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  • Writer's pictureM. Josh Roberts

Is Anybody Out There? Messaging Extraterrestrial Intelligences

The scientific approach to communicating with extraterrestrials is older than one might think. Over the past few centuries, some of the great minds of physics and astronomy have sought to answer that question as best they can but have often run into non-astronomical issues. The major changes that have shifted how we attempt to send messages into space have often come from fields within and outside astronomy and physics - from computers and the digital age to the discovery of extreme life here on Earth, the idea of two-way Communicating with Extra-Terrestrial Intelligence (or CETI) and one-way Messaging Extra-Terrestrial Life (or METI) has grown greatly as a cross-disciplinary science.


Humans are fundamentally social creatures. From our closest evolutionary ancestors to today, one of the biggest parts of what makes us human is our socialization with the rest of our group. We often define ourselves by the groups that we belong to or by the groups we oppose. This us versus the other system can help us understand our fixation with finding life beyond Earth - life that would likely derive from a completely different origin and be wholly separate from us. If we find someone or something else out there in the universe, it might help us better understand each other as humans and earthlings by giving us external context.

The Search for Extra-Terrestrial Intelligence (SETI) is the name given to this initiative, a confederation of scientists and philanthropists no longer directly supported by any national governmental support or oversight. Their formalized history stretches over more than 50 years, (Tarter et al. 2010) but the roots of the movement go back into antiquity. While most affiliated with the project have been keenly focused on how to find and discern signals from life distinct from the complex background signals of the universe, a few forward-looking individuals have stepped up and proposed that we reach out beyond Earth and extend a message or proverbial “olive branch” and see who responds. Those who seek to send a message or show our presence are sometimes identified as METI (or Messaging Extra-Terrestrial Intelligence).

It is necessary for some species to reach out for contact to be possible. Since we cannot be sure that anyone out there is broadcasting, it behooves us to be the ones to broadcast. (SpaceWeb) Some individuals might be ruled by fear and think that a signal might betray our position to those who harbor predatory intentions, but it is far too late for that concern. Humans have been broadcasting our position via strong electromagnetic broadcasts for decades so any predators that might be lurking nearby in the interstellar darkness would already have their sought signal (if these boogeymen do exist…). If Humanity can send out a signal that would be reliable, repeatable, and discernable, our species might alert someone else to our presence and - perhaps - eventually discover that earthlings are not alone in the universe.

In my paper, I will explore the questions of how our notions of the ideal signal have changed over time as our scientific (specifically astrophysical) knowledge has expanded between the late 1800s and 2010. I will be covering early attempts and geophysical engineering by 19th-century visionaries, the advent of speed of light technologies, and a growing understanding of the solar system through the extrasolar planet and extremophile revolutions. This period of history has been a dynamic one for nearly every field of astronomy and related sciences, but the grand shifts in our ability and understanding of communication have been of special interest.

Research Methods:

The fields of astronomical observation to discover signs of extraterrestrial life seem to be ancient and much has been written on the subject. Even modern efforts using more up-to-date technologies and methodologies date back to early 1800s with papers focusing around looking for solid evidence of alien life in the canals of Mars or in the hypothesized jungle of Venus. In order to seek out less well trod ground, this paper will aim towards delving into an explored but less extensive field. While this at first seemed a blessing, the depth and breadth of papers have made locating details of merit quite a challenge. I have sought out papers which address a changing strategy of communication or else discoveries that would necessitate a change.

In order to get verifiable scientific information, I have looked up both historical primary source papers and some recent papers that reflect on those practices from the Astrophysical Data System and the Swinburne library. I have found science texts and books that touch on the subject to gain a more general understanding of the depth and breadth of the field. I have gone out and located interview with some of the major leaders in the SETI/METI fields and even conducted my own interviews with Dr. Jill Tarter via email and Dr. Doug Vakoch over phone. At the conclusion of the literature review, I was able to dig deeper into these resources as well as seek our some additional ones based on that reading and recommendations from my advisor. The sum of these resources have woven a complex tapestry of the history of human transmission one that has changed dynamically over time.

How do We Communicate?

The origins of human communication run as deep as the origins of humanity itself.

Across bands or troops, being a good communicator might have proved beneficial, much like being a good hunter or gatherer. As Homo sapiens spread across Earth, communication stayed important, but strategies changed. As human groups long-separated came back together, like Babel after the sundering, they could no longer understand each other. A new strategy emerged, intuiting, understanding and learning a new mode of communication became a valuable skill. Since that ancient time, nearly all communicating, translating and deciphering across gulfs of space and time has been between humans. No matter how far flung humanity has become, we still communicate in the same basic ways - we use similar minds to understand and relate. While messages might be lost in translation, we still take solace in the fact that some commonalities link us to the message’s recipient, but how complex does communication become when the intelligence “on the receiver” isn’t human?

Attempts to accomplish this feat have been made, but never successfully to date (although we might very well receive a reply tomorrow). While many of these attempts toe the ground of implausible fancy, around 250 years ago, natural philosophers, scientists and mathematicians began to come up with more valid ideas around how this might be made possible. Since then, efforts have waxed and waned over time, but never really ended. They might coarsely be divided into four different periods:

The “lunar” epoch, from 1800 - 1870, wherein models were proposed to communicate simple ideas in a way that might catch the attention of intelligences native to the moon.

The “Solar System” epoch, from 1870-1959 - in which the most likely targets for extraterrestrial life were within the Solar System

The “interstellar” epoch, from 1959 - 1995 where large and powerful transmissions were first hypothesized and then transmitted, as well as physical probes sent forth with inscribed and encoded information mostly targeting stars within our Galactic region.

The “interplanetary” epoch from 1995 - 2010, where computational advances have revolutionized every step of the process in the SETI/METI fields alongside the discovery of other planets around other stars.

In this first period, dubbed “lunar”, humans imagine human-like people on the Moon, a mere quarter of a million miles from the surface of Earth. While it is hard to find much scientific speculation around moon-based civilizations in the scientific record, newspapers do record evidence of the “Great Hoax” of 1853 wherein a scruple-deficient editor of the New York Sun developed and ran a story in print, over the course of several days that a telescope built and run by John Herschel in South Africa had made observations of winged bat-men and intelligent beavers on the Moon. (JSTORweb) While this is beyond ludicrous to us today, modern telescopic observation was still in its infancy and photographic plates from telescopes simply weren’t used, so observations by eye were state of the art. With stories like this in the public eye, imaginations were piqued and great minds of the period began mulling over notions of how to tackle this problem of reaching out in case of there being something a bit less loony on the Moon. To attempt to create something large enough to be seen on the moon would be a terrific challenge, despite what you may have heard about the Great Wall of China or Jeff Bezo’s house, they cannot be easily seen from even low Earth orbit - a mere 250 miles from the surface of Earth - much less a thousand times that distance. In order to make ourselves known to any potential Lunarians, Karl Gauss proposed in 1826 (Cerceau & Bilodeau 2012) cutting down huge swathes of Siberian woodlands and planting corn to see if we could make a gigantic golden proof detailing the pythagorean theorem on the surface of Earth. Eurasia was an ideal choice, due to its broad expanse, but may have proven challenging to irrigate and farm, but the idea is sound astronomically (beyond environmental considerations) as is shown below.

To estimate, assume the Moon covers about half a degree of the sky. (TimeandDateweb) From the Moon, Earth could be considered to cover about 4 times that as the Moon’s diameter is about ¼ of Earth’s and the distance between them would not change. While Earth only subtends about two degrees from the surface of the Moon (just about two fingers held at arm's length) Eurasia is big enough that if the figure covered much of its North to South length, almost 2000km it would likely be noticed from the Moon, even if it would still be hard to see - it would be roughly equivalent in size to some of the larger features of the Moon. In Figure 1.0 you can see an approximation of the view of the proof from the Moon created in Worldwide Telescope. As pointed out by both David Grinspoon in (2016) and in Cerceau & Bilodeau (2012) this would be flawed due to the curvature of Earth and would likely look a bit funky viewed from the lunar surface.

Figure 1.0, a view of Gauss’ figure on the plains of Siberia, rendered in WorldWide Telescope (image credit WWT/AAS)

While Gauss is esteemed for his many mathematical and engineering insights, his environmental engineering and METI ideas might need a little work. He was not alone in his attempts though, another great thinker of the era. Joseph von Littrow was an accomplished astronomer associated with the Vienna Observatory. His proposal in 1840 (Cerceau & Bilodeau 2012) was to inscribe a massive circle in the sahara desert and fill it with kerosene and ignite it when the night side of Earth faced the Moon. While this would be a much more dramatic display that Gauss’ grains, and much easier to irrigate and construct (circles are a bit more geometrically forgiving on a sphere) there is no doubt a tremendous risk and cost associated with lighting a geographically significant puddle of kerosene. It is worthwhile to note that serious work never began on either of these projects and while they are widely reported on - no doubt due to their sensational aspects, they do not seem to be much more that thought experiments. Their similarities run deep though. Both of these accomplished gentlemen decided that geometry and simple math would be the thing to catch the eye of an intelligence that might be capable of reciprocating our messages - an idea echoed from their era onward as subsequent METI concepts encapsulate this idea.

The fatal blow to the idea of Lunarians came from physics, not astronomy, as the kinetic theory of gas was developed. From the formulation of the idea by James Maxwell in 1860 to the formalization of the theory in the 1900’s with the advent of Brownian motion in 1906 - information mounted that meant that the moon’s gravity was insufficient to retain a substantial atmosphere and without it, Lunarians were extremely unlikely. As this evidence was mounting that the moon was indeed lifeless, astronomers were also learning more about our Solar System at large and planets like Mars and Venus were more likely to have and retain atmospheres, so life might be possible there. Yet new challenges arose in that the methods that might have worked to demonstrate our presence and intelligence at a lunar distance would be quite insufficient beyond it. Far from abandoning the idea entirely, astronomers found a new and more likely target not too distant - Mars.

The “Solar System” Epoch

The late 19th and early 20th century were the beginning of a technological bonanza that continues to this day, beginning with wired electrical power and the first hint of the modern information age, the telegraph. Previously, information could only move as quickly as the person carrying it - by horse or by railcar - the limits were fairly severe. With telegraphy, the speed limit increased dramatically, now only hampered my the movement of electrons through the cable and the speed at which an operator might decode the transmission. This communication at a distance seems to have inspired more METI illuminaries to think up signalling methods to relay our ideas to Mars. Between 1869 to 1896, three similar proposals were put forward by Charles Cros, Edward Neovius and Francis Galton (Cerceau & Bilodeau 2012). While the details differ, the broad strokes of all three ideas are basically the same - beginning with a huge array of reflectors and a bright light source, beams of light would be directed to the surface of Mars. They would be shuttered or diverted to allow for a sort of interplanetary signalling lantern that would allow for the transmission of something like Morse code.

However, telegraphy and Morse code on Earth has trained operators fluent in both English and the code transmitted, so how might one build that codebook from scratch at a distance? The first idea was, much like Gauss and Von Littrow, to start with math, but drawn figures would be impossible, so you might just start with a few numbers and add complexity from there. The major advantage of this paradigm was that while transmission would take a not insignificant amount of time (say 20 minutes at the speed of light between Earth and Mars) it would still be possible to change tactics if something was not working, re-aligning and adapting to responses should they be fortunate enough to receive them. Cros and Galton were keen to quickly segue into pictorial representations after contact and a basic code had been established. Neovius was more inclined towards signs for words and a more information rich cipher form of communication based around changes in pulse duration and intensity. Galton intended for a system including a dot, a dash, and a line, a more complex 4 component code overall. Cros’ plan seems the most complex, but also most difficult both to transmit and to receive, using a specific tempo of transmission, including single, double, and triple flashes keeping to a specific cadence.

These methods should be applauded for their versatility. While the theoretical Lunarians of the previous epoch would no doubt be impressed by our geoengineering feats required to reach out to them, they would have a hard time replying (there are no fields in which to plant wheat on the Moon, nor kerosene or oxygen to burn!) and it would take a long time for humans to construct a new symbol or message, especially without a reply, but light might be possible. The communication methods of the Solar System epoch could adapt quickly over subsequent communication after the initial “hello’s” and could become as complex as needed.

In the 1920’s a slight improvement on the method just described by C. W. and H. W. Nieman was offered (Nieman & Nieman 1920) wherein the dots and dashes of Cros’ method would be arranged into a simple matrix (Vakoch 2000) and could be made to replicate a simple sort of pixel. With even a limited ability to transmit images in this way, complexity and representational symbology represent a double edged sword to METI ideas, they can convey culture, context and information much better than blinks and numbers, but also have a huge potential to confuse or muddy communication without shared context.

While these ideas around Mars-Earth communication were taking shape, the technological revolution continued with ever more frantic speed. Electrical light bulbs and lamps phased out oil and gas combustion, making the generation of light much easier and electrical phenomena ignited imaginations here on Earth. The famed Serbian inventor Nikola Tesla became determined to find a way to communicate with Mars after an incident in his lab led him to believe that someone had sent him a transmission. In Collier’s Weekly (1901) he recounted the experience:

“My first observations positively terrified me, as there was present in them something mysterious, not to say supernatural, and I was alone in my laboratory at night; but at that time the idea of these disturbances being intelligently controlled signals did not yet present itself to me. The changes I noted were taking place periodically, and with such a clear suggestion of number and order that they were not traceable to any cause then known to me... The nature of my experiments precluded the possibility of the changes being produced by atmospheric disturbances, as has been rashly asserted by some. It was some time afterward when the thought flashed upon my mind that the disturbances I had observed might be due to an intelligent control. Although I could not decipher their meaning, it was impossible for me think of them as having been entirely accidental. The feeling is constantly growing on me that I had been the first to hear the greeting of one planet to another. A purpose was behind these electrical signals”

So enchanted with this idea of interplanetary communication, Tesla began working on something to transmit power as a message to Mars without “the slightest dispersion” as he put it. Unfortunately, his ideas never came to fruition as he passed away before the design was completed and so few details were known by others that they can only speculate upon his ideas. (Raulin-Cerceau 2012)

In this, we can say that Tesla accomplished just about as much as any of his predecessors. All of these pioneering ideas were long on concept and short on execution. For most, it comes down to both harsh practicality and cost. While the “Lunar” epoch ideas were by far the grandest spectacles, the ideas of the “Solar System” epoch were no simple thing to do. For Cros, Neovius, and Galton, huge luminous beacons of lamplight would need to be lit, and massive and finely crafted parabolic mirrors would need to be made around them. This would require a large pool of resources like fuel, land, and budget for apparati. Many of these ideas show a significant maturation in their content and concept of communication but do not have a lot of drive behind them to make it happen. With the advent of radio technology, andas astronomers were using ever larger telescopes to examine the planets of the Solar system and discovering that worlds like Mars and Venus were less hospitable than imagined, the first serious attempts at communication were drawing closer.

Soviet astronomers made a somewhat serious attempt in 1962 (Zaitsev 2012) to do what others had not and beam a transmission towards another planet (and beyond!). The messages were simple and fundamentally indecipherable (unless we happen to share a language and Morse code with any aliens we meet…) but the words “Mir”, “Lenin” and “SSSR” (initials of the USSR in Russian) were broadcast towards Venus and the constellation Libra in 1962. (Cerceau & Bilodeau 2012) This is a strange (and one cannot help but think politically motivated) transmission, perhaps METI in name only. If (and this would be quite humorous) extraterrestrials DID pick up this transmission, they would likely assume we were quite bad at communicating! What makes this unusual is that while nothing had yet been proven, evidence was beginning to mount that venus was utterly uninhabitable when the broadcast was sent. But this was a simple and low “production value” transmission, and likely an easy way for the Soviets to claim another “first” in the space race. (Zaitsev 2012)

No “seminal paper” has shown up resolutely disproving life elsewhere in the Solar System, but in the first half of last century, the chances of life elsewhere in the inner Solar System had shrunk to nil. Sagan (1971) had measured the temperature on the surface of Venus and discovered it was beyond the tolerances for life as we knew it. Mars was the most disappointing of all. Schiaparelli’s maps of the surface of Mars had prompted a generation of speculation around a potential civilization that was either quiet or dead, but as observational techniques improved we lost hope for intelligent life there too.

With this expanded knowledge, the METI paradigm undergoes a dramatic shift - no longer flashing lights or making signs at the worlds nearby/ Instead, there is a new set of targets, the stars around us and the worlds we suspected resided in their orbits. There is also a new paradigm, ushered in with the Cocconi & Morrison (or C&M) paper.

The “Interstellar” Epoch

As the Origin of Species frames discussion on the evolution of the Theory of Natural Selection, so too does “Searching for Interstellar Communications” frame SETI. Penned by Giuseppe Cocconi and Philip Morrison in 1959 and published in Nature, it went where no author had before, clearly outlining what would need to be done with an idea of how to do it. They delineate the 21 cm line, part of the radio regime of the electromagnetic spectrum, as the best place to start scanning in the sky for three critical reasons:

It reached the surface of Earth, meaning that launching an antenna into space would not be necessary (it had not yet been done at the time).

It is the emission line of hydrogen, the most basic element that comprises the majority of the observable universe and therefore one that will be know of an studied by anyone who is interested in learning about the makeup of the universe.

The information will travel at the speed of light, making the best possible speed between stars.

They went beyond defining how this should be done and offered likely targets, sun-like stars in low noise regions of the sky as well as passing reference to hundreds of other potential candidates beyond them. This paper is short but powerful it its brevity. In its final sentence, it laid down the maxim for generations of SETI/METI/CETI ideas: “The probability of success is difficult to estimate; but if we never search the chance of success is zero.” (Cocconi & Morrison 1959)

This C&M paper did end the era I have dubbed “Solar System” and ushered in the “Interstellar” epoch. In truth, Humans had been leaking electromagnetic (EM) signals for 25+ years. By 1960, our TV carrier waves were powerful enough to escape the ionosphere but these were not coherent signals, merely poorly attenuated static. (Grinspoon 2004) But maybe other species on other worlds were giving off some static of their own? As the C&M publication was hitting the presses, the first major search for Extra-Terrestrial life was being specced out. Dubbed Project Ozma for the character Ozma of Oz from L. Frank Baum’s stories, who sent news of Oz via radio - an appropriate if whimsical name for the survey. For 150 hours, the Green Bank 85’ Telescope scanned two sun-like stars for any potential broadcasts in the 21 cm range but came up empty handed. The Project Ozma search was the brainchild of a different Frank, Frank Drake - a PhD from Cornell University. His pioneering project did succeed in one way, it got people talking about how to do the next search project. At this point, with the C&M paper, the Project Ozma team, and the building international enthusiasm for the project, SETI and METI were on the forefront of science. In order to get all of these scientists moving in the same direction, a conference was planned to meet at Green bank, where the Project Ozma search had happened.

At the Greenbank meeting, experts from the US and Russia came together with physicists, engineers, and astronomers, even some behavioral animals specialists. In late October 1961 the world experts on radio and its potential for communication convened. (Grinspoon 2004) The now infamous Drake equation appeared, both as a mission statement and agenda for the scientists assembled, it detailed the “known unknowns” that would dictate the number of opportunities for contact in the universe around Earth. Amongst their number beyond Drake were Philip Morrison, Carl Sagan (an up-and-coming astronomer from Cornell as well), and a dolphin researcher John Lilly who reported success in being the first to communicate with another species - a valuable person to have when trying to communicate across a species barrier and a distance barrier. The group dubbed themselves “The Order of the Dolphin” in celebration of their new fraternity, but would never reconvene. In Swift’s interview (Swift 1990) Morrison recounts that there was interest, but it never gelled - Grinspoon reports that Lilly’s successes might have been overstated and that his research results were likely flawed due to the experimenter’s consumption of psychedelics. (Grinspoon 2004)While this might be seen as a good reason to only have buttoned up physicists and astronomers affiliated, that was thankfully not the conclusion drawn from the event and later SETI/METI initiatives have benefited greatly from diverse skill sets and experiences in leadership roles. It is from this auspicious group that the SETI project and eventually the SETI institute grew. (Ekers et. al 2002)

Cyclops was the first major project born of that group - although like its namesake, it proved to be something of a mythical monster. Since it was only ever intended to receive and not send a message, it is not a major portion of this paper yet bears mentioning for the document that defined it. Cyclops was a working title for a ongoing and scalable array that would increase in size and sensitivity over time. (Ekers et. al 2002) By monitoring the sky more continuously and in a scientific progression, the project hoped to grow to the size required to receive the signals. What killed the project was a lack of scientific literacy from American elected officials who saw the theoretical end product’s price tag (6-10 billion dollars, 1/150th of what has been committed to production and development of the F-35, the newest war plane) and dropped it like a hot rock. (Swift 1990) Over 253 pages, the document spells out clear and scientific methods to make this idea become realized, but their bullet point conclusions were leaning in towards the spiritual and whimsical and might have been a bit outside the comfort zone of politicians of the age.

In these notes, they do spell out that sending and receiving is the best plan to make contact with an ETI. In SETI 2020 (Ekers et. al 2002) it is explained that the best chance a project like Cyclops has is that a species somewhere out there in the universe is broadcasting a long-term beacon for us to find. It would be in our best interests to broadcast a beacon as well in the hopes that our altruism is reciprocated. Thus began the era of humanity actually sending a message to space.

The first intentional message to the stars (as the Morse message was intended for Venus) (Zaitsev 2011) was a small aluminum plaque depicting the hemispheres of Earth, a brief passage, and the signature of Richard Nixon - affixed to the leg of the Apollo 11 landing module that remains on the surface of the Moon. This was left on the Moon in the summer of 1969. While this is most certainly not the kind of message most of us might imagine, the phrasing of the short passage “Here men from the planet Earth first set foot upon the Moon, July 1969 A.D. We came in peace for all mankind” does imply an audience that is not human, but there is no information included as to how an intelligence not from Earth might decipher it and the chances of someone ETI stumbling across the plaque on the lander without knowing where it was and seeking it out seems infinitesimal, but it, nonetheless, is our first message. Whether or not this should be viewed as a message to ETIs or as a sort of grand historical marker is a semantics issue, but literature on the subject (Cerceau & Bilodeau 2012) supports it as a message, if an inelegant one.

It was at this point that the cadre of thinkers who met at Green Bank produced what might be their most famous product, the Arecibo message. Named for the transmitting antenna it was broadcast from, Arecibo was a realignment and the shining gem of the “interstellar” age. It is nearly synonymous with the idea of SETI for a generation of astronomers and astronomy enthusiasts. While a large step forward above and beyond the technology used for the earlier “Morse messages” from the USSR, it was still of the same basic paradigm - sending an artificial message at a specific region of the sky, repeated a few times with the understanding that those who received it might try to puzzle out what was sent and why.

In its most basic form it is a shifting frequency that could be interpreted as binary. In terms of organization, it is 1679 characters long, so the only way to organize it is either as a 73 x 23 grid or a single long sequence. The hope was that any alien astronomer attempting to suss out what this gibberish was might try and organize the recorded digits a few different ways. If the grid was arrived at, it would either remain gibberish (if organized the wide and not tall way) or snap into the intended message. Figure 2.0 depicts the binary version and figure 3.0 depicts the more commonly seen graphical version.










































































Figure 2.0 - Binary text version of Arecibo message (image credit Uoregonweb)

Figure 3.0 - A Color-Coded Arecibo Message (Image credit SETIweb)

The message itself is very well thought out, given the constraints of time and signalling every bit of information. It starts with a primer on the numbers being used, as Sagan and Drake deduced that this would be discernible, just as the “Solar System” era transmitters supposed. They also immediately used these numbers to include some information on ourselves, including a specific set of numbers (1, 6, 7, 8, 15) for the detailing the atomic numbers elements hydrogen, carbon, nitrogen, oxygen, and phosphorus (respectively) that comprise all life here on Earth. (NAIC 1975) Those sections of figure 3.0 are respectively colored white and purple at the top of the image. The next section gets more complex. In green, the basic makeup of DNA is charted based upon the nucleotides created from those compounds. This is followed by a white and blue section which gives some idea of the basic structure of our DNA as well as the number of base pairs in the human genome - or at least the number of base pairs we thought were in the human genome in 1974. That number was shown in the white “spine” of that portion of the message as 4.3 billion, but has since been measured as 3.2 billion. This is of little concern though, as an error in this portion of the message would in no way hamper its meaning.

The next part of the message is more focused on us - we use the wavelength of the transmission as a baseline and tell the reader how tall we are based upon it (approximately 1.7 meters) and then depict a red human just to the right of the height measurement. This is intended to represent the fundamental human body plan and then show how many humans live on Earth (although the population has nearly doubled since then!) and then, we get to the set of pips shown as yellow in the figure. These are meant to represent the place the transmission came from - the third pip is raised above the rest and positioned beneath the feet of the human figure. Likewise, in purple at the very bottom, the dish is “pointing away” from Earth (not upside down as I have though for years!) in the opposite direction of the human and is shown with another length measurement, this time showing the diameter of the dish in wavelength of transmission units again. (NAIC 1975)

This is a rather spectacular depth of data for a mere 210 bytes. As a message, there is much to be said for it but it is not perfect. Aside from informational drift over time like better estimates of DNA base pairs, an ever-increasing world population and Pluto no longer numbering amongst the major planets, this message assumes that a species that receives it would decipher elements much as we do (not a bad guess since the number of protons is the most fundamental defining characteristic of an element), that they would derive symbolic meaning from a visually represented message (a species that “listens” to the sequence or tries to understand it as a terrifically large binary number will not be able to crack it), and most fundamentally, it presumes that someone is out there with a radio dish.

There can be no doubt that these limitations and others were considered during the genesis of the Arecibo broadcast and that it was sent anyways is a testament to the opportunity it presented. (NAIC 1975) Arecibo was the largest antenna on Earth and had been recently upgraded to be able to transmit to a small window of sky with tremendous power. In order to reach the entire sky with such intensity would require a 20 trillion watt broadcaster (SETIweb). Yet, as much information as the SETI team at Arecibo was able to squeeze into three minutes of transmission at 10 bits a second, this would likely only ever be a one-direction message, (a METI, not a CETI) as the direction of the broadcast was towards M13, a globular cluster 21,000 light years away from us. (NASAAmesweb) This does increase the need for information density, as whatever information sent to an intelligence that far away with not be updatable based on their feedback. Unlike the earlier attempts of the “Lunar” or “Solar System” age, the delay between transmission and reception is non-negligible and two way communication seems impossible (given the timescales of human culture) at distances beyond a few dozen light years - but this is a mark in the favor of the 1974 Arecibo message. It was an attempt to do as much as possible with the technology at hand. While the state of the art has changed, special accommodation must be made for the Arecibo message as humanities most powerful transmission as of that date, as well as forwarding a new paradigm and better practices within the METI field.

The other messages of the “interstellar” age are physical, much like the Apollo plaque. These are the plaques onboard the Pioneer spacecraft, and later, the Voyager missions. These do reflect a scientific mindset and a great step forward in how we think about communicating with non-humans. The Pioneer 10 & 11 probes were our first great interplanetary missions, but were destined to leave the Solar System after their flybys were completed. Onboard, small golden plaques (depicted below, figure 4.0) have figures inscribed on their surface. Designed by Frank Drake and Carl Sagan again, there are similarities and differences between it and the Arecibo message, even though they predate it.

Figure 4.0 The Pioneer plaque (Image credit NASAAmesweb)

Figure 5.0 Voyager “Golden Record” cover plate and inscription detail (image credit: NASAJPLweb)

Once again, the supremacy of hydrogen as the basis of the universe plays a critical role. While this is not a radio transmission, there is a correlation to the 21cm band - it is used as the length measurement again. The neutral hydrogen transition is depicted in the upper left corner and is used not only for length, but a time interval as well, since the transition would be expected to occur over 0.7 nanoseconds. (NASAJPLweb) Two human figures are shown (over-representing a white and fit minority population here on Earth) scaled to the spacecraft shown behind them. The iconic starburst behind them records the fingerprint in terms of pulsations from several pulsars and the positions of each of them with respect to our Sun - the idea being that this is a “return address” of sorts, indicating where we sent the probe from. The last part, the vector arrow within the diagrammatic solar system is the closest match to Arecibo, showing the planet of origin provided the ETI who uncovers the probe is sufficiently familiar with archery as we know it - or else the “arrow” as a vector is likely meaningless.

The later Voyager missions included their famous “Golden Records” which were again similar in many aspects but represent some revision and rethinking of the main ideas. Familiar to us already from figure 5.0 will be the hydrogen transition indicator and the diagram of pulsars for a measure of time, distance and a point of origin. Most of the new information is how to get the media contained within to play back correctly and in the preferred format. Within the case, a sophisticated record includes both images and sound detailing existence here on Earth, from greetings to jazz, baroque piano pieces to Senegalese drumming. The images contained include a familiar circle for calibration - and maybe a nod to von Littrow’s circle in the Sahara (D. Vakoch, pers. comm.) - as well as images of humans from conception to old age, cartoons of evolution and the movement of the continents, daily life intermixed with astronauts on space walks, it is an eclectic mix.

What would an ETI derive from this melange? Likely nothing. As the plate on the side of the Apollo lander is ostensibly addressed to extraterrestrials but actually intended for a human audience, so too are Voyager and Pioneer’s respective messages. According to Dr. Vakoch, their primary intent was less about reaching ETI’s in a way they will comprehend and more about the effects of the voyager recordings here on Earth. From his interview:

“we know it's reached millions of people here on Earth. So I think simply having to think through this process of how we would want to represent ourselves is the greatest benefit of that message.”

The messages they sent are scientifically motivated, but likely not encoded in a useful way. Both Grinspoon (2016) and Tarter (J. Tarter, pers. comm) agree that the intended recipients are likely humans and not extraterrestrial life since the spacecraft’s slow progress away from our star and small size make them unlikely targets for blind interception by another species. Grinspoon offers a dissenting opinion on some points, mentioning how while the information is flawed, a sufficiently advanced species might be able to fill in some of the holes, we are likely not the first species a civilization would have come in contact with if life is ubiquitous. (Grinspoon 2016)

The element of the Voyager message that is perhaps the greatest departure from previous attempts is the recorded media. The vessel that transported it is an inelegant one but the idea of sending lots of diverse information reflected better and more efficient ability to encode information in physical media. As our ability to store information increases over time we also see a shift in awareness over “who gets the mic(rophone)” both issues that stay with METI attempts moving from this point forward.

Vakoch (2000), Tarter (J. Tarter, pers. comm) and others agree expressly that the ongoing but gradual Moore’s law type changes in computational power and the discovery of extra-solar planets, or exoplanets as the deciding factor over the death of the interstellar epoch. The discovery of these worlds brought SETI and METI to the very forefront. Geoff Marcy, Deborah Fisher, and many other prominent astronomers published on these preliminary results from 1995 onward, and did not fail to consider the ramifications on the search for life beyond Earth. Instead of sending our far flung signals and probes, the potential now existed to learn a bit about the worlds that might exist out there and target the most Earth-like in case the life that arose their would have similar adaptation to our own. Between Papagiannis (1980) and Labeque et al (2005) there is a great shift in approach and thinking based upon this technological advancement. The astronomers presenting at the proceedings recorded in the first book are eagerly describing technologies that came to pass within the quarter century. The increases in spectrographic resolution and space telescopes of sufficient quality to locate exoplanets gave them the information needed to allow scientists to expand their horizons.

Another contemporaneous paradigm shaker was the discovery of extremophiles and the vast expansion of what might be considered “habitable” previously. Creatures here on Earth surviving and thriving in hotter than boiling water, extreme acids and the driest deserts know to science taught us that life as we know it is capable of surviving in places we thought impossible. This might seem to have limited applicability to the concept of sending communication when compared to the discovery and confirmation of exoplanets but there is a major connection. Dr Vakoch in his interview (D. Vakoch, pers. comm.) mentioned how much our understanding of life’s capabilities has expanded what we can consider “habitable”:

“In the earliest days of SETI this the targets are as were restricted to class G stars, which are sun is and then also F & K stars, but there's another type of star that's much more prevalent in our galactic neighborhood - red dwarfs M stars. In early stages of SETI those were completely written off as inappropriate for life. The reason being that if and it's related to how we've been thinking about habitable zones. So we think of the habitable zone is this distance from a star the planet needs to orbit in in order for there to be liquid water. So in our solar system, that's Earth and possibly Mars and so that really restricts the planets where there could be life.

With red dwarfs M Stars if you because they are much dimmer, that means that planets in the habitable zone would have to be much closer to that start to get a comparable amount of sunlight star life and there's a good chance they would be tidally locked meaning one side of the planet would always face toward the star one away from it. That leads to these ideas of a planet that's hellishly hot on one side and constantly frozen on the other not especially habitable.

The more we learned about extremophiles - we realized that once life has taken hold. I mean it can exist everywhere from frozen tundra of the Arctic to boiling hot acid springs, hydrothermal vents to the core of nuclear reactors. So we really need to be open to expanding our notion of the habitable zone and then even to redefine the habitable zone, so it isn't defined in terms of getting star light energy from.”

Both of these breakthroughs are regarded by Tarter (J. Tarter, pers. comm.) as the largest changes in the field since its inception and while both are fundamentally astronomical discoveries they reach far afield and bring in disciplines beyond the normal astronomical purview. They are the heralds of the most recent period, the “Interplanetary” epoch - in communication aimed not just at coarse starfields, but one informed by the knowledge of the worlds that might be there.

The “Interplanetary” epoch

Armed with the knowledge that planets did exist beyond our solar system and in great number, the idea of METI has come to the forefront of many projects. While governmental support for the SETI initiative has waxed and waned, these projects have never disappeared. The increase in sophistication of digital tools has meant that instead of an astronomer being hunched over a tuner, shifting between frequencies like Frank Drake in the project Ozma control booth, a digital system can monitor millions of frequencies simultaneously. For METI, a computer cannot make a perfect message, it requires imagination and insight to try and solve a puzzle like this - but it might help compress information or send regular pre-programmed broadcasts.

Some of the messages of the “Interplanetary” epoch embrace this digital revolution. The Cosmic Call and Cosmic Call 2 (CC 1 & 2) were sent from the same radar site as the first Morse broadcast towards Venus. The messages had built upon advances in signalling protocol and were much advanced from Arecibo - Images had frames around them to ensure that they were more likely to be received intact (D. Vakoch, pers. comm.) and they were repeated over the course of the broadcast to ensure that the message was more likely to be received intact. The first Cosmic Call was placed in 1999, it was transmitted 3 times, on May 24th, June 30th and July 1st of that year. The message duration was around 960 minutes, an impressive 320 times the length of the Arecibo message! It had to be much longer than the Arecibo message it part due to the fact that it was more of an “encyclopedia” approach and the Arecibo message itself was part of that encyclopedia. (Zaitsev 2011)

To read the encyclopedia, you would need a language - thankfully the core of the Cosmic Call team, Yvan Dutil, Stephane Dumas, and Alexander Zaitsev included Dumas and Dutil who had created a sort of “Esperanto of the stars”, what they dubbed the IRS, or Interstellar Rosetta Stone (Dumas-dutilweb) designed for being decrypted and to resist errors in transmission. The second Cosmic Call was nearly identical, sent 5 times in 2003, it included the entirety of CC1 alongside 12 binary images and a refinement of the IRS glossary. Sandwiched between the Cosmic Calls was the “Teen Age Message” in 2001. (Zaitsev 2011) It contained a slow doppler shifting wave based upon the signal we would receive on Earth with respect to the sun, ideally helping ETIs tune in before missing anything critical and also potentially helping inform where the signal originated (Earth). The second portion was a 14 minute long theremin performance which makes perfect sense in that music is as close to a universal language as we have on earth and theremin music is already digitally encoded sine waves, but at the same time, might be interpreted as a hostile action by an extraterrestrial with musical taste. The final part was greetings from Russian students and images selected by them. (Cerceau & Bilodeau 2012)

Both projects were identified by Tarter (J. Tarter, pers. comm) as early attempts to crowdsource and address the issues of who speaks for Earth by allowing for a broader swathe of humanity to include their message and both were the brainchild of Zaitsev. The Cosmic Call 1, the Teen Age Message, and Cosmic Call 2 melded public messages with scientifically encoded ones, allowing a more diverse group of earthlings to represent their planet. While this is regarded as a positive by Vakoch, it might be the case that the use of multiple independent but similar cyphers can only make a message harder to decode.

In fact, the crowdsourcing movement has become an integral part of several SETI and METI projects and ideas. SETI@home was launched in 1999 to allow people to donate computing time from their personal computers to the search for ETIs. (seti@homeweb) This had twofold benefit, allowing the SETI Institute to analyze signals without purchasing expensive hardware and building public interest and goodwill. Vakoch (D. Vakoch, pers. comm.) has solicited both advice and recording from the public to incorporate into messages to be transmitted. While adding more and more information might seem like it will only complicate the transmission when compared to the simple primer and bit of science that went into Arecibo, that might not be the case. Building on Ginspoon’s concept that if life is ubiquitous in the universe, ETIs might bump into moments of “first contact” with some frequency. Sending lots of greetings out in different directions might be the best strategy available.

In her 1993 paper Heidmann expresses that as information density increases, the feasibility of transmitting bulk data via the same type of binary signal used by Arecibo and Cosmic Call (CC) 1 & 2 becomes greater. Heidmann also agrees with Grinspoon (2016) that a species advanced enough to pick up our transmission is likely an old and successful one and we will likely not be the first species they have had first contact with (first contact for us, not them). I find this to be a very uplifting sentiment, as it allows for some of our limitations to be “covered” as it were by a more advanced recipient. To that end, Heidmann (1993) advocates for sending them our encyclopedias to show them humans as we are, with all the warts, not the curated and polished “voices from Earth” included with the Voyagers. In more recent publications, it seems that Vakoch has moved towards this point as well. In a paper (Vakoch 2011) he explores the ethics surrounding who communicates and what is communicated to another species to represent us. His conclusions show a stark contrast to the somewhat idealized male and female depicted on Pioneer. He emphasises the need for truth above all else, showing accurately the flaws and diversity of our species and the diversity of the other species on Earth. It would be critical as well to show our conflicts and our challenges, as a species that has survived for longer than us has likely dealt with some similar challenges along the way. It may very well provide the link and universal context we hope for.

Other benefits and lessons learned have included a wider approach to the ideas that might help us crack the case - a lesson hard learned after Lilly’s dolphins. The SETI and METI researchers have to have an open mind and broad imagination, but always maintain a firm footing in science and repeatability. The largest benefit to drawing from a wider pool of talent is that a solution to a problem one cannot solve might come from someone looking at it with a different background and a fresh set of eyes. Since no one has ever deciphered an alien message or located one amidst the background commotion of the universe, we do not know what will be required to do so.

These days, METI is more than an idea, it has become an entire separate entity from the SETI institute. METI international under the leadership of Doug Vakoch and have embraced a wide field of experts across disciplines. In more recent publications, SETI and METI have become much larger “tent” movements, embracing input from more disciplines to allow us better insight and to defeat the bias that comes from experts in a single field. This is seconded by Morrison in Swift’s (1990) interview. In his closing paragraph he encourages many mindsets of volunteers coming to the SETI initiative, all willing to meet regularly and discuss the strategies they are currently pursuing. He also stipulates that there should be no one, or at least very few who make SETI their sole vocation since the likelihood of success is so small and humans have a limited psychological capacity for failure. There is not just the avoidance of a negative, but a true positive in having more people share insight and decentralize the burden, they can add more imagination. From Vakoch:

“A stark reminder of the limitations of our imagination and how they influence our search strategies, you know, even in the 1960s as he was getting started Charles Townes who got a Nobel Prize for inventing the laser suggested looking for signals at optical frequencies and all of his colleagues said ‘Charlie, that’s ridiculous. There's no way it's another civilization has the capacity to transmit powerful laser signals!’, but then as the decades passed and we realized my goodness WE have the ability to do it ourselves (Schwartz and Townes 1961) it became plausible to look for signals from extraterrestrials. So we're always constrained by what we can imagine is possible.”

(D. Vakoch, pers. comm.)

This concern is echoed by both Tarter (Tarter et al. 2010) and Grinspoon (2016), that the limiting fact is our imagination. As Dr. Tarter said, “We cannot imagine what we cannot imagine” (J. Tarter, pers. comm.) so we inherently paint pictures of aliens and intelligences that run parallel to our own in some way. We are working to divorce ourselves from the all-too-easy notions of humans in funny colored skin with strange clothes and craniums. We may (as described by Drake himself) (Swift 1990) discover an extraterrestrial intelligence that is mistakable for a human at distance under non-ideal lighting conditions, but that is hard for me to swallow. On Earth alone we have seen a shocking diversity of shapes and solutions to a biological challenge that use non-homologous structures - I cannot imagine a human shaped extraterrestrial, but perhaps that is why we might find one, “we are prisoners of our own imaginations” is the final quote I recorded from Dr. Vakoch and perhaps the limitation we will never overcome - and yet, humanity does well with impossible challenges. By banding together our minds, our passions, our resources, and our imaginations we can be something gestalt, much greater than the sum of our parts. It is true that we cannot imagine what we cannot imagine, but the more people we have imagining, working, and thinking towards this goal, the less there will be that we have yet to imagine and we will all approach that limit asymptotically together.


From its early origins to today, imagination has been one of the greatest assets we have in the search for life beyond Earth. Over the past 200 or so years, we have allowed our imaginations to push us beyond what is currently possible to see what might one day be accomplished. Across many scientific aisles, hand have been extended and collaboration has bred new insights and ideas about how we might maka signal know and potentially understood. The messages we are capable of making and receiving today might fall outside what was imagined by the pioneers of the project long ago, but as intelligent citizens of the universe, they just might be able to decipher their meaning. Humanity as a species has built greatly upon their work and will hopefully keep building for a long time to come.

When the cornerstone is first laid down for a cathedral, or a block of stone carved for the base of a pyramid, it must be a challenge for the worker who exerts themselves to realize they will not see the fruits of that labor. When we transmit these signals we cannot know who will receive them or when. If they will be received at all, or if they will be dismissed by an uncomprehending recipient as just a strange bit of static but we must keep sending. With each broadcast our ideas have grown and developed, new technologies have been discovered and adapted to these ends and an era of advanced technology and electronic capability might make a continuous broadcast and monitoring system more feasible than ever before.

We must keep trying to find someone else out there. Humanity as a species has built itself up with communication, creativity, cleverness, and collaboration - it would be a profound betrayal of those fundamental principles that make us who we are to give up and resign ourselves to a lonely universe.


Articles and periodicals:

Cerceau, F. & Bilodeau, B. 2012 AcAau 78, 72

Cocconi, G. & Morrison, P. 1959 Natur, 184, 844

Collier’s Weekly (1901) 26, p4 (Tesla, Talking with the planets)

Heidmann, J. 1993. AcAau, 29, 233

Nieman, H., & Nieman, C. 1920 SciAm 122, 298

Raulin-Cerceau, F. 2010 AcAau 67, 1391

Sagan, C. 1971. BAAS 3, 465

Schwartz, R. & Townes, C. 1961 Natur 190, 205

Vakoch, D. 2011 AcAau, 46, 733

Vakoch, D. 2000 AcAau 46, 733

Zaitsev, A. 2012 AcAau 78, 16

Websites and web documents:

Dumas-dutilweb: PDF of their publication on the Interstellar Rosetta Stone or IRS (accessed 5/17/19)

JSTORweb Account of the “great hoax” (accessed 5/16/19)

NASAAmesweb: Ames mission info on Pioneer (accessed 5/10/19)

NASAJPLweb: Resorce page for NASA’s inscription (accessed 5/10/19)

seti@homeweb: Homepage for SETI institute’s SETI@home project (accessed 5/12/19)

SETIweb: SETI’s resource page explaining details of the Arecibo transmission (accessed 5/10/19)

SpaceWeb: What If Everybody Is Listening And Nobody Is Transmitting? (accessed 4/18/19)

TimeandDateweb: “Handy” sky measures (accessed 5/10/19)

UOregonweb: Arecibo as a 73 x 23 character message (accessed 5/19/19)

WWT: WorldWide telescope software - Produced by the American Astronomical society and Microsoft research


Vakoch, D. Interview via phone call 4/8/19



Ekers, R., Cullers, D., Billingham, J., & Scheffer, L. 2002 SETI 2020 (Mountain View: SETI press)

Grinspoon, D. 2004 Lonely Planets (New York, Harper Collins Publishing)

Grinspoon, D. 2016 Earth in Human Hands (New York, Grand Central Publishing)

Swift, D. 1990, SETI Pioneers (Tucson, University of Arizona Press)

Zaitsev, A. 2011, METI: Messaging to ExtraTerrestrial Intelligence: Searching for Extraterrestrial Intelligence (Berlin: Springer)

Conference Proceedings and notes:

Labeque, A., Leger, A., Valette, C., Brachet, F., & Chazelas, B. 2005 39TH ESLAB Symposium on Trends in Space Science and Cosmic Vision 2020, Noordwijk, The Netherlands

Papagiannis, M. 1980 A Joint Session of Commissions 16, 40, and 44, Montreal, Canada, During the IAU General Assembly, August, 1979

Staff of the National Astronomy and Ionosphere Center 1975 Icar 26, 462

Tarter, J. et al. 2010 Proceedings of the SPIE 7819, 2

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