Being the sole entity in the vast universe can feel quite isolating.
For those who may not be aware, the quest for life—especially intelligent life—has been in progress for many years. Yet, thus far, it appears we are alone.
Astronomers employ two primary methods to search for life: they look for biosignatures, which indicate past or present biological activity (like the missions undertaken by Mars rovers), and technosignatures, which are signs of technology produced by intelligent beings. Exploring the latter mainly relies on radio astronomy rather than optical methods, as any activities would be occurring too distantly for visual observation. In essence, astronomers are tuned in to listen for signals.
One leading organization in this field is the SETI Institute, which has been scanning the sky for potential radio signals since its inception in 1984. The Institute has focused on star systems known to host exoplanets, but up to now, no extraterrestrial signals have been identified.
Recently, however, researchers at the Mountain View, California-based institute have devised an innovative approach to detect these signals, utilizing concepts from game theory. This new strategy considers not only where to look for signals but also when to conduct the search.
Game theory is a mathematical discipline that examines decision-making in interactive scenarios, where the decisions of two “players” or “agents” are interdependent. Each player contemplates the other’s strategy while being unaware of their actions. The outcome is contingent on the joint strategies employed.
In the context of the SETI Institute, this involves applying the “Schelling point” concept from game theory. A common example provided by American economist Thomas Schelling is this: Picture two people trying to meet in New York City without pre-arranging a time or location. Both might instinctively choose Grand Central Terminal at noon, as it is a well-known meeting spot and a sensible hour.
Now, consider this analogy in the search for an alien civilization, while thinking about the anti-solar point, which is an imaginary point in the sky directly opposite the sun (180 degrees away). Visualize a straight line from the sun extending through Earth into outer space.
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 sun and decided to send a message in our direction?
We have both the location—Earth—and the timing—during a transit.
Essentially, it’s akin to meeting at Grand Central at noon.
Voices in the void
The idea of using the anti-solar method had been proposed years ago, but lacked the necessary funding for implementation until now.
“I’ve contemplated these concepts that have been evolving in academic discussions for a long time,” remarked Sophia Sheikh, a technosignature research scientist at the SETI Institute and the paper’s lead author. “Now, the anti-solar point concept is finally getting its moment to shine.”
In their recent paper published on November 3, astronomers from the SETI Institute announced they identified 1.9 million radio signals using this approach. However, after thorough filtering, none were found to correlate with extraterrestrial technology—all the signals were terrestrial in origin. It appears that humans, with our satellites and radio broadcasts, create significant noise.
This study has eliminated that specific area of the sky from consideration—but it doesn’t imply there’s nothing else out there. The universe is vast.
As a result, they intend to persist with this method for at least four additional years, stated Sophia Sheikh, the technosignature research scientist 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 specifically searching for what is known as a narrowband signal, according to Sheikh, who characterized it as a “‘we are here’ … akin to an air horn in the radio frequencies.”
“Perhaps there is information embedded within it, or maybe the signal we detect serves as a carrier wave. So the air horn conveys, ‘Hey, there’s something intriguing here.’”
However, don’t envision astronomers donning headphones like Ellie Arroway in the 1997 film Contact. Instead, sophisticated computer programs analyze the incoming data.
The SETI Institute employs the Allen Telescope Array, a set of 42 fully steerable telescopes, each 6.1 meters in diameter, located at the Hat Creek Radio Observatory in California, to facilitate this search. This array has been operational in the search for extraterrestrial signals since the 1980s.
Pictured is 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 pursuit of extraterrestrial signals might seem reminiscent of science fiction narratives. Yet, with our Milky Way galaxy containing over 100 billion stars, many believe there must be other life forms, particularly as we now recognize that most stars harbor at least one exoplanet.
Additionally, the Drake equation, created by American astrophysicist Frank Drake in 1961, aims to estimate the number of communicative civilizations within the Milky Way.
The outcome relies on various unknown factors, but it is certainly greater than zero.
Adam Frank, a professor of astrophysics at the University of Rochester, is also investigating technosignatures. He received NASA’s first 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 was not taken seriously in earlier times.
“The giggle factor, which persisted throughout nearly my entire career, is no longer present,” Frank remarked, referring to the dismissive attitude that prevailed decades ago. “It never made sense.”
This is especially true following the initial discovery of exoplanets in 1992, and the subsequent identification of an exoplanet around a sun-like star in 1995.
In the event of a detection…
Suppose a signal were detected. What would happen next?
Believe it or not, there are established protocols set by the International Academy of Astronautics. Beyond the obvious steps of confirming and validating the discovery, there’s a crucial guideline: do not respond. (If you are familiar with Liu Cixin’s 3 Body Problem, you will understand why this protocol is prudent.)
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However, this is not a significant concern. Signals will traverse across light-years. For instance, if we receive a signal from a star system located 100 light-years away, and we on Earth agree to send a reply, it would take 100 years for our message to reach the alien civilization, and another 100 years to get their response. That totals 300 years just to convey a simple greeting.
“Communication is not the primary objective,” Frank stated.
Frank’s research focuses on uncovering evidence of technosignatures through the analysis of an exoplanet’s chemical composition.
“For example, we can investigate the atmospheres of distant planets for substances like chlorofluorocarbons … a chemical exclusively produced by industrial activity,” he explained. “Such a substance would never originate from a natural biosphere.”
Thus, it may ultimately come down to finding solace in the knowledge that we are not alone.
This image depicts the printout of a significant signal captured at the Big Ear Radio Observatory in 1977. Astronomer Jerry Ehman encircled the unusual signal and noted, ‘Wow!’ in the margin. (Big Ear Radio Observatory and North American Astrophysical Observatory)
While no definitive extraterrestrial radio signature has been identified, the well-known “Wow! Signal” remains a point of interest. This potent radio signal was detected in 1977 by the Big Ear telescope in Ohio, lasting for 72 seconds but never observed again. Since then, there has been speculation suggesting it may have originated from passing comets.
When might we finally detect a message from an alien civilization?
“The sentiment I express,” Sheikh said, “is that I hope by the culmination of my career, we will have clarity regarding whether any radio signals are generated by other technologically advanced civilizations in the galaxy.”