Scientists at the SETI Institute are exploring a new approach to the search for extraterrestrial intelligence by combining astronomy with game theory. Their research investigates whether alien civilizations might independently identify a particular time and location to establish contact with Earth, helping scientists determine when and where to listen for potential signals.
The research team is using the Allen Telescope Array (ATA) at the Hat Creek Radio Observatory in Northern California to investigate this possibility. Their multiyear project focuses on a region of the sky known as the anti-solar point. The underlying idea is that two civilizations could independently recognize the same astronomical alignment as an opportunity to communicate, even without having exchanged messages beforehand.
A new research paper, titled A Large-Scale Technosignature Survey of the Anti-Solar Point with the Allen Telescope Array: Survey Design and Pilot Results, outlines the project’s strategy and findings from its initial observations. Although the pilot survey found no evidence of extraterrestrial technology, it marks the first observational attempt to investigate the anti-solar point as a potential location for interstellar communication.
Game Theory Could Help Scientists Predict Alien Communication
The research draws on a concept from game theory called a Schelling point. It describes a choice that two parties might independently make when they need to coordinate without communicating with each other.
For example, two people planning to meet in New York City without agreeing on a location or time might independently choose noon at Grand Central Terminal because it is a familiar and recognizable meeting point.
The SETI researchers suggest that a similar principle could apply to civilizations attempting to communicate across interstellar distances. Rather than continuously broadcasting radio signals in every direction, an extraterrestrial civilization might conserve energy by transmitting at a particular time when it believes another civilization could be listening.
The researchers propose that the movement of planets around their stars could provide a shared reference point. An observer located elsewhere in the galaxy might detect Earth passing in front of the Sun, an astronomical event known as a transit. This observation could reveal Earth’s existence, its orbital characteristics and its position within the Sun’s habitable zone.
At the midpoint of this transit, Earth would appear directly between the distant observer and the Sun. From Earth’s perspective, the observer would be located in the opposite direction from the Sun, known as the anti-solar point.
Since both civilizations could independently recognize this alignment, researchers believe it could serve as a natural coordination point for sending and receiving signals.
“The challenge in SETI isn’t simply deciding where to point a telescope,” said Dr. Sofia Sheikh, SETI Institute Research Scientist and co-lead author of the paper. “It’s figuring out where and when another civilization might choose to transmit. The anti-solar point gives us a way to think about that problem from the perspective of a potential sender, rather than just the receiver.”
The theory does not establish that extraterrestrial civilizations exist or that they would use this communication strategy. Instead, it offers a specific possibility that researchers can investigate through astronomical observations.
Allen Telescope Array Tracks the Anti-Solar Point
To test the theory, researchers are using the Allen Telescope Array, a radio telescope system designed specifically for SETI research. Its antennas work together to identify narrowband radio signals that could potentially indicate technological activity beyond Earth.
However, the anti-solar point does not remain fixed against the background stars. As Earth travels around the Sun, this region shifts across the sky. Researchers must therefore conduct repeated observations throughout the year to follow its movement and build comprehensive coverage over time.
The survey is planned to operate two to three nights per week, with the objective of covering the relevant positions along Earth’s orbit over approximately four years.
The team has also developed an automated data-processing system to analyze the large volumes of information generated during observations. The Allen Telescope Survey Agnostic Technosignature (ATSAT) system helps identify and examine potential narrowband drifting signals within these datasets.
“Recent development of the Allen Telescope Survey Agnostic Technosignature (ATSAT) system, SETI’s efficient narrowband drifting signal search pipeline, has made finding and analyzing potential technosignatures very effective in such large radio datasets like the ASP survey,” said Isabel Gerrard, Technosignature Researcher with Breakthrough Listen at the University of Oxford and co-author.
A major difficulty in SETI research is distinguishing potential extraterrestrial transmissions from radio interference generated by human technology, including satellites and communication systems.
To address this, researchers examine narrowband signals, track changes in their frequencies over time and compare observations from two slightly different directions in the sky. This helps determine whether a signal originates from a specific astronomical location or is caused by nearby human-made interference.
“Using the ATA’s beamforming capability to compare signals from the ASP to a different point in the sky helps us filter out hundreds of millions of signals from human interference,” said Ananya Kalapatapu, a student at Cupertino High School and SETI Institute volunteer. “Then, our researchers only have to review a compact, manageable set of the most interesting signals, helping us focus on signals with properties that are more likely to be consistent with extraterrestrial intelligence.”
Researchers can then examine promising candidates and conduct follow-up observations.
Initial Survey Finds No Evidence of Extraterrestrial Signals
Before launching the larger observational campaign, researchers conducted a three-night pilot survey during the summer of 2023.
The team used 20 antennas of the Allen Telescope Array to collect approximately 17 hours of observations, producing around 32 terabytes of data.
The initial analysis identified approximately 1.9 million radio signal detections, commonly referred to as hits. However, after filtering the data and examining the most promising candidates, researchers found no signals consistent with extraterrestrial technology. All detections could be attributed to radio interference from human sources.
Despite the absence of potential technosignatures, the pilot study helped researchers improve their approach for the larger survey. The findings allowed them to refine their observing frequencies, strengthen interference-filtering methods and improve techniques for identifying signals originating from specific directions in the sky.
The pilot observations also established the first observational limits for radio transmitters using the anti-solar point as a possible communication strategy. Under certain assumptions, the system was sensitive enough to detect transmissions from a source with power comparable to the former Arecibo planetary radar at distances of approximately 124 light-years.
SETI Campaign Continues Its Search for Signals Beyond Earth
Searching for extraterrestrial intelligence remains a complex scientific challenge. Researchers do not know whether other technological civilizations exist, what communication technologies they might use or whether they would attempt to contact Earth.
The anti-solar point survey investigates one possible way to narrow this uncertainty by examining whether distant civilizations could independently identify the same astronomical event as an opportunity to communicate.
The project also demonstrates how concepts from other disciplines, including game theory and advanced computing, can contribute to the search for extraterrestrial technology.
Since the initial pilot study, the campaign has accumulated more than 121 nights of observations. Researchers plan to publish findings from the first year of data collection in a future study.
Even if the campaign does not identify extraterrestrial signals, its observations will help establish further limits on possible transmissions and determine which regions of the search space have already been examined.
By combining astronomical observations with predictions about how another civilization might choose to communicate, SETI researchers are investigating whether finding extraterrestrial intelligence could depend as much on knowing when to listen as on knowing where to look.
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