Being the sole entity in the universe can feel quite isolating.
For those unaware, the quest to find life—particularly intelligent beings—has been a pursuit for many years. Yet, thus far, we appear to be alone.
Astronomers employ two primary methods in their search for life: they seek biosignatures, which are signs of past or present biological activity (such as those investigated by Mars rovers), and technosignatures, which indicate the presence of technology from an intelligent species. The latter mainly relies on radio astronomy rather than optical methods, since any relevant activity would be occurring far beyond our visual reach. Essentially, astronomers are tuning in for signals.
Among the leading organizations in this field is the SETI Institute. Established in 1984, it has been scanning the heavens for radio signals that may be emanating from the vast universe, attempting to connect with us, the modest inhabitants of Earth. Its focus has been on star systems that host known exoplanets, but to date, no communications from extraterrestrial sources have been identified.
Recently, researchers at the Mountain View, California-based institute have developed an innovative approach to detecting these signals, utilizing game theory. This new technique not only determines where to search for these signals but also when to conduct the search.
Game theory is a mathematical discipline that examines decision-making in situations where players are interdependent. Each participant contemplates the other’s strategy without full knowledge of their actions, and success hinges on their collective approaches.
The SETI Institute is leveraging the concept known as the “Schelling point” from game theory. An often-cited example from American economist Thomas Schelling involves a scenario where two individuals meet in New York City without a predetermined time or location. Both may instinctively choose to gather at Grand Central Terminal at noon, as it is a well-known meeting spot and a suitable timeframe.
Now, applying this to the search for extraterrestrial intelligence, consider the anti-solar point, a hypothetical location in the celestial sphere directly opposite the sun (180 degrees away). Envision a line extending from the sun that passes through Earth and reaches into the cosmos.
What if there exists an alien civilization capable of observing Earth as it transits in front of the sun? What if they were aware of a planet orbiting our sun and directed a signal toward us?
We have already established the location—Earth—and the timing—during a transit.
In essence, we are convening at Grand Central at noon.
Voices in the void
This anti-solar approach was proposed years ago, but financial constraints prevented its execution until now.
“I have been mulling over these concepts that have lingered in the literature for some time,” remarked Sophia Sheikh, a technosignature research scientist at the SETI Institute and the primary author of the study. “Now, the anti-solar point concept is finally receiving its moment to shine.”
In their recent publication released on November 3, astronomers from the SETI Institute announced they had identified 1.9 million radio signals using this technique. However, after thorough filtering, none matched the criteria for extraterrestrial technology—all signals were traced back to us. It appears that we humans, with our satellites and radio waves, generate quite a bit of noise.
This study eliminated a small section of the sky from consideration—but this does not imply a lack of possibilities elsewhere. The universe is vast.
Thus, they plan to persist with this methodology for at least the next four years, as stated by Sophia Sheikh, technosignature research scientist at the SETI Institute and the lead author of the study.
The Sun and our solar system in relation to the Milky Way galaxy. The white circle indicates the area where the majority of exoplanets have been found with current telescopes. (NASA/JPL-Caltech/T. Pyle)
They are in pursuit of what is known as a narrowband signal, according to Sheikh, who likened it to a “‘we are here’ … akin to an air horn in the radio frequencies.”
“Perhaps it contains some information, or the signal we identify may serve as a carrier wave—a sort of air horn that announces, ‘Hey, something intriguing is here.’”
However, don’t envision astronomers wearing headphones, like Ellie Arroway in the 1997 film Contact. Rather, computer software analyzes the incoming data.
The SETI Institute employs the Allen Telescope Array, consisting of 42 steerable telescopes with a diameter of 6.1 meters, located at the Hat Creek Radio Observatory in California. This array has been searching for signals from extraterrestrial sources since the 1980s.
The Allen Telescope Array, the first radio telescope specifically designed for the search for extraterrestrial intelligence (SETI). Located at the Hat Creek Radio Observatory in northern California, it comprises 42 antennas. (Simon Steel)
Science fiction?
The quest for signals from alien civilizations might seem like a concept borrowed from science fiction. Yet, with our Milky Way galaxy containing over 100 billion stars, many believe there must be some form of life out there, particularly since we now understand that most stars harbor at least one exoplanet.
Additionally, the Drake equation, formulated by American astrophysicist Frank Drake in 1961, aimed to estimate the number of communicative civilizations within the Milky Way.
The outcome relies on numerous unknown factors, but it is not zero.
Adam Frank, a professor of astrophysics at the University of Rochester in New York, is also investigating technosignatures. He received NASA’s inaugural grant to explore non-radio technosignatures, focusing instead on chemical signatures or other indicators of intelligent life.
He has noted that the search for extraterrestrial intelligence has not always been taken seriously.
“The giggle factor, which has persisted throughout almost my entire career, is no longer relevant,” Frank remarked, referencing how the notion was dismissed in earlier decades. “It never made sense.”
This shift in perception is especially true following the discovery of exoplanets in 1992 and the first identification of an exoplanet orbiting a sun-like star in 1995.
In the event of a detection…
What would happen if a signal were detected?
Surprisingly, there are established protocols set by the International Academy of Astronautics. Beyond the fundamental requirement of confirming and verifying the finding, a significant guideline is: do not respond. (If you’ve read or watched 3 Body Problem by Liu Cixin, you may grasp why this is a prudent measure.)
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However, this isn’t a major concern. Signals would traverse light-years of distance. For instance, if we were to receive a message from a star system 100 light-years away and decided to send a reply, it would take 100 years for our response to reach the alien civilization, and another 100 years for us to receive their reply. That equates to 300 years just to say, “Hello.”
“Communication isn’t the priority,” Frank stated.
Frank’s investigations focus on identifying technosignatures by examining the chemistry of exoplanets.
“For example, we can analyze the atmospheres of distant planets and search for substances like chlorofluorocarbons … a compound that is solely produced by industrial activity,” he explained. “It’s something you wouldn’t find in nature or a biosphere.”
Ultimately, it’s more about finding reassurance in the notion that we are not alone.
This image displays the printout of a strong signal captured 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)
Although we have yet to uncover a definitive radio signal indicating the presence of an alien civilization, there was the renowned “Wow! Signal.” This notable radio emission was detected in 1977 by the Big Ear telescope in Ohio, lasting for 72 seconds but never observed again. Since then, some have speculated that it may have been caused by passing comets.
So, when could we potentially identify a signal from extraterrestrials?
“The sentiment I like to express,” Sheikh remarked, “is that I hope by the conclusion of my career, we will have a clearer understanding of whether any radio signals generated by other technologically advanced civilizations exist in the galaxy.”
