In the search for other civilizations in space, it is not enough to simply point a telescope at a given spot. It has to be done at the right time. The SETI Institute has announced a new approach to the search that uses game theory to predict when potential extraterrestrials might send a signal.
To search for extraterrestrial civilizations, scientists at the SETI Institute are using the Allen Telescope Array (ATA) at the Hat Creek Radio Observatory in Northern California. They have begun a multiyear search focused on one specific place in the sky: the antisolar point, which is the point in the sky that lies exactly 180 degrees from the Sun’s position from the observer’s perspective.
The approach rests on the assumption that two civilizations, even without communicating beforehand, could independently identify the same time and place for making contact. The strategy is described in a paper published in The Astronomical Journal (the lead author is Sofia Sheikh of the SETI Institute). Preliminary pilot results are also presented, and so far they have provided no evidence of extraterrestrial technology.
Game theory is a branch of mathematics and economics that studies optimal behavior when interests conflict or when decisions must be made in cooperation with others. It includes the concept of the Schelling point, which is a choice two parties can make independently of each other when they need to coordinate but cannot communicate beforehand.
For example, if two people had to meet in Toruń without being able to arrange it in advance, they might think of meeting at noon by the monument to Nicolaus Copernicus (Mikołaj Kopernik) on the Old Town Market Square, because it is a popular meeting place.
One can try to predict something analogous for interstellar communication. An extraterrestrial civilization might, for example, try to communicate with Earth, but to save energy, instead of sending a signal nonstop in all directions, it might focus on transmitting at a specific time. But how do you determine the best time?
According to SETI researchers, the configuration of the Solar System could give both sides of such a contact a reference point. A distant civilization might observe Earth’s passages across the face of the Sun, known as transits, just as Earth’s astronomers do for many exoplanets. At the midpoint of a transit, Earth will be exactly between the Sun and an observer in another planetary system. From Earth’s perspective, an observer in another planetary system will be in the sky in the direction of the antisolar point. Both civilizations, ours and the extraterrestrial one, could independently reach the same conclusion and consider this a good moment for communication.
The antisolar point moves across the sky against the background of the stars as Earth travels around the Sun. For that reason, the researchers have proposed repeating the observations throughout the year, with a multiyear outlook. This is a different strategy from typical searches for extraterrestrial civilizations, which usually focus on specific stars and planetary systems.
The plan is to conduct observations two or three nights a week over four years. An automated pipeline has been built to handle the enormous amount of data from such observations.
Before the main campaign began, pilot observations were carried out over three nights in 2023. Using 20 antennas of the Allen Telescope Array (ATA), about 17 hours of observations were conducted, generating 32 terabytes of data.
Initial analyses found about 1.9 million signal detections. After filtering them and checking the most promising ones, no signals matching potential technosignatures of extraterrestrial civilizations were found. All of the detections could be explained by radio interference from human-made sources.
The researchers also determined how far the pilot observations could detect signals. For a transmitter like the one used in the planetary radar of the former Arecibo radio telescope, signals could be detected from distances of up to 124 light-years.
The SETI Institute was founded in 1984. It is a nonprofit organization whose goal is to search for extraterrestrial civilizations and life in the universe. The institute’s research in this area is funded primarily by private sources. In addition to the Allen Telescope Array, the SETI Institute also uses optical telescopes and space telescopes.
The acronym SETI itself stands for the search for extraterrestrial intelligence, and it is used to describe the full range of efforts to find extraterrestrial civilizations, including those carried out by other institutions and organizations. (PAP)
