Editing Fermi paradox (section)

=== Drake equation ===
{{Main|Drake equation}}

The theories and principles in the [[Drake equation]] are closely related to the Fermi paradox.<ref>Gowdy, Robert H., VCU Department of Physics [http://www.courses.vcu.edu/PHY-rhg/astron/html/mod/019/s5.html SETI: Search for ExtraTerrestrial Intelligence. The Interstellar Distance Problem] {{Webarchive|url=https://web.archive.org/web/20181226013330/https://courses.vcu.edu/PHY-rhg/astron/html/mod/019/s5.html |date=December 26, 2018 }}, 2008</ref> The equation was formulated by [[Frank Drake]] in 1961 in an attempt to find a systematic means to evaluate the numerous probabilities involved in the existence of alien life. The equation is:

:<math>N = R_* \cdot f_\mathrm{p} \cdot n_\mathrm{e} \cdot f_\mathrm{l} \cdot f_\mathrm{i} \cdot f_\mathrm{c} \cdot L</math>

Where <math>N</math> is the number of technologically advanced civilizations in the Milky Way galaxy, and <math>N</math> is asserted to be the product of 
* <math>R_*</math>, the rate of formation of stars in the galaxy;
* <math>f_p</math>, the fraction of those stars with planetary systems;
* <math>n_e</math>, the number of planets, per solar system, with an environment suitable for organic life;
* <math>f_l</math>, the fraction of those suitable planets whereon organic life appears;
* <math>f_i</math>, the fraction of life-bearing planets whereon ''intelligent'' life appears;
* <math>f_c</math>, the fraction of civilizations that reach the technological level whereby detectable signals may be dispatched; and
* <math>L</math>, the length of time that those civilizations dispatch their signals.

The fundamental problem is that the last four terms (<math>f_l</math>, <math>f_i</math>, <math>f_c</math>, and <math>L</math>) are entirely unknown, rendering statistical estimates impossible.<ref>{{cite arXiv|last1=Sandberg|first1=Anders|last2=Drexler|first2=Eric|last3=Ord|first3=Toby|date=2018-06-06|title=Dissolving the Fermi Paradox|class=physics.pop-ph|eprint=1806.02404}}</ref>

The Drake equation has been used by both optimists and pessimists, with wildly differing results. The first scientific meeting on the [[search for extraterrestrial intelligence]] (SETI), which had 10 attendees including Frank Drake and [[Carl Sagan]], speculated that the number of civilizations was roughly between 1,000 and 100,000,000 civilizations in the Milky Way galaxy.<ref>{{cite book | last1 = Drake | first1 = F. | last2 = Sobel |first2 = D. | year = 1992 | title = Is Anyone Out There? The Scientific Search for Extraterrestrial Intelligence | pages = 55–62 | publisher = Delta | isbn = 978-0-385-31122-9}}</ref> Conversely, [[Frank J. Tipler|Frank Tipler]] and [[John D. Barrow]] used pessimistic numbers and speculated that the average number of civilizations in a galaxy is much less than one.<ref>{{BarrowTipler1986|page=588}}</ref> Almost all arguments involving the Drake equation suffer from the [[overconfidence effect]], a common error of probabilistic reasoning about low-probability events, by guessing specific numbers for likelihoods of events whose mechanism is not understood, such as the likelihood of [[abiogenesis]] on an Earth-like planet, with estimates varying over many hundreds of [[order of magnitude|orders of magnitude]]. An analysis that takes into account some of the uncertainty associated with this lack of understanding has been carried out by [[Anders Sandberg]], [[Eric Drexler]] and [[Toby Ord]],<ref>{{cite arXiv |eprint=1806.02404 |title=Dissolving the Fermi Paradox |author=Anders Sandberg |author2=Eric Drexler |author3=Toby Ord |date=June 6, 2018 |class=physics.pop-ph }}</ref> and suggests "a substantial ''[[ex ante]]'' probability of there being no other intelligent life in our observable universe".