Being the sole voice in the universe can feel isolating.
For those unaware, the quest to find life — particularly 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 seek biosignatures, which are indicators of biological processes that may have occurred in the past or present (think Mars rovers), and technosignatures, which signify technology generated by intelligent beings. The latter usually involves radio astronomy rather than optical methods, since any technological activity would be too distant for us to observe directly. Essentially, astronomers are listening for signals.
One of the leading organizations in this area has been the SETI Institute. Established in 1984, it has been scanning the skies for radio signals that might be reaching out to us from the vast cosmos, hoping for a “hello” from other beings. The institute has focused its efforts on star systems with known exoplanets, but to date, no extraterrestrial signals have been identified.
Recently, scientists from the Mountain View, California-based organization have devised an innovative approach to detect these signals by integrating game theory into their strategy. This new method not only considers where to look for these signals but also when to search.
Game theory is a mathematical discipline that examines decision-making in interactive scenarios, where the actions of two “players” or “agents” are interconnected. Each participant assesses the other’s strategy without a complete understanding of the other’s actions. The outcome relies on the combined strategies of both players.
Specifically, the SETI Institute is applying the concept of the “Schelling point” from game theory. One common example provided by American economist Thomas Schelling is this: Suppose you are supposed to meet someone in New York City without prior arrangements for time or location. Both individuals may independently decide to meet at Grand Central Terminal at noon, as it is a well-known public place and a sensible time.
Now, translate that concept to the search for an alien civilization, focusing on the anti-solar point, an imaginary location in the sky directly opposite the sun (180 degrees away). Imagine a line originating from the sun that extends 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 star and decided to send a signal in our direction?
We have the location — Earth — and the timing — during a transit.
In essence, we’re meeting at Grand Central at noon.
Voices in the void
This anti-solar strategy was proposed years ago, but sufficient funding was lacking to pursue it until now.
“I’ve been reflecting on these ideas that have been developing in the 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 due attention.”
In their recent paper published on November 3, SETI Institute astronomers revealed they identified 1.9 million radio signals utilizing this approach. However, after thorough filtering, they found none that corresponded to extraterrestrial technology — all signals traced back to Earth. It appears that we, as humans, with our satellites and radio emissions, create quite a noise.
While this study eliminated a portion of the sky from consideration, it does not imply that there is nothing else out there. 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 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 they call a narrowband signal, described by Sheikh as a “‘we are here’ … akin to an air horn, almost, in the radio frequencies.”
“It might contain information, or the signal we detect could be what we refer to as a carrier wave. So the air horn would indicate, ‘Hey, there’s something intriguing here.’”
However, don’t envision astronomers with headphones on, like Ellie Arroway in the 1997 film Contact. Instead, computer programs analyze the data.
The SETI Institute employs the Allen Telescope Array, a setup comprising 42 fully steerable 6.1m-diameter telescopes located at the Hat Creek Radio Observatory in California, which has been searching for extraterrestrial signals since the 1980s.
Here is the Allen Telescope Array, the first radio telescope specifically created to 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 endeavor to locate extraterrestrial signals may resemble something from science fiction. However, with our Milky Way galaxy hosting over 100 billion stars, many believe that there should be other life forms, especially since 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, aimed at estimating the number of civilizations in the Milky Way capable of communication.
The result hinges 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 engaged in the search for technosignatures. He received NASA’s first grant to investigate non-radio technosignatures and focuses on chemical signatures or other markers of an intelligent civilization.
He has mentioned that the quest for extraterrestrial intelligence was not taken seriously in the past.
“The giggle factor, which persisted throughout most of my career, has dissipated,” Frank noted, alluding to how the concept was dismissed decades ago. “And that was never logical.”
This shift in perception became particularly evident following the first detection of exoplanets in 1992, and the subsequent identification of an exoplanet orbiting a sun-like star in 1995.
In the event of a detection…
Suppose a signal is detected. What happens next?
Believe it or not, there are established protocols by the International Academy of Astronautics. Beyond the essential task of confirming and verifying the discovery, there is a significant guideline: Do not respond. (If you’ve read or watched 3 Body Problem by Liu Cixin, you will understand why this protocol is sensible.)
-
‘Weird’ interstellar asteroid yields no alien signals, resembles worlds beyond Neptune
-
Scientists skeptical about recent claims that signs of life were possibly detected on exoplanet
However, this situation is not a significant concern. Signals will traverse light-years. For instance, if we were to receive a signal from a star system 100 light-years away and decided to reply, it would take 100 years for our response to reach the alien civilization, followed by another 100 years to get their reply. That sums up to 300 years just to convey a greeting.
“Communication is not our primary focus,” Frank stated.
Frank’s research involves investigating technosignatures by analyzing the chemistry of exoplanets.
“For instance, we can examine the atmospheres of distant planets for substances like chlorofluorocarbons … a chemical only produced by industry,” he explained. “You wouldn’t find it purely from nature or a biosphere.”
Thus, the emphasis will be on finding solace in the knowledge that we are not alone.
This image depicts the printout of a powerful signal received 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)
Although we have yet to identify a definitive radio signal that might suggest the presence 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. It lasted for 72 seconds but was never observed again. Since then, some have speculated that it could have been caused by passing comets.
So when can we expect to detect a signal from an alien source?
“I like to say,” Sheikh remarked, “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 emanating from technology-using civilizations.”