Editing Fermi paradox (section)

=== Electromagnetic emissions ===
{{Further|Project Phoenix (SETI)|SERENDIP|Allen Telescope Array}}
[[File:parkes.arp.750pix.jpg|thumb|left|[[Radio telescope]]s are often used by SETI projects.]]
Radio technology and the ability to construct a [[radio telescope]] are presumed to be a natural advance for technological species,<ref>{{cite web
|last=Mullen
|first=Leslie
|date=2002
|url=http://www.space.com/scienceastronomy/alien_intelligence_021202.html
|archive-url=https://web.archive.org/web/20030212141854/http://www.space.com/scienceastronomy/alien_intelligence_021202.html
|url-status=dead
|archive-date=February 12, 2003
|title=Alien Intelligence Depends on Time Needed to Grow Brains
|work=Astrobiology Magazine
|publisher=Space.com
|access-date=April 21, 2006
}}</ref> theoretically creating effects that might be detected over interstellar distances. The careful searching for non-natural radio emissions from space may lead to the detection of alien civilizations. Sensitive alien observers of the Solar System, for example, would note unusually intense [[radio wave]]s for a [[Star#Classification|G2 star]] due to Earth's television and telecommunication broadcasts. In the absence of an apparent natural cause, alien observers might infer the existence of a terrestrial civilization. Such signals could be either "accidental" by-products of a civilization, or deliberate attempts to communicate, such as the [[Arecibo message]]. It is unclear whether "leakage", as opposed to a deliberate beacon, could be detected by an extraterrestrial civilization. The most sensitive radio telescopes on Earth, {{as of|2019|lc=y}}, would not be able to detect non-directional radio signals (such as [[broadband]]) even at a fraction of a [[light-year]] away,<ref>{{cite journal | title=The benefits and harm of transmitting into space | last1=Haqq-Misra | first1=Jacob | last2=Busch | first2=Michael W. | last3=Som | first3=Sanjoy M. | last4=Baum | first4=Seth D. | display-authors=1 | journal=Space Policy | volume=29 | issue=1 | pages=40–48 | date=February 2013 | doi=10.1016/j.spacepol.2012.11.006 | arxiv=1207.5540 | bibcode=2013SpPol..29...40H }} See table 1.</ref> but other civilizations could hypothetically have much better equipment.<ref>{{cite journal |last=Scheffer | first=L. |year=2004 |title=Aliens can watch 'I Love Lucy' |journal=Contact in Context |volume=2 |issue=1 | url=https://lscheffer.com/tv.pdf | access-date=2024-02-02}}</ref><ref>{{cite web |title=Radio Leakage: Is anybody listening? |first=Brian |last=von Konsky |date=October 23, 2000 |url=https://www.researchgate.net/publication/242237960}}</ref>

A number of astronomers and observatories have attempted and are attempting to detect such evidence, mostly through SETI organizations such as the [[SETI Institute]] and [[Breakthrough Listen]]. Several decades of SETI analysis have not revealed any unusually bright or meaningfully repetitive radio emissions.<ref>{{cite arXiv |author=Participants, NASA |year=2018 |title=NASA and the Search for Technosignatures: A Report from the NASA Technosignatures Workshop |eprint=1812.08681|class=astro-ph.IM }}</ref>