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Where and when to listen? SETI turns to game theory to choose where to search for alien radio signals

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Researchers at the SETI Institute used an idea from game theory to decide where to point their radio telescopes: toward the direction from which a distant civilization would see Earth pass in front of the Sun. A pilot survey recorded 1.9 million radio signals, all of them human-made. A four-year observing campaign is already underway.

The hardest question: where and when?

One of the basic problems in the search for technological signals from alien civilizations (SETI) is that the sky is enormous and observing time is limited. "The challenge in SETI isn't simply deciding where to point a telescope," said Sofia Sheikh, a researcher at the SETI Institute. In her view, the task is also to work out where and when another civilization might choose to transmit.

Sheikh and her colleagues looked for an answer using a concept from game theory. Their study was published in The Astronomical Journal, and the SETI Institute announced it on November 3, 2026.

The Schelling point

In game theory, a Schelling point is a solution that two parties would each arrive at independently, without consulting each other. The researchers argue that one such shared point for Earth and a distant civilization could be the anti-solar point, the direction exactly opposite the Sun as seen from Earth.

The reasoning goes like this. If a distant observer sees Earth pass in front of the Sun, then at the midpoint of that transit, that observer lies in the direction of the anti-solar point as seen from Earth. That alignment could give both sides a shared cue in time and place. The SETI Institute stresses that the approach does not assume alien civilizations exist or that they would actually use this strategy.

The anti-solar point drifts across the sky against the background stars over the course of the year, so instead of watching selected stars, the researchers track this moving point regularly throughout the year.

The pilot survey

The observations are carried out with the Allen Telescope Array (ATA), which was built specifically for SETI research at the Hat Creek Radio Observatory in Northern California.

In a pilot survey in summer 2023, the team observed the anti-solar point with 20 antennas over three nights, for a total of about 17 hours. This produced roughly 32 terabytes of data. The processing software searched for narrowband radio signals whose frequency drifts over time. The researchers also compared signals from the anti-solar point with those from a nearby sky position to filter out interference from Earth.

The initial analysis turned up about 1.9 million radio signals. After filtering, every one of them was traced to human-made interference, and none pointed to alien technology.

The pilot did, however, give a first estimate of what the method can do. According to the researchers, under certain assumptions they could detect a transmitter comparable in power to the former Arecibo planetary radar from about 124 light-years away.

Four years of observations

The full campaign is already underway. The researchers observe two to three nights a week for about four years in order to cover every key position along Earth's orbit. Since the pilot, they have collected more than 121 nights of data, and results from the first year will be published in a later study.

A high school student also took part in the work: Ananya Kalapatapu, a student at Cupertino High School in California who volunteers at the SETI Institute. She said that comparing the two sky positions helps filter out hundreds of millions of human-made signals.

The sober take

What did they find? Nothing that points to an alien origin. All 1.9 million radio signals from the pilot survey turned out to be human-made interference.

What does the result mean? The pilot covered only three nights, so it does not prove that there are no transmitters nearby. What it shows is that the method works and, under certain assumptions, how strong a signal it could pick up. The real test will be the four-year campaign.

What is the method based on? The assumption that an alien civilization thinks the way we do and would consider the same moment the obvious choice. This cannot be proven, and the researchers do not claim it must be so. The idea's strength is that it narrows a nearly endless search to a specific direction and time that can be justified.

Connection to UFOs: SETI searches for radio signals from distant star systems and does not study objects seen in Earth's skies. The two fields use different methods, and SETI results on their own say nothing about UFO sightings.