SETI Institute uses game theory to pick when to listen for aliens; first nights of the search find nothing

Scientists at the Mountain View-based SETI Institute have started a years-long radio search that tries to guess not just where an alien civilization might aim a message at Earth, but when, they reported Tuesday in The Astronomical Journal.  Their first three nights of data turned up no sign of extraterrestrial technology.

The idea

The search borrows a concept from game theory called a Schelling point:  a choice two parties can make independently when they need to meet but can't talk.  Two strangers told to meet somewhere in New York with no time or place, the institute notes, might both pick noon at Grand Central Terminal.

For aliens, the team's candidate is the moment Earth passes in front of the sun as seen from their planet, which is how astronomers here find planets around other stars.  At the middle of that crossing, Earth sits exactly between the sun and the watchers.  Seen from Earth, a transmitter there would lie in the direction exactly opposite the sun, the anti-solar point, which is high in the sky around midnight.  Both sides could work that out without ever having traded a message.  "The challenge in SETI isn't simply deciding where to point a telescope.  It's figuring out where and when another civilization might choose to transmit," said Sofia Sheikh, a SETI Institute research scientist and co-lead author.  The researchers stress the idea doesn't assume anyone is out there.

The telescope

The work uses the institute's Allen Telescope Array at Hat Creek Radio Observatory, in a valley just north of Lassen Volcanic National Park, about 300 miles north of San Francisco and about 3,300 feet above sea level.  It has 42 dishes, each 20 feet across, that work together as one instrument.  UC Berkeley and the SETI Institute dedicated it on Oct. 11, 2007, at a cost to date then of $50 million, half from Microsoft co-founder Paul Allen's family foundation.  It was planned to grow to 350 dishes but never did.  It was the first radio telescope built specifically for SETI, and 28 of its dishes now carry new receivers.

What the pilot found

In a three-night pilot in the summer of 2023, the team used 20 dishes for about 17 hours, tuned between 1 and 2.4 gigahertz, the same broad band as cellphones and Wi-Fi.  That produced 32 terabytes of data and about 1.9 million "hits," narrow signals worth a second look.  Software compared each spot with a second patch of sky nearby; a real alien beacon should show up in only one.  The comparison "helps us filter out hundreds of millions of signals from human interference," said Ananya Kalapatapu, a Cupertino High School student and SETI Institute volunteer.  Every one of them traced back to human-made radio interference.

The search was sensitive enough to catch a transmitter as strong as the former Arecibo planetary radar in Puerto Rico, the most powerful transmitter humans have built, out to about 124 light-years, roughly 730 trillion miles.  A radio signal from there would have left around 1900.  Under less favorable assumptions the reach drops to about 44 light-years.

What's next

The full survey runs two to three nights a week and needs about four years to sweep the whole path the anti-solar point traces around the sky, because Earth's orbit and leap years shift which part is visible at night from Hat Creek.  The team has logged more than 121 nights since the pilot and plans to report first-year results in a later paper.  No detection means there is nothing yet for others to confirm; the paper is peer-reviewed.

Source:  Sheikh, Hort and others, "A Large-scale Technosignature Survey of the Antisolar Point with the Allen Telescope Array: Survey Design and Pilot Results," The Astronomical Journal, published Nov. 3, 2026 (doi:10.3847/1538-3881/aeaa59, CC BY 4.0); SETI Institute news release, "When Should We Listen for Alien Signals?" (Nov. 3, 2026); SETI Institute ATA project page; UC Berkeley news release on the ATA dedication (Oct. 11, 2007); U.S. Geological Survey elevation data.  Drafted by AI for San Jose.