Being the sole voice in the vast universe can feel isolating.
The quest for life—particularly intelligent life—has been pursued for many years. However, up to this point, it appears we are alone.
Astronomers approach the search for life in two main ways: by looking for biosignatures, which indicate past or present biological activity (like the Mars rovers), and technosignatures, which would suggest the presence of technology produced by an intelligent species. The latter primarily relies on radio astronomy rather than optical methods, as any signs of activity are likely too distant for us to visually observe. In essence, astronomers are tuning in for signals.
A leading organization in this field is the SETI Institute. Established in 1984, it has been scanning the skies for radio signals that might be reaching us from across the universe, potentially offering a greeting to us as earthlings. The institute focuses on star systems with known exoplanets, yet no messages from extraterrestrial life have been identified thus far.
Recently, researchers at the Mountain View, California-based organization have devised an innovative approach to detect these signals, utilizing principles from game theory. This new technique considers not only where to search for signals but also when to listen.
Game theory examines mathematical interactions where there is a mutual dependency between two “players” or “agents.” Each participant contemplates the strategy of the other without knowing their exact actions, and the outcome relies on their combined strategies.
For the SETI Institute, the concept of a “Schelling point” is being applied. American economist Thomas Schelling often illustrates this with the following scenario: Imagine arranging to meet someone in New York City without specifying a time or place. Both individuals might independently choose to converge at Grand Central Terminal at noon, as it’s a well-known location and a logical time.
Now, consider applying this to the search for an alien civilization and the idea of the anti-solar point, which is an imaginary location in the sky directly opposite the sun (180 degrees away). Envision a straight line extending from the sun through Earth into the void of space.
What if there was an extraterrestrial civilization that witnessed Earth passing in front of the sun, known as a transit? What if they recognized the existence of a planet orbiting our star and directed a signal toward us?
We have the location—Earth—and the timing—when a transit occurs.
Essentially, we’re meeting at Grand Central at noon.
Voices in the void
The anti-solar approach was proposed years ago, but funding limitations prevented its exploration until recently.
“I’ve been reflecting on these concepts that have been brewing in the literature for quite some time,” stated Sophia Sheikh, a technosignature research scientist at the SETI Institute and the primary author of the study. “So, at last, the anti-solar point idea is getting its moment to shine.”
In their latest paper published on November 3, astronomers from the SETI Institute revealed that they identified 1.9 million radio signals using this technique. However, after thorough filtering, none were found to correspond with extraterrestrial technology; all signals were traced back to Earth. It turns out that our own satellites and radio transmissions make quite a racket.
This analysis eliminated a small section of the sky from consideration—but it doesn’t imply that nothing exists beyond. The universe is vast.
They intend to persist with this method for a minimum of four years, according to Sheikh.
The Sun and our solar system depicted in relation to the Milky Way galaxy. The white circle indicates the region where most exoplanets have been detected using current telescopes. (NASA/JPL-Caltech/T. Pyle)
They are on the lookout for what is known as a narrowband signal, described by Sheikh as a “‘we are here’ … akin to an air horn within the radio frequencies.”
“It might contain information, or perhaps the signal we detect is what we would classify as a carrier wave. So the air horn serves as a signal that says, ‘Hey, there’s something noteworthy here.’”
However, don’t envision astronomers donning headphones like Ellie Arroway in the 1997 film Contact. Instead, advanced computer programs analyze the data.
The SETI Institute utilizes the Allen Telescope Array, a network of 42 steerable telescopes with a diameter of 6.1m located at the Hat Creek Radio Observatory in California. This array has been dedicated to the search for extraterrestrial signals since the 1980s.
Here is the Allen Telescope Array, the first radio telescope specifically designed for the search for extraterrestrial intelligence (SETI). Situated at the Hat Creek Radio Observatory in northern California, it consists of 42 antennas. (Simon Steel)
Science fiction?
The endeavor of searching for signals from extraterrestrials may appear reminiscent of science fiction. Nevertheless, with the Milky Way hosting over 100 billion stars, there is a belief that intelligent life should exist somewhere out there, especially given that we now understand that most stars have at least one exoplanet.
Additionally, there is the Drake equation, formulated by American astrophysicist Frank Drake in 1961. Its purpose was to estimate the number of civilizations in the Milky Way capable of communication.
The outcome relies on many uncertain 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 or other markers of intelligent life.
He has noted how the search for extraterrestrial intelligence was not previously regarded with seriousness.
“The giggle factor, which persisted throughout most of my career, has vanished,” Frank remarked, noting that the concept was often dismissed in earlier decades. “It never made sense.”
This shift became particularly evident following the initial discovery of exoplanets in 1992 and the identification of an exoplanet around a sun-like star in 1995.
In the event of a detection…
What happens if a signal is detected?
Surprisingly, there are protocols established by the International Academy of Astronautics. Aside from the essential steps of confirming and verifying the discovery, a significant guideline is: do not respond. (If you’ve read or viewed 3 Body Problem by Liu Cixin, you’ll grasp why this is a prudent protocol.)
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This concern is not overly significant. Signals will traverse light-years of distance. For instance, if we receive a signal from a star system located 100 light-years away and decide to reply, it would take 100 years for our message to reach the alien civilization, followed by another 100 years for their response to return. That’s a total of 300 years just to exchange a greeting.
“Communication is not the top priority,” Frank stated.
Frank’s research focuses on locating technosignatures through the examination of exoplanetary chemistry.
“For instance, we can analyze the atmospheres of distant planets for substances like chlorofluorocarbons… a chemical produced solely by industrial processes,” he explained. “Such a signature wouldn’t be generated by nature or a biosphere.”
Ultimately, the objective will be to find reassurance in the knowledge that we are not alone.
This image depicts the printout of a notable signal captured at the Big Ear Radio Observatory in 1977. Astronomer Jerry Ehman highlighted the unusual signal and wrote, ‘Wow!’ in the margin. (Big Ear Radio Observatory and North American Astrophysical Observatory)
While a definitive radio signal indicating an alien civilization has yet to be discovered, there was the renowned “Wow! Signal.” This strong radio signal was recorded in 1977 by the Big Ear telescope in Ohio and lasted for 72 seconds but was never observed again. Since that time, there have been theories suggesting it may have been caused by passing comets.
So when might we detect a signal from an alien civilization?
“I like to say,” Sheikh commented, “is that I hope by the end of my career, we will have a clearer understanding of whether there are any radio signals in the galaxy being generated by other technologically advanced civilizations.”