Being the sole communicator in the vast universe can feel quite isolating.

For those unaware, the quest for life — particularly intelligent life — has persisted for many years. Yet, thus far, we remain alone.

Astronomers pursue the search for life through two primary avenues: by identifying biosignatures, which indicate past or present biological activities (like the Mars rovers), and technosignatures, which signify technology produced by intelligent beings. The latter primarily relies on radio astronomy rather than optical methods, since any such activities would take place far beyond our visual reach. Essentially, astronomers are tuning in for signals.

The SETI Institute has been a leader in this field since its inception in 1984, scanning the sky for radio waves that might be traversing the cosmos just to greet us. The organization focuses its efforts on star systems hosting known exoplanets, but as of now, it has yet to receive any signals from extraterrestrial sources.

Recently, scientists at the institute, located in Mountain View, California, have devised an innovative approach to search for such signals, utilizing game theory. This method not only determines where to look for them but also when to listen.

Game theory is a mathematical discipline that examines situations involving interactive decision-making, where there’s a dependence between two “players” or “agents.” Each player contemplates the strategies of the other while remaining unaware of their actions. The outcome relies on the combined strategies of both parties.

In the context of the SETI Institute, the focus is on the “Schelling point” from game theory. A well-known illustration by American economist Thomas Schelling involves meeting someone in New York City without specifying a time or location. Both individuals might opt to gather at Grand Central Terminal at noon due to its commonality as a meeting spot and its appropriateness as a time.

Now, relate that to the search for an alien civilization, and consider the anti-solar point, a hypothetical location in the sky directly opposite the sun (180 degrees away). Envision a straight line extending from the sun through Earth and into 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 particular star and directed a signal towards us?

We have the location — Earth — and the timing — during a transit.

In essence, we’re convening at Grand Central at noon.

Voices in the void

This anti-solar strategy was proposed years ago, but insufficient funding prevented its pursuit until now.

“I reflected on these concepts that have been lingering in the literature for a long time,” stated Sophia Sheikh, a technosignature research scientist at the SETI Institute and the lead author of the recent paper. “Now, the idea of the anti-solar point is finally receiving its due attention.”

In their newly published paper on November 3, astronomers from the SETI Institute revealed that they identified 1.9 million radio signals using this approach. However, after filtering through them all, none matched extraterrestrial technology — they were all produced by us. It turns out that humans, with our satellites and radio broadcasts, create considerable noise.

This study excluded that section of the sky — but it does not imply that there isn’t anything out there. The universe is incredibly vast.

Therefore, they intend to continue utilizing this method for at least four additional years, according to Sophia Sheikh.

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 in the radio frequencies.”

“It could contain information, or the signal we detect might be what we refer to as a carrier wave. So, the air horn signals, ‘Hey, there’s something of interest here.’”

However, don’t picture astronomers wearing headphones like Ellie Arroway in the 1997 film Contact. Instead, computer programs analyze the 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. This array has been utilized to search for alien signals since the 1980s.

The Allen Telescope Array, the first radio telescope designed specifically for the search for extraterrestrial intelligence (SETI), is shown here at the Hat Creek Radio Observatory in northern California, featuring 42 antennas. (Simon Steel)

Science fiction?

The endeavor to find extraterrestrial signals may appear to belong in the realm of science fiction. However, with the Milky Way galaxy containing over 100 billion stars, many believe there should be others out there, especially 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 intended to estimate the number of potentially communicative civilizations within our galaxy.

The outcome relies on numerous unknown factors, but it is not zero.

Adam Frank, an astrophysics professor at the University of Rochester in New York, is also engaged in the search for technosignatures. He received NASA’s inaugural grant to investigate non-radio technosignatures, focusing instead on chemical signatures or other signs of intelligent life.

He has discussed how the pursuit of extraterrestrial intelligence was not taken seriously in the past.

“The giggle factor, which persisted throughout most of my career, has vanished,” Frank remarked, referring to how the concept was dismissed decades ago. “It never made sense.”

This shift in perception became particularly evident following the initial 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 happens if a signal is actually detected?

Believe it or not, there are established protocols set forth by the International Academy of Astronautics. Beyond the essential steps of confirming and authenticating the discovery, there’s a significant directive: Do not respond. (If you’ve read or watched 3 Body Problem by Liu Cixin, you’ll understand why this precaution is sensible.)

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This isn’t a significant concern. Signals will traverse light-years. Imagine receiving a signal from a star system 100 light-years away; if we decided to reply, it would take 100 years for our message to reach the alien civilization, and another 100 to get their response. That equates to 300 years just to say, “Hello.”

“Communication isn’t the primary focus,” Frank stated.

Frank’s research centers on identifying technosignatures by analyzing the chemistry of exoplanets.

“For instance, we can examine the atmospheres of distant planets for substances like chlorofluorocarbons … a chemical exclusively produced by industry,” he explained. “Such a substance cannot be derived from nature or a biosphere.”

Ultimately, it’s more about finding reassurance in knowing we are not alone.

This image depicts the printout of a strong signal received 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)

While no definitive radio signal indicating an alien civilization has been identified, the renowned “Wow! Signal” remains famous. This intense radio wave was captured in 1977 by the Big Ear telescope in Ohio, lasting 72 seconds but never detected again. There has been speculation that it could have resulted from passing comets.

So when might we finally observe an alien signal?

“I like to express my hope,” Sheikh remarked, “that by the end of my career, we will have a clearer understanding of whether radio signals produced by other technology-possessing civilizations exist in the galaxy.”