At the heart of the Fermi paradox is the question, ” So? Where is everybody?”
The argument is that if our solar system is typical of solar systems in the Milky Way, and the Earth is typical (or even atypical) of the planets in these solar systems then there should be life on many other planets. If there is life on all these other planets then why haven’t we, on planet Earth, found evidence of that life?
If there are billions of other civilisations in the universe at varying stages of evolution shouldn’t we have been visited by more advanced civilisations or simply have found evidence of them via radio signals?
Enrico Fermi first asked the question,So? Where is everybody? in a casual discussion with colleagues at the Los Alamos laboratory in 1950, but the question has been discussed, analysed and expanded ever since.
Mathematicians have used a statistical approach to the paradox using equations to estimate the probability of life on other planets, the most famous of these equations being the Drake Equation by Frank Drake (1960). This approach is fatally flawed in that it makes assumptions based on our planet and solar system that may not necessarily be true (anthropic bias). These assumptions include the fraction of planets that will support life, the time for a civilisation to arise and fall, the odds of life becoming intelligent and the odds of a civilisation becoming communicative.
The flaws in the equation are illustrated in the widely different answers that users can achieve using it. Carl Sagan used the equation to predict up to one million civilisations in the Milky Way, whilst Frank Tippler predicted less than one. Both sides admit that the equation fails if one assumes that civilisations leave their own solar system to colonise, surely a pre-requisite of our planet being visited by inter stellar travellers.
The common sense approach to the statistical problem is that even if Earth is atypical of planets then in a galaxy that contains 250 billion stars and is over 13 billion years old then surely there must be life out there somewhere, and it has had time to leave evidence of its presence.
The likelihood of extra-terrestrial life, it is argued, is increased by the fact that intelligent life would seek to overcome adversity and scarcity by adapting to new environments and seeking out new resources where necessary. This would include inter-stellar travel for more advanced civilisations, which even if it did not reach our back water of the galaxy, should surely leave its marks close enough for us to see or hear.
Given this vast supposed statistical probability of life on other planets Fermi’s question seems even more valid,” So? Where are they?”
Various approaches have been made to proving life exists on other planets. Again we are limited by the anthropic bias of looking for us. We search for radio signals, assuming other life forms will use some form of radio waves, we look for energy consumption in far off solar systems, assuming energy production and consumption along lines typical to our own.
Our technology means that inferences are made from minor fluctuations. As our technology advances we may be able to see other planets directly, at least clearly enough to conduct spectrographic analysis of their atmospheres. At the moment cutting edge technology is still only inferring the presence of planets in other solar systems, along with their possible mass and atmosphere, from the properties of their suns.
The technology argument, that we don’t have the technology to detect other life, can also be used both ways. Maybe other civilisations don’t have the technologies to see us, or if they do, maybe we can’t detect their technology. We send out probes and long range radio messages, Do other civilisations? Would we recognize them if we found them?
The absence of evidence has been taken by some observers to be evidence of absence. These theories take the view that the earth is special is some way (Rare Earth hypothesis), or that life is harder to maintain than we assume (The Great Filter).
Maybe it is the nature of life to destroy itself (Doomsday argument), or to destroy other life, in which case we don’t wan to receive visitors as surely visitors would be more advanced than us. Of course the religious argument for us being alone falls into this camp.
The Fermi Paradox can only be answered by conclusive evidence for life from other planets, ET at my local supermarket. ET on the Whitehouse lawn won’t do in this age of computer graphics and special effects. Fermi’s Paradox asks “So? Where are they?” Statistically, life from other planets should be here with us, but we have no evidence to support its existence.
http://zebu.uoregon.edu/~js/cosmo/lectures/lec28.htmlEW56Bhttp://zebu.uoregon.edu/~js/cosmo/lectures/lec28.htmlWH6PDZ6EFP
http://en.wikipedia.org/wiki/Fermi_paradox
