Editing Drake equation (section)

===Range of results===
As many skeptics have pointed out, the Drake equation can give a very wide range of values, depending on the assumptions,<ref>"The value of {{mvar|N}} remains highly uncertain. Even if we had a perfect knowledge of the first two terms in the equation, there are still five remaining terms, each of which could be uncertain by factors of 1,000." from {{cite journal |title=The search for extraterrestrial intelligence
 |author=Wilson, TL
 |journal=Nature
 |volume=409
 |issue=6823
 |pages=1110–1114
 |year=2001
 |publisher=Nature Publishing Group |bibcode = 2001Natur.409.1110W |doi = 10.1038/35059235 |pmid=11234025
 |s2cid=205014501
 }}, or more informally, "The Drake Equation can have any value from "billions and billions" to zero", Michael Crichton, as quoted in {{cite book |author=Douglas A. Vakoch |title=The Drake Equation: Estimating the prevalence of extraterrestrial life through the ages |publisher=Cambridge University Press |date=2015 |isbn=978-1-10-707365-4|display-authors=etal}}, p. 13</ref> as the values used in portions of the Drake equation are not well established.<ref name="schilling2011">{{cite web |author=Schilling |first=Govert |date=November 2011 |title=The Chance of Finding Aliens: Reevaluating the Drake Equation |url=http://www.astro-tom.com/technical_data/alien_life.htm |work=astro-tom.com}}</ref><ref name=renamed_from_2011_on_20160211035411>{{cite web|url=https://www.e-education.psu.edu/astro801/content/l12_p5.html|title=The Drake Equation|work=psu.edu}}</ref><ref>{{cite web|url=http://www.space.com/22648-drake-equation-alien-life-seager.html|title=The Drake Equation Revisited: Interview with Planet Hunter Sara Seager|author=Devin Powell, Astrobiology Magazine|work=Space.com|date=4 September 2013}}</ref><ref name=schilling2009>{{cite news|url=https://skyandtelescope.org/astronomy-news/the-chance-of-finding-aliens/|title=The Chance of Finding Aliens|author1=Govert Schilling|author2=Alan M. MacRobert|date=3 June 2009|work=Sky & Telescope}}</ref> In particular, the result can be {{math|''N'' ≪ 1}}, meaning we are likely alone in the galaxy, or {{math|''N'' ≫ 1}}, implying there are many civilizations we might contact. One of the few points of wide agreement is that the presence of humanity implies a probability of intelligence arising of greater than zero.<ref name="Dean">{{better source needed|date=August 2015}}
{{cite web
 |last        = Dean
 |first       = T.
 |date        = 10 August 2009
 |title       = A review of the Drake Equation
 |url         = http://www.cosmosmagazine.com/features/are-we-alone-a-review-drake-equation/
 |work        = [[Cosmos Magazine]]
 |access-date  = 16 April 2013
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20130603043832/http://www.cosmosmagazine.com/features/are-we-alone-a-review-drake-equation/
 |archive-date = 3 June 2013
 |df          = dmy-all
}}</ref>

As an example of a low estimate, combining NASA's star formation rates, the [[rare Earth hypothesis]] value of {{math|''f''<sub>p</sub> · ''n''<sub>e</sub> · ''f''<sub>l</sub> {{=}} 10<sup>−5</sup>}},<ref>Rare Earth, page 270: "When we take into account factors such as the abundance of planets and the location and lifetime of the habitable zone, the Drake Equation suggests that only between 1% and 0.001% of all stars might have planets with habitats similar to Earth. [...] If microbial life forms readily, then millions to hundreds of millions of planets in the galaxy have the ''potential'' for developing advanced life. (We expect that a much higher number will have microbial life.)"</ref> Mayr's view on intelligence arising, Drake's view of communication, and Shermer's estimate of lifetime:
:{{math|''R''<sub>∗</sub> {{=}} 1.5–3 yr<sup>−1</sup>}},<ref name=Robitaille/> {{math|''f''<sub>p</sub> · ''n''<sub>e</sub> · ''f''<sub>l</sub> {{=}} 10<sup>−5</sup>}},<ref name="RareEarth"/> {{math|''f''<sub>i</sub> {{=}} 10<sup>−9</sup>}},<ref name="Ernst Mayr on SETI"/> {{math|''f''<sub>c</sub> {{=}} 0.2}}<sup>[Drake, above]</sup>, and {{math|''L'' {{=}} 304}} years<ref name="Why ET Hasn’t Called"/>
gives:
:{{math|''N'' {{=}} 1.5 × 10<sup>−5</sup> × 10<sup>−9</sup> × 0.2 × 304 {{=}} 9.1 × 10<sup>−13</sup>}}
i.e., suggesting that we are probably alone in this galaxy, and possibly in the [[observable universe]].

On the other hand, with larger values for each of the parameters above, values of {{math|''N''}} can be derived that are greater than 1. The following higher values that have been proposed for each of the parameters:
:{{math|''R''<sub>∗</sub> {{=}} 1.5–3 yr<sup>−1</sup>}},<ref name=Robitaille/> {{math|''f''<sub>p</sub> {{=}} 1}},<ref name="bbc.co.uk"/> {{math|''n''<sub>e</sub> {{=}} 0.2}},<ref name="W. von Bloh, C.Bounama, M. Cuntz, and S. Franck. 2007 1365">
{{cite journal
 |last1=von Bloh |first1=W.
 |last2=Bounama |first2=C.
 |last3=Cuntz |first3=M.
 |last4=Franck |first4=S.
 |year=2007
 |title=The habitability of super-Earths in Gliese 581
 |journal=[[Astronomy & Astrophysics]]
 |volume=476 |issue=3 |pages=1365–1371
 |arxiv=0705.3758
 |bibcode=2007A&A...476.1365V
 |doi=10.1051/0004-6361:20077939
|s2cid=14475537
 }}</ref><ref name="F. Selsis, J.F. Kasting, B. Levrard, J. Paillet, I. Ribas, and X. Delfosse. 2007 1373">
{{cite journal |doi=10.1051/0004-6361:20078091 |bibcode=2007A&A...476.1373S |title=Habitable planets around the star Gl 581? |journal=[[Astronomy and Astrophysics]] |volume=476 |issue=3 |year=2007 |pages=1373–1387 |last1=Selsis |first1=Franck |last2=Kasting |first2=James F. |last3=Levrard |first3=Benjamin |last4=Paillet |first4=Jimmy |last5=Ribas |first5=Ignasi |last6=Delfosse |first6=Xavier |arxiv=0710.5294 |s2cid=11492499 |ref=Selsis |url=https://hal.archives-ouvertes.fr/hal-00182743 }}</ref> {{math|''f''<sub>l</sub> {{=}} 0.13}},<ref name="Lineweaver, C. H. & Davis, T. M. 2002 293–304">
{{cite journal
 |last1=Lineweaver |first1=C. H.
 |last2=Davis |first2=T. M.
 |year=2002
 |title=Does the rapid appearance of life on Earth suggest that life is common in the universe?
 |journal=[[Astrobiology (journal)|Astrobiology]]
 |volume=2 |issue=3 |pages=293–304
 |arxiv=astro-ph/0205014
 |bibcode=2002AsBio...2..293L
 |doi=10.1089/153110702762027871
 |pmid=12530239
|s2cid=431699
 }}</ref> {{math|''f''<sub>i</sub> {{=}} 1}},<ref name="acampbell.ukfsn.org"/> {{math|''f''<sub>c</sub> {{=}} 0.2}}<sup>[Drake, above]</sup>, and {{math|''L'' {{=}} 10<sup>9</sup>}} years<ref name="David Grinspoon 2004"/>
Use of these parameters gives:
:{{math|''N'' {{=}} 3 × 1 × 0.2 × 0.13 × 1 × 0.2 × 10<sup>9</sup> {{=}} 15,600,000}}

[[Monte Carlo method|Monte Carlo]] simulations of estimates of the Drake equation factors based on a stellar and planetary model of the Milky Way have resulted in the number of civilizations varying by a factor of 100.<ref>
{{cite journal
 |last1=Forgan |first1=D.
 |year=2009
 |title=A numerical testbed for hypotheses of extraterrestrial life and intelligence
 |journal=[[International Journal of Astrobiology]]
 |volume=8 |issue=2 |pages=121–131
 |arxiv=0810.2222
 |bibcode=2009IJAsB...8..121F
 |doi=10.1017/S1473550408004321
|s2cid=17469638
 }}</ref>