Of all the mysteries of the universe, the possibility of meeting other intelligent species must be the most provocative. It would be the most important event in the History of humankind to establish contact with other intelligent species. One question, as I debate below, I whether we would survive.
Cosmological Time and Civilization
Geological time is in the order of millions or even billions of years. Our planet is roughly 4.5 billion years-old. Life, which depends on the chemistry and conditions of a planet, also follows such large time scales and it is thought that life on earth appeared 3.5-4 billion years ago. Our galaxy, the Milky Way, is over 10 billion years-old. Therefore, other intelligent species in the galaxy are not likely to be in the Bronze Age or in any age that happened to us in the past thousands of years. Possibly, if they are less intelligent than us, they are still animals. But if we are to face a more advanced civilization then they will be millions of years ahead of us because, by chance, they originated millions of years before.
At a cosmological time scale, energy manipulation is a good way to classify a civilization. Nikolai Kardashev and Freeman Dyson developed the following classification for alien civilizations:
|Type||Level of Energy Control|
|I||Absolute control over a planet's energy.|
|II||Domination of stellar energy (e.g., Dyson's sphere).|
|III||Galactic civilization where several stars are controlled.|
|IV||Space-time manipulation (something we don't understand very well yet, as discussed elsewhere).|
A type IV civilization is almost a god and we are mere dust to them; if such civilization exists they would be so advanced when compared to us that our mind is probably not even able to understand them so I won't even try to. A type III civilization is likely try to conquer an inferior species like ours because they are possibly a spacefaring society expanding its reach. It is obviously speculative to think how they may think but, based on the encounters between human civilizations (e.g., the conquest of the Americas by European countries), I would expect a type III civilization to destroy or subjugate us. Lower level civilizations of type I and II may not have the power to attack us but neither will we be able to attack them in a near future. Cooperation among us might be a possibility, though it is also plausible that eventually one civilization would prevail through science or warfare.
Alien civilizations will have nuclear power and therefore the power to exterminate themselves. Why didn't they solve their problems with the element 92 is one of the most important questions to ask, which is similar to the question Ellie, the main character in Carl Sagan's Contact, would ask an alien if she was only allowed one question. Perhaps some aliens have a genetic structure such as ants in which a queen controls everyone. One possibility that may happen to humankind is that one or a few entities -- either human, computer or hybrid -- gain control over the entire species, as I discuss elsewhere; alien civilizations may have to suppress individual freedom to a large extent. Either way, advanced alien civilizations may have their individuals united if they are to survive, and that is one reason why I suspect humans would find it hard to cooperate with alien civilizations.
The Fermi Paradox
If the rise of intelligent life occurs on a cosmological time scale and space travel is possible then why have we not been contacted by other civilizations? As mentioned above, the Milky Way is over 10 billion years-old and yet life on earth appeared less than 4 billion years ago. Even if life is extremely rare, chances are it has appeared in some of the other 200 billion plus star systems in the galaxy and intelligence could have emerged billions of years ago. Given that the galaxy is roughly 100,000 light-years across, a couple of billion years was enough time for another civilization to explore and expand across the galaxy. But then why haven't we seen any signs of them? In a nutshell, these were the calculations made by Enrico Fermi over 60 years ago and the absence of evidence of the existence of other civilizations is now known as the "Fermi paradox" or the "great silence."
The Fermi paradox is one of the most debated topics in exobiology. If alien civilizations are abundant in our galaxy then why haven't we detected them or at least why haven't they made their presence felt? It is certainly plausible that we have not yet reached the technological capacity to detect more advanced civilizations; after all, we only developed electromagnetic (e.g. radio) communications little over a century ago and there may be more efficient ways of communicating. So it is perhaps not surprising that we have thus far failed to detect intelligent life on other planets. Nonetheless, if aliens have been around for millions of years then they must know that our planet harbors life because of the signatures of life earth emits. Assuming that traveling between stars is possible, and we have no reason to think it is not, then they had enough time to come here, even if only to destroy us and conquer our planet to exploit its resources. Why haven't they?
There are multiple explanations to the Fermi Paradox. Perhaps the emergence of intelligent life is harder than we think -- known as the "Rare Earth hypothesis." After all, while life emerged on earth relatively soon after the planet's formation, it was only about a billion years ago that multicellular organisms evolved -- and animals only evolved 400 million years later. As such, it is possible that the universe is teeming with microbial life but absent of intelligent animals. Another hypothesis is that civilizations are destined to self-destruct; even though we only developed nuclear weapons less than a century ago these could well have already been used to destroy life on earth. Natural disasters, including cosmological disasters, may also be more frequent than we think and a number of civilizations may have perished that way. Maybe we are indeed alone in the galaxy.
Even if we are not alone there may be reasons for the lack of extraterrestrial communications. Perhaps space travel is so expensive and/or dangerous that exploring and colonizing the galaxy occurs at an extremely slow pace. Another hypothesis is that, even though the galaxy is over 10 billion years of age, only more recently did it become stable enough to allow planets to remain undisturbed for the several billion years of evolution necessary for intelligent life to appear. Therefore, perhaps there are other civilizations in the galaxy but they are relatively recent. Finally, one hypothesis is based on the idea that alien civilizations have chosen not to communicate with us. This so-called "zoo hypothesis" argues that, even though aliens are aware that we are here, they choose not to establish contact perhaps because they want to study us better first or because they feel we are still too primitive.
Are Aliens Around Us?
Not having other intelligent civilizations contact us is evidence that they don't exist. On the other hand, we don't know how other civilizations think and they might not want to interfere with us on purpose, in line with the zoo hypothesis discussed above. But is it possible that aliens are watching and studying us right now?
Arguably the single most important evidence of extraterrestrial intelligent life is the "Wow!" Signal detected in 1977. Without going through much details, the signal's origin was at least lunar distance, it had an intelligent origin, no known satellites were in the position from where the signal was detected, the frequency used was forbidden by international agreements, and the signal was coming from no particular star system or planet. It could have been a secret satellite but, if so, why would it send a signal? It could always be some unknown natural phenomenon. For example, in 1967 Jocelyn Bell detected signals that strongly indicated the presence of extraterrestrial life; unfortunately, it was later proven that these signals had a natural origin, a celestial entity called a pulsar. Today, the "Wow!" Signal is one of the few hints of extraterrestrial intelligent life, even if of course far from proven.
Many claim to have established contact with aliens and ETs, as popularized in science fiction like in the X-Files. UFO sightings have also been widely reported, particularly in the United States, some of which by credible witnesses. On the other hand, many claim to have been contacted by god, which as an atheist I find impossible.
We must keep an open mind, though. Not far into the past people thought meteors were impossible to occur and did not believe in those who claimed to have seen them. I do think other civilizations exist in our galaxy. I think it is possible for them to come here. But I do not think it is likely they would just abduct people and perform tests without being detected.
"I think that it is much more likely that the reports of flying saucers are the results of the known irrational characteristics of terrestrial intelligence than of the unknown rational efforts of extra-terrestrial intelligence." Richard Feynman
Sources and Links
Bizony, Piers; "The Rivers of Mars: Searching for the Cosmic Origins of Life" (1997).
Brookesmith, Peter; "The Complete Sightings" (1995).
Caidin, Martin; "Ghosts of the Air" (1991). Excellent book.
Sagan, Carl.; "Contact" (1997). It doesn't feature Jodie Foster but it's still good.
Active SETI; about transmitting messages to extraterrestrial intelligences and inviting them to respond.
The Alien Jigsaw; mainly dedicated to alien abductions.
The Great Filter; interesting.
UFO Documents; at the NSA.