Universe Today
In 1977, a volunteer scanning data from the Big Ear Radio Observatory in Ohio circled an unusually strong signal on a printout and wrote ‘WOW!’ next to it. The signal lasted 72 seconds and has never been detected again. For nearly half a century it has been held up as the most tantalising moment in the search for extraterrestrial intelligence. There's an irony, then, in the fact that by the UCLA team's own strict definition of what constitutes a genuinely technological signal, the ‘Wow!’ signal doesn't quite make the cut, its frequency spread is just broad enough to allow a natural origin. We are, it turns out, still waiting for the first confirmed one.
The Wow! signal represented as "6EQUJ5" which articulates the signal strength (Credit : Big Ear Radio Observatory)
A team at UCLA has been trying harder than most. For the past ten years, they have been using the Green Bank Telescope in West Virginia which is the largest fully steerable radio telescope on the planet, with a dish spanning 100 metres. They used it to scan the sky for narrowband radio signals, the kind that, in theory, only a technologically advanced civilisation would produce. Natural astrophysical processes don't tend to emit radio waves at a precise, unwavering frequency. Technology does.
Over a decade, they captured radio emissions from more than 70,000 stars and planetary systems. Their detection pipeline which was efficient enough to catch between 94 and 99 % of any genuine narrowband signals across the full range of possible frequencies eventually flagged 100 million candidate signals for investigation. But sadly not one of them survived scrutiny.
Every single signal, with 99.5 % eliminated automatically, the remaining 0.5 % checked by human eyes turned out to be of human origin. Mobile phones, satellites, aircraft and ground based transmitters. The universe, at least within the slice of it the team examined, remained stubbornly quiet. But this result is not a failure, it’s a measurement.
The Robert C. Byrd Green Bank Telescope, located in Green Bank, West Virginia, US (Credit : NRAO/AUI/NSF)
The data allows the team to place what scientists call an upper limit on transmitter prevalence, a statistically rigorous statement about how common alien broadcasts can possibly be, given that we haven't found any. At 95 % confidence, fewer than one in sixteen thousand stars within 20,000 light years of Earth hosts a transmitter powerful enough to be detectable by the search.
That's a remarkable constraint and whilst it doesn't say intelligent life isn't out there, it says that if it is, it's either not broadcasting at the frequencies and power levels we're searching, or it's further away than we've yet looked, or it's rarer than even our most conservative estimates suggested.
Over 40,000 volunteers have contributed to the project through the citizen science platform arewealone.earth, reviewing the most interesting candidate signals with human judgement that no algorithm can fully replicate. There is one more number worth highlighting. Between 1994 and 2024, NASA invested a total of $5.57 million (adjusted for inflation) in the search for technosignatures across all funded programmes. That represents 0.0007 % of the agency's total budget over that period. A decade of UCLA's work, 70,000 stars, and 100 million signals… on a shoestring.
No results yet but the search continues and with next generation telescopes about to come online, the volume of sky we can monitor is set to increase by orders of magnitude.
Source : Results of ten years of UCLA SETI searches with the Green Bank Telescope
