Searching for radio signals from extraterrestrial civilizations has yet to yield evidence of extraterrestrial technological activity. Research conducted at EPFL suggests continuing the search by optimizing the use of available resources. For over six decades, amateur and professional astronomers have been watching the skies in search of extraterrestrial intelligence (SETI). To no avail so far. But how do we understand the absence of extraterrestrial radio signals? Is it time to stop searching? Or should we double down and take a closer look and look deeper into our galaxy? A recent statistical analysis of sixty years of silence offers a simple, optimistic explanation and encourages the SETI community to continue investigating but be patient as the chances of finding signals in the next sixty years are slim.

Valid explanations for the absence of electromagnetic signals from extraterrestrial societies fall into two extreme categories, says Claudio Grimaldi of EPFL’s Statistical Biophysics Laboratory. The “optimistic” camp believes we’re using detectors that aren’t sensitive enough or that we’re missing incoming signals because we’re pointing our radio telescopes in the wrong direction. The “pessimistic” camp interprets the silence as an indication that there is no extraterrestrial life in our galaxy.

According to research by Grimaldi Astronomy JournalThere is a third explanation. “We’ve only been searching for 60 years. “Earth could be in a bubble devoid of radio waves emitted by extraterrestrial life,” he says.

Modeling the Milky Way as a sponge

Grimaldi’s research is based on a statistical model originally developed to model porous materials such as sponges, and he sees it as an apt analogy for the question: “You can imagine that the solid matter of a sponge represents electromagnetic signals radiating globally from a planet to extraterrestrial life. . into space”. In this analogy, the sponge’s openings – its pores – represent regions where signals are absent.

By redesigning the mathematical tools for the study of porous materials and using Bayesian statistics, Grimaldi was able to draw quantitative conclusions from sixty years of silence. His conclusions are based on the assumption that there is at least one electromagnetic signal of technological origin in the galaxy at any given time, and that Earth has been in a silent bubble or “pore” for at least 60 years.

“If it’s true that we’ve been in the vacuum zone for sixty years, our model suggests that somewhere in our galaxy there are one to five electromagnetic emissions per century. That would make them as rare as the supernovas on Chumatskaya. Way,” Grimaldi says. In the most optimistic scenario, we would have to wait more than 60 years for one of these signals to reach our planet. In the least optimistic scenario, that number would increase to about 2,000 years. Whether we will detect signals when they come our way is another question. Either way, our radio telescopes need to be pointed in the right direction to see them.

Identifying best practices for continuous search

The quest for extraterrestrial intelligence, fueled by the discovery of the first planets outside our solar system nearly 20 years ago, now has the wind in its sails. Today, researchers suggest there could be as many as 10 billion Earth-like planets that are rocky, the right size, and just the right distance from the Sun to host life. Their large numbers make it more likely that technological life has evolved in one of them.

This led to new initiatives in the SETI community. Breakthrough Listen, the largest privately funded project of its kind, spent nearly $100 million in radio telescope time searching for technical signals from extraterrestrial civilizations. With the venture ending in two years, Grimaldi says now is a good time to consider how to continue the search for extraterrestrial intelligence in the future.

“The dream of the SETI community is to constantly search for signals all over the sky. Even the largest modern telescopes can only see a small part of the sky. Today there are groups of telescopes such as the Allen Telescope Array (ATA) in California that point in different directions and can be pointed at specific areas to get more detailed information as needed. The same is true for optical telescopes.”

“But,” Grimaldi says, “the truth is we don’t know where to look, at what frequencies and wavelengths. We are currently observing other events with our telescopes, so the best strategy may be to borrow from the background of the SETI community. An approach to using data from other astrophysical studies by detecting radio emissions from other stars or galaxies to see if they contain any technical signals and to make this standard practice.”

Inefficient or just bad luck?

When asked if he found his findings encouraging or disappointing, Grimaldi laughed and said, “This is something we need to think about. Perhaps we were unlucky because we discovered how to use radio telescopes as we traversed a part of space without electromagnetic signals from other civilizations. To me, this hypothesis seems less extreme than the assumption that we are constantly being bombarded with signals from all sides, but somehow fail to detect them.