Fermi paradox
The Fermi paradox is the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilizations and the lack of evidence for, or contact with, such civilizations. The paradox takes its name from physicist Enrico Fermi, who put it forward in informal discussions during the 1950's.
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[edit] Premise
A succinct paraphrase might be where is everybody? As far as we can tell from our limited data set (we only have one documented case of the emergence of intelligence and civilization), intelligent life in the universe should be relatively common. The Fermi paradox is an open question, an invitation to ponder what particular assumption we are making that has led there to be no apparent evidence for extraterrestrial intelligence.
Given even conservative estimates for the components of the Drake equation, it is still possible to arrive at very large figures for the number of intelligent civilisations in the galaxy, hence the reasons that many scientists consider exobiology a reasonably respectable subject to ponder rather than outright quackery. However, there is still no empirical evidence for extraterrestrial life or intelligence. Essentially, either one or more components of the Drake equation has a value far lower than even our most conservative estimates, or there is one factor missing. In more recent years, the focus has been on the final component of the Drake equation; that of the longevity of civilisations and their ability to be observed.
[edit] Resolving the paradox
There are several possible resolutions to the Fermi paradox based around looking at components of the Drake equation and figuring out the plausibility of each, indicating what is and what is not particularly likely:
- It is rare for life to evolve. It's hard to evaluate this plausibility of this until we know more about the origin of life. But, speaking from the Copernican principle, there isn't anything about the physical or chemical composition of the Earth or the solar system that suggests extreme rarity. Even if only one in a billion star systems have earthlike planets in them, that's still hundreds of billions of potential sources for life that we could recognise as such.
- It is rare for intelligence to evolve. Again, going by what we know about Earth, and assuming in general that the Earth isn't in any sort of cosmically privileged position, this proposed rarity is hard to account for; but impossible to decide either way until we have more evidence. In general, the more closely we examine them, the more we find intriguing evidence of cleverness in many animals. Given the millions of potential years for an evolutionary timescale, it's not unreasonable to posit that wherever life evolves, something intelligent must pop up sooner or later.
- It's rare for intelligent beings to reach a sufficient level of technology to communicate their presence. In the case of Earth, our radio transmissions have made us visible to anyone who may have been interested for the past several decades - but the switch to wired internet, directional satellites and short-range microwave transceivers for mobile phones is quickly diminishing this. Another possibility is that alien civilizations develop means for communication that are as efficient as ours or more but far less detectable. However - as with the SETI program - species could always deliberately advertise themselves. Even if most species don't, statistically speaking we should be able to come across signals from those that do.
- Intelligent beings are vulnerable to (self)-destruction Intelligence typically evolves prior to the psychological traits that are necessary to use that intelligence sanely. Humans have conceived of nuclear, radiological, chemical, and biological weapons of mass destruction, yet have not progressed very much psychologically since the age of killing each other with rocks and spears. Maybe the period during which an intelligence can survive without being destroyed, either by itself or some kind of natural catastrophe, is too small to allow contact.
- The evidence is already there, but we can't detect it. The possibilities range from a government conspiracy to withhold contact to messages/media that are quite literally too "alien" for us to perceive. (e.g. Our own era of pumping out vast quantities of easily-decoded AM audio and video may only run about a hundred years, as broadcasting shifts to digital encoding with the frequency spectrum of white noise if you don't know what's encoded in it.)
- We're just not interesting enough to contact. We probably shouldn't write this one off - the more we explore the cosmos, the more human pretensions to uniqueness and importance we tend to have punctured. But - if extraterrestrial intelligence is everywhere, the more likely it is that one aspect of it will contact us - even if it's a rogue or a renegade. Alternatively, if intelligence is an extreme rarity, it makes all the more sense to try and contact someone else. Of course, there is the possibility that we are being shepherded carefully by some advanced indetectible intelligence, but if that's the case it isn't clear how we should be modifying our behavior or that we should stop looking for anyone else.
- Maybe we're just early to the party. It took about half of the estimated habitable time frame of Earth for humans to evolve. On a universal scale, we're estimated to be relatively early in the possible time frame of the universe (The Earth being 4.54 billion years old in a universe that is "only" 13.75 ± 0.11 billion years old.). It's entirely possible that we're one of the first intelligences to evolve, and thus everyone else that exists are simply in currently non-intersecting light cones.
- Humans evolved from a uniquely social species. Other intelligent species might not have the same motivation to communicate as humans do, or have a natural system of communication that obviates the need for radio technology. Or frequently leapfrogged past broadcast technology for other reasons.
[edit] Go away
Consider what usually happened in Earth's history when a technologically superior civilization encountered a less advanced one. Odds are any intelligent life form out there will be more interested in any resources Earth could offer them than they are in us. It might not be a good idea to deliberately attract their attention.
[edit] See also
- Drake Equation
- The Great Filter
- Stephen Webb. 2002. Where Is Everybody? Fifty Solutions to the Fermi paradox and the Problem of Extraterrestrial Life. New York: Copernicus Books. ISBN 978-0387955018.