Editing Fermi paradox (section)

==Chain of reasoning==
Some of the facts and hypotheses that together serve to highlight the apparent contradiction:
* There are billions of stars in the [[Milky Way]] similar to the [[Sun]].<ref>{{cite encyclopedia |title=Star (astronomy) |encyclopedia=Encyclopædia Britannica |url=https://www.britannica.com/topic/star-astronomy |access-date=February 4, 2016 |archive-url=https://web.archive.org/web/20160301055912/https://www.britannica.com/topic/star-astronomy |archive-date=March 1, 2016 |url-status=live}} "With regard to mass, size, and intrinsic brightness, the Sun is a typical star." Technically, the sun is near the middle of the main sequence of the [[Hertzsprung–Russell diagram]]. This sequence contains 80–90% of the stars of the galaxy. [http://astro.unl.edu/naap/hr/hr_background3.html] {{Webarchive|url=https://web.archive.org/web/20110716170751/http://astro.unl.edu/naap/hr/hr_background3.html|date=July 16, 2011}}</ref><ref>{{cite news |last1=Grevesse |first1=N. |last2=Noels |first2=A. |last3=Sauval |first3=A. J. |title=Standard abundances |journal=ASP Conference Series |volume=99 |page=117 |year=1996 |quote=The Sun is a normal star, though dispersion exists.|bibcode=1996ASPC...99..117G }}</ref>
* With high probability, some of these stars have Earth-like planets in a [[circumstellar habitable zone]].<ref>{{cite journal |last1=Buchhave |first1=Lars A. |last2=Latham |first2=David W. |last3=Johansen |first3=Anders |last4=Bizzarro |first4=Martin |last5=Torres |first5=Guillermo |last6=Rowe |first6=Jason F. |last7=Batalha |first7=Natalie M. |last8=Borucki |first8=William J. |last9=Brugamyer |first9=Erik |last10=Caldwell |first10=Caroline |last11=Bryson |first11=Stephen T. |last12=Ciardi |first12=David R. |last13=Cochran |first13=William D. |last14=Endl |first14=Michael |last15=Esquerdo |first15=Gilbert A. |last16=Ford |first16=Eric B. |last17=Geary |first17=John C. |last18=Gilliland |first18=Ronald L. |last19=Hansen |first19=Terese |last20=Isaacson |first20=Howard |last21=Laird|first21=John B. |last22=Lucas |first22=Philip W. |last23=Marcy |first23=Geoffrey W. |last24=Morse |first24=Jon A. |last25=Robertson |first25=Paul |last26=Shporer |first26=Avi |last27=Stefanik |first27=Robert P. |last28=Still |first28=Martin |last29=Quinn |first29=Samuel N. |display-authors=3 
|date=2012 
|title=An abundance of small exoplanets around stars with a wide range of metallicities 
|journal=[[Nature (journal)|Nature]] 
|volume=486 |issue= 7403 |pages=375–377 
|bibcode= 2012Natur.486..375B 
|issn=0028-0836 
|doi=10.1038/nature11121 
|pmid=22722196 
|s2cid=4427321}}</ref> 
* Many of these stars, and hence their planets, are much older than the Sun.<ref>{{cite journal 
|last=Schilling |first=G. |date=June 13, 2012 |url=https://www.science.org/content/article/scienceshot-alien-earths-have-been-around-while |title=ScienceShot: Alien Earths Have Been Around for a While |journal=[[Science (journal)|Science]] |access-date=January 6, 2015 |archive-url=https://web.archive.org/web/20150809002119/http://news.sciencemag.org/2012/06/scienceshot-alien-earths-have-been-around-while |archive-date=August 9, 2015 |url-status=live
}}</ref><ref>{{Cite journal |author1=Aguirre, V. Silva |author2=G. R. Davies |author3= S. Basu |author4=J. Christensen-Dalsgaard |author5= O. Creevey |author6=T. S. Metcalfe |author7= T. R. Bedding |title=Ages and fundamental properties of Kepler exoplanet host stars from asteroseismology |journal=Monthly Notices of the Royal Astronomical Society |volume=452 |issue=2 |pages=2127–2148 |date=2015 |arxiv=1504.07992|display-authors=etal |doi=10.1093/mnras/stv1388 |doi-access=free |bibcode=2015MNRAS.452.2127S |s2cid=85440256}} Accepted for publication in MNRAS. See Figure 15 in particular.</ref> If Earth-like planets are typical, some may have developed [[human intelligence|intelligent]] life long ago.
* Some of these [[civilization]]s may have developed [[interstellar travel]], a step that humans are investigating.<ref>{{Cite web|url=https://science.nasa.gov/mission/voyager/interstellar-mission|title=Voyager Interstellar Mission|date=March 14, 2024 |publisher=NASA|access-date=2024-11-16}}</ref>
* Even at the slow pace of envisioned interstellar travel, the Milky Way galaxy could be completely traversed in a few million years.<ref name="Hart">{{cite journal
|title = Explanation for the Absence of Extraterrestrials on Earth
|last = Hart
|first = Michael H.
|journal = [[Quarterly Journal of the Royal Astronomical Society]]
|volume = 16 |pages = 128–135
|date = 1975
|bibcode=1975QJRAS..16..128H}}</ref>
* Since many of the Sun-like stars are billions of years older than the Sun, the Earth should have already been visited by extraterrestrial civilizations, or at least their probes.<ref>{{cite book |title=The Living Cosmos: Our Search for Life in the Universe |author=Chris Impe |publisher=Cambridge University Press |date=2011 |isbn=978-0-521-84780-3| page=282}}</ref>
* However, there is no convincing evidence that this has happened.<ref name="Hart"/>