On August 15, 1977, the Ohio University Big Ear radio telescope received a very strong, narrow-band signal. It lasted the 72 seconds that the radio telescope had to observe it, and has never been detected since. This peculiar incident would have gone unnoticed were it not for the fact that Big Ear was then devoting part of its observing time to the SETI program, an acronym for Search for Extraterrestrial Intelligence. But what is really surprising is that this signal fit like a glove what the SETI scientists expected to find if they detected a radio emission from an extraterrestrial civilization . The radio astronomer in charge of the observation, Jerry R. Ehman, was so surprised to discover it that on the printed record he circled the alphanumeric code that described it, 6EQUJ5, and wrote ‘Wow!’ (Wow!) aside. Since then it has been known as ‘the wow signal’ .
The signal met all the criteria to be of artificial origin : the emission frequency was very close to the 21 cm line (1420 Mhz) of hydrogen that SETI astronomers the magic frequency; if a civilization with knowledge of radio astronomy wants to announce its existence to the Cosmos, it must emit in that wavelength. Hydrogen, the most abundant element in the universe, leaves its ‘mark’ in the radio frequency range at that value, making it the best option for studying the processes that occur in interstellar space.
The reasoning of the SETI scientists is as follows: all the possible extraterrestrial races that have a scientific level similar to or higher than ours know about the astronomical importance of the 21 cm line, and they also know that the rest should know about it. So the best way to greet other civilizations is to send a message on that frequency, as they will surely be listening. But not everything ended here. The received signal was powerful, 30 times larger than the interstellar background, and the bandwidth was less than 10 kHz, as one would expect from an intelligent signal if it does not want to be confused with others of natural origin. It apparently came from the constellation of Sagittarius, particularly near a small star cluster known as Chii Sagittarii. The Wow signal has all the ballots to be an extraterrestrial broadcast; the problem is that it has never been heard again.
has not been heard again
Both the Big Ear and other SETI searches over the years have searched in vain for a repeat of this mysterious signal. To explain the failure, some have proposed that it was an effect of interstellar scintillation, while others say that it was a reflection of a terrestrial emission in a piece of space debris. But despite everything, it is not crazy to believe that for 72 seconds we receive a genuine broadcast from another civilization. So, just in case, in 2012, the 35th anniversary of the signal, the then largest radio telescope in the world, Arecibo, sent 10,000 Twitter messages in the direction of Chii Sagitarii. Now it is only necessary to see if they respond… And if they understand it.
Still, for many the SETI program is perilously situated on the fine line that separates science from pseudoscience. In addition, by its very nature it has suffered from the dalliances of fashion: it lived its golden age in the 70s and 80s -also a peak moment in the world of ufology- and it declined until it almost disappeared at the beginning of this century. But now it has been reborn because in 2016 the Russian billionaire Yuri Milner donated 100 million dollars to finance the Breakthrough Listen project for 10 years , with which it is intended to observe around a million stars in search of some signal of extraterrestrial origin.
For the defenders of the existence of extraterrestrial civilizations, the easiest option they have to contact us is through radio waves: they are easy and cheap to generate and go far, in addition to not being affected by interstellar gas clouds. . This is the basis of the SETI program that became a legitimate line of research when in 1959 two physicists, Philip Cocconi and Guiseppe Morrison, published an article in the journal Nature proposing that the best way to search for other civilizations was to use the strategy of the “magical frequencies”. In essence it is a variant of “I know that you know that I know”: if the ETs have a science similar to ours they will have radio telescopes with which they will be studying the universe, and they will know that the best way to do it is by tuning the emission from neutral hydrogen at 1420 MHz, also known as the 21 cm line. Therefore, if they want to send us signals, they will use that frequency because they will know that we listen on that wavelength.
Over time, and the increase in the speed of signal analysis, the “SETI radio” dial increased to cover from 1,000 to 10,000 MHz. Now, for an emission to be effective and not dissipate, the bandwidth – the interval of frequencies that a station occupies on the dial – must be, at most, 1 Hz. This gives us a whopping 10 billion channels to explore in each star: spending only one second per channel , analyzing just one star would take us 317 years. A technological breakthrough was needed, which occurred in 1981 when Paul Horowitz created the SETI Suitcase, a device capable of analyzing 128,000 channels. And in the 90s BETA was born, capable of analyzing one billion channels.
Natural or artificial?
False alarms like the ‘Wow signal’ happen with some frequency. On May 15, 2015, when Russian astronomers using the RATAN-600 radio telescope, located in the Caucasus, detected a strange radio emission that seemed to come from the star HD 164595, which is known to have a planet the size of Neptune. And as always happens in these things, the media soon echoed the news. A short time later came disenchantment: the mysterious signal had a terrestrial origin. The same thing happened with the gigantic Chinese radio telescope FAST: in June 2022 it jumped into the headlines of the press that it had detected three signals that could have extraterrestrial origin. Everything has been in borage water.
Of course, our ability to detect extraterrestrial signals depends heavily on our technology. Beings like the Time Lords from the long-running British television series Doctor Who could exist in the universe, a race that sees all that is, was, will be, and all that could be in time and in time. space, but contacting them would be impossible: neither would we be of interest to them -except for purely anthropological issues- nor would there be a way to establish an intelligible communication. To what extent will we be able to detect the signals that civilizations more intelligent than us send us?
Goldsmith, D. y Owen, T. (1993) The search for life in the universe, Addison-Wesley
Harrison, A. A. (1997) After Contact, Plenum Press
Sagan, C., Shklovskii, IS (1981) Intelligent life in the universe, Editorial Reverté