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Are we alone? For more than six decades, scientists have tried to answer that question not with spaceships but with radio telescopes, listening for a signal that nature could not produce. Today the best-known efforts are run by the SETI Institute and by Breakthrough Listen, a privately funded program launched in 2015. Here is how the search actually works, what has been found so far and why "nothing yet" is still a meaningful result.
The Idea Behind SETI
SETI stands for the Search for Extraterrestrial Intelligence. Rather than looking for microbes, it looks for technosignatures: evidence of technology, such as a radio transmitter or a laser. The logic is simple. Natural radio sources such as stars, gas clouds and pulsars spread their energy across a wide range of frequencies. A deliberate transmitter, like the ones humans build, can pack its power into a very narrow slice of the spectrum, sometimes just a few hertz wide. Finding a narrowband signal coming from a distant star would be very hard to explain naturally.
Funding has always been the challenge. As ScienceAlert notes, NASA stopped its SETI work after Congress cancelled its High Resolution Microwave Survey in 1993, leaving the field to private donors and research institutes.
Breakthrough Listen: The Biggest Search Yet
Breakthrough Listen was announced on 20 July 2015 with 100 million US dollars of funding for a ten-year effort, backed by Yuri and Julia Milner and led scientifically from the University of California, Berkeley. Its stated goal was to survey the nearest million stars, the plane of the Milky Way and 100 nearby galaxies.
To do that, it buys or shares time on some of the world's largest radio telescopes, including the Green Bank Telescope in West Virginia, the Parkes "Murriyang" telescope in Australia, the MeerKAT array in South Africa and, since a 2024 partnership, the Sardinia Radio Telescope in Italy. At MeerKAT, the team runs in "commensal" mode, recording data in the background while other astronomers observe, which greatly increases the number of stars it can cover.
How a Signal Gets Checked
Modern radio receivers produce enormous amounts of data, and almost every "hit" turns out to be human interference from satellites, aircraft, phones or radar. Researchers use a series of filters to weed them out:
- Look for narrowband hits. Software scans the spectrum for signals much narrower than any natural source.
- Check the drift. A transmitter on a spinning, orbiting planet would slowly shift in frequency because of the Doppler effect. Tools such as Berkeley's turboSETI search for these drifting lines.
- Point on, then off. The telescope alternates between the target star and nearby empty sky. A real signal should appear only when pointed at the star; interference tends to show up in both.
- Re-observe. Anything that survives is checked again, ideally with another telescope. A genuine beacon should repeat.
The SETI Institute's Allen Telescope Array in California follows similar principles. In a study published in 2024, SETI Institute and Penn State researchers spent 28 hours scanning the TRAPPIST-1 system across 0.9 to 9.3 GHz, timing observations to moments when one planet passed in front of another. Millions of detections were filtered down to about 11,000 candidates, and none turned out to be of non-human origin.
False Alarms: The Case of BLC1
The best-known recent example is BLC1, a narrowband signal detected with the Parkes telescope while observing Proxima Centauri, our nearest neighbouring star. It lasted over five hours and had some features expected from a distant transmitter. After careful analysis published in Nature Astronomy in 2021, the Berkeley team concluded that it "appears to be interference from human technology." A 39-hour follow-up of Proxima Centauri found no repeat. This is the process working as intended: exciting candidates are tested, and the evidence decides.
Verified Facts vs Speculation
It is worth being clear. As of October 2026, no confirmed technosignature has ever been detected by SETI or Breakthrough Listen. Famous events such as the 1977 "Wow!" signal were never repeated, and claims online that a signal "proves" aliens should be treated with caution until scientists publish and others confirm. What is verified is that the searches have become far larger and more sensitive, with new tools such as AI-assisted analysis developed with NVIDIA. For more on the official side of the topic, see our round-up of Pentagon UFO file releases.
Conclusion
SETI is a patient science. Every survey that comes back empty narrows down where, and how loudly, other civilisations could be transmitting. With bigger arrays, smarter software and decades of experience in spotting interference, the search for alien signals is more capable than ever, even if the universe is still keeping quiet.