Nearly 50 years ago, following the turmoil of the Vietnam War, during President Jimmy Carter’s era, humanity launched the Golden Record into space, hoping extraterrestrial civilizations might find it. At the same time, people were captivated by Star Wars, marking the golden age of sci-fi films from director Steven Spielberg.
At that moment, humanity looked up at the sky and asked: Could it be that amid this vast universe, we are not alone?
Back then, the SETI (Search for Extraterrestrial Intelligence) project was already searching for intelligent life beyond Earth, and on the quiet night of 15 August 1977, a strange radio signal never seen before was detected by the Big Ear radio telescope at Ohio State University.
A few days later, Jerry Ehman reviewed the signal data on printout paper, circled the anomaly in red, and wrote the word “Wow!” next to it.
This marked the start of the mystery suggesting it might be a signal from an extraterrestrial civilization—nearly half a century later, humans have never detected it again, and no definitive explanation has proven its origin.
The Big Ear telescope lived up to its name as Earth’s “ear,” listening for radio waves from space to find alien signals. Humans believed radio waves were the most universal medium, especially the ‘specific frequency’ emitted by hydrogen, the universe’s most abundant element. Any intelligent life would likely recognize this frequency.
The signal printout from Big Ear showed a peculiar code ‘6EQUJ5,’ representing signal strength levels recorded by computers at the time as numbers 1 to 9 (mostly 1 or 2). When strength exceeded 9, letters A to Z were used instead.
The presence of the letter ‘U’ indicated the signal was about 30 times stronger than the normal cosmic background noise, and coincidentally had a frequency near 1420 MHz, the hydrogen emission line. The signal was narrowband, a feature typical of human-made technology.
However, it was nearly impossible for the signal to have come from Earth due to the 1420 MHz frequency being a globally protected radio band reserved exclusively for astronomy research.
Although scientists later used more advanced radio telescopes to re-examine the coordinates for decades, no similar signal was ever found again. It seemed as if ‘someone’ from beyond Earth pressed a transmit button and immediately shut it off.
Despite arguments suggesting the Wow! signal might have been sent by ‘someone,’ examining its details reveals the radio wave was actually ‘empty.’
Real information transmission requires modulation—altering amplitude (AM) or frequency (FM)—but the Wow! signal showed no modulation at all.
For comparison, the 1974 Arecibo message sent to star cluster M13 contained extensive encoded data. Humans modulated frequency shifts to represent binary 1s and 0s forming a 1,679-bit string that produced a pictorial message about Earth, unlike the Wow! signal’s brief, single ‘knock.’
Additionally, in the 1970s, humanity was likely unaware of natural phenomena generating narrowband signals like the Wow! signal, so it seemed incredible. Scientists noted that such a sudden energy burst could be caused by radiation emission, reflection, or gas fragmentation rather than an engineered mechanism.
In 2015, Antonio Paris proposed that the Wow! signal might have originated from radio waves emitted by hydrogen clouds around two previously unknown comets passing through the Big Ear’s sightline in 1977.
This hypothesis was quickly rejected because calculations showed comets couldn’t emit radio waves that strong. If from a comet, signals should appear in both receivers of Big Ear, but Wow! was detected only on one side. The signal’s rapid onset also conflicted with the slow movement of hydrogen clouds. Moreover, the signal should have been repeatable if this were true.
In 2024, Abel Méndez and colleagues proposed that the Wow! signal originated when a magnetar excited a cold hydrogen cloud.
The coordinates detected by Big Ear in 1977 correspond to a region dense with cold hydrogen clouds near a magnetar—a neutron star with a magnetic field 10^14–10^15 times stronger than Earth’s. This star can release massive energy bursts directed at surrounding hydrogen clouds.
As hydrogen atoms absorb this energy, they become excited and emit a brief, intense flash at 1420 MHz, producing a narrowband signal matching the Wow! signature.
Researchers analyzed observatory data from 2017 to 2020 and found evidence that cold hydrogen clouds can generate narrowband signals resembling Wow!, though these newer signals are 50 to 100 times weaker than the original 1977 detection.
Although this theory is the most accepted, it remains hypothetical because an identical signal has never been detected again, preventing a definitive conclusion.
In the silent cosmos where humanity shouts out loud, hoping to be heard, we may seem alone now, but the vastness of the universe does not confirm our solitude. Perhaps ‘someone’ hides in some corner, and only a brave species like humans dares to reveal itself amid the darkness.
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