Editing Fermi paradox (section)

==== Intelligent alien species have not developed advanced technologies ====
[[File:Neanderthal Flintworkers (Knight, 1920).jpg|thumb|300px|''[[Le Moustier]]'' [[Neanderthal]]s ([[Charles R. Knight]], 1920)]]
It may be that while alien species with intelligence exist, they are primitive or have not reached the level of technological advancement necessary to communicate. Along with non-intelligent life, such civilizations would also be very difficult to detect.<ref name="Tarter-NYAS">{{cite journal| last1=Tarter| first1=Jill| title=What is SETI?| journal=Annals of the New York Academy of Sciences| volume=950|issue=1|pages=269–275|date=2006| pmid=11797755|doi=10.1111/j.1749-6632.2001.tb02144.x|bibcode = 2001NYASA.950..269T | s2cid=27203660}}</ref> A trip using conventional rockets would take hundreds of thousands of years to reach the nearest stars.<ref>{{cite magazine |title=Are Alien Civilizations Technologically Advanced? |url=https://blogs.scientificamerican.com/observations/are-alien-civilizations-technologically-advanced/ |magazine=Scientific American |first=Abraham |last=Loeb |date=January 8, 2018 |access-date=January 11, 2018 |archive-url=https://web.archive.org/web/20180112100817/https://blogs.scientificamerican.com/observations/are-alien-civilizations-technologically-advanced/ |archive-date=January 12, 2018 |url-status=live }}</ref>

To skeptics, the fact that over the history of life on the Earth, only one species has developed a civilization to the point of being capable of [[spaceflight]] and radio technology, lends credence to the idea that technologically advanced civilizations are rare in the universe.<ref>{{cite news |title=The Intelligent-Life Lottery |url=https://www.nytimes.com/2014/08/19/science/in-search-for-intelligent-life-consider-the-lottery.html |newspaper=The New York Times |date=August 18, 2014 |first=George |last=Johnson |access-date=March 1, 2017 |archive-url=https://web.archive.org/web/20170324212404/https://www.nytimes.com/2014/08/19/science/in-search-for-intelligent-life-consider-the-lottery.html |archive-date=March 24, 2017 |url-status=live }}</ref>

Amedeo Balbi and Adam Frank propose the concept of an "[[oxygen]] bottleneck" for the emergence of technospheres. The "oxygen bottleneck" refers to the critical level of atmospheric oxygen necessary for [[fire]] and [[combustion]]. Earth's [[Atmosphere of Earth|atmospheric]] oxygen concentration is about 21%, but has been much lower in the past and may also be on many exoplanets. The authors argue that while the threshold of oxygen required for the existence of complex life and [[ecosystem]]s is much lower, technological advancement, particularly that reliant on combustion, such as [[Smelting|metal smelting]] and [[Energy development|energy production]], requires higher oxygen concentrations of around 18% or more. Thus, the presence of high levels of oxygen in a planet's atmosphere is not only a potential biosignature but also a critical factor in the emergence of detectable technological civilizations.<ref>{{Cite journal |last1=Balbi |first1=Amedeo |last2=Frank |first2=Adam |date=28 December 2023 |title=The oxygen bottleneck for technospheres |url=https://www.nature.com/articles/s41550-023-02112-8 |journal=Nature Astronomy |language=en |volume=8 |issue=1 |pages=39–43 |doi=10.1038/s41550-023-02112-8 |issn=2397-3366|arxiv=2308.01160 }}</ref>

Another hypothesis in this category is the "Water World hypothesis". According to author and scientist [[David Brin]]: "it turns out that our Earth skates the very inner edge of our sun's continuously habitable—or '[[Habitable zone|Goldilocks]]'—zone. And Earth may be anomalous. It may be that because we are so close to our sun, we have an anomalously oxygen-rich atmosphere, and we have anomalously little ocean for a water world. In other words, 32 percent continental mass may be high among water worlds..."<ref name="DB_2012" /> Brin continues, "In which case, the evolution of creatures like us, with hands and fire and all that sort of thing, may be rare in the galaxy. In which case, when we do build starships and head out there, perhaps we'll find lots and lots of life worlds, but they're all like Polynesia. We'll find lots and lots of intelligent lifeforms out there, but they're all dolphins, whales, squids, who could never build their own starships. What a perfect universe for us to be in, because nobody would be able to boss us around, and we'd get to be the voyagers, the ''Star Trek'' people, the starship builders, the policemen, and so on."<ref name="DB_2012">{{cite magazine |url=https://www.wired.com/2012/08/geeks-guide-david-brin/ |title=Why David Brin Hates Yoda, Loves Radical Transparency |archive-url=https://web.archive.org/web/20190406204416/https://www.wired.com/2012/08/geeks-guide-david-brin/ |archive-date=April 6, 2019 |url-status=live |magazine=Wired |date=August 8, 2012}}</ref>

The rapid increase of scientific and technological progress seen in the 19th and 20th centuries (the [[Industrial Revolution]]), compared to earlier eras, led to the common assumption that such progresses will keep growing at exponential rates as time goes by, eventually leading to the progress level required for space exploration. The "universal limit to technological development" (ULTD) hypothesis proposes that there is a limit to the potential growth of a civilization, and that this limit may be placed well below the point required for space exploration. Such limits may be based on [[#Lack of resources needed to physically spread throughout the galaxy|economic reasons]], natural reasons (such as [[faster-than-light]] travel being impossible), and even limitations based on the species' own biology.<ref>{{cite web |url= https://www.space.com/lack-of-intelligent-aliens-universal-technological-development-limit|title= Why haven't we found intelligent alien civilizations? There may be a 'universal limit to technological development'|author= Conor Feehly|date= October 9, 2024|publisher= Space.com|accessdate=October 21, 2024}}</ref>