Fermi paradox
From The Book of THoTH (Leaves of Wisdom)
The Fermi Paradox is a physical paradox in which high estimates of the probability of the existence of extraterrestrial life are contrasted with a lack of evidence.
The age of the universe and its vast number of stars seem to suggest that extraterrestrial life should be common. Considering this with colleagues over lunch in 1950, the physicist Enrico Fermi is said to have asked: "Where are they?" If there are a multitude of advanced extraterrestrial civilizations in the Milky Way galaxy then why have we not seen any evidence, such as probes, spacecraft or radio transmissions? The simple question "Where are they?" (alternatively, "Where is everybody?") is possibly apocryphal but Fermi is widely credited with simplifying and clarifying the problem of the probability of extraterrestrial life.
There have been attempts to resolve the Fermi Paradox by locating evidence of extraterrestrial civilizations, along with proposals that such life could exist without our knowledge. Counterarguments suggest that intelligent extraterrestrial life does not exist or at least occurs so rarely that we will never make contact with it. The belief that the lack of evidence conclusively demonstrates the non-existence of extraterrestrial civilizations is known as the Fermi principle.
A great deal of effort has gone into developing scientific theories and possible models of extraterrestrial life and the Fermi paradox has become a theoretical reference point in much of this work. The problem has spawned numerous scholarly works addressing it directly, while various questions that relate to it have been addressed in fields as diverse as astronomy, biology, ecology and philosophy. The emerging field of astrobiology has brought an interdisciplinary approach to the Fermi paradox and the question of extraterrestrial life.
Basis of the paradox: argument by scale and a lack of evidence
The Fermi paradox is a conflict between an argument of scale and probability, and a lack of evidence. A more complete definition could be stated thus:
The size and age of the universe incline us to believe that many technologically advanced civilizations must exist. However, this belief seems logically inconsistent with our lack of observational evidence to support it. Either the initial assumption is incorrect and technologically advanced intelligent life is much rarer than we believe, our current observations are incomplete and we simply have not detected them yet, or our search methodologies are flawed and we are not searching for the correct indicators.
The first aspect of the paradox, "the argument by scale", is a function of the raw numbers involved: there are an estimated 250 billion stars in the Milky Way and seventy sextillion (7 x 1022) in the universe. Even if intelligent life occurs on only a minuscule percentage of planets, there should still be a great number of civilizations extant in our galaxy alone. This argument also assumes the mediocrity principle, which states that Earth is not special, but merely a typical planet, subject to the same laws, effects, and likely outcomes as any other world. Some estimates using the Drake equation (see below) support this argument, although the assumptions behind those calculations have themselves been challenged.
The second cornerstone of the Fermi paradox is a rejoinder to the argument by scale: given intelligent life's ability to overcome scarcity, and its tendancy to colonize new habitats, we have assumed that any advanced civilization would seek out new resources and colonize first their solar system, and then surrounding solar systems. As there is no evidence on Earth or anywhere else of attempted alien colonization after 13 billion years of the universe's history, we must assume that intelligent life is rare in our part of the galaxy, or that our assumptions about the general behavior of intelligent species is flawed.
Several writers have tried to estimate how fast an alien civilization might spread through the galaxy. There have been estimates of anywhere from 5 million to 50 million years to colonize the entire galaxy; a relatively small amount of time on a geological scale, let alone a cosmological one. Even if colonization is impractical or undesirable to an alien civilization, large scale exploration of the galaxy is still possible with minor investment in energy and resources. The means of exploration and theoretical probes involved are discussed extensively.
--Angel 15:49, 15 May 2006 (CDT)
