Researchers at the SETI Institute are applying game theory to the search for extraterrestrial life. Their approach targets the so-called anti-solar point, the point in the sky that lies exactly opposite the Sun as seen from Earth. The idea behind it: two civilizations could coordinate without ever communicating directly, by independently settling on the same obvious location.
The concept is based on the so-called Schelling point, named after the economist Thomas Schelling. It refers to a natural choice that both sides make independently because it appears obvious to both. Applied to astronomy, this would mean that a distant civilization wanting to discover Earth could direct its signals exactly where we search first. One such point of contact would be Earth's transit across the Sun, through which our planet could become visible to distant observers. The anti-solar point offers the advantage that, from Earth's perspective, it always lies exactly opposite the Sun and thus marks a clearly defined spot in the sky.
Over the course of an Earth year, the anti-solar point moves across the fixed stars, so the search area shifts continuously. For the study, the team uses the Allen Telescope Array in California. The software searches the data specifically for narrowband radio signals, which are often of artificial origin, since natural sources generally emit across a broader frequency spectrum. To distinguish signals from distant sources from local interference, the method compares observations from two directions. A signal originating from a great distance should appear from both viewing directions, while interference from the immediate surroundings usually appears in only one direction.
In a pilot campaign in the summer of 2023, observations were carried out over three nights. Initially, around 1.9 million radio signals were found. After filtering, however, all of these signals could be traced back to human-made sources of interference, that is, devices and radio services on Earth. The pilot phase also showed that a transmitter of the power class of the Arecibo telescope would be detectable at a distance of about 124 light-years. This figure gives an idea of how far the search reaches with today's instruments.
For the full survey, the researchers plan to observe two to three times a week over about four years. So far, observational data from more than 121 nights has already been collected. The results were published in the journal The Astronomical Journal; the lead author is Sofia Sheikh. As things currently stand, there is no indication of extraterrestrial technology. Nevertheless, according to the researchers, the study is useful because it sets new limits on how strong possible transmissions would have to be to have gone undetected so far. In this way, the search remains valuable even if it initially produces no hits.