The Hart–Tipler conjecture is the idea that an absence of detectable

Von Neumann probe The concept of self-replicating spacecraft, as envisioned by mathematician John von Neumann, has been described by futurists and has been discussed across a wide breadth of hard science fiction novels and stories. Self-replicating probes are som ...

s is

contrapositive In logic and mathematics, contraposition, or ''transposition'', refers to the inference of going from a Conditional sentence, conditional statement into its logically equivalent contrapositive, and an associated proof method known as . The contrap ...

evidence that no intelligent life exists outside of the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

. This idea was first proposed in opposition to the

Drake equation The Drake equation is a probability theory, probabilistic argument used to estimate the number of active, communicative extraterrestrial life, extraterrestrial civilizations in the Milky Way Galaxy.Physics Today 14 (4), 40–46 (1961). The e ...

in a 1975 paper by Michael H. Hart titled "Explanation for the Absence of Extraterrestrials on Earth". 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". The conjecture is the first of many proposed solutions to the

Fermi paradox The Fermi paradox is the discrepancy between the lack of conclusive evidence of advanced extraterrestrial life and the apparently high likelihood of its existence. Those affirming the paradox generally conclude that if the conditions required ...

(the conflict between the lack of obvious evidence for alien life and various high probability estimates for its existence). In this case, the solution is that there is no other intelligent life because such estimates are incorrect. The conjecture is named after astrophysicist Michael H. Hart and mathematical physicist and cosmologist

Frank Tipler Frank Jennings Tipler (born February 1, 1947) is an American mathematical physicist and cosmologist, holding a joint appointment in the Departments of Mathematics and Physics at Tulane University. Tipler has written books and papers on the Ome ...

Background

There is no reliable or reproducible evidence that

aliens Alien primarily refers to: * Alien (law), a person in a country who is not a national of that country ** Enemy alien, the above in times of war * Extraterrestrial life, life which does not originate from Earth ** Specifically, a lifeform with ext ...

have visited

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

. No transmissions or evidence of intelligent extraterrestrial life have been detected or observed anywhere other than

in the

Universe The universe is all of space and time and their contents. It comprises all of existence, any fundamental interaction, physical process and physical constant, and therefore all forms of matter and energy, and the structures they form, from s ...

. If intelligent life existed, it would have produced enough self-replicating spacecraft, known as von Neumann probes, to cover the universe by now, which runs counter to the knowledge that the Universe is filled with a very large number of planets, some of which likely hold the conditions hospitable for life. Life typically expands until it fills all available niches. These contradictory facts form the basis for the

, of which the Hart–Tipler conjecture is one proposed solution.

Relationship to other proposed Fermi paradox solutions

The firstborn hypothesis is a special case of the Hart–Tipler conjecture which states that no other intelligent life has been discovered because humanity is the first intelligent life in the universe. According to the

Berserker hypothesis The Berserker hypothesis, also known as the deadly probes scenario, is the idea that humans have not yet detected intelligent alien life in the universe because it has been systematically destroyed by a series of lethal Von Neumann probes. The hypo ...

, the absence of interstellar probes is not evidence of life's absence, since such probes could "go berserk" and destroy other civilizations, before self-destructing.

References

Astrobiology Hypotheses Astronomical hypotheses Astronomical controversies Search for extraterrestrial intelligence Fermi paradox {{DEFAULTSORT:Hart-Tipler conjecture