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SETI: Figuring Out the Beacon Builders

Several interesting papers on SETI have appeared in recent days, among them Gregory, James and Dominic Benford’s attempt to place SETI in the context of economics. Equally useful is Duncan Forgan’s new look at the Drake Equation, presenting a way to estimate the distribution of the crucial parameters. I’ll bypass the Forgan paper temporarily because I’ve asked Marc Millis to tackle it as soon as he gets back from the Jet Propulsion Laboratory, where he’s gone to attend a workshop. Forgan’s study has direct bearing on a Tau Zero initiative we hope to have in place by the end of the year and thus is a natural for Marc to write up.

But back to the Benfords, who have offered up twin papers (as seems reasonable for the brothers), one on SETI (with Gregory as principal author) and the other on its METI offshoot (transmitting messages rather than listening for them). James Benford is lead author on the latter. This work is so rich that I won’t try to encapsulate it in a single post, but rather draw on the ideas here over the course of a few (perhaps non-consecutive) days. In any case, I don’t want to be rushed in these discussions, where the issues are as large as the distances involved, and our philosophical approach may be as significant as our technology. And the two papers should be read in connection with each other in any case, for the analysis in the METI paper is directly relevant to developing the argument of the SETI discussion.

We’re close to the 50th anniversary of the Project Ozma attempts, and in SETI’s first half-century we have found no clear detections in our search of nearby stars. But over the course of the decades, our initial SETI assumptions have been challenged. We’ve gone from a Sagan-esque optimism that the galaxy is aswarm with civilizations to a far more measured (and surely more realistic) view that takes into account factors like the galactic habitable zone, and the sheer difficulty facing living things on the long evolutionary road toward intelligence.

Image: The spiral galaxy M74 (NGC 628), perhaps the home of technological civilizations that, like us, are trying to figure out whether they are alone. Credit: GMOS/Gemini North Observatory.

The Benfords — Jim at Microwave Sciences, Gregory at the University of California’s Irvine campus, and Dominic (Jim’s son) at NASA GSFC — believe that advanced societies, if they are to be found, ought most likely to exist toward the galactic center, and probably at distances of over a thousand light years. We’re thus talking, in all likelihood, about interstellar beacons rather than targeted transmissions when it comes to SETI. And if beacons are indeed at play, what can we say about their costs, and do our own standards of terrestrial cost have any application in an ETI context?

The message here is that any SETI search has to make assumptions about the beacon builders, and if we can determine something about the economics of the situation, we may learn how to target our searches more effectively. Here’s the essence of the argument about ETI:

We assume that if they are social beings interested in a SETI conversation or passing on their heritage, they will know about tradeoffs between social goods, and thus, in whatever guise it takes, cost. But what if we suppose, for example, that aliens have very low cost labor, i. e., slaves? With a finite number of slaves, you can use them to do a finite number of tasks. And so you pick and choose by assigning value to the tasks, balancing the equivalent value of the labor used to prosecute those tasks. So choices are still made on the basis of available labor. The only case where labor has no value is where labor has no limit. That might be if aliens may live forever or have limitless armies of self-replicating automata, but such labor costs something, because resources, materials and energy, are not free.

Our point is that all SETI search strategies must assume something about the beacon builder, and that cost may drive some alien attempts at interstellar communication.

SETI always seems to come with a built-in willingness to think the best of extraterrestrial cultures. If an alien civilization is sending out a message, it must be doing so out of altruism. The Benfords, though, are interested in exploring motivations from a different angle. They’d like to relate them to the only case of a technological civilization we know of, ourselves, and speculate based on human history. From that perspective, there are two reasons for sending out messages across vast time scales.

Think about what people do. You can go to the Tower of London and explore the chambers where famous prisoners like Thomas More were kept. Invariably, on the walls, you’ll find graffiti, names written into the stone. People have an apparently robust need to engage in one-way communication, putting a note in a bottle and throwing it. Indeed, the Pioneer and Voyager spacecraft are examples of the impulse. Is it likely that any of these tiny vessels will ever be intercepted? Yet putting our names, our stories, our music and our pictures on board outgoing vehicles is a method that resonates. We have a need to encapsulate who we are.

A second reason is the drive to communicate the optimum things about our culture, what Matthew Arnold called “…the best that has been thought and said in the world.” Here the Benfords cite time capsules and monuments as examples of our need to propagate our culture. The contemplation of a legacy is involved here, especially in a scenario where human lifetimes are rising. Here again the communication can be one-way. The statue of King Alfred my wife and I admired in Winchester some years back was not built to impress people within a tight time frame, but to stand as a monument that would reach future generations.

So imagine scenarios like this: A civilization with an ability to plan over millennial time scales foresees problems that are beyond its capabilities. A SETI beacon might encapsulate a call for information and help — send us everything you have on stellar warming…

Here’s another: A civilization in its death throes decides to send out an announcement of its existence. We were here and are no longer, but as long as this message endures, so in a sense do we. And let’s not discount sheer pride of the sort that could keep a beacon in operation long after the beings that built it were gone. Robotically maintained, it might boast of achievements set against the backdrop of the ruin that may eventually attend all technological cultures. Or perhaps we’ll run into interstellar proselytes, out to convert the galaxy to a particular set of beliefs by placing their highest values into their outgoing signal.

High powered signals may even be unintentional, such as the signatures of planetary radars that scan for asteroids, or perhaps the industrial activities of a space-faring civilization that boosts payloads deep into its system using beamed power. Beam-driven sail expeditions might leave such a signature (recall Niven and Pournelle’s The Mote in God’s Eye). These activities seem more likely to be detected than the far fainter signatures of isotropic radio and television broadcasts, and would carry the unmistakable message of a working technology.

Image: Does the best SETI strategy involve listening for directed messages from nearby stars? Or do we concentrate on short burst transmissions from deep in the galactic plane? Credit: VLA/NRAO.

Given all these motivations — and we don’t know how to choose between them — microwaves seem to be the best carriers of a civilization’s message, if only because interstellar absorption is minimal at those wavelengths. Can we make any guesses based upon cost and perceived value about how such a culture would proceed with a microwave beacon? If so, our conclusions would have a material impact on how we conduct the SETI search. From the paper again:

…even altruistic Beacon builders will have to contend with other competing altruistic causes, just as humans do. They will confront arguments that the response time for SETI is millennia, and that anyway, advanced societies leak plenty of microwaves etc. into deep space already. We take up these issues below. It seems clear that for a Beacon builder, only by minimizing cost/benefit will their effort succeed. This is parsimony, meaning ‘less is better’ a concept of frugality, economy. Philosophers use this term for Occam’s Razor, but here we mean the press of economic demands in any society that contemplates long term projects like SETI. On Earth, advocates of METI will also face economic constraints.

The Benfords believe that evolution will always seek for economy of effort. Their analysis is bracing stuff and it calls into question a SETI strategy that is not optimized for short bursts of pulsed microwaves and the observation times necessary to see repeat events. Another question is inevitable — have we inadvertently picked up such signals already and dismissed them? More on this in coming days. The paper, “Cost Optimized Interstellar Beacons: SETI,” is available online. We’ll look at “Cost Optimized Interstellar Beacons: METI,” available here, tomorrow.

Comments on this entry are closed.

  • Adam October 29, 2008, 17:21

    Hi Paul

    They’ve definitely set the pace for a new generation of SETI studies IMHO. EM beacons will incur costs regardless of the underlying social system – the old SETI dream of big, flashy beacons for all to see being an unrealistic dream. Instead of isotropic “We’re Here” signs, there might be Galactic Lighthouses sweeping past us intermittently.

    Will be very interesting to see if any amateur SETI watchers take up the challenge of watching previous brief ‘hits’ for extended times to see if they recur on a weekly-to-yearly timescale. Someone with no other need for their microwave antenna could potentially confirm a Beacon – it won’t be a pro either.

    So where to look? In 1990 a radio antenna in West Australia picked up a strong signal from a K7 star in Ophiuchus (HD157881, if you must know), just 26 light years away. The signal only lasted an hour or so and faded before another scope could be turned towards it. It might’ve been just a false alarm, but it’s an teasing hint of what might be seen if we (and ETIs) follow the Benfords’ strategy.

  • James M. Essig October 29, 2008, 22:24

    Hi Paul and Adam;

    The possibility of beaming the knowledge accumulated by contemporary human civilization is very interesting and potentially very profound in its scope of influence.

    Imagine beaming information packets in AM, FM, or digital form wherein large volumes of data would be incorporated within the information carrier waves. One can imagine petabytes or perhaps even 1,000 petabytes of information being transmitted from a single installation per year using microwave carrier waves. The MW encoded information could perhaps be broadcast with phased array apparatus with a time averaged power output of anywhere from one MegaWatt to a Whoping one GigaWatt.

    Perhaps a multitude of such installations could use phased array methods to beam such signal in dozens or more directions such that, at some distant future epoch, a distant galaxy that would house any existent ETI civilizations would receive the signal wherein the ETIs could intercept the signal and learn from the legacy of our current civilization.

    The beautiful thing about using EM signals to transmit our legacy is that such signals, as we know, have an essentially unlimited range. Perhaps a Galaxy 1 trillion lightyears away from earth at some cosmically distant time would receive the signal with ultra sensitive ultrahigh gain antennas with extreme ability to detect signals with a low signal to noise ratio and ponder where the heck the signal originated.

    If doubly special relativity or similar theories are correct about the frequency dependent velocity of EM radiation, using low frequencies such as microwaves, or perhaps even IR lasers to send the information, would likely permit the fidelity of the signal to be maintained compared to high frequency AM or FM or even digital schemes using high energy photon lasers. Recall that according to doubly special relativity, the low end value of C as computed by the formula [(Mu naugh)(Epsilon naught)] EXP – (1/2) is bounded by the long wave-length lower limit. The effects of the frequency dependent value of C only become obtusely obvious as the photon energies approach that of the Planck Energy.

    The signals could loose their fidelity by other mechanisms such as subtle effects of interstellar and intergalactic gravitational field potential gradients, interaction with interstellar dust and gas and the like.

    Regardless, once the EM signal is launched, the really cool thing is that it will travel for ever thus, not only broadcasting our presence over cosmic spatial distances, but also over cosmic temporal distances into the future.



  • david lewis October 30, 2008, 7:46

    Of course ETI might not bother with building beacons, figuring the biosphere of their world would be one big beacon that any reasonably advanced civilization would be capable of detecting. And once detected would be of intense interest to such a civilization who would then try to examine that world further – such as via probes to their stars gravitation lens. Not trying to examine such worlds further would indicate a lack of interest in communication and hence not worth trying to communicate with.

    Such a civilization might have examined their neighborhood for life bearing worlds millions of year ago and have sent such probes to their own stars gravitation lens for each life bearing world. Probes, or even colony ships capable of colonizing comets and other bodies, that would have built massive telescopes to observe those worlds. They might just now be starting to detect the industrial pollution we started to emit into our atmosphere centuries ago.

    They might now be building the transmitters to transmit to our world. Or they might be waiting to see what sort of civilization we develop into, to see if we will want to communicate or are worth communicating with. Such transmitters would not need to be excessively powerful since we would both know where to transmit and know that someone is waiting on the other end – all it might take is developing the technology to find the worlds, and building the receivers that can detect signals that might be only a billionth of the power that we can now detect.

    No beacons because they aren’t needed. No signals because they are focused in directions that don’t intercept us and are too weak for us to detect.

    Of course if I were an advanced rational ETI I wouldn’t want to communicate with anyone until I was pretty sure they were rational themselves. Imagine transmitting “hello” to a world and having them launch a jihad against you because their religion says all conversations must start with “good day”. Or you are a species with three sexes and their religion says only sex by a female and a male are allowed and anyone violating that law is to be stoned. Might sound silly to us, but imagine an extremist christian or muslim gaining power globally and what they might decide as holy law. Abortion clinic bombers and people threatened with death because someone makes an image of their prophet. And that is with humans, who knows how aliens might think or reason. Even beyond religion might they have built in reflexes that can be triggered that could cause them to attack. Might they be capitalists conditions by their leaders over thousands of years to hate socialists.

    We got enough trouble getting along amongst ourselves and we are all humans with the same genes and evolutionary history. Whatever we decide to do when it comes to aliens, we should be careful.

  • ljk October 30, 2008, 17:13

    Adam, do you have any more information on the signal from
    (presumably) HD157881 detected in 1990 by Australia?

    By info I mean written documents on the subject. I have
    heard stories about this event from several SETI folk, who
    take it as being even more significant than the Wow! signal
    found by Big Ear in 1977. However, unlike the latter one,
    there seems to be very little literature on the event. But
    please prove me wrong here, thanks.

    I also want to know if anyone has done followup scans
    in that area, in case the presume beacon comes back
    around our way again. The fact that I have not seen
    anything else about it since 1990 may mean the answer
    is no. Perhaps it is time to change that.

    About the ETI beacons: It may be cost-effective to send an
    initial “ping” in pulse format, but if you are trying to get the
    attention of a variety of intelligences – some of whom may
    be like us, having looked at the sky only sporadically for the
    past few decades with just a few methods – how do they really
    hope to make it clear to us that their signal is not natural?

    Our science, especially when it comes to SETI, insists on more
    than one data point. This is why the Wow! signal and the one
    from 1990 have not been declared artificial and alien because
    we only saw them once. Presumably it is not too much to ask
    that even alien science also demands more than one incident
    to have an idea go from a theory to proof?

    Maybe we just haven’t been paying the proper attention, but
    there has never seemed to be any interstellar signals that
    repeated themselves. Does it take a really long time for
    these beacons to cycle around? Or do they expect to ping
    our system and others just once and figure that if the beings
    there are REALLY curious, they will ping back? If the latter,
    this runs into the issues currently flying around METI.

    As for those METI attempts which have happened, I am also
    unaware of any aimed at those promising signals mentioned
    in the Benford papers. When people do agree on what and
    how to send a METI signal, will those promising areas finally
    be pinged?

    While I am here, I also hope SETI will spend more time checking
    the cold, outer regions of the Milky Way where objects are more
    prominent in the infrared than anywhere else on the electromagnetic
    spectrum. Those may be good places for Dyson Shell type
    Matroishka Brain, plus it has the benefit of not falling into the
    ETIs must live on a planet around a Sunlike star paradigm.

  • James M. Essig October 31, 2008, 13:23

    Hi Folks;

    The possibility of building large scale data/information broadcasting stations is a consideration that we, as the collective civilization of humanity, should take seriously.

    While absolutely no intent is being made to convert anyone here nor is there any attempt being made to advance spiritualistic concepts, from a contemporary cultural perspective as a conservative Catholic, I am keenly aware of the possibility, accordingly to some of the Catholic Church’s most promenant theologians and Vatican advisors, that the human race could go completely extinct in this world as well as perhaps all other life forms on the planet.

    Regardless of our religious belief systems or lack thereof, I feel that planning for the continued existence of our civilization as an ever far reaching space faring species should definately continue with all the more vigor, but I also strongly feel that broadcasting our most notable scientific, culteral, technological, philosophical, mathematical, and faithbased notions should be attempted. Either way, I feel that any ETI civilizations that would be on the receiving end of such signals, millions, billions, if not trillions of years from now would be profoundly effected to have received intellegent information from an era, that relatively speaking, could have come from a cosmically remote era in the past.

    We have gained to much scientific, technological, philosophical, faithbased, and cultural wisdom to let it all be lost in the event that we do our selves in. It would be a great act of charity to permit ETI beings and their civilizations to benefit from our more noble of accomplishments.



  • Ronald November 1, 2008, 11:49


    I commend your spiritual ‘open-mindedness’ and endorse your vision: ” I feel that planning for the continued existence of our civilization as an ever far reaching space faring species should definately continue with all the more vigor”.

    Yes, I fully agree: I believe that space faring and colonization of our Milky Way galaxy is almost like a mission, a sacred duty. First of all for the very survival (through risk-spreading) of humankind, but also to spread life, intelligence and civilization among the stars of our galaxy. It is very well possible that we are the only advanced intelligence and technological civilization in our galaxy, making this duty and mission even more important and urgent. So many sunlike stars and probably terraformable earthlike planets as well. And maybe so little time and window of opportunity.

  • James M. Essig November 1, 2008, 14:07

    Hi Ronald;

    Thanks for the kind words.

    I once read of an account of some philosophical/theological work by one of the promenent thinkers in these fields that matter, or perhaps more accurately, mattergy is the urge to live. Accordingly, this aspect of mattergy is a fundamental principle that we can only infer experimentally, empirically, and experiencially in this life in an indirect manner. This urge to live can accordingly be discerned in these three ways by the observation of all of the living organisms on Earth, and presumably throughout the cosmos, as the mattergy attempts to become all the more fully alive through the evolution of physical systems.

    I definately think it is within our destiny to take part in the transformation of the raw mattergy and raw space-time into living organisms, or atleast into forms that approach life like entities evermore closely.

    Assumming that there are 100 billion stars with the mass of the Sun or less within our Galaxy, and that each of these stars has on average one terrestrial-like, or terraformable planet, the Milky Way could potentially support (10 EXP 11)(10 EXP 10) humans simultaneously, or 10 EXP 21 humans. The totality of the galaxies in the visible universe might be able to support (10 EXP 21)(10 EXP 11) humans simultaneously, or 10 EXP 32 humans. These values assume that each Earth-like planet can support 10 billion humans and that there are 100 billion galaxies within the observable universe.

    Although I am not trying to advance faithbased notions or spirituality here, I will say as a common courtesy for those with a belief in immortal human souls, or even for those who believe in an afterlife of some form in general, that this works out to the creation or otherwise comming into existence of (10 EXP 32)(10 EXP 9) human souls within the visible universe over the following 80 billion years assumming a life expectancy of 80 years planetary frames of reference. This is 10 EXP 41 human persons! And the math represents only the resources of the observable universe. When one considers that the entire universe is probably much, much larger than the observable universe, perhaps even infinitely so, one can see the huge number of human beings that can come into existence, and accordingly, from a guys perspective, the huge number of beautiful, intellegent, and in other ways, attractive woman that can exist.

    The possibilities for our species are boundless. I am a firm believer that by our very work here at Tau Zero/Centauri Dreams in terms of our desire for our species to reach out ever further into the Cosmos, we are indeed accomplishing the most noble of quests. All of us who post comments on Tau Zero, the site Administrator Paul Gilster, and Marc Millis are each individually and collectively working to build a civilization of love and an era of peace, as well as having a whole lot of fun contemplating the mysteries of the cosmos.


    Your Friend Jim

  • Ronald November 1, 2008, 16:34


    further to your interesting calculations above, a cautionary footnote: I sincerely hope that, while spreading our species and civilization through the cosmos, humankind will exercise self-restraint and treat already living and inhabited planets with the utmost respect and care.
    Rather refrain from settling those inhabited planets (except maybe for study and exchange of knowledge) and focus on non-living but terraformable planets for spreading earthlike life.

  • James M. Essig November 1, 2008, 20:25

    Hi Ronald;

    Excellent point.

    I would say that we must, as our moral and ethical duty based on natural law, avoid the occupation, takeover, or otherwise stealing of planets from any ETI civilizations. We must respect fellow rational creature species as ourselves and treat them like brothers and sisters.

    I will even go as far as to say that even social and sentient animal lifeforms such as the analogues of felines, canines, and the like social animals on otherworlds must be respected. I am a little bit of an oddball regarding treating animals here on Earth with respect with regards to the opinions of my family and other significant others, because I believe that animals have a right to live confortable and social lives to the extent that we can provide such for them. Despite the fact that I am not a vegetarian and eat a lot of beef, and have even been tempted to go hunting and/or fishing from time to time in order to experience the opportuinity to have delicious venison stew or fresh blue fish fellets, I cannot bring myself to even cutting the head off of a live fish although I am sure I could do such if I had to.

    In fact, my first instincts and feelings that come from within when I see puppies or kittens, especially friendly dogs like golden retrievers and black labradors is ‘How cute!”. I grew up with lots of pets around the house and this has no doubt helped me developed into a more nurturing person.

    The point is that I am of the utmost belief that we must treat any rational ETI civilization beings as other selves although I would not mind bringing home the analogue of cute kittens from a distant Earth-like planet as pets if our biosphere could support such.



  • Ronald November 2, 2008, 5:33


    yes, agreed. But in addition to the respectful treatment of other intelligences (ETI) and other higher social and sentient beings, there is the more general moral issue of how to treat living planets in general, i.e. planets that already possess *any* forms of biological life.
    Would we settle such planets, if there are biological lifeforms, but no intelligent ones? Would we compete with them and (partly or entirely) replace such lifeforms with our earthly ones, if it served our purposes better? And what if the planet contains only microbial lifeforms? What would be our criteria and self-limitations in those cases?

    Such moral issues would not or hardly be problematic in the case of terraforming uninhabited but potentially inhabitable planets (by such I mean planets without any lifeforms of maybe with microbial life at the most).

    Surely there must be multitudes of such terraformable earthlike planets near sunlike stars, probably billions in our MW galaxy alone. Each with its own slightly different and unique conditions, suitable for terraforming and settling with genetically adapted organisms.
    An advanced civilization does not require living planets with fully developed biospheres; yes, even more so: in case advanced life appears to be rare, an advanced civilization might even decide to leave those entirely alone and in peace (except for careful scientific study) as a kind of reserves, and limit settlement entirely to the do-it-yourself earthlike planets.

    I see a future with a combination of planetary (particularly atmospheric) engineering and bio-engineering.

  • James M. Essig November 2, 2008, 12:30

    Hi Ronald;

    Thanks for the above insights.

    The concepts of planetary atmospheric and planetary bio-engineering, I also, believe will become a reality.

    I can imagine the university course catalogues of various institutions around the globe offereing introductory through advanced coursework in planetary engineering by the year 2100 if not sooner.

    In fact, I would like to be able to somehow have a peak course catalogues in the year 2100 or even the year 2200 and see what they have to offer.



  • james Brown November 2, 2008, 14:40

    After looking at the software and hardware requirements for my Project Argus station, and mulling over such technical questions as integration time constant and Doppler shift correction, I have come to the following epiphany:

    I must look for the most obvious signal – and that is the signal that I would choose to send myself, if I had the money to do so.

    What that means (and it seems obvious once put on paper) is that I must look for myself. This is necessary to make the signal recognizable to us when finally detected.

    Any ETI that I might hope to detect must be more like than unlike me, in most basic ways. Not to put too fine a point on it, but, for example, I think this ET would think in the same time frame as we do. Not at the speed of a glacier or at the speed of bullet, but somewhere near our ‘thinking speed’. ET’s physical makeup would have to be about the same as ours. Not as small as a bacterium or as large as one of the rolling hills I can see from my window, but somewhere in-between. This would give him the same type of control over his environment, and the same capability as I have to construct the needed transmitter, which could produce a signal which I can recognize. Not all ETI need be like me; only those who I have a realistic chance of detecting.

    ETI’s transmitter must be an RF signal generator. Some other, more exotic form of communication may well be in use, but since I can’t construct a receiver to detect exotica, it’s not worth considering. This leaves optical SETI open – but not for me. I know nothing about the optics required on that scale. As a microwaver, I’ll stick to the area where I have a shot at SETI success.

    The signal must be a deliberate beacon. That’s the only type I, and most other Argus stations, would have a ghost of a chance of hearing. Leakage detection seems less likely, if only because of the transmit power requirements needed to show up on my system. Detecting planetary radar also seems unlikely, because it seems that it would only be sent for short periods. Once a radar echo was recovered, the transmitter would most likely be turned off or pointed somewhere else. The modulation scheme needed for an effective planetary radar might also make it difficult to recognize on this end.

    I would set my beacon up in the waterhole to maximize its chances of discovery. I would want to be heard, and that is the most obvious place to start. The hydrogen line is at 1420 MHz and the hydroxyl line at 1662 MHz. I would transmit at exactly halfway between the two, at 1541 MHz. (One could also make a case for the geometric mean of the hydrogen and hydroxyl lines, which is 1536 MHz. But we’re splitting hairs here.) I would expect ETI to similarly transmit somewhere near the middle of the waterhole, if he wants me to detect him. Unfortunately, my Project Argus system (receiver and filter) can’t tune this frequency, but if I were to make changes to my system, that is where I would choose to monitor.

    An ideal interstellar beacon should be narrow band to concentrate the transmit power, and to make it distinguishable from natural sources. It must be directed at our star. This is necessary to conserve power, and to make possible reception over huge distances. So a directed beacon is what I am looking for. I can see ETI pointing such a beacon at each candidate star, one at a time, sending the beacon for some length of time, and then moving to the next star.

    The above targeted beacon strategy implies that Earth rotation Doppler compensation is a minimum requirement of our Project Argus receiving stations, if only to exclude local signals. Correcting for the Doppler shift due to our travel around the Sun is also a requirement. I have the Earth rotation Doppler chirp running now – the other compensation is an unknown quantity to me at this point, but something which Project Argus participants should be working on.

    My hypothetical interstellar beacon would be locked onto each star for about a year at a time. We may have missed ETI’s signal already, and may have to wait another 300 million years for it to show up again. Or, it may be starting tomorrow. Since we just don’t know, we may as well assume that it starts tomorrow.

    If I were sending a beacon, its transmitter frequency would be Doppler-adjusted to the Galactic center of rest. Since the purpose of a beacon is to be seen against a background of other signals, this would make it clear to anyone receiving it that it was an intentional signal. Again, I have no idea how to design this correction into my receiver chirp. If it’s small (less than about 0.01 Hz/sec), no matter where I point my antenna I can’t use it anyway, because my 10Hz/Bin resolution and planned 30-minute integration time constant make such small Doppler rates moot. If the compensation for the Galactic center of rest is a sizeable fraction of a Hz per second, I’d better figure out how to implement it!

    My beacon would be a CW signal on/off modulated in a regular way. I might send Morse code in a repetitive pattern, and I would send it at a speed slow enough to allow integration of each character, but not so slow as to allow the signal to drift across many bins during a given key-down period.

    If I concentrate on looking for myself, I may well miss signals sent by those not like me. But I know that creatures who think like me exist (if only by Earth’s own example.) Designing our search around those not like us involves pure speculation, and may reduce our chances for SETI success.

  • Mr. Intense November 3, 2008, 19:25

    The presumption of the Benford brothers, in each of their respective papers, that an extraterrestrial intelligence might actually be interested in transmitting, via ~10 Ghz microwave beacons, or similar technology, METI (Messaging Extraterrestrial Intelligence, aka Active SETI) signals over thousands of light years strikes me as both utterly presumptuous and deeply anthropocentric in nature, and without any real consideration of the possible consequences.

    While I agree with them that the standard SETI protocols and assumption that listening for radio signals in the ~1 Ghz band from nearby (400 or less light years away) systems is likely to be fruitless, their implicit assumption that the majority of advanced civilizations, which they posit would be closer to the galactic hub, and thus far more than 1000 light years away from us, in a kind of “goldilocks civilization zone,” and should motivate us to revise SETI assumptions to listen for microwave transmissions at a higher bandwidth as some of such non-human advanced civilizations may be employing high-band microwave “beacons,” is nearly as misguided and improbable to yield results.

    Why? Because METI is a terrible, insane idea for humanity (or any non-human form of intelligence) to seriously consider acting upon. It would be the equivalent of yelling, “Hey, come get me!” in the cosmological night of the intragalactic jungle, without knowing just what might be out there actively listening for or capable of detecting such a signal.

    What do you do if or when some extremely advanced and unknowably intelligent predators show up, attracted by the “signal within the noise” you have so conveniently provided as a “beacon” to vector them to your location?

    Even if “the other” were “benign,” the consequences (considering, as historical example, even just our own history of inter-cultural contact effects) would most probably have such an incredibly disruptive impact on our relatively primitive human culture, precluding our presumed independence, that we could end up either destroyed (or co-dependently “enslaved”) as a species. This fact would not escape other, even more intelligent and capable non-human species. So why would they engage in METI, either?

    METI beacons could result in inadvertent species suicide, either way. Once the signal is sent, it cannot be recalled. And several METI signals have, foolishly, already been sent, directed at various star systems.

    Who dares speak into the darkness for earth as a whole? The solipsistic needs and quasi-religious desires of some should not be allowed to overcome logical caution and the potential dangers of such blind signaling. I personally think METI should be absolutely prohibited until and unless, by international treaty, there would be a comprehensive, justified rationale for doing it.

    IMHO, I don’t think there is any legitimate reason for doing so that I am aware of, and considering the possible, non-zero existential risks entailed in doing so. I would, in fact, be interested in hearing more about, or logical reasons for METI that would suggest a justified rationalization for doing so, and again, considering the potential risks thereof.

    For further information:



    See also:

    Shall We Shout Into the Cosmos?
    An information/resource page concerning a fast-developing scientific controversy.
    Organized by David Brin, Ph.D.


  • James Benford November 7, 2008, 9:40

    Adam: Yes, I think amateurs looking for Beacons is a clear implication of our ideas. They would have the time to ‘stare’ at a piece of the sky for periods up to years to see any repeats. For example, the WOW! signal location and frequency has been looked for by Robert Gray and co-workers, who ruled out recurrence times of less than 14 hours.

    James Essig: There’s a limit to the range at which a signal can be detected. See my METI paper for the relations and the Table. The background that limits the signal-to-noise ratio in the microwave is the 3-degree cosmic background. Your trillion-light year distance is metaphorical, right? Physically, it’s impossible. The principal signal propagation limitation you refer to is the dispersion produced by interstellar and intergalactic plasma.// One point of our METI paper is that beaming information over galactic or larger distances will be very costly. Advocates of METI must realize that they’re pushing a big project, beyond present-day manufacturing capability. So, it would mean diverting funds from other of societies objectives, which is why we look at it as being constrained by economics.

    David Lewis: Detecting signals a billionth of what we can do now is not on; see my reply to James Essig.// By the industrial pollution of centuries past I suppose you mean CO2. That’s been around as long as life, and varies for many reasons, so is not a signature of civilization.

    ljk: Signals sent so far by METIists have not been beamed at any of the promising areas we mentioned. Several papers by Zaitsev describe them in detail. //The relation between time the Beacon would be on-target to the time it returns is related to the fraction of the sky it’s trying to cover. See Figure 11 of the METI paper.

    James Brown: Your discussion is very much like my thinking, with some exceptions: 1) There is more noise at the lower end of microwaves, better signal-to-noise is at higher frequencies nearer 10 GHz. On page 12 of our METI paper, “Note that this is quite different from some SETI thought, which privileges the “water hole” region between 1 and 2 GHz. Indeed, the metaphorical resonance between the spectral lines of H I and OH with “meeting at the water hole” may be a classic case of anthropic reasoning. The secondary reasons given as early as Project Cyclops–that the low end of this band demands less stringent frequency stability– vanishes if the Beacon is broadband, as we argue in Appendix B. Since that era, detection of over 100 spectral lines in the interstellar medium, many of them organic, undermines the classic argument. Further, synchrotron radiation in the 1 GHz region increases going inward toward the galactic center, where the highest density of older stars peaks. A further benefit of higher frequencies for both Beacon and receiver: interstellar scintillation fades quickly with frequency, and can be ignored around and above 10 GHz. As Beacon builders we will prefer that the listener not be confused by scintillation. Our conclusion is that cost, noise and scintillation argue for radiating above the “water hole’, especially if space-based.” We also argue that Doppler-shift compensation doesn’t matter because high power sources are wideband (again, Appendix B). // Your picking a one-year dwell time puts you into the lower right corner of the nomograph, figure 11 of our METI paper, continuous beaming. Why choose that? Short-pulses bursts are more noticeable, but they don’t have to be a year long to be noticed. One motivation of our paper is to get SETI people to think more broadly. Reconsider the range of possibilities.

    Mr. Intense: We do not presume anything about ETI. We cover this question: If we do build Beacons, what will the Beacons be like? This is a scientific/technical question, not a matter of opinion. In the METI paper, we cover how to make a Beacon,. In the separate SETI paper, section 2.2 (pg. 4-6), we do address the question of Beacon-builder motives, and point out that communication is only one of those. (There’s also High Church, Kilroy Was Here, Funeral Pyre, Help!, Join Us (Religion), Ozymandias and of course, Leakage Radiation.) //You are saying that METI is a bad idea. You seem to think that we take a position on its merit as an idea but we do not. It isn’t necessary and would not be appropriate in a scientific paper. We do point out that it’s costly. That does in no way make our quantitative analysis of Beacon parameters and costs ‘misguided and improbable’.

  • ljk December 24, 2008, 0:39

    For those old enough to remember, there was a show on Saturday
    mornings called The Curiousity Shop/ It came out in 1971 to 1973
    on ABC.

    They used to show animation shorts from around the world. I so
    distinctly remember this one from Canada titled “What on Earth!”

    It’s a “documentary” film about the first Martian space probe
    mission to our planet, where they show film footage of what they
    think are the dominant Earthlings:


    The “punch line” at the end is a good one.

    I have been wanting to see this for decades, literally, and it
    finally came out on Youtube just over a month ago. I am amazed
    I remember as much of it as I do.

    Enjoy, Earthlings!

  • ljk January 27, 2009, 10:46

    Jill Tarter of the SETI Institute talks with Will Writer, the guy
    who developed Spore: