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December 18th, 2022
Allen Telescope Array dedicated to astronomical observations and a simultaneous search for extraterrestrial intelligence (SETI).
Image credit: Seth Shostak/SETI Institute
The well-known Fermi Paradox, “Where are they?” proposes that Earth may be the only civilization, since there is no evidence for extraterrestrial visits.
A research paper offers a new solution to the Fermi Paradox, authored by Amri Wandel of the Racah Institute of Physics, The Hebrew University of Jerusalem.
“Probes or visits from putative alien civilizations have a very low probability until a civilization reaches a certain age (called the Contact Era) after the onset of radio communications,” Wandel explains in the paper: “The Fermi Paradox revisited: Technosignatures and the Contact Era.”
“Where is everybody?” asked physicist Enrico Fermi during a discussion with colleagues in 1950.
Image credit: National Archives
Physical probes
The Contact Era, Wandel adds, is the time since the onset of radio transmissions at which the contact probability becomes of order unity.
“At that time alien probes (or messages) become more likely. Unless civilizations are highly abundant, the Contact Era is shown to be of the order of a few hundred to a few thousand years and may be applied not only to physical probes but also to transmissions (i.e. SETI),” the research paper explains.
“Consequently, it is shown that civilizations are unlikely to be able to inter-communicate unless their communicative lifetime is at least a few thousand years,” Wandel’s research paper observes.
Lack of detection
Wandel notes that, of course, there are many caveats, such as:
- the civilization may not be communicative, or directed signals may have been sent when we were not listening.
- if a civilization sufficiently nearby has sent probes to the Solar System, its eventual communication with the probes would be directed at Earth and may be detected by SETI.
- the probes may be autonomous or communications may be seldom.
The Atacama Large Millimeter/submillimeter Array (ALMA) in northern Chile’s Atacama desert.
Credit: ESO/B. Tafreshi (twanight.org)
The paper, accepted for publication in the Astrophysical Journal, concludes that for directed signals, “the Contact Era may apply not only to physical probes and alien visits but also to alien intended transmissions, and eventually explain the lack of detections by SETI.”
To access the paper — “The Fermi Paradox revisited: Technosignatures and the Contact Era” – go to:
Posted in Space News
To me, the strongest evidence both FOR and AGAINST extraterrestrials from advanced civilizations is self-replicating machines. It is argued that sufficiently advanced civilizations would be capable if and would have disseminated such machines. Certain estimates suggest self-replicating spacecraft could populate the galaxy in as little as 500,000 years following the exponential factor in base 2 to the power of n, where the exponent n is the number of doublings, thus 2n=population of self-replicating machines in the Milky Way. The argument stops there with the resounding question of Professor Fermi slightly adjusted as “If sufficiently advanced civilizations exist in the Milky Way (NOTE: arguably humans would not be numbered amongst them, yet) that are capable of creating and disseminating self-replicating machines, we should see them if such a civilization ascended to the proper advancement – yet we do not. Where are they?” But, there is the answer has been proposed “Perhaps we do. Perhaps they are us.” And, perhaps when we also ascend to that level of advancement, we will send a biological response.