Hart–Tipler conjecture

{{Short description|Idea that there is no evidence of aliens because they do not exist}}

The Hart–Tipler conjecture is the idea that an absence of detectable Von Neumann probes is contrapositive evidence that no intelligent life exists outside of the Solar System.{{cite journal |last1=Costa-Leite |first1=Alexandre |title=Formalizing the Fermi paradox and combining consistent explanatory hypotheses |journal=International Journal of Astrobiology |date=18 October 2022 |volume=22 |issue=2 |pages=111–117 |doi=10.1017/S1473550422000374 |s2cid=253014320 |url=https://www.cambridge.org/core/journals/international-journal-of-astrobiology/article/formalizing-the-fermi-paradox-and-combining-consistent-explanatory-hypotheses/BD46970FFDCDD657ADB3698756CB98E3 |access-date=18 October 2022|url-access=subscription }}{{cite journal |last1=Gray |first1=Robert H. |title=The Fermi Paradox Is Neither Fermi's Nor a Paradox |journal=Astrobiology |date=March 2015 |volume=15 |issue=3 |pages=195–199 |doi=10.1089/ast.2014.1247|pmid=25719510 |arxiv=1605.09187 |bibcode=2015AsBio..15..195G }} This idea was first proposed in opposition to the Drake equation in a 1975 paper by Michael H. Hart titled "Explanation for the Absence of Extraterrestrials on Earth".{{cite journal |last1=Hart |first1=Michael H. |title=Explanation for the Absence of Extraterrestrials on Earth |journal=Quarterly Journal of the Royal Astronomical Society |date=1 June 1975 |volume=16 |pages=128 |bibcode=1975QJRAS..16..128H |url=https://ui.adsabs.harvard.edu/abs/1975QJRAS..16..128H/abstract |access-date=18 October 2022 |issn=0035-8738}} Assuming that the probes traveled at 1/10 the speed of light and that no time was lost in building new ships upon arriving at the destination, Hart surmised that a wave of Von Neumann probes could cross the galaxy in approximately 650,000 years, a comparatively minimal span of time relative to the estimated age of the universe at 13.7 billion years. Hart’s argument was extended by cosmologist Frank Tipler in his 1981 paper entitled "Extraterrestrial intelligent beings do not exist".{{Cite web |last=Patton |first=Paul |date=2015-04-08 |title=Beyond "Fermi's Paradox" II: Questioning the Hart-Tipler Conjecture |url=https://www.universetoday.com/119735/beyond-fermis-paradox-ii-questioning-the-hart-tipler-conjecture/ |access-date=2024-02-23 |website=Universe Today |language=en-US}}

The conjecture is the first of many proposed solutions to the Fermi paradox (the conflict between the lack of obvious evidence for alien life and various high probability estimates for its existence).{{cite book |last1=Dick |first1=Steven J. |title=Space, Time, and Aliens |chapter=Bringing Culture to Cosmos: Cultural Evolution, the Postbiological Universe, and SETI |date=2020 |pages=171–190 |doi=10.1007/978-3-030-41614-0_12 |chapter-url=https://link.springer.com/chapter/10.1007/978-3-030-41614-0_12 |access-date=18 October 2022 |publisher=Springer International Publishing |isbn=978-3-030-41613-3 |s2cid=219414685 |language=en}}{{cite journal |last1=Ostro |first1=Steven J. |last2=Sagan |first2=Carl |title=Cosmic Collisions and the Longevity of Non-Spacefaring Galactic Civilizations |journal=Astronomy & Geophysics |date=May 1998 |volume=39 |issue=4 |pages=4.22–4.24 |doi=10.1093/astrog/39.4.4.22 |url=https://academic.oup.com/astrogeo/article-pdf/39/4/4.22/464255/39-4-4.22.pdf |access-date=18 October 2022}} In this case, the solution is that there is no other intelligent life because such estimates are incorrect.{{cite news |last1=Williams |first1=Matt |title=Beyond "Fermi's Paradox" V: What is the Aestivation Hypothesis? |url=https://www.universetoday.com/147161/beyond-the-fermi-paradox-v-what-is-the-aestivation-hypothesis/ |access-date=18 October 2022 |work=Universe Today |date=7 August 2020}} The conjecture is named after astrophysicist Michael H. Hart and mathematical physicist and cosmologist Frank Tipler.{{cite news |last1=Patton |first1=Paul |title=Beyond "Fermi's Paradox" II: Questioning the Hart-Tipler Conjecture |url=https://www.universetoday.com/119735/beyond-fermis-paradox-ii-questioning-the-hart-tipler-conjecture/|access-date=18 October 2022 |work=Universe Today |date=8 August 2015}}