe’s physics and in our symbology. At the same time, of course, symbols such as letters or numerals are normally arbitrary, bearing little resemblance to what they signify, so it is difficult to say whether an alien civilization could make heads or tails of our messages, and vice versa. Still, Drake and Sagan were optimistically banking on the commonalities that we would share with another species. They knew the differences would be vast but thought it better to begin with the traits that we likely share, such as a similar chemistry involving hydrogen, one of the most common elements in the known universe.
For all our cryptographic abilities, however, we again assume much. We assume, for example, that any intelligent recipients generally think the way we do, that they organize information in more or less the same manner we do, and that they are primarily visual creatures. We are limited by our lack of knowledge of how an intelligence from another world might “think.” We must be careful not to assume that life based on a completely different biology would have anything but the most fundamental chemical elements in common with us.
As we are contemplating extraterrestrial life, one of the more exciting exercises is to imagine what such life might actually look like. If extraterrestrial life is built by DNA, or some equivalent of it, we might hypothesize that such organisms reproduce much as we do. Life evolving on any planet would certainly need to adjust to its gravity, so any sort of alien animal life would have to evolve an anatomy to move through its environment. Such organisms would be very recognizable to us as life forms, but perhaps it is not that simple. British astronomer Martin Rees has posited that there could be organisms and extraterrestrial intelligence in forms we can’t even conceive. We tend to think in terms of “animals” and “plants.” Moreover, the basis of all Earth life appears to be cellular. Whether those cells are eukaryotes, prokaryotes, or archaea, living things on our planet are either single-celled or multicellular organisms. But what if non-Earth life is built of something other than DNA or even an equivalent? We might not recognize it at all. Certainly an intelligence evolved from a profoundly different biology would function very differently than our own. Sagan wrote that extraterrestrial intelligence would be “elegant, complex, internally consistent, and utterly alien.” If we restrict our theorizing to intelligences recognizable to us, however, we could hypothesize that an intelligent extraterrestrial species might have evolved as social life forms. If such a species were also aggressive and highly competitive, as Stephen Hawking recently suggested in an article in the London Sunday Times, we could easily be faced with alien versions of the worst aspects of our human selves. In fact, Hawking cautioned against broadcasting our existence to potential extraterrestrial civilizations, stating that we only have to look at ourselves to see how intelligent life might develop into something we wouldn’t want to encounter. Rather than benevolent extraterrestrials as depicted in much science fiction, he posited that intelligent alien life might come to Earth “in massive ships, having used up all the resources from their home planet. Such advanced aliens would perhaps become nomads, looking to conquer and colonize whatever planets they can reach.” Humanity would almost certainly be helpless in a confrontation with any species advanced enough to locate our planet and travel here.
In all of our theorizing about extraterrestrial intelligence, we may just as easily suppose that, if such a civilization developed technology sufficiently advanced to explore the stars, they must have harnessed that better nature and progressed beyond base instincts. Such a species might therefore not be bent on conquering the Earth or appropriating its resources. It might ignore us altogether, or it might attempt to contact us, perhaps even engage with us. For the moment, until we have irrefutable evidence of intelligent life beyond Earth, it is impossible to know.
Despite the interesting possibilities raised by Drake’s equation and continuing discoveries of new Earth-sized worlds in our galaxy, physicist Enrico Fermi’s question still nags: “Where are they? Where is everybody?” Could humanity be alone in this vast cosmos? For the moment, it seems that we are far distant from any other life forms that we can recognize in our obscure corner of the Milky Way.