The Wow! signal, a one-off detection at the Ohio State ‘Big Ear’ observatory in 1977, continues to perplex those scientists who refuse to stop investigating it. If the signal were terrestrial in origin, we have to explain how it appeared at 1.42 GHz, while the band from 1.4 to 1.427 GHz is protected internationally – no emissions allowed. Aircraft can be ruled out because they would not remain static in the sky; moreover, the Ohio State observatory had excellent RFI rejection. Jim Benford today discusses an idea he put forward several years ago, that the Wow signal could have originated in power beaming, which would necessarily sweep past us as it moved across the sky and never reappear. And a new candidate has emerged, as Jim explains, involving an entirely natural process. Are we ever going to be able to figure this signal out? Read on for the possibilities. A familiar figure in these pages, Jim is a highly regarded plasma physicist and CEO of Microwave Sciences, as well as being the author of High Power Microwaves, widely considered the gold standard in its field.
by James Benford
The 1977 Wow! signal had the potential of being the first signal from extraterrestrial intelligence. But searches for recurrence of the signal heard nothing. Interest continues, as two lines of thought continue to ponder it.
An Astronomical Maser
A recent paper proposes that the Wow! signal could be the first recorded event of an astronomical maser flare in the hydrogen line [1]. (A maser is a laser-like coherent emission at microwave frequencies. The maser was the precursor to the laser.) The Wow frequency was at the hyperfine transition line of neutral hydrogen, about 1.4 GHz. The suggestion is that the Wow was a sudden brightening from stimulated emission of the hydrogen line in interstellar gas driven by a transient radiation source behind a hydrogen cloud. The group is now going through archival data searching for other examples of abrupt brightening of the hydrogen line.
Maser Wow concept: A transient radiative source behind a cold neutral hydrogen (HI) cloud produced population inversion in the cloud near the hydrogen line, emitting a narrowband burst toward Earth [1].
Image courtesy of Abel Mendez (Planetary Habitability Laboratory, University of Puerto Rico at Arecibo).
Could aliens use the hydrogen clouds as beacons, triggered by their advanced technology? Abel Mendez has pointed out that this was suggested by Bob Dixon in a student’s thesis in 1976 [2]! From that thesis [3]:
“If it is a beacon built by astroengineering, such as an extraterrestrial civilization that is controlling the emission of a natural hydrogen cloud and using it as a beacon, then the only way that it could be ascertained as such, is by some time variation. And we are not set up to study time variation.”
How could such a beacon be built? It would require producing a population inversion in a substantial volume of ionized hydrogen. That might perhaps be done by an array of thermonuclear explosives optimized to produce a narrowband emission into such a volume [4]. Exploded simultaneously, they could produce that inversion, creating the pulse seen on Earth as the Wow.
Why does the Wow! Signal have narrow bandwidth?
In 2021, I published a suggestion that the enigmatic Wow Signal, detected in 1977, might credibly have been leakage from an interstellar power beam, perhaps from launch of an interstellar probe [5]. I used this leakage to explain the observed features of the Wow Signal: the power density received, the Signal’s duration and frequency. The power beaming explanation for the Wow accounted for all four of the Wow parameters, including the fact that the Wow observation has not recurred.
At the 2023 annual Breakthrough Discuss meeting, Mike Garrett of Jodrell Bank inquired “I was thinking about the Wow signal and your suggestion that it might be power beam leakage. But it’s not obvious to me why any technical civilization would limit their power beam to a narrow band of <= 10 kHz. Is there some kind of technical advantage to doing that or some kind of technical limitation that would produce such a narrow-band response?”
After thinking about it, I have concluded that there is ‘some kind of technical advantage’ to narrow bandwidth. In fact, it is required for high-power beaming systems.
Image: The Wow Signal was detected by Jerry Ehman at the Ohio State University Radio Observatory (known as the Big Ear). The signal, strong enough to elicit Ehman’s inscribed comment on the printout, was never repeated.
A Beamer Made of Amplifiers?
High power systems involving multiple sources are usually built using amplifiers not oscillators, for several technical reasons. For example, the Breakthrough Starshot system concept has multiple laser amplifiers driven by a master oscillator, a so-called master oscillator-power amplifier (MOPA) configuration. Amplifiers are themselves characterized by the product of amplifier gain (power out divided by power in) and bandwidth, which is fixed for a given type of device, their ‘gain-bandwidth product’. This product is due to phase and frequency desynchronization between the beam and electromagnetic field outside the frequency bandwidth [6].
Therefore, for wide bandwidth, a lower power per amplifier follows. That means many more amplifiers. Likewise, to go to high power, each amplifier will have a small bandwidth. (Then the number of amplifiers is determined by the power required.) For power beaming applications, to get high power on target is essential: higher power is required, so smaller bandwidth follows.
So why do you get narrow bandwidth? You use very high gain amplifiers to essentially “eat up” the gain-bandwidth product. For example, in a klystron, you have multiple high-Q cavities that result in high gain. The high-gain SLAC-type klystrons had gains of about 100,000. Bandwidths for high power amplifiers on Earth are about one percent of one percent, 0.0001, 10-4. The Wow! bandwidth is 10 kHz/1.41 GHz, about 10-5.
So yes, the physics of amplifiers limits bandwidth in beacons and power beams because both would be built to provide very high power. So, with very high gain in the amplifiers, small bandwidth is the result.
This fact about amplifiers is another reason I think power beaming leakage is the explanation for the Wow. Earth could have accidentally received the beam leakage. Since stars constantly move relative to each other, later launches using the Wow! beam will not be seen from Earth.
Therefore I predicted that each failed additional search for the Wow! to repeat is more evidence for this explanation.
The Wow search goes on
These two very different explanations for the origin of the Wow! have differing future possibilities. I predicted that it wouldn’t be seen again. Each failed additional search for the Wow! to repeat (and there have been many) is more evidence for this explanation. Mendez and coworkers are looking to see if their process has occurred previously. They can prove their explanation by finding such occurrences in existing data. These are two very different possibilities. Only the Mendez concept can be realized soon.
References
1. Abel Mendez,1 Kevin Ortiz, Ceballos, and Jorge I. Zuluaga, “Arecibo Wow! I: An Astrophysical Explanation for the Wow! Signal,” arXiv:2408.08513v2 [astro-ph.HE], 2024.
2. Abel Mendez, private communication.
3. Cole, D. M. (1976). “A Search for Extraterrestrial Radio Beacons at the Hydrogen Line,” Doctoral dissertation, Ohio State University, 1976.
4. Taylor, T., 1986, “Third generation nuclear weapons,” Sci. Am., 256, 4, 1986.
5. James Benford “Was the Wow Signal Due to Power Beaming Leakage?”, JBIS 74 196-200, 2021.
6. James Benford, Edl Schamiloglu, John A. Swegle, Jacob Stephens and Peng Zhang, Ch. 12 in High Power Microwaves, Fourth Edition, Taylor and Francis, Boca Raton, FL, 2024.
You cannot make that inference. Failed searches for a repeat only increase the confidence that this is a rare event, not that the event is caused by power beaming. The same applies to Mendez’ astrophysical explanation.
For example, suppose that some rare event on Earth was “explained” as a supernatural intervention. Would repeated failure to observe that event confirm that the cause was supernatural?
From the Mendez et al paper:
I would want to rule out this natural explanation (and others) before claiming the power beaming was a transient technosignature. What other evidence and inferences can be gathered to support this explanation? For example, does it say anything about the distance to the power beam source, or its input energy?
In one way it is shame that the Wow! signal of 1977 didn’t happen now – going under the assumption here it is an artificial signal from an ETI – because modern technology would have signaled the operators at Big Ear immediately so either they or specialized software could track the signal for those critical details to determine if it were terrestrial or not.
SETI personnel have also said that if the Wow! signal had happened in recent years, it probably would have been dismissed as RFI or some other kind of stray signal from this planet. There are certainly plenty of them and human civilization is only getting noisier in multiple areas.
Yes, astronomical radio telescope facilities have a technology no-use zone, but if you think those zones are not blatantly ignored all the time by the military, teenagers, et al, then I have bridge in Brooklyn for you at a very affordable price.
Even the first modern era SETI program, Project OZMA in 1960, was likely buzzed by a military aircraft that made Frank Drake think finding alien transmissions from the stars was even easier than he imagined.
Remember when the Parkes radio telescope SETI program picked up microwave ovens being used by astronomers at that facility? The media had fun with that because that is the level of technology they are able to grasp, plus making fun of real scientists who make honest mistakes as part of doing real science are the kind of thing they enjoy.
As for professional scientists, it is amusing to note how they tend to bend themselves into pretzels to give a cosmic find a natural, non-intelligent alien reason for something new and mysterious they come across in the heavens, rather than claim it is due to aliens.
Yeah, yeah – I know all about pulsars and LGMs and how they need to be conservative as they follow the scientific process. I agree with that method, but I also think we should stop dismissing the ETI angle since we should be a bit smarter and less socially conservative from the olden days. SETI should no longer be considered fringe, nor should religious bias be used to make us once again the only smart creatures in the Universe, etc.
I am not against this new theory to explain the Wow! signal being detailed here. But recall not too long ago, we had someone claiming it was comets – and they were subsequently found to be lacking in several important details. I am also reminded of all the natural explanations for Oumuamua, even though it did not behave like a regular planetoid or comet, such as accelerating AFTER it entered the Sol system.
I do not want to go to the level of one Dr. Loeb, who started out with the intention of keeping aliens in the science detection game, only to go off the rails by anyone’s reasonable standards. But this is the 21st Century and we need to start acting and thinking with a much wider mindset. The Cosmos is vast and ancient and full of all sorts of possibilities.
The history of such discoveries supports the natural explanation. I don’t see astronomers avoiding the ETI explanation despite the evidence, but rather that they should, rightly, assume a natural explanation first. With ‘Oumuamua. Loeb went out of his way to criticize natural explanations, despite his claims of going where the science leads. He actively avoided natural explanations in favor of artificial ones.
His escapade looking for superdense meteorite debris in the ocean is an example. Suppose, against all odds, he found grains of the meteorite that had atomic masses far in excess of anything we know of on Earth. Does that require manufacture, or a natural process that might create such material? Shouldn’t we explore the possibility of a natural process before accepting one that requires creation by agency?
That doesn’t mean we shouldn’t keep a lookout for ETI artifacts or other evidence, but we should not jump to the “It’s aliens” hypothesis, especially because we have been so wrong in the past. If anything, media from newspapers to movies have hyped the ETI claims. Aren’t the tabloids supposed to be the “real news” source of alien interaction on Earth?
Speaking of which, weren’t we supposed to have a major government release that confirms something astonishing about aliens?
Alex Tolley said:
“Speaking of which, weren’t we supposed to have a major government release that confirms something astonishing about aliens?”
It’s like stable fusion power: It’s either right around the corner or just twenty years away. Sixty years ago.
When it comes to ETI as part of the science equation, I want to see more of a middle ground of acceptance.
What I see now are extremes: Either a public with limited education screaming that aliens are here now doing all sorts of things to us, or the professional sciences going to the other end to avoid the extreme fringe but ending up looking like someone from 1600. There has to be a middle ground.
I suppose it depends on what you see as “extreme” and “middle ground”.
Humanity is infused with the middle ground. Religions of all sorts with supernatural and natural agencies. The “Just asking questions” of the Von Daniken “Ancient Aliens” genre, now a perennial on the US’ History Channel. Even Clarke put his name to the UK’s “Mysterious…” series that left viewers questioning how could humans have done [X]. And Clarke was very much a UFO disbeliever on quite rational grounds, but of course allowed for ancient ET in a number of his novels. I am a fan of Sydney Jordan’s “Jeff Hawke” cartoon strip that populated the galaxy with aliens, both natural and supernatural, often invoking biblical angels and Ancient Greek mythology. But I keep those stories separated from reality.
Science works best when the object of study is not sentient. Physics, chemistry, and most of biology works well. Where it gets iffy is with psychology. Sociology and economics are kept in Humanities schools. For example, psychology experiments have to be designed to distract the test subject from divining the true nature of the experiment. The Milgram experiment has been shown to be non-repeatable because we know about it and can adjust our responses.
Douglas Adams could riff on the need for non-sentient test subjects by making laboratory white mice actually very intelligent pan-dimensional beings doing experiments on their human “experimenters”. If you for a moment accepted that mice had sufficient sentience, it would throw certain experimental results into question. If beings can interfere with natural phenomena, then what?
Science in 1600 was much more infused with such influences than you imply, not to mention Aristotle’s influence, which was regarded as arguments of authority on any enquiry of relevance to his ancient pronouncements. For the Christian and Muslim faiths, G*d can change any outcome at his will. What does that imply about any study of phenomena? Let’s not forget that the majority of Americans believe in angels, and I knew a colleague who did not accept evolution. Should I accept that a “middle ground” allowing for supernatural agency overturns the huge weight of evidence that evolution is correct? Should it be acceptable that a supernatural entity has tricked the science establishment into believing the Earth is billions of years old, and so is life?
If we are going to involve ETI, let us be sure of the evidence as conclusive and not explainable by other means. Speculation is fine to open minds, but don’t let it influence how we do science and why we do it a certain way. Non-repeatable phenomena are items for a museum of curiosities.
Your examples are not quite the middle ground I was referring to. As for the year 1600, it was not meant to be taken too literally. I chose it symbolically as the year Giordano Bruno was burned at the stake by the Church. And yes, I know he was executed for reasons other than his views on extraterrestrial life.
I am a big proponent of science and its workings. I just think the alien equation is left out too often as part of a potential solution by those who fear the fringe elements and may also be influenced by their religious backgrounds, to say nothing of peer/societal pressure.
You can tell me upside down and backwards that you saw a UFO/UAP and it landed in your back yard, but you still need empirical proof for such a claim to be taken seriously. That is all I am saying and asking.
“… I knew a colleague who did not accept evolution.”
Funny you should say that…
I once worked for a major oil company in their exploration department, and one of my colleagues was a devout fundamentalist Christian and intelligent design creationist . He completely rejected all non-supernatural forces contributing to biological adaptation, evolution and change. His world was indeed 6000 years old.
This gentleman’s job was the study of microfossils (such as foraminifera) in rock strata that were used to study the age and development of geological formations and their suitability for petroleum exploration.
How these two fundamentally contradictory viewpoints could somehow be reconciled and held in the mind simultaneously has always amazed me. Not only did his work demand an acceptance of Darwinian evolution, his university education must have been grounded on it! It is a perfect example of how Faith will always trump Reason.
Humans can be very good at holding and acting upon two contradictory ideas at once.
Just ask Alice…
“Alice laughed. ‘There’s no use trying,’ she said. ‘One can’t believe impossible things.’
I daresay you haven’t had much practice,’ said the Queen. ‘When I was your age, I always did it for half-an-hour a day. Why, sometimes I’ve believed as many as six impossible things before breakfast. There goes the shawl again!”
― Lewis Carroll
https://www.gutenberg.org/ebooks/19033
One pill makes you larger
And one pill makes you small
And the ones that mother gives you
Don’t do anything at all
Go ask Alice
When she’s ten feet tall
And if you go chasing rabbits
And you know you’re going to fall
Tell ’em a hookah-smoking caterpillar
Has given you the call
Call Alice
When she was just small
When the men on the chessboard
Get up and tell you where to go
And you’ve just had some kind of mushroom
And your mind is moving low
Go ask Alice
I think she’ll know
When logic and proportion
Have fallen sloppy dead
And the White Knight is talking backwards
And the Red Queen’s off with her head
Remember what the dormouse said
Feed your head
Feed your head
Grace Wing Slick
I think it is very important to have the historical background of the Wow! signal discovery so that especially those who grew up in the first quarter of the 21st Century truly grasp just how comparatively primitive the setup for SETI was at the Big Ear radio facility at Ohio State University (OSU).
FYI: Sadly, you can no longer visit Big Ear in Ohio, as the university decided to make a few extra transient dollars by tearing down the radio telescope and turning the land into condos and a golf course. In case you need another reason to wonder why we have detected superior intelligences yet.
But don’t worry, there is a historical marker at the site…
http://www.setileague.org/photos/bigear00.htm
Here are the nitty-gritty technical details:
http://bigear.org/Wow30th/wow30th.htm
Not that Big Ear astronomers weren’t conducting actual radio SETI, but it must be understood that they had a volunteer, Jerry Ehman, checking printouts from the daily sky scans hours and even days after the event. The myth that teams of astronomers are sitting at consoles watching the skies and listening for signals 24/7 is just that, a myth. Especially back in the day. SETI was often a token effort at best.
You should also inquire as to what happened with all the much-touted SETI@Home data – it will make you first shocked, then sad, and then angry. More evidence that astronomy is not taking SETI as seriously as it should.
Here is a newspaper interview with Jerry Ehman from 1994:
http://www.bigear.org/wow.htm
I cannot recommend this 2022 documentary on the Wow! signal enough:
https://www.youtube.com/watch?v=TjQUucV83w4
Here is an interview from 2015 that includes discussions on the Wow! signal. I quote Gerry Harp’s take on it after the link…
https://phys.org/news/2015-07-aliens-day-nowseti-scientists-discuss.html
Harp: “It isn’t at all special or different from signals that we observe every day at the ATA. I hope you’re not disappointed that I’m not so impressed by the “Wow!” signal. I think you will find that many professional scientists in the field do not find the “Wow!” signal very convincing. But that doesn’t mean that SETI isn’t a good thing to do. There is still a 50% chance, by my estimates, that our first discovery of life off of our planet will be a discovery of a transmitting civilization.”
Harp: “The “Wow!” signal was almost certainly radio frequency interference. The signal failed to pass even the simplest tests to exclude interfering signals from that observation campaign. From another perspective, at the Allen Telescope Array (ATA), we see dozens of signals comparable to “Wow!” every day. This is simply because we have much more computational power than they did back when “Wow!” was seen. If the “Wow!” signal were seen today, it would be a yawn. However, there is a silver lining to the “Wow!” signal. “Wow!” has inspired a lot of public interest in SETI. Despite being a not very scientific result, public awareness of “Wow”! has been beneficial to SETI. So I generally think of “Wow!” as being a good thing from that perspective.”
Here is another take on the Wow! signal by Dr. Harp from 2014:
http://cosmicdiary.org/gharp/2014/05/18/seti-your-opinion-doesnt-matter-part-2/
The Very Large Array (VLA) was put into service to look for the Wow! signal in 2001:
http://www.bigear.org/Gray-Marvel.pdf
Here are some earlier blog posts on the Wow! signal from Centauri Dreams:
https://www.centauri-dreams.org/2021/01/22/was-the-wow-signal-due-to-power-beaming-leakage/
https://www.centauri-dreams.org/2023/01/19/an-appreciation-of-setis-robert-gray-1948-2021/
https://www.centauri-dreams.org/2016/01/12/return-to-wow/
https://www.centauri-dreams.org/2007/08/18/the-wow-signal-reexamined/
https://www.centauri-dreams.org/2016/08/27/an-interesting-seti-candidate-in-hercules/
Harp:
Doesn’t Gerry Harp’s comment about seeing a Wow!-like signal every day potentially undermine the “it must be artificial” argument? Unfortunately, there are no details, so IDK if these events are like the Wow! signal or not.
I would make this analogy about repeatability based on Harp’s quote, and assuming the other signals are similar to the Wow! :
One day, while watching something nearby, you see lightning strike the ground for the first time. Thereafter, you only observe that same spot, yet you never see a similar lightning strike on that spot again. Yet periodically, lightning does strike the ground, but elsewhere. So a repeating general phenomenon of lightning striking the ground, but an unrepeated one of lightning striking a specific spot.
In terms of interpretation, the lightning striking the ground nearby might be explained by G*d/Zeus smiting someone or something (or just letting off steam). Failure to see the same spot struck ever again wouldn’t support that explanation.
The referenced Youtube video was good, although it drifted off topic to human matters, especially towards the end. I thought the expert opinion was balanced, and the consensus was that it was not likely a signal but no one could explain it as a natural phenomenon. Power beams were not mentioned, likely because this documentary was made a decade ago, before the possibility was raised. It also clarified for me that the Wow! signal was 30x background and not 30 sigma as I commented elsewhere.
From his question, I gather that Alex Tolley has not read my paper, where such estimates are made.
@Jim,
I would attempt to read your paper (ref 5) in the hope of it not going way over my head, but it is behind the JBIS paywall, and therefore inaccessible to me.
But that isn’t really my point, which is that your assertion of continued non-detection of the signal strengthens your hypothesis, isn’t a valid claim. The lack of further detections only strengthens a claim that the event was rare, insofar as it has been looked for.
[If someone claimed the emission was from a clandestine foreign military, and that lack of further detection was proof of this claim, wouldn’t you expect some positive further hard evidence to support the claim?]
Now let’s turn this around. Let’s say that several very similar events are detected. Does this invalidate your hypothesis and support Mendez’s hypothesis? While I would think this biases the explanation towards a natural one, it does not invalidate the ETI one. One could simply say that there are more beaming events that happen to be detected by our greater number of radio telescopes. Maybe the galaxy is littered with ETI that is polluting the em spectrum by extensive use of power beams that inevitably create these signals in hydrogen clouds.
Is there a copy not behind the JBIS pay wall? If not, please discuss the errors you see in Alex’s arguments.
Would this article in Centauri Dreams from 2021 be sufficient?
https://www.centauri-dreams.org/2021/01/22/was-the-wow-signal-due-to-power-beaming-leakage/
Thank you, but no. Jim Benford’s 2021 post provides the basic information about the signal—that it is a high-power narrow-band signal that appears to be a point source in the sky and has not been found again. There is no information on possible sources. The arguments only support a power beam, against a communication beam (no repeats), and against RFI.
There is no argument against a natural source, such as the Mendez hypothesis (which may have been proposed subsequently).
Given the signal power was 30 sigma greater than background, the obvious, but naive question is: “What sources could provide that energy for that transient duration (no repeat 24 hours later)?” FRBs are transient (millisec) but natural sources, but IDK what their power is. I must read the Mendez paper carefully to understand their hypothesis and whether it is sufficient to account for the Wow! signal.
At this point, I will only say that:
1. We should assume a natural source before an artificial one.
2. Lack of repetition only supports transience, not the cause of the signal.
It is worth comparing this post to one in 2017 where Avi Loeb suggests fast radio bursts may be power beams for ships.
Fast Radio Bursts: Signature of Distant Technology?
We should regard an explanation requiring ETI as an extraordinary claim requiring extraordinary proof. Or as the famous Baker Street private detective once said:
“Impossible” in our case should refer to natural phenomena that cannot explain the observation, leaving” improbable” as the ETI explanation. Unlike Holmes, we cannot eliminate all natural phenomena as we keep discovering new ones, often fitting the explanation we need. This seems to be the path that many such claims follow, whether UFOs (lights and artifacts in the sky), Ancient Alien influence (pyramid construction), or astronomical observations that are initially difficult to explain (Wow! Signal, FRBs, Tabby’s Star, etc.).
A Klystron is used to amplify microwaves and does use a narrow bandwidth, but a maser does not need or use a kylstron since a maser cavity uses the microwave stimulated emission of radiation and population inversion. These are two different types of technology. Radar transmitters use klystrons which spread out much more over long distances than Masers which use coherent microwaves so all the waves are at the same phase, direction and frequency. The wow signal could be either of these. We don’t need a hydrogen cloud to make our own masers, so any ET’s with our level of technological advancement also would not need to use naturally occurring space masers or space lasers from gas clouds. We can build are own.
It could also be space masers or megamasers associated with active galactic nuclei?
The most exasperating aspect of the Wow! signal is its choice of frequency, the 21 cm line, perhaps the most ubiquitous wavelength in nature. Why build a transmitter to operate at that frequency? If someone is trying to attract attention, it makes sense to emit at a frequency where others are bound to be listening. But if that is the case, why such a brief, non-repeatable event?
If they are trying to avoid being detected, then picking a common, natural wavelength makes sense so a potential interception might be dismissed as just cosmic noise, no big deal. But if THAT is the case, why a narrow band brief burst
that shouts out its artificiality? Either way, it just doesn’t make sense.
Is there any reason why a narrow band 21 cm burst would be optimal in some technological sense? Is there some potential application that would require that particular frequency? Perhaps it was chosen so in the event someone detected it they would simply ignore it.
The maser hypothesis solves the issue neatly: its perfectly natural, its not an artifact, and it fits the facts. Its not an explanation by any means, but right now its the best we’ve got.
The only other alternative is that it was a deliberate hoax. Some clever prankster with access to the right equipment and skills, and with some knowledge of what the astronomers were up to at the radio telescope (as well as an understanding of how their equipment works) decided to have some fun at their expense. These conditions are likely to be expected in a university environment.
I agree. I came to that same conclusion. If an ET civilization wanted to get the attention of another one, it wouldn’t use a radio frequency that also was made naturally by the energy levels in neutral hydrogen in empty space, the 21 centimeter line which is 1450.495 MHZ. When the hydrogen atom flips its spin it goes to a lower energy level and must radiate the additional energy at the 21 centimeter line. It seems more logical that ET’s would make a signal anyone else listening couldn’t confuse with natural phenomenon in space, but must stand out as unusual and different.
Or they would utilize a powerful natural cosmic phenomenon that would get the attention of any sufficiently advanced civilization with astronomers, such as supernovae.
See these articles for the details and the reasons why SETI researchers should be aiming their scopes at supernovae – and novae:
https://www.researchgate.net/publication/226326523_Passive_and_active_seti_strategies_using_the_synchronization_of_SN1987A
https://www.space.com/seti-alien-signals-supernova-1987a-ellipsoid
I’ve always felt the ideal frequency to use to to attract attention would be some integer harmonic of the 21 cm line, say half, or twice. Conversely, this would also be the most logical freq to listen on for those wishing to find such a beacon. No “natural” process emits at those frequencies, but the signal is still in a range where little natural interference and noise exists–its in the waterhole.
Others have suggested the beacon be transmitted at the frequency of the 21 cm line multiplied by a dimensionless natural constant (such as pi or e) or its reciprocal.
This was the first book I bought back in the mid seventies on what was then called CETI. It made the point of why the so-called waterhole was the best place to look for beacons.
“The book edited by Carl Sagan in 1973 called ‘Communication with Extraterrestrial Intelligence (CETI)’. In this collection of papers, Bernard M. Oliver from Ames Research, described project Cyclops and cited a 1959 ‘Nature’ by Cocconi and Morrison that suggested the use of the hydrogen line at 1420 megahertz as the natural frequency on which to search for beacons.”
https://www.seti.net/indepth/waterhole/waterhole.php
Let us not forget prime numbers, digits divisible only by themselves and one, which – so far as we know – are not produced by anything in nature, so should attract attention to aliens with radio telescopes and basic math:
https://math.dartmouth.edu/~carlp/PDF/extraterrestrial.pdf
https://modulouniverse.com/2015/02/16/prime-numbers-and-et/
https://www.youtube.com/watch?v=8qDjg8mdd8c
http://setileague.org/articles/primes/
https://empslocal.ex.ac.uk/people/staff/mrwatkin/isoc/sagan.htm
https://arxiv.org/ftp/arxiv/papers/2203/2203.04288.pdf
Here is the Project Cyclops book online:
https://ntrs.nasa.gov/api/citations/19730010095/downloads/19730010095.pdf
While well-written, researched, and a fascinating glimpse into the early days of SETI, its proposal for a huge and expensive fleet of radio telescopes scanning the skies 24/7 turned off government funding for decades, especially in the wake of Apollo’s winding down.
I feel like SETI is still recovering from this era and this report. I also have memories from some people involved in the field who felt its bloated plans and funding were on purpose to keep SETI from seriously happening.
The paper that kicked off the modern SETI era, just before Project Ozma…
Searching for Interstellar Communications
by Giuseppe Cocconi and Philip Morrison
Published in Nature, Vol. 184, Number 4690, pp. 844-846, September 19, 1959.
http://coseti.org/morris_0.htm
Here is a page with links to other NASA books on SETI and astrobiology online:
https://www.nasa.gov/history/nasa-and-seti/
Especially note NASA SP-419.
Here is NASA Reference Publication 1021 Bibliography on SETI from 1978:
https://ntrs.nasa.gov/api/citations/19780013076/downloads/19780013076.pdf
SETI.Net also has a nice page on their own search for the Wow! signal…
https://www.seti.net/indepth/wow/wow.php
The page includes some useful and relevant links of its own, such as Dr. Jerry Ehman’s details on the Wow! signal from its twentieth anniversary:
http://www.bigear.org/wow20th.htm
FYI quote: “The Wow! source radio emission entered the receiver of the Big Ear radio telescope at about 11:16 p.m. Eastern Daylight Savings Time on August 15, 1977.”
Note the time, which is seldom mentioned. Little wonder no one was around when the signal arrived.
Please read this quote from the following SETI.Net page regarding discrepancies over the reported frequencies the Big Ear was tuned to:
https://www.seti.net/database/ra-19/sagittarius/wow/target.php
“The Ohio State University’s “Big Ear” – The system that reported the WOW signal. There is some difference in opinion on the frequency the Big Ear was tuned to when the WOW signal was detected. I usually use the frequency reported by Dr. Jerry Ehman of 1420.4556 +/- 0.005 MHz but in his book ‘The elusive WOW’ Robert Gray reports that John Kraus thought that the receiver might have been tuned to 1420.356 MHz, so I set aside some observing time at this frequency as well.”
SETI.Net also recommends this video on the Wow! signal, so I shall too:
https://www.youtube.com/watch?v=aseyBWZa3pY
The SETI Institute conducted its own searches for the Wow! signal as detailed here:
https://www.seti.org/wow-signal
This is consistent with my hypothesis on virtual Von Neumann machines:
Virtual Von Neumann Probes using Self Amplification and Replication of Electromagnetic Signals through Natural Stellar Processes
https://www.centauri-dreams.org/2017/01/30/virtual-von-neumann-probes-using-self-amplification-and-replication-of-electromagnetic-signals-through-natural-stellar-processes/
There is another SETI avenue: See if any of the planetoids or comets look like they’ve been mined. Also the moons.
This article also wonders if we can detect such a probe calling home:
https://phys.org/news/2021-11-alien-probes-solar-home.html
At this point, China will probably be the ones to find such vessels:
https://phys.org/news/2021-10-china-fast-telescope-self-replicating-alien.html
For those who want the details on von Neumann probes, especially the whys…
https://arxiv.org/pdf/2005.12303
Has anyone ever checked which terrestrial satellites were over Big Ear on August 15, 1977? How about aircraft? The latter might be more difficult to check, but not impossible as airports do keep records of all plane flights in their vicinity. For how long is another matter.
Remember this story from 2016…
https://www.centauri-dreams.org/2016/08/27/an-interesting-seti-candidate-in-hercules/
The Russians claimed it was terrestrial satellite interference, but they never bothered to reveal which satellite was doing the interfering. The media and many in the professional science community swallowed that answer without bothering to check further.
BTW: Both Elvis and Groucho Marx died right around the time of the Wow! Signal. Just sayin…
The problem of satellite RFI is 2 fold.
1. Using the “illegal” radio spectrum
2. The satellite would have to be in a very close to geosynchronous orbit to appear stationary. If so, wouldn’t it be known? OTOH, the lack of a repeat could be a single test transmission. If so, what would the source power be, and is it within the capability of a satellite? [We don’t want to fall into a rabbit hole of military conspiracy theory.]
An aircraft wouldn’t stay stationary in the sky.
Alex Tolley wrote on April 16, 2025 at 10:53…
The problem of satellite RFI is 2 fold.
1. Using the “illegal” radio spectrum
2. The satellite would have to be in a very close to geosynchronous orbit to appear stationary. If so, wouldn’t it be known?
That, sir, is the question: If such a geosync satellite would be known hovering over Ohio on August 15, 1977, why have I never seen anyone state which satellite or satellites it might be? Maybe I missed it, so I am happy to be proven wrong here.
Helicopters hover and they existed in 1977. Would it be impossible for a helicopter to hover in the area on that day and its signals were captured by Big Ear? No less plausible than other theories, and we know helicopters were and are real and are famous for their hovering abilities.
And keep in mind: No one we know was in the Big Ear facility at the time. Jerry Ehman didn’t check the printouts until hours later, so he wasn’t about to witness any aircraft nearby. I am also willing to bet there were no security cameras in or outside the facility then, either.
Thus, my earlier lamentation in this thread that this didn’t happen in more modern times, when we probably would never have heard of the Wow! Signal then.
Good point about the helicopter.
Military satellite positions were kept secret, but I don’t believe any would be in geosync. Spy satellites are in lower orbits. Comsats wouldn’t be using that frequency either, and wouldn’t disappear.
The YouTube documentary made a point I wasn’t aware of. There were 2 receivers so that a signal would be received by one, and then the other. But apparently only one receiver recorded the signal. The explanation was that the signal was absent by the time the 2nd receiver should have detected it. This meant it was a very transient signal.
What was done to stop radio emissions from devices at the time? (When I was young, electric razors emitted radio noise that was detectable on broadcast radio and tv channels. Car and truck engines did the same until radios were common additions, and the emissions were suppressed. However, I would have thought these emissions were not very narrow bandwidth.)
On the brighter side, as Shostak noted, the Wow! Signal is a brand that ensured SETI was kept in the public eye and funded, at least federally, for a while. The unremarked signals at other facilities vanished from consciousness.
>Has anyone ever checked which terrestrial satellites were over Big Ear on August 15, 1977?
There was a bunch of them but many are now deintegrated so we no longer have the orbital data or they would have to find them. However, I detected a satellite still in service whose coverage could cover Big Ear: LAGEOS. It is interesting because it has a plate of Carl Sagan! The laser signal from this passive satellite could have disturbed Big ear? Could the “window” of 72s of the radiotelscope cut its orbit? one can imagine many things. It is necessary to work with what we have…
satellite list in august 1977 ( sort by date) :
https://in-the-sky.org/search.php?searchtype=Spacecraft&s=&startday=2&startmonth=4&startyear=2025&endday=31&endmonth=12&endyear=2035&ordernews=ASC&satorder=1&maxdiff=7&feed=DFAN&objorder=1&distunit=0&magmin=&magmax=&obj1Type=0&news_view=normal&distmin=&distmax=&satowner=0&satgroup=0&satdest=0&satsite=0&lyearmin=1977&lyearmax=1977&page=11
Fred, thank you for sharing that very interesting site/tool for tracking satellites. I was unaware that LAGEOS 1 was in the vicinity right around the same time as the Wow! Signal. Wow would be the proper response. :^)
My big question would be: Since LAGEOS is a passive satellite, how would a *radio* telescope like Big Ear be able to detect optical light transmissions bounced off it – assuming they were in the beam path at all, which I find very doubtful.
Fun thought and coincidence, though. Here is more on LAGEOS and the special plaque inside it that is meant as a gift to future Earth inhabitants 8.4 million years from now, when it returns from orbit…
https://lageos.gsfc.nasa.gov/Design/Message_to_the_Future.html
https://lageos.gsfc.nasa.gov/docs/1976/NASA_LAGEOS_presskit_e000045273.pdf
https://www.nasa.gov/history/now-40-nasas-lageos-set-the-bar-for-studies-of-earth/
https://www.eoportal.org/satellite-missions/lageos#mission-status
https://ilrs.gsfc.nasa.gov/missions/satellite_missions/current_missions/lag1_general.html
https://arxiv.org/abs/1506.00055
[Submitted on 30 May 2015 (v1), last revised 14 Sep 2018 (this version, v3)]
The Application of Autocorrelation SETI Search Techniques in an ATA Survey
G. R. Harp, R. F. Ackermann, Alfredo Astorga, Jack Arbunich, Kristin Hightower, Seth Meitzner, W. C. Barott, Michael C. Nolan, D. G. Messerschmitt, Douglas A. Vakoch, Seth Shostak, J. C. Tarter
We report a novel radio autocorrelation (AC) search for extraterrestrial intelligence (SETI). For selected frequencies across the terrestrial microwave window (1-10 GHz) observations were conducted at the Allen Telescope Array to identify artificial non-sinusoidal periodic signals with radio bandwidths greater than 4 Hz, which are capable of carrying substantial messages with symbol-rates from 4-1000000 Hz.
Out of 243 observations, about half (101) were directed toward sources with known continuum flux > ~1 Jy over the sampled bandwidth (quasars, pulsars, supernova remnants, and masers), based on the hypothesis that they might harbor heretofore undiscovered natural or artificial, repetitive, phase or frequency modulation. The rest of the targets were mostly toward exoplanet stars with no previously discovered continuum flux.
No signals attributable to extraterrestrial technology were found in this study.
We conclude that the maximum probability that future observations like the ones described here will reveal repetitively modulated emissions is less than 1% for continuum sources and exoplanets, alike.
The paper concludes by describing a new approach to expanding this survey to many more targets and much greater sensitivity using archived data from interferometers all over the world.
Comments: 33 pages, 4 figures, 3 tables
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:1506.00055 [astro-ph.IM]
(or arXiv:1506.00055v3 [astro-ph.IM] for this version)
https://doi.org/10.48550/arXiv.1506.00055
Focus to learn more…
Journal reference: Astrophysical Journal (2018), 869, 66
Related DOI:
https://doi.org/10.3847/1538-4357/aaeb98
Focus to learn more…
Submission history
From: Gerald Harp Ph.D. [view email]
[v1] Sat, 30 May 2015 01:26:23 UTC (707 KB)
[v2] Mon, 29 Jan 2018 22:27:24 UTC (1,971 KB)
[v3] Fri, 14 Sep 2018 01:17:45 UTC (878 KB)
https://arxiv.org/pdf/1506.00055
https://astrobiology.com/2023/06/real-time-technosignature-strategies-with-sn-2023ixf.html
Real-Time Technosignature Strategies With SN 2023ixf
By Keith Cowing
Status Report
astro-ph.IM
June 7, 2023
Several technosignature techniques focus on historic events such as SN 1987A as the basis to search for coordinated signal broadcasts from extraterrestrial agents.
The recently discovered SN 2023ixf in the spiral galaxy M101 is the nearest Type II supernova in over a decade, and will serve as an important benchmark event. Here we review the potential for SN 2023ixf to advance ongoing techonsignature searches, particularly signal-synchronization techniques such as the “SETI Ellipsoid”.
We find that more than 100 stars within 100 pc are already close to intersecting this SETI Ellipsoid, providing numerous targets for real-time monitoring within ~3∘ of SN 2023ixf. We are commencing a radio technosignature monitoring campaign of these targets with the Allen Telescope Array and the Green Bank Telescope.
James R. A. Davenport, Sofia Z. Sheikh, Wael Farah, Andy Nilipour, Bárbara Cabrales, Steve Croft, Alexander W. Pollak, Andrew P. V. Siemion
Comments: 3 Pages, 1 Figure, Submitted to RNAAS.
Collaboration welcomed
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Popular Physics (physics.pop-ph)
Cite as: arXiv:2306.03118 [astro-ph.IM] (or arXiv:2306.03118v1 [astro-ph.IM] for this version)
https://doi.org/10.48550/arXiv.2306.03118
Focus to learn more
Submission history
From: James RA Davenport
[v1] Mon, 5 Jun 2023 16:22:46 UTC (190 KB)
https://arxiv.org/abs/2306.03118
Astrobiology
https://arxiv.org/abs/2402.11037
[Submitted on 16 Feb 2024]
Searching the SN 1987A SETI Ellipsoid with TESS
Bárbara Cabrales, James R. A. Davenport, Sofia Z. Sheikh, Steve Croft, Andrew P. V. Siemion, Daniel Giles, Ann Marie Cody
The SETI Ellipsoid is a strategy for technosignature candidate selection which assumes that extraterrestrial civilizations who have observed a galactic-scale event — such as supernova 1987A — may use it as a Schelling point to broadcast synchronized signals indicating their presence.
Continuous wide-field surveys of the sky offer a powerful new opportunity to look for these signals, compensating for the uncertainty in their estimated time of arrival.
We explore sources in the TESS continuous viewing zone, which corresponds to 5% of all TESS data, observed during the first three years of the mission. Using improved 3D locations for stars from Gaia Early Data Release 3, we identified 32 SN 1987A SETI Ellipsoid targets in the TESS continuous viewing zone with uncertainties better than 0.5 ly.
We examined the TESS light curves of these stars during the Ellipsoid crossing event and found no anomalous signatures. We discuss ways to expand this methodology to other surveys, more targets, and different potential signal types.
Comments: 17 pages, 6 figures, AJ published
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Earth and Planetary
Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2402.11037 [astro-ph.IM]
(or arXiv:2402.11037v1 [astro-ph.IM] for this version)
https://doi.org/10.48550/arXiv.2402.11037
Focus to learn more
Submission history
From: Bárbara Cabrales [view email]
[v1] Fri, 16 Feb 2024 19:30:58 UTC (1,016 KB)
https://arxiv.org/pdf/2402.11037
I highly recommend this classic book on alien science titled Xenology: An Introduction to the Scientific Study of Extraterrestrial Life, Intelligence, and Civilization, written by Robert A. Freitas, Jr.
It covers many subject topics broadly and fearlessly and is online here:
https://www.inverse.com/article/30886-robert-freitas-alien-life-xenology-book-qa
Here is the chapter on Beamed Power Laser Propulsion:
https://www.xenology.info/Xeno/17.3.4.htm
Orion’s Arm has a fascinating if all too brief look at using a Dyson Shell as both a means of propulsion and a weapon that puts the mega in megaweapon:
https://www.orionsarm.com/eg-article/48fe49fe47202
How about these signals, which have been referred to as Benford Beacons, the second of which was observed for over one hour in 1990!
Why aren’t these candidates getting the attention that the 1977 Wow! Signal always does? Are they being re-examined now? If not, why not?
They apparently came from these star systems. First up…
TYC 1220-91-1
I link to this post next because it has some useful scientific information, also to show just how scare info on this event is:
https://strangesounds.org/2014/03/is-this-the-new-alien-wow-signal-seti-has-recently-detected-a-new-unexplained-strange-sound.html
To quote from the above link:
In 2010, SETI picked up a new “Wow!” type signal. Unlike the 1977 signal this one was not from that fairly blank area of sky. This new Wow signal seemed to come from the vicinity of a star called TYC 1220-91-1. Moreover, this new unexplained signal was detected and tracked in realtime during 10 seconds. This new “Wow!” signal exhibited the characteristics an interstellar beacon signal might be expected to, with the exception that it did not repeat.
That incident is mentioned on page 12 of the following paper on a new theoretical type of alien beacon: “A new class of SETI beacons that contain information” (Aug 22, 2010).
The mentioned paper here:
https://arxiv.org/pdf/1211.6470
A relevant video on this from 2016:
https://www.youtube.com/watch?v=X-ox0u9DQDo
Here are two links to some astronomical data on the star TYC+1220-91-1 itself:
https://www.universeguide.com/star/144255/tyc1220911
http://simbad.u-strasbg.fr/simbad/sim-id?Ident=TYC+1220-91-1
This next candidate is Gliese 673, also known as HD 157881:
http://crowlspace.com/?p=177
To quote from the above link:
I chucked in a comment about my favourite star HD 157881 or Gliese 673 as it is otherwise known. In 1990 – according to an interview I saw on an ABC Science Doco in 1992 – a Western Australian radio telescope picked up a really strong signal (like the “Wow!” signal of 1978) from Gliese 673 but didn’t get another ‘scope on it before it faded.
According to the Benfords that’s exactly what we should expect from economically practical beacons. Not saying it really was a signal from ETIs, but it’d be so cool if it was.
The star itself is a K7V, with an absolute visual magnitude of 8.1 and an effective temperature of 4020 K. A planet could easily exist in its habitable zone – the extended habitable zone of James Kasting, not Michael Hart’s ultra-tight hab-zone that is.
…
At 25.2 ly away that’s 50.4 years round trip for signalling. Since high-powered RADAR were used extensively during the “Battle of Britain” in 1940 what’s the minimum time-span for ETIs to signal back with what they received? Just like Ron Bracewell first suggested – send back the signal you receive to get noticed. Well 1940 plus 50.4 is… 1990!
Astronomical data on Gliese 673 and more links to more data here:
https://www.stellarcatalog.com/stars/gliese-673
So, to refresh: TYC 1220-91-1 and Gliese 673. They need another look or ten.
WWII radars started operating in the centimeter wavelengths (1-10 cm) with the klystron. However, I don’t see the detected wavelengths of the Wow!-like detections. If they were at the 21cm wavelength, that wouldn’t be like returning the signal they received. Then again, would WWII radar have had the energy to be detectable 25 ly away?
As Michael Fidler was at NORAD, perhaps he can chime in with some details of radar wavelengths and power, and whether they could be detected at that distance, and whether WWII era radar was powerful enough too.
Someone can spend time doing that, if they want. Meanwhile I think we need to re-examine those two signal areas I listed first. That they have been neglected this long while the Wow! signal is rehashed over and over is a problem.
As for types of signal detection, this article is a good place to start:
http://www.coseti.org/lemarch1.htm
True a radar is definitely not powerful enough for interstellar communication. What I meant was that any type of conventional radiowave transmitter that has powerful signal uses a klystron and a magnetron and the signal spreads out which is why one needs a million watts of power to get to the next star system, so this paper is right about that. As we now not any of our TV and radio stations have the power to make that trip. Lasers and masers use coherent waves and don’t spread out as nearly as much as radio waves since they use different technology.
I know a little bit about the radar and NORAD radar which uses a scanned array type system, a Solid State Phased Array Radar System (SSPARS), and AESA (Active Electronically Scanned Array) Radar according to Wikipedia. An AESA radar type of radar is made of many antenna’s bunched together on the rectangular transmitter. Each antenna is tuned to a different frequency so there is a range of frequencies. Consequently, it can scan back and fourth quickly without having to turn. The nose cone or front of the F22 Raptor also has an AESA radar so it does not have to turn but the antenna go off an left and right which mimics turning and has fast scanning.
These type of radars can detect other aircraft with stealth technology. Interesting, No?
I was waiting to see what people would say here about Madhusudhan, 2025, but got impatient. (I linked the Eurekalert summary, but the DOI linked at the end is open access) It is being publicized as evidence of life on another planet, though it sounds like it might just be what happens when you have a lot of CH4 and SH2 in a reducing atmosphere.
Mike, as it happens, I’ll be writing Madhusudhan’s paper up tomorrow.
Might there be a natural explanation for energy to travel along focal lines?
That might help rule out ET—but maybe it is something sails can catch a ride on without having to build huge lasers.
Like catching a wave…
A French astrophysicist explains in some astro-news, that one of Wow’s hypotheses is the activation of a Hydrogen cloud by the energy beam of a magnetar.
Source : at 8’53” (in french, sorry)
https://www.canal-u.tv/chaines/observatoire-lyon/actualites-astronomiques-de-septembre-2024
if the energy beam is cyclic, the ‘mirror’ hydrogen cloud was random both in its position in space and in the hydrogen atoms themselves. Could this coincidence of events explain the non-repetition of this signal ? We’re still looking for an explanation in the Arecibo archives.
The other interesting aspect is that we are all passionate about this subject; just look at the number of comments here :) It shows that the human species subconsciously likes contact.
Opinions are divided: was it a natural or artificial signal? (I’m leaning more towards something natural because of the randomness of the phenomenon; if an ETI was capable of such a high level of technology, we can assume that it would have been perfectly capable of determining our presence* and therefore either deliberately avoiding us or spotting the contact.
BTW : here’s a stunning image from a web sat. tracker, of a magnificent technosignature…of the earth. Do you think that an ETI, even a very distant one, would not have its signal disrupted by our satellites ?
https://ibb.co/0jnSnL3x
Wow is a fascinating subject that has helped develop scientific thinking. Thanks to Dr Benford.