Being the sole voice in the universe can be quite isolating.
For those unaware, the quest for life, particularly intelligent life, has been in progress for many years. Yet, up until now, it appears to be just us.
Astronomers investigate life in two primary ways: by searching for biosignatures, which are indicators of past or present biological activity (like the Mars rovers), and by looking for technosignatures, which indicate technology produced by intelligent beings. The latter mainly relies on radio astronomy, as any potential activity would be too distant for optical observation. Essentially, astronomers are tuning in for signs of communication.
Among those leading this initiative is the SETI Institute. Established in 1984, it has been scanning the skies for radio signals that might be traversing the vast cosmos to greet us earthly beings. The organization has targeted star systems that host known exoplanets, yet no signals from extraterrestrial sources have been identified thus far.
Recently, researchers at the Mountain View, California-based organization have devised an innovative approach to detect these signals, utilizing game theory. This method not only determines where to look for these signals but also when to search.
Game theory is a mathematical discipline focused on interactive decision-making, where the decisions of two “players” or “agents” are interdependent. Each participant considers the other’s strategy without knowing what the other is doing. The outcome hinges on the overall strategy adopted by both parties.
In the context of SETI, they are applying the concept of the “Schelling point” from game theory. The most commonly referenced example by economist Thomas Schelling is as follows: Imagine you’re meeting someone in New York City without having set a specific time or location. Both individuals might independently choose to converge at Grand Central Terminal at noon, as it’s a familiar and logical meeting spot.
Now, apply this idea to listening for an alien civilization by considering the anti-solar point, a theoretical location in the sky that lies directly opposite the sun (180 degrees away). Visualize a straight line from the sun passing through Earth and extending out into the cosmos.
What if there existed 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 know where to look—Earth—and when to do it—during a transit.
In essence, it’s like meeting at Grand Central at noon.
Voices in the void
This anti-solar approach had been proposed years prior but lacked sufficient funding for implementation until now.
“I have been contemplating these ideas that have been simmering in the literature for quite some time,” commented Sophia Sheikh, a technosignature research scientist at the SETI Institute and the lead author of the paper. “And now, the anti-solar point concept is finally getting its moment in the spotlight.”
In their recent paper published on November 3, astronomers from SETI reported that they identified 1.9 million radio signals using this technique. However, after thorough filtering, none of the signals matched those from extraterrestrial technology—all were of terrestrial origin. It turns out that humans, with our satellites and radio broadcasts, create quite a racket.
The research excluded that small section of the sky, but this does not imply that there is nothing beyond it. Space is immensely vast.
Thus, they intend to persist with this method for at least four more years, stated Sophia Sheikh, technosignature research scientist at the SETI Institute and lead author of the paper.
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 searching for what is known as a narrowband signal, which Sheikh described as a “‘we are here’ … akin to an air horn, almost, in the radio frequencies.”
“Perhaps it contains information, or maybe the signal we detect is what we term a carrier wave. So, the air horn signifies, ‘Hey, there’s something noteworthy here.'”
However, don’t envision astronomers donning headphones like Ellie Arroway in the 1997 film Contact. Instead, computer algorithms analyze the data.
The SETI Institute employs the Allen Telescope Array, a set of 42 fully steerable telescopes, each measuring 6.1 meters in diameter, located at the Hat Creek Radio Observatory in California. This array has been used to search for extraterrestrial signals since the 1980s.
Pictured here is the Allen Telescope Array, the first radio telescope designed specifically for the search for extraterrestrial intelligence (SETI). Located at the Hat Creek Radio Observatory in northern California, it consists of 42 antennas. (Simon Steel)
Science fiction?
The pursuit of extraterrestrial signals may appear to belong in the realm of science fiction. Nevertheless, with our Milky Way galaxy containing over 100 billion stars, many believe that there should be someone else out there, especially given that we now know that most stars host at least one exoplanet.
Additionally, the Drake equation, formulated by American astrophysicist Frank Drake in 1961, aims to estimate the number of civilizations in the Milky Way capable of communication.
The results depend on several unknown factors, but it is not zero.
Adam Frank, an astrophysics professor at the University of Rochester in New York, is also on the lookout for technosignatures. He received NASA’s inaugural grant to investigate non-radio technosignatures, focusing on chemical signs or other indicators that could point to intelligent life.
He has noted that the quest for extraterrestrial intelligence was not regarded seriously in the past.
“The giggle factor, which lingered throughout nearly my entire career, is now absent,” Frank remarked, referencing the fact that the possibility was dismissed decades ago. “And it never made sense.”
This shift in perception became particularly evident following the discovery of exoplanets in 1992 and the first 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, protocols have been established by the International Academy of Astronautics. Beyond the obvious steps of confirming and verifying the discovery, one significant guideline is: do not respond. (If you’ve read or viewed 3 Body Problem by Liu Cixin, you’ll understand why this protocol is prudent.)
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In reality, this isn’t a significant concern. Signals would traverse light-years of space. For instance, if we receive a signal from a star system 100 light-years away and decide to reply, it would take 100 years for our message to reach the alien civilization and another 100 years for their response to return to us. That’s 300 years just to say, “Hello.”
“Communication is not the top priority,” Frank stated.
Frank’s research focuses on identifying technosignatures by examining the chemistry of exoplanets.
“For instance, we can explore the atmospheres of distant planets for chemicals like chlorofluorocarbons … a substance solely produced by industrial processes,” he explained. “Such chemicals cannot be generated by nature or a biosphere.”
Ultimately, it’s more about finding solace in the knowledge that we are not alone.
This image shows the printout of a strong signal received at the Big Ear Radio Observatory in 1977. Astronomer Jerry Ehman circled the unusual signal and wrote, ‘Wow!’ in the margin. (Big Ear Radio Observatory and North American Astrophysical Observatory)
While we have yet to uncover a definitive radio signal that might suggest the presence of an alien civilization, the notable “Wow! Signal” remains in memory. This robust radio signal was detected by the Big Ear telescope in Ohio in 1977 and lasted for 72 seconds but was never observed again. Since then, there has been speculation that it was caused by passing comets.
So, when might we detect an alien signal?
“As I like to say,” Sheikh remarked, “I hope that by the end of my career, we’ll have a clearer understanding of whether any radio signals produced by other technologically advanced civilizations exist in the galaxy.”