The Wow! signal has a storied history in the SETI community, a one-off detection at the Ohio State ‘Big Ear’ observatory in 1977 that Jim Benford, among others, considers the most interesting candidate signal ever received. A plasma physicist and CEO of Microwave Sciences, Benford returns to Centauri Dreams today with a closer look at the signal and its striking characteristics, which admit to a variety of explanations, though only one that the author believes fits all the parameters. A second reception of the Wow! might tell us a great deal, but is such an event likely? So far all repeat observations have failed and, as Benford points out, there may be reason to assume they must. The essay below is a shorter version of the paper Jim has submitted to Astrobiology.
by James Benford
In 1977 the Big Ear radio telescope (Ohio State University Radio Telescope) recorded the famous Wow! Signal, which is the most serious contender for artificial interstellar radiation. It is called the ‘Wow!’ Signal. It has never been seen again. Its origin and nature remain a total mystery.
I offer an alternative explanation for it: The Wow! could have been leakage from an interstellar power beam. I propose that this class of radiation, which is not widely understood, can explain the observed features of the Wow! signal.
The Three Wow! Parameters
The Wow! signal has 3 prominent parameters: the power density received, the signal’s duration and its frequency .
Power Density: The Wow! signal was very strong, the strongest they ever recorded in the seven-year Ohio State SETI Survey. The shape is shown in the Figure.
Figure: The Wow! Signal. The peak is 32 times the signal to noise ratio of the observations. Courtesy of Sam Morrell.
Duration: The Big Ear was fixed in orientation, so rotated with the Earth. From Gray : “The amount of time it took the Wow! to pass through the antenna’s beam closely matches the expected transit time for celestial sources. Sources fixed amid the stars should take about 36 seconds to transit the sensitive middle half of the beam, the full-width-half-max. The Wow! signal took about 38 seconds”.
So we don’t know how long the signal lasted, just that it was on as the antenna rotated past.
Frequency: The Wow! Signal was at 1.42 GHz. The 1.4-1.427 GHz band is protected internationally, meaning, as John Kraus, designer and director at the Big Ear, says in a letter to Carl Sagan , “all emissions are prohibited” . The band was set aside to allow radio astronomy of the H 1 line, the hyperfine transition of neutral hydrogen (1.420 GHz), which is of great astronomical interest for imaging atomic hydrogen in interstellar space. Consequently, this part of the L-band is a protected radio astronomy allocation all over the world. Therefore the Wow! couldn’t be a transmission from Earth satellites or aircraft.
The Fourth Wow! Parameter
There is a fourth parameter, although it has not received attention: the Revisit Time. This is the interval until the signal is seen again. If ET were rastering their beam across the sky, the beam would be seen to repeat later. Searches have been conducted from the META array at Oak Ridge, the Green Bank National Radio Astronomy Observatory in West Virginia and the Tasmanian Mount Pleasant Radio Observatory in Australia [3, 4].
Recent extensive observations on the Allen Array by Gerry Harp, Robert Gray and colleagues, which used the 42 dishes of the ATA as an interferometer, monitored the entire 1.5 degree field of view for 100 hours. They did not see the Wow! and summarized : “As for the possibility that the Wow! signal is a repetitive transient, our observations rule out almost all periods under 40 hours, which covers many repetitive scenarios such as rotating planets or blinking beacons with periods comparable to a terrestrial day and several times longer. Our extended observations cannot rule out scenarios such as occasional targeted transmissions with repetition rates of many days or varying repetition rates.”
The Wow! observation has never recurred. I take this absence as a clue to its origin.
Power Beaming and the Wow! Signal
The most observable leakage radiation from an advanced civilization may well be from the use of power beaming to accelerate spacecraft and transfer energy. Power beams are now more credible because we’re building our own: The Starshot project plans launching probes to nearby stars in this century, making power beaming a credible source concept . And power beaming is being developed for military applications, where it is termed ‘directed energy’ . See reference 8 for a review of power beaming concept studies.
Applications suggested for power beaming are:
- launching spacecraft to orbit,
- raising satellites to a higher orbit,
- interplanetary space–to–space transfers of cargo or passengers,
- beam-driven launch of interstellar probes,
- beam-driven starships.
Leakage of the beam around the sides of the vehicle being accelerated would be observable at great range because of the highly directed high power. The spilled energy can be reduced to less than half, but that is not the cost optimum. Spillage losses of more than half are typical of Starshot calculations, for reasons of economics and performance that will apply to other civilizations .
For power beam missions involving changing orbits of spacecraft, the first three applications on the above list, an important quantity is the slew rate, the rate at which the beam propelling the spacecraft sweeps to direct it toward its orbit . A review of representative parameters for applications of power beaming shows that, for orbit–related missions, the slew rates are high, so the observation time of the beam leakage is too short, ? 1 second. So the orbit–related applications cannot explain the Wow! But interstellar probes and starships have small slew rate, so are the best candidates.
Power Beaming Examples
In beaming of power, the power density S at range R is determined by W, the effective isotropic radiated power (EIRP), which is the product of radiated peak power P and aperture gain G . Since we know the power density of the Wow! received and its frequency, we can calculate both the range to the source of Wow! and the power needed at a given range.
For example, if the Wow! source had the EIRP of Arecibo, it would have to be at range < 2 light-years, so it must be far more powerful.
Bob Forward’s ultralight microwave-propelled Starwisp, a 1-kg sail reaching 0.1 c, would be at a range of ~ a million light-years, so from extra-galactic distances .
An interstellar precursor probe described by Benford and Matloff for 100 km/sec = 0.03% c would be at range 116 light-years, a nearby star .
We can also assume a distance, then calculate the EIRP that would be required. First, choose 2000 light-years for the distance to the Wow! source. (Maccone estimates that the mean distance to a communicative civilization is ~2,000 light-years away ). Then choose an aperture diameter of 3 km. (Starshot envisions a ~3-km diameter laser array to drive its interstellar probe.) The required beam power is 11 GW. This is similar to Starshot, with ~ 11 GW.
From these examples, it is credible that the Wow! signal was leakage from launch of an interstellar probe.
Will we see it again? Probably not
Probably not if it was due to power beaming. With a launch driven by an intense beam, to arrive years later at a neighboring stellar system, the starship would be launched toward where the stellar system will be when the starship arrives. The ratio of the distance the star would move to the beam spot size is given by vs/(vss ??), where vs is the average velocity of the star relative to stars on our stellar neighborhood, typically 20 km/sec, and vss is the starship velocity, ?? the angular beamwidth. For the starship concepts proposed, that ratio varies from 104 to 107 .
The angle of the radiated beam with respect to the light path between the two stars is larger than the width of the beam. Thus, the beam is generally not observable from the target planetary system. If the Wow! was driving a probe to a star, that star was at that time far from the direction of the beam. Earth could accidentally receive the leakage from the beam, since stars move relative to each other. So leakage radiation from star probe launches using the Wow! beam will not be seen again from Earth. This fits the non-observations to date.
Comparison of Explanations for the Wow! Signal
There are three suggested explanations for the Wow!: either spurious emissions from Earth, an interstellar communication or leakage from a power beam. Here is a brief summary of the evidence for and against each explanation:
Arguments for power beaming leakage as a cause:
- The power beaming explanation for the Wow! accounts for all four of the Wow! parameters: the power density received, the duration of the signal, its frequency, and the reason why the Wow! has not occurred again. The Wow! power beam leakage hypothesis gets stronger the longer that listening for the Wow! to recur doesn’t observe it repeat.
- Power beams are now more credible because we’re building our own: the Starshot project plans launching probes to nearby stars in this century. The technology required for the Beamers for such interstellar probe launches are within our grasp.
Arguments against ET communication as a cause:
- The theory that the Wow! Signal was an interstellar communication predicts that it will recur. It fits within the overall SETI strategy, which looks for deliberate beaming of messages to us from ETI. But the long series of the subsequent non-observations of the Wow! shows that the SETI messaging hypothesis is gradually being falsified by being tested.
Arguments against radio frequency interference (RFI) as a cause:
- The Wow! Signal was at 1.42 GHz. The band from 1.4 to 1.427 GHz is protected internationally, meaning, all emissions are prohibited . Therefore it is very doubtful that the Wow! Was a transmission from Earth satellites or aircraft because they are forbidden to transmit in this band. Secret satellites would avoid it because they would be detected by radio astronomers. (Emissions in this band are sometimes detected, but at very low levels. These are likely due to intermodulation products, which are nonlinear effects in electronics.)
- Aircraft would be unlikely to remain static in the sky. Spacecraft would pass through the beam much faster. To match that lack of angular motion, an Earth satellite would have to be millions of kilometers distant, out far beyond the Moon.
- Ohio had good RFI rejection because what was recorded was the difference between two offset beams, so a local signal appearing in both horns simultaneously would cancel. This was frequently verified.
- The possibility that the signal was a harmonic or sub-harmonic of a local signal is countered by Ohio State having monitored the 21 cm band for many years, would have noticed a local interfering signal.
- A deliberate hoax? This lacks credibility, as hoaxes are a practical joke, which succeed if they are later revealed. Then why keep it secret for decades?
Conclusion and Implications
I’ve looked at the various power beaming applications and found that credible ones are low mass interstellar probes such as Starwisp and Starshot. This does not mean that the orbit–changing power-beaming applications cannot be seen.
The power beaming explanation for the Wow! accounts for all four of the Wow! parameters. This includes the absence of any later observation, for it has not been seen since, despite the several attempts to repeat observing it. This allows a prediction: the Wow! signal will not be seen again.
If one accepts the possibility that Wow! was power beam leakage, several lines of action should be followed for the future of SETI:
- Such interstellar power beams would be visible over large interstellar distances. All-sky surveys in both the microwave and laser could detect more power beam leakages. Instruments with large instantaneous field of view could detect infrequent transitory leakage signals. Ultimately, we should have a full-sky capability for both hemispheres.
- Because ET would understand that its beam leakage could be observed, there may well be modulations on the beam to communicate to any inadvertent listener. This would add little additional energy or cost for ET. Therefore all-sky surveys should have sufficient electronics to capture messaging embedded on the beam. Extraterrestrial intelligences would know their power beams could be observed. That message may use optimized power-efficient designs such as spread spectrum and energy minimization [12, 13].
On the other hand, if one thinks that the Wow! signal was an attempt to communicate, one should follow up on a possibility that is not been explored: If with Wow! we inadvertently intercepted a radio link between one star and another, we should look in the opposite direction to see if signals are transmitting toward the Wow! direction. To my knowledge this has not been explored.
1. R. H. Gray, The Elusive Wow!, Palmer Square Press, 2012.
2. J. D. Kraus, “The Tantalizing “Wow!” Signal”, letter to Carl Sagan, NRAO Archives, accessed December 3, 2020, https://www.nrao.edu/archives/items/show/3684, 1994.
3. R. H. Gray, “Intermittent Signals and Planetary Days in SETI”, Int. J. Astrobiology, https://doi.org/10.1017/S1473550420000038
4. R. H. Gray, A Search For Periodic Emissions At The Wow! Locale”, Astrophysical Journal, 578:967–971, 2002.
5. G. Harp et al., “An ATA Search for a Repetition of the Wow! Signal”, Astrophysical Journal 160:162, 2020.
6. K. Parkin, “The Breakthrough Starshot System Model”, Acta Astronautica 152, 370, 2018.
7. J. Benford, J. Swegle and E. Schamiloglu, High Power Microwaves, 3rd Ed., Taylor & Francis, Boca Raton, FL 2016.
8. J. Benford and D. Benford, “Power Beaming Leakage Radiation as a SETI Observable”, Astrophysical Journal 101 825, 2016.
9. R. L. Forward, “Starwisp: An Ultralight Interstellar Probe,” J. Spacecraft and Rockets, 22 345-350 1985.
10. J. Benford and G. Matloff, Intermediate Beamers for Starshot”, JBIS 72, 51, 2019.
11. C. Maccone, “The Statistical Drake Equation”, Acta Astronautica 67, 1366, 2010.
12. D. Messerschmitt, “The case for spread spectrum”, Acta Astronautica, 81, 227, 2012.
13. D. Messerschmitt, 2015, ‘Design for minimum energy in interstellar communication”, Acta Astronautica, 107, 20-39, 2015.
I wonder how long energy beaming remains state of the art. The time frame would need to approach galactic time scales to produce an overlap.
We can’t rule out pranksters, there are no hard cases for hypotheses predicting their behavior. It is the same problem we keep encountering with potential ETI.
Does 1.42 GHz offer any advantages in terms of beamed power?
The microwave spectrum does offer economic advantages because equipment is cheaper in that regime. That’s because the scale, set by wavelength, is on the size of the human hand, allowing simpler and cheaper fabrication techniques. It’s always been cheaper to operate at lower frequencies. That’s why microwave ovens operate at ~2.5 GHz, far below the resonance of water at a much higher frequency. Ovens work by forcing the energy to be absorbed eventually because it can’t escape the cavity the food is in.
I must say you come up with a more compelling hypothesis for an ET event that Loeb’s for ‘Oumuamua. (Maybe you should expand it into a book!)
However, I would argue that the weakness in the argument is the frequency. It is one that was reserved for investigating natural phenomena. Why would a power beam be operating at that frequency? If there is some good argument for that, then it might strengthen your hypothesis. But while it was a narrow bandwidth signal, and perhaps less likely to be natural, narrowband signals do exist in nature (Z mode waves as the source of Saturn narrowband radio emissions).
So is it a natural narrowband signal that was a transient which we have not detected from that direction or elsewhere, or a possible power beam using a frequency that just happens to be one the SETI people thought would be most useful for communication? It needn’t be either/or. If it was artificial, and ET wanted to attract attention to the source, they might power a spacecraft with a beam of frequency that we humans proposed as a likely communication band. Starshot is proposing to fly many craft to its target, which would be seen as power beam leakage with some sort of irregular frequency of operation. If we were beaming multiple craft to the solar gravitational focal line the same argument would apply. Yet if this was a power beam, it was for a single craft.
Then there is the coincidence factor. As with the recent signal from the direction of Proxima, why were we so lucky to receive the signal just now? If the Wow! signal was a power beam, then just perhaps there might be a number of civilizations doing something similar to increase the probability we should chance on one of the events. If so, we need to do an all-sky search like GAIA but looking for narrow-band transients.
Finally, just because the signal came from the direction of Sagittarius, doesn’t mean that the point of origin was from a distant star. It could be from a starship sending a small probe ahead of it (or any direction). It might even be a Lurker in deep space in our system sending a probe to Earth for a quick close up reconnaissance.
The Wow! Signal
As I’ve been saying, we need an all-sky search for transients listening all the time. The SETI community has gradually realized that and we may have some capability within this next decade.
Hello mr Benford, thank you for presenting your interesting hypothesis. Yes the beam would indeed be accidentally seen in our direction, if any probe were to be sent to Sol. We could not see it as the beam would be aimed at the position where Sol will be in the future.
Though I have reason to believe that advanced life is very rare, I fully support the idea of an all sky monitor program. One such will also lead to other discoveries. So it will not need to be exclusive SETI when the funding applications is to be written.
It seems like there are obvious specific times to look for retransmissions of signals like this: multiples of 2^n divided by the base frequency, with n as large as you have patience for. (With some allowance for error, considering that movement of the Earth and source could alter the precise timing of the scan) Has anyone targeted these times?
If the solar focal line is important and it is, we may need to look in the opposite direction. If an alien craft transmitted back to its home world it would want to take advantage of the magnification corridor. Perhaps they sent a warning signal back home to stay away from the us, saying WoW they are nuts !
If say the signal came from a focal line of our sun there is I think the gemini constellation, opposite the signals apparent direction, which has some interesting stars in it, and a global cluster way off in the distance. If an alien species makes a home in a globular cluster they will be pretty damn powerful, thousands of stars packed in a very small volume of space !
Off topic, but would the high stellar density in a globular cluster result in a high number of relatively close stellar encounters resulting in disruptions of the Ort cloud of a given star. If so, any planets in orbit around that star would suffer comet impacts rate much higher than, say, the Earth.
On the otherhand, one could argue that global catastrophes can spur evolution.
In any event, if intelligent life could evolve on a planet in a globular cluster, besides having a night time vista of breathtaking beauty, they/it/ could seriously contemplate interstellar travel using what would be modest extrapolations of our own technology.
The planets would be more stable in the outer reaches of the cluster or even a star system could travel close to it and the species jumps aboard. Even so getting to one has enomous potential for colonising the gallaxy as they wonder far and wide and due to gravilens they would see vast distances indeed.
The late great Robert Bradbury said that globular star clusters would indeed make great places for advanced ETI to utilize. They would not necessarily have to be natives who evolved there, either.
I cannot find his original paper online on this very subject, unfortunately, but I did find this thread comment by him here:
These are the objects/Artilects he imagined might occupy such stellar constructs:
The Pleiades is I think our nearest cluster of around 1000 stars at around 8ly in diameter, 444 ly’s away.
But the Pleiades consist of very young stars which are still developing. Bradbury is referring to much older and far more populated globular star clusters like Messier 22.
It was just an example of our closest one.
Then there is Omega Centauri, the GSC that is more likely the remains of a galaxy absorbed by the Milky Way…
There have been many similar “signals”…Proxima, TYC 1220-91-1, and eleven mentioned by Sagan in his discussion of SETI. Do they have similar characteristics?
Interesting analysis. One question, though. Is 1.42 GHtz and optimal microwave frequency for power beaming ? If this is an ET attempt to launch spacecraft would they choose a frequency that would conflict with their own radio-astronomy activities? Is this frequency good for power transfer to an accelerating spacecraft? It seems to me that there might be arguments against this being power transfer leakage.
Power beaming usually uses short transmission times; therefore it would be easy to simply notify astronomers. /The frequency used depends on two major factors. The first is that atmosphere must allow transmission at that frequency. The second is cost: at present, the cheapest equipment is in the microwave. Alien costs are of course unknown.
Your contention is that the Wow! Signal was a potentially leakage from a microwave power beam and you mention cost as a factor. Why is Starshot then focusing on laser beam transmission if microwaves have advantages?
If mankind were to build power-beaming transmitters now, they would operate at microwave frequencies. That’s because at present it’s cheaper: Microwaves have reached economies of scale and are available at low cost in quantity. Millimeter waves and lasers may never be economical. Lasers now cost about a thousand more than microwaves per watt. Furthermore, lasers have losses when propagating through atmospheres, so must be based at very high altitude, Starshot for example, or be based in space. Microwaves transmit easily through our atmosphere. Starshot assumes that large drops will occur in laser costs due to automated production and great economies when built in very large quantities.
As one who knows next to nothing about mcrowave generation technology, but is fascinated by the “search for E-T”, I would first ask just how close in frequency the “WOW!” signal actually was to the “Earthly” known value for the ‘Hydrogen-line’, about 1.42 405 752 GHz?
Secondly, if you are planning to use microwaves for Power Beaming, would you naturally, (for the efficiency of operating the generator), want the beam to have an extremely narrow frequency-range?
Thirdly, from am engineering perspective, is the ‘side-leakage’ of the laser-beam virtually inescapable?
Fourthly, does the cost of such beaming change dramatically with slight changes in the chosen beaming frequency?
If the answers to the above questions are: 1) Within 1%; 2) Yes, 3) Yes and 4) No, then I would conclude that Dr. Benford’s essay should allow us to estimate rather accurately, (depending on the actual ‘Galactic direction’ from which “WOW!” signal originated), just how far from us the (intentional) signal-generator was at the time we detected it.
I have assumed, of couse, that the 1%, Yes and No answers above greatly increases the probability that the “WOW!” signal frequency was deliberately chosen by a ‘Civilization’ concluding that their main-purpose in generating the beam would also lead to its possible detection by another Civilization within perhaps a few hundred light-years.
Thank you very much to Drs. Benford and Gilster for all they have given the rest of us.
The answers are1) <1%, 2) No, 3) Yes, 4) No.
As several of our correspondents have implied, there is really no good reason to be transmitting on the 21 cm frequency. As a beacon, it would be lost in the background roar of interstellar hydrogen, and there seems to be no other good reason to do so. A harmonic, or a multiple of 1.42 GHz and pi, e or some other fundamental constant would be more effective. If the signal was NOT meant for communication, however, broadcasting briefly at that frequency would increase the chances the signal NOT be heard, or if heard, dismissed as an anomaly or transient.
That is an interesting idea. Make a power beam less obvious as an artificial signal by using a frequency that might be expected to be common. Beaming in stealth mode, I suppose.
Unfortunately, the beam was narrow band which immediately flagged this as possibly artificial. 40+ years have gone by, and still, this signal intrigues us. Hardly a good result for an intended stealthy beam.
Just a few years ago, FRBs were transients, and “are they alien signals?” was [predictably] raised. Fortunately, the number of signals, plus a number that were found to repeat, led to them being interpreted as natural phenomena.
“Unfortunately, the beam was narrow band which immediately flagged this as possibly artificial. 40+ years have gone by, and still, this signal intrigues us. Hardly a good result for an intended stealthy beam.”
Not necessarily. It may be impossible to fully disguise this emission (whatever its original purpose) except by making it brief. so hopefully no one will pick up! However, if it is accidentally detected, making it a common natural wavelength might confuse the recipient into thinking it was a natural emission or a technical glitch in the receiver.
If I were an alien civilization determined to protect my privacy and conceal my location, but still forced (for other reasons) to broadcast high energy microwaves into space, disguising them as a common natural frequency might be a worthwhile strategy. Its sort of like native tribesmen simulating bird calls to communicate with their fellows. Even if an enemy hears one, he might not think much of it and he would find it difficult to follow up.
Since these signals, if intercepted, would appear brief and transitory, they might simply be ignored. The listener would monitor that spot again forever and hear nothing else. One example, if these signals are communications or navigational beacons, or power transmissions. and they are directed to or sent from moving objects, they might be intercepted occasionally by a third party, but they would only be heard once. Only if the third party (the intercepting agent) is perfectly lined up with the sender and intended recipient, will he detect it. And if he does detect it, it could be masked by or mistaken for the ubiquitous 21 cm background hum.
I remember a preprint a couple of years ago, reported in the popular press, that theorized that the Wow! signal was emission from a solar system comet and that back in 1977 we did not recognize it because we did not know about them. Also that paper claimed that in a couple of years that comet (it proposed one, I don’t remember which) would be back in the same place so it should emit again. I mention this mostly because I did not see it among the 3 possibilities noted
Antonio Paris’ comet hypothesis was rejected immediately upon its publication because the comets were found to not be within the beam at the time the signal was received and that they do not emit at that frequency. This hypothesis was dismissed by astronomers, including members of the original Big Ear research team / Alberto Caballero’s error is that he assumed that Claudio’s statistical argument would predict you location of nearby civilization. In fact, Claudio’s estimate was of the mean distance to ET civilization. These are simply not the same thing.
Thanks for clarification. I read that a couple years ago too and assumed it was best explanation. I should have dug a little.
Well, after looking at amateur astronomer Alberto Caballero “An approximation to determine the source of the WOW! Signal” “https://arxiv.org/pdf/2011.06090.pdf” I see again the same major flaw as in Amir Siraj and Abraham Loeb; “The Copernican Principle Rules Out BLC1.” The bias toward only K5V to G0V stars and further to only G2V stars that seems to be very limiting in scope.
I propose that a study of the area for the nearest stars in the RA: 19h25m31s ± 10s (for the positive horn), 19h28m22s ± 10s (for the negative horn), and DEC: ?26°57? ± 20?, (both in J2000 equinox) should be from the AoV to Y9V stars and brown dwarfs. This should show many nearby stars that have parallax data from Gaia’s data and have lived long enough to have been colonized.
Further note of interest;
Now after putting the R.A and Dec. coordinates for WOW in Stellarium planetarium software “https://stellarium.org/” and setting it to the OSU Big Ear coordinates plus the August 15, 1977, 22:16 EST date and time I found a 30 minute error to the west in the position. I’m sure something is wrong in the way I set it up but everything looks correct and the radio telescope should be pointing due south. The feed horn was stationary at that time and was not put on a movable track until the 1980’s.
Try Aladin lite
And Gaia is on there too.
An insightful, analytic essay, from an astute mind backed by a lifetime’s work in this domain.
“there may well be modulations on the beam to communicate to any inadvertent listener”: indeed. Civilizations using propulsive beams may (should?) by custom and agreement mark each beam with an identification including source, target (and purpose?), intensity, duration, frequency, in reference to some identifiable coordinates of space and time. The big question would be a format comprehensible to unknown aliens.
Signal identity spoofing could be an interesting Sci-Fi subplot.
That error is 30 minutes in Right Accession (R.A.), being hours, minutes and seconds which equals 6 degrees 30 minutes at latitude -27 degrees across the sky. That is a very large error! Hope I’m wrong!!!
Well, sorry but after redoing the data on Stellarium, it did show it at the right R.A. and Dec., for the life of me I can not see what I set up wrong???
Well like carpenters, measure twice before you cut!
I once met a carpenter who cut by visual estimatieon without using his measuring tools. He explained that that that was his mentor’s way, and his mentor had advised him that measuring would make him dependent on the measuring tools.
The use of 21 cm was suggested by Cocconi and Morrison in 1959 ( http://www.coseti.org/morris_0.htm ). Apparently background is low in this region, despite the occasional emission by hydrogen, and it is a “unique, objective standard of frequency, which will be known to every observer in the universe.” For the same reason it was mimed on the Pioneer plaque.
Nonetheless, the relatively low background makes me wonder about another use. There have been some bewildering publications of light bending itself by substantial angles, and it is claimed it can be made to bend, on its own, in a complete circle. ( https://www.sciencemag.org/news/2012/04/light-bends-itself ) Is it conceivable that by some sophisticated optical method a light beam directed at some irregular target, such as the Earth, could be made to reflect back solely toward its origin, as if an immense corner reflector had been placed on our planet? With sufficient knowledge of a planet’s future location, such a mode of reflection astronomy could be a powerful tool of exploration.
Ok, so is the portion of the sky associated with WOW in any way correlated with where oumuramura was thought to have originated? Arvi Loeb seems to reckon it’s artificial.
Let me point out that a starship launched from a distant star will not arrive from the direction of that star. It would be launched ahead to where the moving target will be in when it arrives. Therefore power beaming leads the target.
That could be why we see the beam!
Yes certainly, I’d have thought this was implied in the question itself. One has to account for where we are in 3D space and direction at time of wow! and compare to current 3D position vs projected point of origin of oumuramura and direction of solar system entry, etc. Just wondered if anyone had looked to see. The solar system is moving at some speed around the galactic center, we are quite a distance from where we were when wow! was detected, etc.
I never understood time travel stories. Pick spot on earth, dial to go back 2 days. Assuming you go back in time you’re ending up in space because the earth isn’t physically located in the same 3D space as 48 hrs prior.
So the question remains, has anyone looked at the positions etc enough to know if these events can be correlated?
“Assuming you go back in time you’re ending up in space because the earth isn’t physically located in the same 3D space as 48 hrs prior.”
This common sci-fi trope is also very very wrong. There is no absolute space. There is no absolute time. It is only possible to travel in spacetime. I am traveling through spacetime while typing this comment.
Perhaps in human distance terms, but hardly in relative star position or galactic terms. The night sky looks pretty much the same as it did hundreds of years ago. Star positions can change over 1000s of years changing constellations, but hardly 40 years ago.
I calculate that the sun travels a few tens of AUs/year (a few ten-thousandths of a light year) around the galaxy. Most of the nearby stars in the Orion arm are traveling with us, so this is perhaps a high value for relative motion. A starship on a 1000 year journey must aim less than a light-year ahead of its target at the most, and probably a lot less. As there are no other stars within that radius of us, it is also likely that the same applies to the star system that launched the ship. IOW, the beam will still appear to be coming from close by the originating star.
Wikipedia has some quite nice illustrations at https://en.wikipedia.org/wiki/Oumuamua . From an insurance perspective, the Solar system was definitely at fault here; ‘Oumuamua was essentially parked (Local Standard of Rest – https://blogs.scientificamerican.com/observations/6-strange-facts-about-the-interstellar-visitor-oumuamua/ ) stationary relative to the galactic disk. By that consensus of the local stars, the Sun smacked into ‘Oumuamua and started it moving. But from our perspective ‘Oumuamua came from Lyra and left to Pegasus, both northern constellations, while the Wow signal was from Sagittarius in the southern sky.
We are building a similar telescope to the Big Ear in the UK. We will be following a similar design to that of Dr John Kraus and his team. Perhaps we might recieve the Wow! Signal the second time around?
I have been looking for a project such as the EAAROCIBO project to donate to, do you have any place to send a donation yet? If your crowd funding works out good what about putting a similar scope in Australia or New Zealand to cover the southern hemisphere?
Stealth and information imbalances in general provide many strategic advantages. I would expect strategic advantage to be a more common motivation than pure altruism. There are undeniably effective strategies where altruism or an embrace of diversity, emerges from self interest.
Using 1.42 GHz could be an attempt to hide but not a very good one. The beam would have to be doing something very important and there would have to be no other way to accomplish the same goal. In probability space, it isn’t a large target.
Without a better understanding of the diverse population of transients it’s impossible to predict which transients are atypical.
Harold, I think your statement about the need to understand the population of transients is spot on. Has a database been started?
The coincidence of the 1.42 Ghz is very intriguing but no one has asked about doppler shift – surely the signal’s frequency was sent at a frequency other than 1.42Ghz. Relative motions would stretch or compress it by the time the Ear received it, unless I’m missing something.
Dr. Benford, when you say a 3km aperture, are you imagining a giant dish or flat phased array or something else? Which would be easiest to build? Would a build location on a planet or asteroid’s surface be preferable to one in space?
Thanks much for this thought provoking article, to all the great commenters (as usual), and of course Paul!
Question: Given the H1 frequency how could you generate the signal?
And based on that frequency, what would the signal be used for?
As in – how much neutral H2 would you need, was the signal “laser like” (in phase) and what would be be necessary to generate that signal?
A more general comment, on the matter of wavelength, which has come up in several of the replies here: In the electromagnetic spectrum the microwave region has the lowest attenuation for receiving from the sky. Due to such interference, it makes little sense to send a signal lower than 1 GHz or above 30 GHz because in a water-rich atmosphere that region offers the least interference from the sky. Neutral hydrogen strongly emits at 1.42 GHz and hydroyl at 1.64 GHz. Both are related to water, so this is called the ‘waterhole’. Otherwise, this is the quietest part of the microwave spectrum. That’s why early SETI observers we’re looking at this frequency region. And alien astronomers would likewise be looking to study the structure of the galaxy by looking at the distribution of ubiquitous hydrogen.
Using 1.42 GHz or a harmonic might make you suspect a natural phenomonum. If you want to advertise intelligence, use 1.42 times pi or phi or e or SQRT(2)…
Shouldn’t the power beaming signal be longer in time than the wow signal or maybe it was not pointed in our exact direction and we only got a bit of it?
Very interesting reading and discussion
Geoffrey: We don’t know how long the signal lasted, just that it was on as the antenna rotated past. / For interstellar probes, there is no need for scaning the beam in angle. You just point at that part in space where your target star will be and beam for as long as needed to accelerate to the speed needed.
Does anyone know what a detonating thermonuclear device would look like, maybe a 100MT device at say 10, 100, 1000 LY’s? I’m wondering about the radio spectrum from such an event.
Also, has an object falling into a black hole been eliminated? I’m wondering if a survey has been made of the target area looking for stars that appear to be moving around a central point? Or old photos of that region that now show a dwarf star missing?
You may find these articles useful, as using nuclear detonations as a signaling device to ETI have been seriously considered, including by none other than the Soviet Father of the Hydrogen Bomb, Andrei Sakharov (1921-1989):
Another source for Sakharov’s SETI paper:
The article linked here next discusses if we detonated all the nuclear weapons humanity had in 1989 (roughly 55,000 such devices – talk about literal overkill), how far would the x-ray radiation from the combined explosions be detectible in deep space:
Elliot (1973) pointed out that X-rays are not appropriate as a means of transmitting a continuous stream of information because of their high quantum noise. As a means of sending and receiving the “first beacon signal”, however, he considered that X-rays could have certain advantages. Elliot analyzed the X-ray emissions of the terrestrial nuclear explosions carried out in the early 1960s. When a nuclear weapon explodes, about seventy percent of the energy released is in the form of kilovolt X-rays. This X-ray pulse is formed in less than one microsecond. If the explosion occurs above eighty kilometers, the X-rays are not absorbed by the atmosphere and are free to propagate into space.
Other advantages of using the X-ray pulse generated by a high-altitude nuclear explosion are: (a) The pulse is short and will not be broadened or appreciably attenuated by propagation through the interstellar medium; (b) there are no stringent frequency requirements on the receiver, since the pulse covers a broad X-ray spectrum; and (c) the X-ray flux involved is much larger than that of a solar-type star, a natural source of X-rays.
Elliot estimated the distance at which the United States “Starfish” nuclear test could be detected by our present technology of X-ray detectors. Assuming that the energy of the explosion is equivalent to 1.4 megatons and that the X-ray pulse was equally intense in all directions, he found that this explosion should be detected from a distance of ~400 Astronomical Units, about ten times the radius of Pluto’s solar orbit.
Supposing that all the terrestrial nuclear powers  pooled their nuclear weapons stockpiles to produce a single explosion in space (E~2×10 to the 4 power megatons). Considering that the X-ray pulse could be concentrated into a conical beam of about thirty degrees in angle with no loss of radiation, a typical terrestrial X-ray detector should be able to detect a signal from a distance of ~190 light years.
3 – In 1989 the United States and the Soviet Union had almost 55,000 nuclear warheads with a combined destructive power of 15,500 megatons (Source: Bulletin of Atomic Scientist, 1990).
This article ponders if we might be able to detect an alien nuclear war:
Has any research been done on co-orbital positions for 1977,any of which could have had Benford Beacons on the surface?
I was also under the impression that,although one of the most looked at parts of the sky,the actual viewing time only amounts to a few hundred hours.We would have to be incredibly lucky to catch a repeat signal and could have missed it on numerous occasions.
If you want to find out how many SETI searches have been conducted since the modern era of the field which starts in 1960 with Frank Drake’s Project Ozma, this Centauri Dreams article links to the Technosearch archive of most major SETI efforts here:
I know there are many amateur efforts not listed in that Technosearch archive with either limited or no records of their efforts at all.
Although the chances were nil here, folks did try to listen for radio signals from Mars in 1924, which I think could be counted as the proto modern start of SETI:
Here is my question about the SETI efforts with Big Ear: How serious were they really about searching for alien radio signals?
I ask this mainly due to the fact that they had no way I see to alert an operator if an interesting signal was captured in real time. Yes, I suppose you could blame this on being the 1970s, but still, the Wow! signal has remained elusive largely because no one was there when it was detected, no alert was sent out, and the operator didn’t even look at the data printout until hours after the signal had come and gone.
Here is the history of the Wow! signal as written by those who were involved with the Big Ear effort on its twentieth anniversary:
I have long maintained that most SETI efforts until recent years, with few exceptions, have been largely token efforts. I am not saying those who did try to search for alien signals were not being serious or lazy or scientifically lacking. What I am saying is I know they often tried their best with the limited resources, money, and technology they had. Sadly this often turned into what I label as token efforts.
In one sense, then, the Big Ear SETI project was such a token effort, even though they did search for a long time – but not continuously, please note. To top it off, the college the radio telescope owned, Ohio State University (OSU), couldn’t wait to sell all that land to developers in 1998 so it could be torn down and replaced with condos and a golf course…
Even someone like Carl Sagan was not immune to the SETI token behavior of the day. If you read one of his biographies from 1999, they detail how he personally operated an effort to listen for signals from the Andromeda galaxy (Messier 31) using the Arecibo radio telescope in 1974 or 1975. Sagan literally sat at the operator’s station for a few hours waiting for a transmission from the distant galaxy. He soon became bored and listless, then left.
So tell me how wrong or right I am about Big Ear SETI and most other SETI efforts back in the day. Even now I still do not think we are doing enough or looking more widely than we should.
I didn’t know about Carl Sagan’s Andromeda search,that’s very enlightening!As I said in my previous post,as far as I am aware,we’ve only spent a few hundred hours searching the part of the sky where the Wow!Signal originated.I understand that radio telescope time is limited and we have to piggyback on other more important searches.But what could be more important than the search for extraterrestrial intelligence?
Is there anybody working out there? Cambridgeshire astronomers to search for alien factories
By Paul Brackley- firstname.lastname@example.org
Published: 07:30, 04 February 2021 | Updated: 10:31, 04 February 2021
Cambridgeshire astronomers hope to listen to the noise made by alien factories and spaceships using the first telescope in the UK dedicated to the search for extra-terrestrials.
They are undaunted by decades of failed attempts to find ET – and believe their new approach could improve our chances of proving we are not alone in the universe.
Full article here:
Jason Williams and Jeff Lashley, of the East Anglian Astrophysical Research Organisation (EAARO), intend to hunt for the “techno-signatures” of interplanetary industry and mining operations.
They hope to find the noise produced by alien industrial technologies such as machinery and spacecraft.
And unlike traditional approaches to the search for extra-terrestial intelligence (SETI), their ground-based telescope will be trained on a particular area of space with the largest number of stars, an approach similar to that adopted by the orbiting Kepler Telescope, which is searching for extra-solar planets.
They have named the project EAAROCIBO after the space telescope at Arecibo in Puerto Rico that featured in the 1997 movie Contact, starring Jodie Foster.
Operations at the 57-year-old observatory were closed by the US National Science Foundation last November after two cables gashed a 30-metre hole in the telescope’s huge reflector dish.
EAARO managing director Mr. Williams said: “EAAROCIBO will be the first dedicated SETI instrument of its kind ever to be built in the UK. Our novel research strategy and innovative approach to combining classic and cutting-edge technologies will give us a refreshing new perspective in this exciting field of research.”
EAARO has a space operations centre (SOC) at Alconbury, a fully operational radio observatory and satellite ground station in Hertfordshire and an ongoing meteor radar system project on the Orkney Islands.
But the group of scientists and businessmen are looking at two other sites – one near Bodmin in Cornwall and the other on the edge of a national park in North Yorkshire – for their telescope.
First though, money must be raised. Filming started last month for a documentary that will be used to aid a crowd-funding effort.
The first funding stage is to build a scale working model of the antenna, while the second will be for the materials and services required for the antenna and associated equipment.
The concept is based on an idea by British-born physicist Professor Paul Davies, who worked for a time in the 1970s at the Institute of Theoretical Astronomy in Cambridge, alongside Prof Stephen Hawking.
Prof Davies said: “I’m delighted that EAARO will be dedicated to this new approach to SETI. While all searches are welcome, what the subject really needs is some innovative thinking. Under Jason Williams’ leadership, the EAARO project will serve as an inspirational trailblazer for SETI 2.0.”
Hello, I really enjoy reading your articles though I have no (natural) science background. Curious / stupid question: I read that our galactic core / supermassive blackhole is unusual in that it seems to be without a relativistic jet. One of the theories proposed to explain it, is that we can‘t detect it because it is pointed right in our direction. Given that the Wow!-Signal came from the direction of the Saggitarius constellation is there a chance / can it be ruled out the source of the signal is Saggitarius A*?
I don’t think a relativistic jet can explain the Wow! Signal — it was too sharply defined and never recurred (as far as anyone knows). It would be hard to reconcile a burst from a relativistic jet with the brief Wow! reception.