Posted by In November 1967 a Cambridge graduate student named Jocelyn Bell Burnell noticed a bit of “scruff” on a chart recorder: a radio source pulsing every 1.33 seconds, as regular as a metronome. Her group half-jokingly labelled it LGM-1, for Little Green Men. Within weeks they had found more of them in other parts of the sky, which made a chorus of alien beacons far less likely than a new kind of star. It was the first pulsar. Anyone asking what alien existence proof would look like should start here, because the history of the search is mostly a history of brilliant false alarms, and each one taught astronomers how to tell the difference.
The pulsar episode left a useful rule behind. Bell Burnell’s team did not announce aliens; they kept observing, found a second source, then a third, and let the boring explanation win once the data favoured it. Her supervisor Antony Hewish shared the 1974 Nobel Prize in Physics for the work, a decision that is still argued about, since she was the one who spotted the scruff.
The signal nobody could repeat
On 15 August 1977 the Big Ear radio telescope at Ohio State University recorded a burst that rose and fell over about 72 seconds, exactly as a fixed point in the sky should as Earth’s rotation carried it through the beam. It sat close to the 1420 MHz hydrogen line, a frequency SETI researchers had long argued a civilisation might choose. Jerry Ehman, reading the printout days later, circled the sequence and wrote “Wow!” in the margin.
Then nothing. Ehman and others went back to that patch of Sagittarius many times, with Big Ear and with larger instruments. The signal never returned.
That single fact is why the Wow! signal remains a curiosity rather than a discovery. A transmission that cannot be re-observed cannot be checked for its source, its structure, or whether some unknown glitch produced it. Explanations have been proposed over the years, some more convincing than others, and the honest position is that nobody knows what Big Ear picked up that night. The telescope itself cannot help. It was dismantled in 1998 when the land was sold for development.
Microwave ovens and a star next door
Interference is the constant enemy, and it can be absurdly mundane. For years the Parkes radio telescope in Australia recorded strange bursts that researchers called perytons. In 2015 Emily Petroff and colleagues traced them to the staff kitchen: a microwave oven, opened before its timer finished, leaked a short burst at just the right frequency.
BLC1 was a far more serious case. In spring 2019, Breakthrough Listen observations at Parkes picked up a narrowband tone near 982 MHz while the dish was pointed at Proxima Centauri, the nearest star to the Sun and home to at least one rocky planet. It drifted in frequency the way a source on a moving planet might. It seemed to vanish when the telescope looked away from the star. News of it leaked to the press in December 2020, and for a few weeks it was the most talked-about signal in decades.
The team that analysed it, in papers published in 2021, concluded it was almost certainly human-made, an artefact produced when signals from local electronics mixed together. The giveaway was that they found many similar “lookalike” signals at related frequencies, appearing even when the telescope was pointed elsewhere. BLC1 was not a failure of the search. It was the search working exactly as designed.
What a real transmission would have to do
So suppose a candidate appears tomorrow. What would turn it into genuine alien existence proof rather than another entry in the false-alarm file?
First, it would have to come back. Second, it would need to track the sky: stay locked to one celestial position as Earth turns, and disappear when the dish moves off. Third, a different observatory on a different continent, with different electronics and a different local radio environment, would have to see it too. A signal that shows up at Green Bank and at MeerKAT cannot be blamed on one kitchen.
If it carried structure, such as prime numbers, regular modulation or anything that looked engineered, the case would grow stronger again. But structure is not required, and it is not enough on its own. Pulsars are wonderfully structured.
The SETI community wrote down what to do in exactly this situation decades ago. A declaration of principles adopted by the International Academy of Astronautics in 1989 asks a discoverer to verify the detection, alert other observers so they can check independently, and only then announce it publicly. No reply should be sent without international consultation. It is a slow, slightly bureaucratic protocol, which is precisely what a world-changing claim needs.
Oumuamua and the problem with strange objects
In October 2017 the Pan-STARRS survey in Hawaii spotted the first known interstellar object passing through the Solar System. ‘Oumuamua was elongated or flattened, tumbling, and it accelerated slightly as it left the Sun’s neighbourhood without any visible tail of gas or dust. Harvard astronomer Avi Loeb suggested it might be a fragment of alien technology, perhaps a light sail.
Most astronomers disagreed. Several natural explanations have been put forward, including one in 2023 proposing that hydrogen trapped in its ice was escaping as it warmed. None is universally accepted. But the object was observed for only a few weeks before it faded, and the data simply cannot settle the matter. Strange, yes. Proof of anything, no.
The biology side has false positives too
Remote biosignatures have their own version of the microwave oven. Oxygen is the textbook example. On Earth, an atmosphere one-fifth oxygen exists because of photosynthesis, so for years oxygen looked like an ideal sign of life on an exoplanet.
Then modelling work, including studies by Rodrigo Luger and Rory Barnes in 2015, showed how a planet around a young red dwarf could build up large amounts of oxygen with no biology at all: intense ultraviolet light splits water vapour, the light hydrogen escapes to space, and the oxygen stays behind. A detection of oxygen on such a world could be a geochemical leftover. James Lovelock’s older idea, from the 1960s, still holds up better: look for gases that should destroy each other, like oxygen and methane together, which suggests something keeps replenishing them.
Even then, context about the star, the planet’s age and its geology would be needed before anyone used the word life.
Waiting for the one that sticks
None of this means the search is futile. It means the bar is high and visible. Every false alarm so far was eventually explained by careful people with access to the data, and that process is itself reassuring, because it would work just as well on a real signal.
The first credible alien existence proof, if it comes, will probably begin like BLC1 did: a strange line in a dataset, a few nervous emails, a request for more telescope time. The difference will be that it survives.
For more on the signals, the false starts and the people who chase them, SETIworld keeps a running account of the search, and the rest of the portal is a good place to keep reading.
