"Where is everybody" An exploration of the Fermi Paradox

Historical background

Over a 1950 summer lunch at the Los Alamos National Laboratory, the great physicist Enrico Fermi asked his colleagues an unexpected question – “Don’t you ever wonder where everybody is?” Laughter went around the table as everyone immediately knew that he was talking about extraterrestrial intelligence [1]. If life arises fairly commonly, as Fermi believed, it follows that there should be advanced civilizations with the desire to visit and colonize Earth close enough to do so. However, there is no incontrovertible evidence of aliens on Earth, either now or in the past. This is called the Fermi Paradox. The lack of observational evidence for extraterrestrial intelligence is known as the ‘Great Silence.’[13]

Giuseppe Cocconi and Philip Morrison published a paper in Nature in September 1959, in which they suggest a probable frequency at which alien civilizations would attempt to communicate: 1.420 GHz. This is the frequency of electromagnetic radiation emitted by neutral Hydrogen during a change of energy state. The frequency is an important physical and astronomical value, would almost certainly be known by any civilization capable of communication, and it requires only relatively simple technology to broadcast at this frequency. As Cocconi and Morrison put it, “It is reasonable to expect that sensitive receivers for this frequency would be made at an early stage of the development of radioastronomy. That would be the expectation of the operators of the assumed source, and the present state of terrestrial instruments indeed justifies the expectation.” In other words, it makes sense that aliens would come to the same conclusion about the 1.420 GHz frequency. If the aliens want to communicate with us...

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...ky & Telescope. Retrieved 11/29/2013

[8] http://www.webcitation.org/5n7VYJBUd Hanson, Robin (1998). "The Great Filter — Are We Almost Past It?". Archived from the original on 2009-01-28.

[9] Ward, Peter D.; Brownlee, Donald (2000). Rare Earth: Why Complex Life is Uncommon in the Universe. Copernicus Books (Springer Verlag). ISBN 0-387-98701-0.

[10] http://adsabs.harvard.edu/abs/1973Icar...19..347B

[11] http://www.daviddarling.info/encyclopedia/S/sentinelhypoth.html

[12] http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1975QJRAS..16..128H&db_key=AST&page_ind=0&plate_select=NO&data_type=GIF&type=SCREEN_GIF&classic=YES

[13] http://www.brin-l.com/downloads/silence.pdf

[14] Kukla, A. (2009). Extraterrestrials: A Philosophical Perspective. Lexington Books. p. 20.ISBN 9780739142455. LCCN 2009032272.

[15] http://news.bbc.co.uk/2/hi/uk_news/8642558.stm