Life could be common in the universe, given the abundance of stars with planets and the fact that life arose on this planet within a relatively short cosmic time. One could conclude from this that there should be an abundance of civilizations capable of contacting or visiting Earth. This does not seem to have happened. UFOs notwithstanding, there is no scientific evidence for alien visitations or of efforts to communicate, such as might be revealed through programs like SETI. This discrepancy was first pointed out by physicist Enrico Fermi, after whom it was named.
Our search for extraterrestrial intelligence (SETI), and attempts to message it (METI), involve detecting or sending electromagnetic signals—especially radio waves. Indeed, our primary means of knowing about the universe is through electromagnetic radiation—light—one of the four fundamental known forces. A modern revelation, however, holds that less than 5% of the “bulk” of the universe is visible to us by means of that force. The mysterious remainder of the universe does not seem to interact with electromagnetism. It does interact gravitationally, however, which is how we can even know about its existence. Let us put aside the possibility that so-called dark matter and dark energy may be no more than artifacts of a defective understanding of gravitation. Perhaps our search for alien life has been like the man who was looking at night for his lost keys under the lamppost—because that’s where the light was. Could we be using the wrong medium to seek out extraterrestrial intelligence?
Faster-than-light communication or travel is commonly thought to be prohibited by Special Relativity. However—as argued in my paper “Why Is c a Cosmic Speed Limit?” (archived on this site)—the speed of light imposes an absolute limit only if light itself remains the unique standard for measuring speeds. The apparent speed limit represented by c results from the circularity of using light itself to investigate even its own properties. That does not, of itself, preclude the existence of a superluminal force that could serve as a signal. To be clear, there is no evidence for the existence such a thing. If it did exist, however, the paradoxical effects of faster-than-light travel (such as going backward in time) would only appear if light continued to serve as the standard by which to measure and investigate the new medium. If this new signal itself became the standard, the speed of light would take a modest place like the speed of sound, perhaps well below the new cosmic speed limit imposedby the new medium.
This suggests a possible explanation of the Fermi paradox: advanced civilizations simply don’t use electromagnetism for communication, but some unknown medium to which we are not (yet) sensible. By analogy, we can imagine our present situation as like blind creatures who only know of the world through touch and through sound—who build huge sound detectors and emitters in the vain hope of making contact with extraterrestrials. On the other hand, the para-luminal signalling medium of advanced civilizations might enable aliens to “see” dark matter if it involves a causal interaction resembling that of electromagnetism with ordinary matter.
This brings us to an aside about black holes. In present theory, by definition a black hole is a region of gravitational force so strong that even electromagnetic radiation cannot escape from it (except by “leaking” through Hawking radiation). But gravity itself does readily escape from it. Curiously like very long and subtle electromagnetic waves, gravity is supposed to travel at the speed of light. But why should gravity resemble electromagnetism in having the same characteristic speed and wave-like nature, yet be unlike it in escaping black holes? (Indeed, what does it mean for gravity to escape itself?) Gravity waves may be thought of as disturbances propagating in the structure of spacetime itself. But that spacetime structure is defined in terms of the speed of light, c, which makes the whole business suspiciously circular.
Of course, many other explanations for the Fermi paradox have been proposed, which is not really a paradox so much as a mystery. A reasonable explanation (while bearing ominous implications for us) is that technological civilizations inevitably destroy themselves before they can accomplish serious space travel. Carl Sagan was perhaps the first to write about the Fermi paradox. In his relevant novel, Contact, the main character is asked what question she would pose to the aliens who have (in the story) initiated contact with Earth in a message that has been received by a radio telescope and deciphered. Her answer: “How did you do it?” Meaning: how did you survive your hazardous technological adolescence?
Technological civilizations might actually be rare. Natural evolution may not favour our kind of tool-using intelligence. On the other hand, our brand of technology and intelligence may lead us to conceive aliens in too-human terms. They could operate on other time scales, using novel means of communication. Their form of advancement might be post-technological: they might not be interested in space travel or contact with distant civilizations. They might be cautious, if not paranoid, about contact—deliberately hiding. They might be ignoring us because we are too primitive—or too small or too big.
Humans exist on a scale intermediate between the largest and smallest we can conceive. There may be as many possibilities for existence in the realm of the very small as in the very large. Aliens might not occupy our physical scale, with our expansionist ideals of “conquering space.” They might have opted for miniaturization, maximizing possibilities in the micro realm of computation and information flow rather than energy flow. Such a mentality would have no interest in expansion in outer space, terra-forming, Dyson spheres, massive engineering projects on a galactic scale, or communicating with us.
Perhaps we should not expect to encounter biological aliens at all, or their signals. For, in order to persist over cosmological periods, biological life forms would logically give place to more durable artificial successors. Since such beings, unlike us, could have the ability to re-configure their minds and bodies voluntarily, their motivations and thinking could be incomprehensible to us and unimaginable. We cannot anticipate what they might become. Indeed, with some feasible means to overcome the limitations of physical embodiment, they might migrate to cyberspace, no longer interested in what we call physical reality. Yet, even living in a virtual world, their digital reality would necessarily exist as some form of computation in the physical world. According to our present limited thinking, that would involve massive use of energy, which might itself constitute an identifiable signature of alien civilization.
Similar reasoning applies to the human future. In order to persist, we too would be succeeded by artificial beings. Will they have the same interests in space exploration and contact with alien intelligence? How much will they have in common with present humanity at all? If supra-luminal space travel is possible (such as through worm holes), then the distances involved would be less a deterrent to contact than the conventional speed of light currently presents as a limiting factor. But our successors might not have the motivation or mentality to reach out, even if freed from that limit.