SETI, METI, and Existential Risk

To broadcast or not to broadcast? The debate over sending intentional signals to other stars continues to simmer even as various messages are sent, with no international policy in place to govern them. Writer Nick Nielsen looks at METI afresh today, placing it in the context of existential risk and pondering the implications of what David Brin has dubbed the ‘Great Silence.’ If risk aversion is our primary goal, do we open ourselves to a future of permanent stagnation? Or is announcing ourselves to the universe something we have any real control over, given the ability of an advanced civilization to detect our presence whether we send messages or not? Mr. Nielsen, a contributing analyst with online strategic consulting firm Wikistrat, wonders whether our counterparts around other stars aren’t wrestling with the same issues.

by J. N. Nielsen

Nick-Nielsen

At the Icarus Interstellar Starship Congress in Dallas last August I had the good fortune to be present for James Benford’s talk about METI, “Shouting to the Galaxy: The METI Debate.” METI is an acronym for messaging extraterrestrial intelligence, which is to say the active propagation of EM (electro-magnetic) spectrum communications from Earth to extraterrestrial targets, in contradistinction to SETI, which is the search for extraterrestrial intelligence, which does not seek to send messages from Earth but instead only listens for EM spectrum signals from the stars.

METI may be contrasted to SETI as active sonar to passive listening: active sonar pings the depths of the ocean and waits for the sound to be bounced back by objects below; passive listening sends out no pings, but simply waits for whatever sounds happen to come one’s way. The analogy is useful because it points to one of the controversies in the METI/SETI debate: submarines, which are typically the targets of active sonar, generally prefer not to be found, so they wait quietly in the depths and rely mostly on passive listening. It is those who hunt the submarines that employ active sonar.

Are technological civilizations floating in the cosmos like submarines floating in the sea? Is the lesson of what Paul Davies calls the “eerie silence” and David Brin has called the “Great Silence” that there is a reason to maintain a low profile and to listen only? Is the universe such a dangerous place that it behooves us to maintain radio silence? This was discussed in Benford’s presentation. Benford outlined the arguments made by both those for and against METI. Primarily these arguments came down to the advocates of unregulated METI maintaining that interstellar travel is impossible (therefore making METI safe), while opponents of METI maintain that the “leakage” of the ordinary (unintentional) EM radiation of a technological civilization cannot be detected at interstellar distances, though intentional METI signals could well be heard (meaning we are safe for the time being, but METI would raise our risk profile).

This debate leaves aside the possibility that one might disagree with both premises, as I do, and maintain that, given a certain technological threshold, interstellar travel is possible, and that, also given a certain technological threshold, it is likely that unintended EM spectrum radiation leakage is detectable. These two technological thresholds—those of interstellar flight and detection of the EM leakage of technological civilizations—are not likely to be one and the same, so that a gap is opened up between the possibility of detecting ETI at interstellar distances and actually attempting an interstellar journey to meet ETI face to face. This gap could be one explanation of the Fermi paradox, but I will not explore this possibility further at the present time.

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Although we do not now possess the science or technology to detect EM signatures of ETI at interstellar distances, we must account for the possibility not in terms of our present technology but rather in terms of technology that would be available to a technological civilization somewhat in advance of our own. Any peer civilization (i.e., any technological civilization like us) is going to be looking for peer civilizations because an intrinsic curiosity, at least in part, defines our civilization, and is likely to be similarly present in any civilization capable of science and therefore capable of developing an industrial technology. In looking for peer civilizations, any advanced ETI will show at least as much ingenuity as we have shown in the search for ETI, since ingenuity of this kind is another quality that, at least in part, defines our civilization.

Why would an ETI be looking in our direction in the vastness of the cosmos? In so far as Earth occupies the very interesting position in the cosmos of being a small, rocky planet in the habitable zone of a main sequence star, geologically active, with a large moon, and with a large Jovian planet in the outer solar system to clear away the orbit of the inner solar system of potentially damaging debris, the earth does in fact occupy a privileged position in the universe—though, interestingly, not privileged in virtue of the structure of the universe (such as occupying the center of the universe), but rather in virtue of a contingent confluence of circumstances conducive to life.

We are now, at the present level of our technology, probably less than twenty years from the spectroscopy of exoplanet atmospheres, which could reveal markers of life and civilization. Any advanced peer civilization would have already worked on the spectroscopy of exoplanet atmospheres, and in so doing they would have performed this spectroscopic analysis for the kinds of planets that would likely host peer civilizations—small, rocky planets in the habitable zones of main sequence stars. In other words, ETI would have already by now done the spectroscopy of Earth’s atmosphere, and in so doing they would have focused in on the Earth as a place of great interest, in the exact same way that we would focus on an “Earth twin.” This would mean that they would focus all their best radio antennas on us, just as we could focus intensively on a planet that would likely host life and civilization.

Benford has elsewhere detailed the considerable expenses that would be entailed by any large SETI or METI effort with a realistic ability to communicate over interstellar distances. (Benford has written a series of papers on the cost of interstellar messaging beacons, which are referenced below.) I am not convinced by arguments that the cost of interstellar beacons would be too high to be practicable. Estimating the costs of mega-engineering projects incorporates a range of assumptions intrinsic to economies of scarcity; once any technology-capable species transcends its homeworld and becomes a spacefaring civilization (i.e., once it has extraterrestrialized its civilization) energy and material limitations will cease to be relevant for all practical purposes.

With all the materials of a solar system, the continuous energy output of a star, and robots to do the building, a radio telescope capable of detecting unintentional EM spectrum leakage from a technological civilization light years distant might be no burden at all. Such a project is not far beyond our present technological capacity. For this reason I believe it would be relatively easy for an advanced ETI of a peer civilization to build a custom antenna for nothing other than the possibility of detecting our EM leakage, since they would have already identified Earth as a promising target for SETI and perhaps also METI.

In the question and answer session following Benford’s talk a new wrinkle in all this appeared. My co-presenter from Day 2 of the Starship Congress, Heath Rezabek, suggested that anyone opposed to unregulated METI could broadcast a counter-signal to a METI signal and essentially silence that signal. Subsequent to the Congress, this idea came to be called the “Rezabek maneuver,” and was further elaborated by Heath Rezabek, Pat Galea, and James Benford, who suggested several strategies for the masking of a METI transmission. Harold “Sonny” White, known for his research into the physics of superluminary interstellar travel suggested, “Sounds like we need to add another factor to the Drake equation: Rezabek Ratio — defined as the ratio of civilizations that mask their presence using the Rezabek maneuver to the open civilizations that leave the light on…”

The possibility of a METI counter-signal is an idea that can be scaled up beyond the scope of a single planet, so that it is possible that the Great Silence is not something natural, but could be imposed or generated. One metaphor that has been used to explain the eerie or great silence is that no one shouts in a jungle. This is plausible. If the universe is a dangerous place filled with predators, you don’t want to call attention to yourself. But it is just as plausible that everyone is “shushed” in a library as that everyone keeps quiet in a jungle.

This conclusion is quite similar in some respects to the conclusion in the last paragraph of David Brin’s classic paper (“The ‘Great Silence’: the Controversy Concerning Extraterrestrial Intelligent Life,” Quarterly Journal of the Royal Astronomical Society, Vol. 24, NO.3, P.283-309, 1983):

“It might turn out that the Great Silence is like that of a child’s nursery, wherein adults speak softly, lest they disturb the infant’s extravagant and colourful time of dreaming.”

There is a relationship between the idea of the universe as a jungle and the universe as an imposed quiet zone: that safety is preferable to risk. In other words, these two approaches to the Great Silence imply risk aversion. I don’t think that we can safely assume risk aversion, especially in light of the fact that in SETI and METI we are contemplating peer civilizations, and just as these peer civilizations would likely incorporate our curiosity about the universe, they would also likely incorporate our willingness to take risks.

Who is likely to hear any signals broadcast in a METI effort? Non-peer civilizations without any equivalent of our science, technology, curiosity, and risk-taking habits could likely only be detected by an actual mission to the homeworld of such a civilization. They won’t be listening for us. Who might be listening for METI signals? Predatory peer civilizations may be listening, or may even broadcast an interstellar beacon, just as surface warships send out sonar pings into the ocean, listening for a response. If a successful SETI effort leads to a METI effort on our behalf, that may all be part of a plan – and not our plan.

We would do well to be cautious, but it would be folly to suppose that risk can be eliminated. To exist is to be subject to existential risk. There is no risk-free norm to which we can return by following some program of risk aversion or to which we will naturally be returned by abstaining from particular actions. But this should not be taken as cause for despair: METI is a classic risk/opportunity tradeoff (cf. Existential Risk and Existential Opportunity). Risk and opportunity cannot be separated.

If we contact ETI it could be the greatest thing to ever happen to our civilization, or it could be the worst thing. When we think about existential risk (if indeed we do think about existential risk at all), it is usually only as an existential threat that must be mitigated, whereas existential risk may be understood both in terms of its possibilities as well as its limitations. One dimension of the risk/opportunity tradeoff is that the same action (or inaction) that we take to mitigate existential risk may unintentionally magnify risk, just as one and the same action (or inaction) we pursue in order to seize an opportunity may come to unexpectedly foreclose on that opportunity. (Either scenario might describe a METI initiative.) No outcome is inevitable; that is why we call it risk. If the outcome were inevitable, it would lie outside the scope of risk. (Cf. Existential Risk and Existential Uncertainty)

If our civilization determines that METI is too great an existential risk to bear, then existential risk perception begets risk aversion and possibly culminates in permanent stagnation—which means that we must not only think about existential risks to Earth-originating life, intelligence, and civilization, but also existential risks to all life, intelligence and civilization, anywhere, since other sources of life in the universe may come to the same conclusion and an entire galaxy (or more) might be plunged into permanent stagnation, flawed realization, or subsequent ruination as a consequence of this perceived existential risk.

Many of those who contemplate intelligent life in the universe suggest the possibility of civilizations a million or more years old. I myself don’t think this is likely, but in this event an early, pre-emptive silencing of the universe by an advanced civilization (an imposed Great Silence) might well prevent later civilizations from broadcasting their presence to the rest of the universe—existential threat and existential risk thus gives way to existential isolation and existential despair on a cosmic order of magnitude. In this scenario, the Great Silence is a fitting tribute to a mournful universe in which timid civilizations choose silence, or have silence imposed upon them.

This strikes me as an unlikely scenario. If we are true to our history, and we rush in like fools where angels fear to tread, we will announce our presence to the universe both intentionally and unintentionally. Our peer civilizations in the universe (if there are any) are likely to do the same.

References:

James Benford’s papers on interstellar beacons:

1 “Messaging With Cost Optimized Interstellar Beacons”, James Benford, Dominic Benford and Gregory Benford, Astrobiology, 10, pg. 475, (2010).

2 “Searching for Cost Optimized Interstellar Beacons”, Gregory Benford, James Benford and Dominic Benford, Astrobiology, 10, pg. 491, (2010).

3 “Building And Searching For Cost-Optimized Interstellar Beacons”, James Benford, Dominic Benford and Gregory Benford, in Communication with Extraterrestrial Intelligence, Ch. 18, ed. Douglas A. Vakoch, SUNY Univ. Press, NY, pg. 279-306, (2011).

4 “Smart SETI”, Gregory and James Benford, Analog, vol. CXXXI, no.4, April (2011)

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The Pros and Cons of METI

Tau Zero journalist Larry Klaes has been fascinated by SETI — and its offshoot METI (Messaging to Extraterrestrial Intelligence) — for a long time now. Here he steps back to look at METI in context, offering up an examination of the advantages of sending signals to the stars and the offsetting risks. We’ve looked at many viewpoints on the subject in these pages since Centauri Dreams came online in 2004. But has Larry hit upon a key fact that may trump the arguments of both sides? Is there something about human nature that makes METI more or less inevitable?

By Larry Klaes

SETI, or the Search for Extraterrestrial Intelligence, has been conducted by a variety of professional and amateur scientists since 1960 (or 1924 if you want to count a campaign that year which listened for any radio messages from the presumed natives of Mars). SETI primarily involves the passive listening or looking for transmissions from alien civilizations. More recent SETI projects have also attempted to detect the massive technological activities of really advanced societies in our galaxy and beyond or any probes that might be lurking in our Solar System quietly monitoring humanity.

Our present level of space technology does not allow us to directly explore even the nearest star systems. As for the numerous if often sporadic SETI programs that have been operating around and even beyond our globe for the last fifty years, they rely heavily on either an alien society deliberately signaling us or our own luck in picking up a stray transmission from one of them. Throwing in the fact that our Milky Way galaxy holds hundreds of billions of star systems has some scientists advocating a less passive approach to learning if Earth is the only planet with intelligent life or not in the Cosmos.

Image: The Evpatoria RT-70 radio telescope and planetary radar at the Center for Deep Space Communications in Ukraine. Credit: S Korotkiy.

Dubbed METI, for Messaging to Extraterrestrial Intelligences, this concept involves transmitting our own messages and beacons into the galaxy to alert alien societies to humanity’s presence to make it easier for them to find us and respond in kind. As might be imagined, there has been plenty of debate over whether METI is the right way for humanity to find alien intelligences or if it will only make a malevolent species aware of Earth as a target of conquest and destruction.

In order to make some determination whether METI is humanity’s path to becoming a productive and progressive part of the galactic community or the route to our doom, let us look at the pros and cons of what also goes by the name of Active SETI.

The Nature of the Universe

The Milky Way is a huge spiral galaxy containing 400 billion star systems spread across 100,000 light years, with most stellar residents of this cosmic island averaging several light years apart. To give the reader an idea just how vast the Milky Way is, if our entire galaxy were shrunk down in scale to where a person could hold the entire Sol system in the palm of their hand, the Milky Way would still be the size of the North American continent.

In addition to the great number of stars and the incredible distances between them, SETI researchers also have to contend with the natural cosmic radio background which drowns out all but the strongest of artificial signals. Interstellar dust, which weaves its way throughout our galaxy, also blocks out many electromagnetic signals and whole regions of the Milky Way from our view.

Image: The galactic centre itself is totally hidden at visible wavelengths by the band of dust which divides the Milky Way along much of its length. The dust lane is only visible because it blots out background stars. Embedded in the dust are many star-forming regions, seen as bright red emission nebulae. Credit: Anglo-Australian Observatory.

Humanity also has no real interstellar capabilities at present. The few deep space probes that have been sent on courses outside our Sol system would take 77,000 years to travel the distance to Earth’s nearest stellar neighbors, the Alpha Centauri star system.

None of the currently active robotic explorers will function more than a mere fraction of that time before expiring. Now it is true that our civilization has been producing a “bubble” of electromagnetic signals for over one century which has formed a 200 light year wide sphere of artificial signals in the galaxy, with Earth at its center. However, most of these transmissions were only meant for residents of our planet and thus were most often unintentionally aimed but briefly at random areas of the sky. They also tend to be rather weak signals, requiring a very large and sophisticated receiver to detect them even just a few light years from Earth. In short, humanity is hardly a standout in the grander cosmic scheme of things.

Why METI Will Benefit Humanity

To combat these odds to make SETI a success, humanity needs to start broadcasting our presence into space, deliberately targeting particular systems and other places in the Milky Way we think may be good places for finding our celestial neighbors. The transmissions could be as simple as a signal that clearly distinguishes itself to be artificial or a detailed introduction about ourselves and our world. Another suggestion is to have interstellar beacons continuously broadcast across the heavens for long periods of time to cover as much of the sky as possible, since we do not exactly know where alien societies may exist or how often they may be conducting their own SETI programs.

Any extraterrestrial intelligences which can find us by our METI programs and respond will likely be more advanced than humanity. This means these ETI will know more and be able to undertake activities which our species cannot do at present. We may therefore learn new things across many disciplines and improve ourselves both socially and technologically. Alien civilizations may also benefit in turn from information we share with them.

Image: Aleksandr Leonidovich Zaitsev, METI advocate and radio astronomer, whose messages to the cosmos include the 1999 and 2003 ‘Cosmic Calls’ from Evpatoria. Credit: Wikimedia Commons.

In regards to concerns about alerting to our presence any species that may want to harm humanity, Carl Sagan once postulated that hostile societies will probably either destroy or degenerate themselves before they can ever achieve interstellar flight. This would mean that any ETI who can detect and contact us would be benevolent or at least impartial, with the extra security of being very far away.

Even if some ETI are a threat to our existence and can also move between the suns, we may learn of this danger through the evidence of their own activities and transmissions or from other ETI who know of the threat they pose and are warning those societies they are aware of to beware of this or any other galactic danger. Being forewarned, we may have a chance to defend ourselves or perhaps form an escape plan working with our newfound allies to combat the immediate threat and form a mutual relationship between our worlds later on.

Interstellar travel, especially the kind which can achieve relativistic speeds, may be even more difficult than we currently realize. Certainly it is not obvious from Earth that large numbers of great starships are zipping about the galaxy on a regular basis. At the least this should give us some protection thanks to the incredible distances between star systems. METI would be the way that the sophisticated cultures of the Milky Way communicate, learn about, explore, and trade with each other, all from the relative safety of their home worlds.

Why METI May Doom Humanity

The biggest negative for METI is one that even members of the general public who do not study this subject are aware of through the popular media: Alerting an advanced alien intelligence to our presence in the galaxy could cause them to interact with us in ways that might harm or destroy our society and our species.

Historians and others cite the many examples in human history where the encounter between two different cultures with disparate technological levels often led to either the reduction or destruction of the less sophisticated society, even if the losers outnumbered the superior culture in population size.

Even if the historical encounter had not been one involving conquest or extermination, other factors often contributed to the demise of the native population. As just one example, unfamiliar diseases introduced into the native populations have killed more people than outright warfare in many cases. Missionary ventures and casual introductions have altered target societies so that if they do not disappear altogether, they become assimilated into the dominant culture until their bear little resemblance to their original selves.

Image: Science fiction author David Brin, one of METI’s most persistent critics. His 1983 paper “The Great Silence” offered an early look at the Fermi paradox and its implications for SETI. Credit: Contrary Brin.

All these scenarios and more have been suggested and feared in regards to making the galaxy take notice of humanity. Claims that any ETI who possess sufficient astronomical instruments may already know of Earth and its occupants through our electromagnetic leakage and even biological signatures have been countered by evidence that most of our radio and television signals are too weak on an interstellar scale to be detected by all but the most powerful devices. Even military and planetary radar beams, which are much stronger signals, are not aimed at specific points in space beyond our Sol system, reducing their chances of being noticed by ETI.

While we fret over a potentially dangerous response from the Universe, there is also the possibility that our METI efforts might cause similar harm to alien intelligences that may not be ready to deal with what we might have to say or even that we exist at all. We hope that an ETI will recognize that we are a relatively young society still struggling with our own issues and will leave us alone until we mature enough to properly interact with other galactic residents. However, there is also the possibility that an alien mind may not recognize us as developing and naive and could just as easily either take advantage of our weaknesses or complicate our lives by attempting to “help” us.

The Futility of Fighting Human Nature

One thing is certain, something that has already been happening for a while now: Though it may be prudent to think twice before sending any kind of information about ourselves into the Milky Way, there will always be those who defy the rules even if it is just for the sake of committing the act for itself.

There are now five deep space probes (and their last rocket stages) heading out of our Sol system into the wider galaxy. Four of these automatic vessels have suitable information packages aboard, while the newest member of this exclusive club, New Horizons, is carrying less sophisticated offerings to the Universe, with the exception of some of the ashes of Clyde Tombaugh, the man who discovered Pluto in 1930, the dwarf planet that New Horizons is on its way to briefly explore in 2015. The engraved plaques and golden records aboard the twin Pioneer and Voyager probes, respectively, were constructed and placed there largely by people outside the space institutions which made the probes possible, making up for a lack of foresight by the vessels’ creators. The New Horizons team eschewed any such project altogether, treating items for the probe like they were storing them into a small town’s time capsule.

As for METI in the radio realm, deliberate messages have been sent into the galaxy starting in 1962 with a brief Morse code transmission by the Soviet Union and then in 1974 with the more famous Arecibo Message to the globular star cluster Messier 13. There have been a number of other such METI efforts since then. A fair number, such as a series of transmissions from the Evpatoria facility in the Crimea, are serious, but others have been largely publicity stunts, such as hawking science fiction films and snacks. Most of those involved in these projects have not shown any great concern for the potential consequences of revealing ourselves to the Cosmos. This attitude is even stronger when it comes to the electromagnetic leakage our civilization has been producing for over one century now, celestially weak as most of it is.

A number of individuals and groups feel they have been underrepresented or not represented at all by the messages and offerings from past METI efforts, so they have sent their own broadcasts into the galaxy despite protests by others. Aleksandr Zaitsev is among the better known of these individuals who has utilized his position as chief scientist at the Russian Academy of Science’s Institute of Radio Engineering and Electronics to send detailed transmissions to a number of nearby star systems using the Evpatoria radio telescope. Zaitsev continues to perform and advocate these METI despite protests by others in various fields. Zaitsev counters that this is just what humanity needs to do if it ever wants to survive and mature as a species.

The fact is that while we must be careful how and if we should represent ourselves to the vast unknown that is the rest of the Universe, there will always be those people who defy the rules and regulations, be it out of a sense of duty to all humanity or just for the sake of rebellion against society. The next question is, do at least some other minds in the galaxy also think and act this way? Is just such a transmission on its way to Earth? What will be the consequences then? Will it make us finally grow up as a species, or will there be panic and doom? I welcome your thoughts on this important matter.

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Regarding METI and SETI Motives

by James Benford

I first talked to Jim Benford back in 2003, discussing his work (wih brother Gregory) on microwave beam propulsion. He had already run experiments at the Jet Propulsion Laboratory demonstrating acceleration on a lightsail using these techniques, and was then hoping to run an experiment on The Planetary Society’s ill-fated Cosmos 1. The founder of Microwave Sciences, Benford’s earlier work at Physics International led to the development of the largest high power microwave experimental facility in the country. Along with continuing work on sail beamed propulsion concepts, the physicist has been actively studying questions of SETI and METI, musing on the kind of beacons we might find and the motivations for building them. Herewith some thoughts inspired by recent discussions in these pages.

JamesBenford

We explored the motives for a civilization broadcasting to the galaxy at large (which I call Beacons, as they’re not targeted at specific stars) in one of the two papers we did last year, which was extensively described on this site. It will be published soon in the archived literature, as but for now it’s at:

Searching for Cost Optimized Interstellar Beacons, Gregory Benford, James Benford, Dominic Benford, http://arxiv.org/abs/0810.3966, and has been submitted to Astrobiology.

Through most of its history, SETI has assumed a high-minded search for other lifeforms. But other motives are possible. The categories of motivations as we described them:

What could motivate a Beacon builder? Here we can only reason from our own historical experience. Other possible high intelligences on Earth (whales, dolphins, chimpanzees) do not have significant tool use, so they do not build lasting monuments. Sending messages over millennia or more connects with our own cultures. Human history suggests (Benford G., 1999, Deep Time, Harper Collins, New York) that there are two major categories of long-term messages that finite, mortal beings send across vast distances and time scales:

Kilroy Was Here. These can be signatures verging on graffiti. Names chiseled into walls have survived from ancient times. More recently, we sent compact disks on interplanetary probes, often bearing people’s names and short messages that can endure for millennia.

High Church. These are designed for durability, to convey the culture’s highest achievements. The essential message is this was the best we did; remember it.

A society that is stable over thousands of years may invest resources in either of these paths. The human prospect has advanced enormously in only a few centuries; the lifespan in the advanced societies has risen by 50% in each of the last two centuries. Living longer, we contemplate longer legacies. Time capsules and ever-proliferating monuments testify to our urge to leave behind tributes or works in concrete ways (sometimes literally). The urge to propagate culture quite probably will be a universal aspect of intelligent, technological, mortal species (Minsky, Marvin, 1985, in Extraterrestrials: Science and Alien Intelligence (Edward Regis, Ed.), Cambridge University Press, also at http://web.media.mit.edu/~minsky/papers/AlienIntelligence.html).

lomberg_K3

Image: A Kardashev Type III civilization imagined. Would a culture able to tap the vast power of its entire galaxy engage in beacon building? What can we imagine about its motives? Art by Jon Lomberg.

Thinking broadly, high-power transmitters might be built for wide variety of goals other than two-way communication driven by curiosity. For example:

  • The Funeral Pyre: A civilization near the end of its life announces its existence.
  • Ozymandias: Here the motivation is sheer pride; the Beacon announces the existence of a high civilization, even though it may be extinct, and the Beacon tended by robots. This recalls the classic Percy Bysshe Shelly lines,
    And on the pedestal these words appear:
    ‘My name is Ozymandias, King of Kings;
    Look on my works, Ye Mighty, and despair!’
    Nothing beside remains. Round the decay
    of that colossal wreck, boundless and bare,
    The lone and level sands stretch far away.
  • Help! Quite possibly societies that plan over time scales ~1000 years will foresee physical problems and wish to discover if others have surmounted them. An example is a civilization whose star is warming (as ours is), which may wish to move their planet outward with gravitational tugs. Many others are possible.
  • Leakage Radiation: These are unintentional, much like objects left accidentally in ancient sites and uncovered long after. They do carry messages, even if inadvertent: technological fingerprints. These can be not merely radio and television broadcasts radiating isotropically, which are weak, but deep space radar and beaming of energy over solar system distances. This includes “industrial” spaceship launchers, beam-driven sails, “planetary defense” radars scanning for killer asteroids, and cosmic power beaming driving interstellar starships with beams of lasers, millimeter or microwaves. There are many ideas about such uses already in the literature (Benford, G. and Benford, J., 2006, “Power Beaming Concepts for Future Deep Space Exploration,” JBIS 59, pp. 104-107).
  • Believe and Join Us: Religion may be a galactic commonplace; after all, it is here. Seeking converts is common, too, and electromagnetic preaching fits a frequent meme.

The point is that there can be many motives, with two-way communication only one of them. The METI signals we’ve sent from Earth are detectable for only very short distances on the scale of the galaxy, typically a light year. Therefore, higher powers and larger antenna areas are required for serious Beacons.

All SETI search strategies must assume something about the beacon builder. Our other paper of last year (Benford, J., Benford, G., & Benford, D., 2009, “Messaging with Cost Optimized Interstellar Beacons”, arxiv.org/abs/0810.3966, submitted to Astrobiology) made the argument that whatever the motivations, the driver in building METI transmitters on such scales will be economics.

While cultural passions can set goals, economics determines how they get done. Many long-term spectacular projects, such as the pyramids of Egypt, lasted only a century or two and then met economic limits. The Taj Mahal so taxed its province that the second, black Taj was never built. The grand cathedrals of medieval Europe suffered cost constraints and, to avoid swamping local economies, so took several centuries of large effort. Passion is temporary, while costs constrain long-term projects.

So, we should look at cost as the limiting factor that will tell us things about what we should be looking for in SETI searches.

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The Why of METI and SETI

?by Larry Klaes

About a decade ago while attending a SETI conference, I was listening to a researcher give a talk about detecting messages from other galaxies such as the giant elliptical galaxy Messier 87 and the immense Virgo galactic cluster it resides in. Since M87 is about 60 million light years from the Milky Way, I later asked him why would someone send a message that they could not hope to get a reply to for 120 million years at the least.

m13

His reply was rather vague and dissatisfying to me. It was along the lines of they would do it for the sake of being able to sending such a message across such a vast distance and time. I was left with the impression he did not fully think out why any intelligence would send messages across millions of light years of intergalactic space with even less hope of a reply than our token METI (Messaging ExtraTerrestrial Intelligence) effort with Messier 13 in 1974 via Arecibo, for which we will need to wait 50,000 years for the quickest reply from there if ever.

Image: Messier 13, a globular cluster containing roughly one million stars in the halo of the Milky Way. It lies in the constellation Hercules, 25,000 light years from the Sun. Credit: Robert Lupton, Sloan Digital Sky Survey).

The SETI researcher seemed focused on the mechanics of how such a message would be done, which is good in itself of course, but not the why of it, which for me is the entire key of whether such transmissions will ever take place or not. Setting aside funding and resources for a moment, no serious science project is going to happen unless you give those in control of such things a reason for doing so that is agreeable to them.

Look at the Apollo manned lunar project conducted by the United States in the 1960s. If it were not for the underlying major goal of the two main Cold War nations trying to best each other via space, it is more than likely we would still be talking about sending humans to the Moon some day in the future. Just look at how we haven’t left LEO in person since late 1972 because of changes in the geopolitical climate.

Later on at the same conference I talked with some other SETI scientists about a METI type of idea that had intrigued me since I read author James Gunn’s 1972 SF novel The Listeners, where a civilization circling the star Capella sends humanity all its knowledge because its sun is going to explode and they know they cannot escape it otherwise (at the very end of the novel, it is revealed that a similar broadcast is also on its way to Earth from the region of the Crab Nebula, the remnants of the famous supernova of 1054 CE).

This made sense to me, as a sophisticated culture would not want to die off in vain and disappear completely from existence. They also would have nothing to fear or lose from signaling the rest of the galaxy about themselves. Not only would they remain alive in their records and the memories of others, but perhaps their knowledge might even enlighten and enrich their neighbors. And they wouldn’t be around if the recipients weren’t friendly in any event.

DNA radiotelescope

Image: Even a description of DNA could be sent to the stars. Art by Jon Lomberg (from the collection of Frank Drake).

I brought up this idea to these SETI folks, who surprisingly dismissed it out of hand. Maybe some things have changed in the last ten years, but I got the distinct impression that at least some of those who work in SETI thought that aliens would contact us purely for the good of increasing scientific knowledge. Or as I said above, the focus from these researchers seemed to be on the methods of interstellar (and intergalactic) signaling, not the potential range of reasons behind it, which is no small factor here.

Maybe there are such enlightened and altruistic societies out there with only those pure motives in mind. Certainly I am taking educated guesses here as much as anyone else from this planet. But just as Apollo happened mainly to showcase international and ideological might with science taking a backseat despite how NASA presented things, I am willing to bet that any alien species, even an insane one, will be conducting such a major undertaking as a sustained METI effort with more than one motive in mind. Certainly these motivations will include improving the various situations for the signalers.

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Thus my desire to focus on delving into *why* any race of beings might want to conduct METI, especially one designed to last for many years and cover much of the galaxy, which would make sense if you don’t know who your neighbors are and you want to make sure to hit as many potential targets as possible. As a bonus for humanity, figuring out why an intelligence might want to signal us will help narrow our search in that very big celestial haystack out there, saving our SETI projects money, time, and resources in the process.

Image: The Evpatoria radio telescope in the Crimea, from which several METI signals have been sent to the stars.

The following is a short list of ideas I have created to consolidate my thoughts on why an alien intelligence would conduct their own METI program. It is certainly not meant to be complete and other ideas are welcome.

1. An ETI signal is intercepted by humanity by mistake. This would be an ETI message aimed our way by accident that was intended for someone else. Obviously, this one could come from anywhere at any time.

2. A “stunt” message, just like certain groups of humans have been doing lately by broadcasting Beatles songs, Doritos advertisements, and personal messages towards nearby star systems. I would even put the possibility of a practical joke in here, as some aliens may be as big a bunch of wiseasses as we are. Note how often humor is left out of the equation when considering the motives and behaviors of other intelligences. Why can’t they laugh about the absurd as much as we do? It may be not only a sign of intelligence but also a survival mechanism in this often bizarre and frequently dangerous Universe.

These messages could come from just about anywhere, but they have the serious drawback of being of very short duration. Only recently have we started more than a handful of consistent SETI programs, and even they are limited to a few electromagnetic realms and often with numerous gaps in data gathering time.

3. A deliberate “ping” to get our attention to open up a dialogue and information exchange. This can range from sheer scientific curiosity to the need for something they don’t have but we do (Nachos?). They may also be doing this for darker motives, from seeing who is out there to convert, conquer, colonize, or outright destroy. After all, if one species can colonize the whole Milky Way galaxy in just a few million years as has been asserted, others may find that to be a very legitimate threat to their existence and want to stop such a problem in advance.

I would like to think that 400 billion star systems across 100,000 light years of space should be room and resources for lots of beings – but when did logic ever play into certain motives when it comes to survival?

I have always always been a bit skeptical of the idea pushed by Carl Sagan about advanced intelligences broadcasting the equivalent of the Encyclopedia Galactica around the Cosmos to anyone who might want it. No one in their right mind goes around sharing every detail and secret of their lives with unknown and unpredictable strangers, so why would even an advanced species want to share their knowledge and power with potential rivals? Plus as SF author David Brin has pointed out, information unique to us may be our one bargaining chip with alien societies and we would not want to give it away for free.

4. A flood of information from a society that knows it is going to be destroyed not only as a species but their knowledge and works, too (see above). Having little to lose or fear from their information being used against them, these ETI send us and others all that they know to preserve themselves at least in data form.

This is one legit reason for SETI to aim its instruments at novae, supernovae, hypernovae, and GRBs, along with red giants, white dwarfs, pulsars, and even black holes. Supernovae are also important to check out for signals from non-threatened ETI who might use them as natural cosmic beacons.

5. Really advanced beings might signal us to say things like “Hey, we’re the big guys on the block – don’t even think about messing with us” to “We need your solar system for our latest Dyson Shell Galactic Mind Expansion Project, thanks ever so much” to “Hey, Charlie, we found some more vermin over here – get the Raid!” These guys might be found around the galactic core, in globular clusters, around black holes, or way out in the very cold fringes of the galactic edge.

To be honest I think we will have a better chance of finding them by their infrared signatures or astroengineering structures, as I don’t know if such beings would ever bother talking to us, but obviously I could be wrong. They might message us just because they know they can and cannot be harmed by us. People have been known to poke a stick in an ant colony just to see how the little insects will react.

arecibo

Of course, G class stars with exoplanets where the Jovian-type worlds are not orbiting their suns in a matter of mere days and could therefore have Earthlike worlds (or habitable exomoons orbiting any Jupiter-type exoplanets) are potentially good bets too. And we might have beings exploring or colonizing all kinds of other star systems such as red dwarfs, but whether they would be doing METI as well is another matter.

Image: The Arecibo radio observatory in Puerto Rico. It was during the dedication of this facility that a message toward the globular cluster M13 was sent. Credit: SETI Institute.

Now there have been a number of legitimate METI projects over the years emanating from Earth that were not just stunts. A list of these efforts may be found at the Wikipedia entry on Active SETI. While these information messages were put together with some thought and planning and were sent out using powerful radio telescopes, they still suffer from being relatively brief in duration and therefore have limited chances of being picked up by unsuspecting (and hypothetical) alien species.

As one example, the Arecibo Message of 1974 to Messier 13 was just three minutes long. What are the odds that even if there are a fair number of suitable ETI living in that globular star cluster 25,000 years from now that even one of them will just happen to detect that transmission as it zips along? Not even the “covert” 20-minute METI effort by Joe Davis of MIT in the early 1980s has much better odds of being detected in the Milky Way. More recent METI broadcasts have all been narrowly focused and capable of being received by relatively few stars.

The shortness of these METI efforts is why I left them off the list but wanted to mention them just the same. ETI could be doing similar such broadcasts, but the odds of our detecting them with our current SETI programs are slim. Thus our chances lie with the sustained METI programs, which as has been pointed out already, may have some very interesting reasons behind their existence.
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METI: Learning from Efficient Beacons

If we want to consider how to pick up transmissions from a distant civilization, it pays to consider the most effective strategies for building interstellar beacons here on Earth. This is the method James, Gregory and Dominic Benford have used in twin papers on SETI/METI issues, papers that should be read in conjunction since the METI questions play directly into our SETI reception strategies. It pays to have a microwave specialist like James Benford on the case. Our METI transmissions to date have used radio telescopes and microwaves to send messages to nearby stars. Longer distances will cost more and take much more power.

How much would a true interstellar beacon cost, one not limited to the relatively short ranges of recent METI transmissions? Count on something on the order of $10 billion. As to power, Jim is able to quantify the amount. To reach beyond roughly a thousand light years with a microwave beacon, an Effective Isotropic Radiated Power (EIRP) greater than 1017 W must be deployed. A beacon designed for communication across galactic distances goes even higher, with ranges up to 1020 W. We can compare this to the Arecibo radio telescope, famously used for sending a message to the Hercules Cluster (M13) in 1974. Arecibo can muster 1013 W, and most (short-range) METI messages have managed 1012 to 1013 W.

We learn in these pages that microwave emission powers have increased by orders of magnitude, while the introduction of new technologies has changed our methods for emitting powerful signals since the days when Project Ozma was but a gleam in Frank Drake’s eye. The paper lays out the necessary background, noting that most high power devices operate in bursts of short pulses and are not extremely narrow band. Economical beacons are likely to be pulsed, as Drake himself would note back in 1990. The Benfords liken this strategy to that of a lighthouse, with a pulsing beam that moves and calls attention to itself.

Go through these pages for a useful survey of high power microwave (HPM) technology as it developed, with implementations through the decades ranging from the relativistic klystron to modern intense relativistic electron beam technology. The paper notes that arrays of antennas are the only practical way to produce the large radiating areas necessary for an interstellar beacon, arrays like those already used in radio astronomy work. The construction of an efficient beacon is then considered against the constraints of cost optimization, considering the crucial relations between cost-optimal aperture and power.

I leave you to the relevant equations and turn toward the implications in terms of transmission strategy. Mindful of the concept of a galactic habitable zone, the Benfords focus on stars that lie inward toward the galactic center at distances of greater than 1000 light years, a strategy they hope will target the highest number of possible civilizations. So if you are broadcasting in an attempt to reach likely ETIs, here is a method: Broadcast in a limited way, targeting the 90 percent of the galaxy’s stars that lie within nine degrees of the sky’s area, in the plane and hub of the galaxy, with special attention to areas along the galactic disk.

Whatever races might dwell further in from us toward the center, they must know the basic symmetry of the spiral. This suggests the natural corridor to communicate with them is along the spiral’s radius. (A radius is better than aiming along a spiral arm, since the arm curves away from any straight-line view of view. On the other hand, along our nearby Orion arm the stars are roughly the same age as ours.) This avenue maximizes the number of stars within a Beacon’s view, especially if we broadcast at the galactic hub. Thus, a Beacon should at least broadcast radially in both directions. Radiating into the full disk takes far more time and power; such Beacons will rarely visit any sector of the plane. Of course such distances imply rather larger Beacons.

Image: Beautiful, but this young cluster imaged by Hubble is an unlikely home to alien civilizations. Better to look in the direction of the galactic plane, and think in terms of older stars with higher prospects. Credit: NASA/ESA/STScI/AURA).

Thus we scan the plane of the galaxy often, broadcasting toward and away from galactic center frequently, with occasional bursts toward the densest collection of nearby stars along the Orion arm. And this is interesting: Broadcast toward the locations of transient but powerful bursts that have occasionally shown up in past SETI surveys. The paper concludes that cost-efficient beacons will be pulsed, narrowly directed and broadband in the 1-10 GHz region, with a preference for higher frequencies. If we apply these thoughts to other civilizations, assuming their own tendency to minimize costs and obtain the most efficient result, we develop the necessary counterbalancing strategy for SETI.

Given current SETI methods, would we detect such ‘searchlight beam’ beacons with short ‘dwell’ times as they sweep past? More on these issues next time. The paper is James, Gregory and Dominic Benford, “Cost Optimized Interstellar Beacons: METI,” available online.