Being the lone voice in the universe can feel quite isolating.
For those unaware, the quest for life—particularly intelligent life—has been in progress for many years. Yet, up to this point, it appears we are alone.
Astronomers pursue the search for life through two primary methods: looking for biosignatures, which are signs of historical or current biological activity (like the Mars rovers), and technosignatures, which are indicators of technology produced by an intelligent species. The latter mainly relies on radio astronomy instead of optical methods, as any potential signals would originate from far beyond our visual range. Essentially, astronomers are tuned in to listen for something out there.
Among the leading organizations in this field is the SETI Institute. Established in 1984, this institute has been diligently scanning the skies for radio waves that might carry a greeting from other civilizations. It has focused on star systems with identified exoplanets, but to date, no extraterrestrial signals have been received.
Recently, scientists from this Mountain View, California-based organization have developed an innovative approach to detect these signals, utilizing principles from game theory. This technique not only identifies where to search for these signals but also when to do so.
Game theory examines decision-making in situations where multiple parties are involved, with their choices affecting one another. Each participant takes into account the strategies of their counterpart while remaining unaware of the other’s actions. The outcome hinges on the combined strategies of all involved.
In SETI’s case, researchers are applying the “Schelling point” concept from game theory. A frequently referenced illustration by economist Thomas Schelling involves two people meeting in New York City without prior communication about the time or place. Both might independently choose to arrive at Grand Central Terminal at noon, as it is a well-known location and a convenient time.
Now, consider this in the context of seeking signals from an alien civilization, and focus on the anti-solar point, an imagined location in space opposite the sun (180 degrees away). Picture a line that extends from the sun through Earth and beyond.
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 star and decided to send us a signal?
We have the location—Earth—and the timing—during a transit.
In essence, we are meeting at Grand Central at noon.
Echoes in the emptiness
The anti-solar approach was proposed years ago, but funding limitations hindered its implementation until now.
“I’ve contemplated these ideas that have been circulating in literature for quite some time,” stated Sophia Sheikh, a technosignature research scientist at the SETI Institute and the lead author of the study. “Now, the anti-solar point concept is finally receiving its moment in the spotlight.”
In a recently published paper on November 3, astronomers from the SETI Institute reported detecting 1.9 million radio signals using this method. However, after filtering through them, none were found to correspond with extraterrestrial technology; all signals originated from our planet. It turns out humans, with our satellites and radio broadcasts, create quite a racket.
Although this analysis ruled out a specific section of the sky, it does not imply there is an absence of life elsewhere. The universe is vast.
Thus, they intend to persist with this method for at least four more years, according to Sophia Sheikh, technosignature research scientist at the SETI Institute and 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 searching for what is known as a narrowband signal, which Sheikh describes as a “‘we are here’ … akin to an air horn in the radio frequencies.”
“It may contain information or perhaps the signal we detect is what we’d refer to as a carrier wave. So the air horn indicates, ‘Hey, something interesting is happening here.’”
However, don’t envision astronomers donning headphones like Ellie Arroway in the 1997 film Contact. In reality, computer programs analyze the incoming 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 facility has been dedicated to searching for alien signals since the 1980s.
The Allen Telescope Array, the first radio telescope specifically designed for searching for extraterrestrial intelligence (SETI). Located at the Hat Creek Radio Observatory in northern California, it features 42 antennas. (Simon Steel)
Is it science fiction?
The quest for alien signals may seem like the stuff of science fiction. However, with the Milky Way galaxy containing over 100 billion stars, many believe there must be life out there, particularly since we now know that most stars harbor at least one exoplanet.
Additionally, the Drake equation, formulated by American astrophysicist Frank Drake in 1961, was designed to estimate the number of civilizations in the Milky Way capable of communication.
The outcome relies on numerous unknown factors, but it is certainly 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 and other markers indicative of intelligent life.
He has remarked on how the pursuit of extraterrestrial intelligence was not taken seriously in earlier times.
“The giggle factor, which persisted throughout much of my career, has diminished,” Frank noted, reflecting on the lack of seriousness surrounding the topic decades ago. “It never made sense.”
This shift in perception is particularly evident following the inaugural discovery of exoplanets in 1992 and the first detection of an exoplanet orbiting a sun-like star in 1995.
If a signal is detected…
What would happen in the event of a detection?
Believe it or not, there are established protocols outlined by the International Academy of Astronautics. Beyond the essential steps of confirming and validating the discovery, a significant guideline is: Do not respond. (If you’re familiar with Liu Cixin’s 3 Body Problem, you will understand why this is considered a wise precaution.)
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This isn’t deemed a major concern, as signals would traverse light-years. For instance, if we were to receive a message from a star system located 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 to get their reply back. That’s a total of 300 years just to say “hello.”
“Communication is not our primary objective,” Frank stated.
Frank is investigating technosignatures by analyzing the chemical composition of exoplanets.
“For instance, we can examine the atmospheres of distant planets for substances like chlorofluorocarbons, a chemical that is solely produced by industry,” he explained. “Such compounds cannot be generated by nature or a biological ecosystem.”
Ultimately, it will be more about finding solace in the knowledge that we are not alone in the universe.
This image displays the printout of a strong signal recorded at the Big Ear Radio Observatory in 1977. Astronomer Jerry Ehman circled the unusual signal and annotated, ‘Wow!’ in the margin. (Big Ear Radio Observatory and North American Astrophysical Observatory)
Although we have yet to identify a definitive radio signal indicative of an alien civilization, there was the notable “Wow! Signal.” This intense radio signal was captured in 1977 by the Big Ear telescope in Ohio and lasted for 72 seconds but was never recorded again. Speculation has since arisen that it could have resulted from passing comets.
When might we discover an alien signal?
“I like to say,” Sheikh remarked, “I hope that by the conclusion of my career, we will have a clearer understanding of whether any radio signals in the galaxy are being emitted by civilizations with technology.”