The only thing left is to give up? The most likely hypotheses of why humanity has not found aliens yet are named
After decades of searching for alien life and many theories about the likelihood of its existence, humanity has only two hypotheses that can explain why we are still a lonely species. Neither of them is likely to appeal to those who are most eager to see representatives of extraterrestrial civilization.
This is the message of a study by Ian Crawford, Professor of Planetary Science and Astrobiology at the School of Natural Sciences and Center for Planetary Science at the University of Burbank, and Dirk Schulze-Makuch, Professor of Planetary Habitability and Astrobiology at the Technical University of Berlin, GFZ German Research Center for Geosciences, and Adjunct Professor at Washington State University, published in the journal Nature Astronomy.
The main question that space scientists ask themselves sounds extremely simple, "Where is everyone?" It was first formulated in 1950 by the famous physicist Enrico Fermi. He assumed that, given the age of the universe (13.8 billion years), the fact that the solar system has existed for 4.5 billion years and that the ingredients for life are everywhere in abundance, it seems strange that humanity still has no evidence of extraterrestrial intelligence.
The so-called Fermi paradox was once again discussed when humanity began to find potentially habitable exoplanets in distant star systems. It turned out that although the planets were biologically self-sufficient for life to emerge on them, none of them showed technosignatures, signs of technological activity that would indicate the existence of an advanced extraterrestrial civilization.
Over time, the Fermi paradox has been extended. In 1975, astronomer Michael Hart estimated that it would take only 650,000 years for an advanced civilization to spread across the Milky Way galaxy, so Earth should have been visited by an extraterrestrial civilization long ago.
According to Universe Today, in 1980, mathematical physicist and cosmologist Frank Tipler refined Hart's arguments using the Copernican principle, according to which neither humanity nor the Earth is in a privileged position to observe the universe. He estimated that it would take "less than 300 million years" for an extraterrestrial civilization to explore our entire galaxy.
This gave rise to the Hart-Tipler hypothesis, which essentially stated that the lack of evidence could only be explained by the absence of extraterrestrial civilizations.
However, in 1983, the famous astronomer and astrophysicist Carl Sagan and physicist, astronomer, and mathematician William Newman refuted this hypothesis in their own work, arguing that "absence of evidence is not evidence of absence." As arguments, they used numerous assumptions contained in the Hart-Tipler hypothesis. Subsequently, other scientists have proposed potential solutions to why we have not yet seen any extraterrestrial bodies.
However, 40 years later, humanity still has no definitive proof that advanced extraterrestrial civilizations exist. This is despite decades of observations and research by the SETI Institute, which searches for radio signals and anomalous infrared signatures among distant stars and galaxies. Scientists call this situation The Great Silence.
According to Crawford and Schulze-Makuch, this can mean only one of two things. First, there is a possibility that the Hart-Tipler hypothesis is correct and no advanced extraterrestrial civilizations exist, or that intelligent life (or life in general) is rare in the universe because the chances of its emergence or evolution are too low.
Second, the ruthless "zoo" hypothesis may also be correct. It states that advanced civilizations understand the risks of the universe, so they keep their distance to avoid being detected.
The authors of the latest study note that both the existence and absence of extraterrestrial civilizations will be a miracle, but one of these options must be true. In fact, everything can be reduced to two answers:
- we will never see aliens because space is too big, etc.
- we will not see them because they have taken measures to prevent us from seeing them.
The second option is an explanation of the zoo hypothesis, which was proposed in 1973 by John A. Ball, an astrophysicist at Harvard University and a scientist at the Haystack Observatory at the Massachusetts Institute of Technology. He argued that evolved species "deliberately avoid interaction and that they have set aside the territory in which we live as a zoo.
That is, we will never find them because they don't want to be found, and they have the technological capabilities to ensure that. The good news is that the zoo hypothesis assumes that the intentions of extraterrestrial civilizations are benevolent and they probably want to avoid interfering with our technological or social development.
However, based on the above, Crawford and Schulze-Makuch urge not to give up and continue to systematically explore the universe. According to them, humanity will be able to claim that there is no evidence of the existence of aliens only when it searches for it thoroughly enough.
Further research, as Schulze-Makuch notes, may reveal that the zoo hypothesis is correct because even if we are not able to make contact, we will be able to detect traces of an alien civilization.
Given the development of Earth's technology, he suggests that it is possible to find traces of aliens within the next 15 years but admits that "the time frame is, of course, difficult to predict."