Being the sole communicator in the vast universe can be quite isolating.
The quest for extraterrestrial life, particularly intelligent life, has been pursued for many years. As of now, however, we appear to be alone.
Astronomers employ two primary methods in their search for life: one is the hunt for biosignatures, which are indicators of biological processes that have either occurred in the past or are ongoing (such as the missions of Mars rovers), and the other is the search for technosignatures, which signal the presence of technology created by intelligent beings. The latter approach mainly utilizes radio astronomy rather than optical methods, as any signs of activity would be too distant to be viewed visually. Essentially, astronomers are tuning in for potential communications.
One leading organization in this endeavor is the SETI Institute. Since its establishment in 1984, it has been scanning the skies for radio waves that might be traversing the universe in an attempt to connect with us, the modest inhabitants of Earth. Although it has focused on star systems that host known exoplanets, no signals from extraterrestrial sources have yet been identified.
Recently, however, researchers from the Mountain View, California-based institute have devised an innovative approach to detect these signals, utilizing concepts from game theory. This new method not only assesses where to search for signals but also when to do so.
Game theory is a mathematical field that examines decision-making in scenarios where the choices of two “players” or “agents” are interconnected. Each participant considers the potential strategies of the other, despite lacking knowledge of the other’s actions. The ultimate outcome hinges on the combined strategies of both players.
In the context of the SETI Institute, the focus is on the “Schelling point” from game theory. A commonly referenced example by American economist Thomas Schelling is this: Imagine making plans to meet someone in New York City without specifying a time or location. Both individuals may choose to converge at Grand Central Terminal at noon, as it’s a well-known meeting spot and a sensible hour.
Now, apply this reasoning to the search for an alien civilization and consider the anti-solar point, a hypothetical location in the sky directly opposite the sun (180 degrees away). Visualize a straight line emanating from the sun that extends through Earth and into the cosmos.
What if an alien civilization could observe Earth as it transits in front of the sun? What if they were aware of a planet orbiting our specific star and directed a signal towards us?
We have established the where — Earth — and the when — during a transit.
In essence, we are coordinating a meeting at Grand Central at noon.
Voices in the void
This anti-solar strategy was proposed years ago, but lacked the necessary funding for implementation until now.
“I reflected on these concepts that have been simmering in academic literature for quite some time,” explained Sophia Sheikh, a technosignature research scientist at the SETI Institute and the lead author of the recent study. “Now, the anti-solar point concept is finally receiving the attention it deserves.”
In their latest paper released on November 3, astronomers from the SETI Institute reported detecting 1.9 million radio signals using this approach. However, after filtering, none were found to correspond to extraterrestrial technology — all signals were attributed to Earth. It appears that we, as inhabitants of Earth, are rather noisy with our satellites and radio communications.
While this study eliminated a portion of the sky from consideration, it doesn’t imply that there is nothing else out there. The vastness of space remains a significant factor.
Therefore, they intend to continue utilizing this method for a minimum of four years, according to Sophia Sheikh, who emphasizes the importance of this research.
The Sun and our solar system depicted in relation to the Milky Way galaxy. The white circle marks the area where most exoplanets have been detected using current telescopes. (NASA/JPL-Caltech/T. Pyle)
They are specifically searching for narrowband signals, which Sheikh describes as a “‘we are here’ … akin to an air horn within the radio spectrum.”
“There may be information embedded within it, or the signal we detect could serve as a carrier wave. Think of the air horn as a signal saying, ‘Hey, there is something intriguing here.’”
However, don’t envision astronomers sitting with headphones like Ellie Arroway in the 1997 film Contact. Instead, sophisticated computer programs analyze the data collected.
The SETI Institute utilizes the Allen Telescope Array, which consists of 42 steerable telescopes with a diameter of 6.1 meters located at the Hat Creek Radio Observatory in California. This array has been operational in the search for alien signals since the 1980s.
The Allen Telescope Array is shown here, being the first radio telescope specifically designed for the search of extraterrestrial intelligence (SETI). It is situated at the Hat Creek Radio Observatory in Northern California and comprises 42 antennas. (Simon Steel)
Science fiction?
The pursuit of extraterrestrial signals may resemble a concept from science fiction. Yet, with our Milky Way galaxy housing upwards of 100 billion stars, many believe there must be other intelligent beings out there, especially given that we have confirmed that most stars host at least one exoplanet.
Additionally, the Drake equation, formulated by American astrophysicist Frank Drake in 1961, was created to estimate the number of potential communicative civilizations within the Milky Way.
The result hinges on numerous unknown factors, but it certainly isn’t zero.
Adam Frank, an astrophysics professor at the University of Rochester in New York, is also engaged in the search for technosignatures. He received NASA’s inaugural grant to investigate non-radio technosignatures, focusing on chemical indicators or other signs of an intelligent civilization.
He has noted that the search for extraterrestrial intelligence was often dismissed in earlier years.
“The giggle factor, which persisted throughout nearly my entire career, has dissipated,” Frank remarked, emphasizing that the possibility was not taken seriously in decades past. “It never made sense.”
This is especially true following the initial discovery of exoplanets in 1992, followed by the detection of an exoplanet orbiting a sun-like star in 1995.
In the event of a detection…
What if a signal were detected? What would happen next?
Surprisingly, there are established protocols laid out by the International Academy of Astronautics. Beyond the obvious steps of confirming and validating the discovery, a significant protocol exists: do not respond. (If you are familiar with 3 Body Problem by Liu Cixin, you’ll grasp why this might be a prudent guideline.)
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This isn’t viewed as a major complication. Signals will be traveling across light-years of distance. For instance, if we were to receive a signal from a star system located 100 light-years away and decided to reply, it would take 100 years for our response to reach the alien civilization, followed by another 100 years to get their reply back. That totals 300 years just to exchange a simple “hello.”
“Communication isn’t our top priority,” Frank noted.
Frank’s research centers on locating technosignatures through the analysis of an exoplanet’s atmospheric chemistry.
“For instance, we can examine the atmospheres of distant planets looking for substances like chlorofluorocarbons … a chemical that can only be produced by industrial processes,” he explained. “Such compounds cannot occur naturally within a biosphere.”
Thus, the focus may shift towards finding solace in the knowledge that we are not alone.
This image captures the printout of a strong signal detected at the Big Ear Radio Observatory in 1977. Astronomer Jerry Ehman circled the unusual signal and noted, ‘Wow!’ in the margin. (Big Ear Radio Observatory and North American Astrophysical Observatory)
While a definitive radio signature indicating an alien civilization has yet to be found, the notable ” Wow! Signal” remains a significant mention. This intense radio signal was captured in 1977 by the Big Ear telescope in Ohio, lasting for 72 seconds before it was never observed again. Some have speculated that it may have been caused by passing comets.
So when can we anticipate detecting a signal from extraterrestrial sources?
“I like to say,” said Sheikh, “that I hope by the conclusion of my career, we will have a clearer understanding of whether there are radio signals in the galaxy being emitted by other technologically advanced civilizations.”
