Humans have never received any contact from aliens, despite our efforts to scan the skies for signs of intelligent life. Why is that? A new theory suggests that we may be in a quiet bubble of space that happens to have no alien signals passing through it.
The idea comes from Claudio Grimaldi, a biophysicist at the École Polytechnique Fédérale de Lausanne in Switzerland. He used a statistical model that was originally developed to study porous materials like sponges. He applied it to the distribution of possible alien emitters in the Milky Way, assuming that there is at least one such emitter at any given time.
The model showed that the probability of detecting an alien signal depends on how densely packed the emitters are and how long they last. If they are rare and short-lived, then Earth could be in a region of space that is devoid of any radio waves from extraterrestrial civilizations.
Grimaldi estimated that if there are fewer than one to five alien signals per century in our galaxy, then we are unlikely to catch them with our current technology. That would mean that alien signals are as rare as supernovas in the Milky Way.
He also calculated that, depending on how optimistic or pessimistic we are, it could take us anywhere from 60 to 2,000 years to detect an alien signal, assuming we keep looking and pointing our telescopes in the right direction.
“We’ve only been looking for 60 years,” Grimaldi said. “Earth could simply be in a bubble that just happens to be devoid of radio waves emitted by extraterrestrial life.”
He added that this hypothesis seems less extreme than assuming that we are constantly bombarded by signals from all sides but are unable to detect them for some reason.
Grimaldi’s theory is not the first one to try to explain the Fermi paradox, which is the apparent contradiction between the high likelihood of alien life and the lack of evidence for it. Other possible solutions include the idea that aliens are hiding from us, that they are extinct, or that they are too different from us to communicate.
However, Grimaldi’s theory has the advantage of being testable, at least in principle. If we keep searching for longer and cover more of the sky, we may eventually find a signal that proves we are not alone. Or we may confirm that we are indeed in a cosmic sponge.
Grimaldi suggests that the best way forward is commensal investigations: so looking for signals in data collected by telescopes that are focussed on other missions, rather than using telescopes specifically to look for alien communications.
“The best strategy might be to adopt the SETI community’s past approach of using data from other astrophysical studies – detecting radio emissions from other stars or galaxies – to see if they contain any technosignals, and make that the standard practice,” says Grimaldi.
The research has been published in the The Astronomical Journal.