Interstellar Beacons: A Silence in Heaven?

by Paul Gilster on September 21, 2009

by Jon Lomberg

It seems fitting that we should be in the midst of a three-part series on SETI and METI issues. As Larry Klaes reminded me in a recent comment, September 19th was the fiftieth anniversary of the paper that began the modern SETI era, Morrison and Cocconi’s “Searching for Interstellar Communications” (available here). Artist, lecturer and polymath Jon Lomberg now adds his own take on the discussion. Pay particular attention to the question of signal duration — would a METI signal be continuous or intermittent? Much rides on the answer.

Lomberg is a familiar figure to Centauri Dreams readers. Creator of the Galaxy Garden (Kona, Hawaii), Jon is an astronomical artist working in many media whose work is known throughout the space community and beyond. Viewers of COSMOS will know that he was chief artist on that project, serving as Carl Sagan’s principal artistic collaborator for many years. His splendid work on CONTACT, where he storyboarded many of the film’s astronomical animations, showed what could be achieved in film with an adherence to scientific fact and solid conjecture.

Jon designed the cover for the Voyager Interstellar Record, the human artifact now pushing its way into true interstellar space. In other words, this is a man with experience at creating messages designed to reach out across vast gulfs of space and species. Here Jon adds to our discussion of SETI and METI with a look at what an interstellar beacon might be, and what it might be designed to do.

Let’s step back from the consideration of methods of transmission and the relative virtues of radio,optical, etc. The physics of these are well understood, so naturally it is the domain of search space that is easiest to study and manipulate. We can choose what kind of transmitters and receivers we will use. The only real progress in SETI has been the improvement of the sensitivity and bandwidth of the receivers. No doubt we will soon have the ability to monitor MOST of the radio/microwave spectrum at once. But perhaps that will not solve our problem of finding beacons.

What are the ideal properties of an interstellar beacon from a human perspective, whether sending or listening?

  • It should be as easy as possible to detect.
  • It should transmit/receive using technology we possess.
  • It should be detectable from the planet’s surface. as well as from instruments in space.
  • It should be sent in as many wavelengths possible (radio, microwave, IR, optical, x and gamma)
  • It should be as loud/bright as possible.
  • It should be beamed directly toward us.
  • It should be uninterrupted, constantly repeating some pattern.
  • If there is an interval of silence between repetitions, it should be short.
    (defining short and long in the context is a topic for another post. For the sake of argument let’s say a duty cycle of one hour is short. A duty cycle longer than 1 day is long)

The most significant limiting factor of all METI done so far, as well as most attempted SETI strategies, is the “haystack” of duration (how long a beacon signal lasts) and the duty cycle (how often is it repeated). Even if we were so amazingly lucky as to reach a planet of radio-smart ETs , the chances of any of our METI transmissions being detected is small because the signals only last a short time and are not repeated. (Indeed, acquiring the signal a second time is the filter through which any possible messages must pass. All the various WOW signals we have heard have not).

lomberg_seti

Image: Thinking about how a METI signal might be sent may cause us to re-evaluate our methods as we search for extraterrestrial intelligence. Artwork by Jon Lomberg.

Larry Klaes points out that sending uninterrupted powerful beacons is expensive. I would add to that annoying. Tests of tsunami sirens here in Hawaii are necessary but annoying, so they happen in my neighborhood only at 11:45 a.m.on the first Monday of each month. We want the tests and we want the test alarm to be very loud, but not happen too often.

A loud isotropic SETI beacon may temporarily inconvenience somebody doing something else in the society sending the beacon. Shielded, directed beacons are less problematic locally, but also impossible to detect if you are not in the beam. So short, powerful all-directional beacons on many wavelengths may be a better fit for societies living near their own beacon transmitters. Make a really loud noise only intermittently, but one very easy to spot for the time it is on the air, whatever instrumentation you are using to listen.

Duration and power seem inversely related: the briefer the transmission, the cheaper the energy. Is it better to have a very powerful beacon at the expense of length of transmission? A brief, very powerful burst could be detectable at much larger distances than a weaker one that lasts longer.

Duty cycle is the key variable. How long does a sender wait to charge up the capacitor (or whatever) before transmitting again? How often will the neighbors tolerate it? In my opinion, senders will likely opt for briefer and stronger beacons, because they are much easier to detect and reach many more potential targets while minimizing local inconvenience. Beacons must therefore be repeated– but at what interval?

Unless we can devise strategies that allow continuous monitoring of targets (or send repeated METI beacons ourselves) we could be looking in the right place at the right frequency– when they are off the air. Very strong, brief bursts simultaneously in many known wavelengths and “Z-waves” (Sagan’s generic term for methods we don’t know about yet) would reach the greatest diversity of searchers. Senders really interested in finding others would cast their net as widely on the EM spectrum as possible.

Uninterrupted continuity of observation is the strategy that is most likely to detect intermittent but powerful beacons. A new SETI strategy would use arrays of low-cost, small receivers to look in many selected “special” directions: nearby exoplanets, sunlike stars, galactic center/anticenter axis, etc. By passing off to receivers worldwide we sustain continuous searching without a lapse. Perhaps such a search could be piggybacked on home satellite dishes, like seti@home.

The reason I am unconcerned about any risk with current METI is that the very brief transmissions sent only once are probably too short to be detected, and in any case impossible for recipients to confirm with a second observation.

Long-lived civilizations will be patient civilizations. They will expect searchers to be patient as well. A patient search is not one constantly changing targets. It is choosing your direction of search and settling in to listen constantly until you hear something. Until we do that, it is premature to speak of any “silence in Heaven.”

tzf_img_post

{ 47 comments }

djlactin September 21, 2009 at 9:50

To reduce inconvenience to the locals (here, astronomers performing detection experiments in whatever part of the spectrum involved), “simply” place the beacon on the far side of the moon. Some reflections would return from planets and the like, but could also be used as tools to study them. The signals would have to be chosen carefully, so as not to ‘confuse’ interplanetary probes.

Mark September 21, 2009 at 10:15

I’ve long thought that we’re looking in the wrong spectrum –nay, the wrong medium– for these signals.

We’re looking for EM signals. Advanced civilizations are probably signalling us by modulating a dark energy source, or a graviton source, or some other carrier that’s beyond our current understanding of physics. Once we attain that level of understanding, we’ll discover we’ve been bathed in such signals for millenia.

Nearest analogy I can come up with is the primitive and isolated society in the jungle, cut off from contact with all other human cultures and unaware of their existence, fruitlessly scanning the horizon for alien smoke signals. One day their medicine man accidentally invents the crystal radio receiver and they discover that there are other cultures out there, they just haven’t been sending smoke signals, they’ve been using radio.

Radio & Optical are like smoke signals. Once we understand dark energy or subspace or ______ fill in the blank (could be something we have not even thought of yet), we’ll find the galactic party line.

ASJ September 21, 2009 at 11:05

Given advancements in large CCD detectors and wide field optical telescopes,
optical SETI searches merge easily into conventional observing programs designed to locate other astronomical phenomena such as optical GRB flashes, etc. The search for unusual signals could include looking for very brief flash sequences occuring within a very short time window from two slightly different directions.

Gregory Benford September 21, 2009 at 13:21

I agree, it is premature to speak of any “silence in Heaven.”
A worldwide net of small radio telescopes, dedicated and funded by an independent body, would seem optimal.
There are other sharpening ideas, too. We three Benfords have put newer versions of our two papers online, at arXiv:0810.3964 and arXiv:0810.3966 of astro-ph about all this.

tacitus September 21, 2009 at 14:05

I can add some more ideal properties (in order of wishful thinking… :)

1. It should be unmistakably artificial (e.g. repeating the value of pi)
2. It should contain information on the location of the source of the signal (to aid further communications)
3. It should contain information on how to access and decipher information embedded within the signal (or perhaps in a different, more intermittent or weaker signal that contains much more data).

Regarding no.3, if there are better or more efficient ways of communicating than through a powerful beacon that is trying to be obvious to as much of the surrounding galaxy as possible, then perhaps the beacon is merely stage one in a two or three stage process to full, two-way communications.

For example, the beacon simply indicates a radio frequency to tune to or tells listeners to look out for a specific laser light source. And a second-stage signal doesn’t have to be that frequent either. If you embed a countdown signal in the beacon then you could put as much as ten years or more between full long-lasting informational broadcasts if necessary. All eyes/ears would be sure to be tuning in.

Finally, if there is an even better, future-tech way to communicate (e.g. ansible radio or some other FTL short-cut) then the second-stage signal could provide all the necessary theoretical and engineering details on how to build a device capable of such communication. (Yeah, like in “Contact”, though with an extra step in the process.)

tacitus September 21, 2009 at 14:19

We’re looking for EM signals. Advanced civilizations are probably signalling us by modulating a dark energy source, or a graviton source, or some other carrier that’s beyond our current understanding of physics. Once we attain that level of understanding, we’ll discover we’ve been bathed in such signals for millenia.

You could be right, Mark, but one would hope that these advanced civilizations would remember the little guys, and when they were once bound by the same technological constraints as we currently are, so hopefully they would leave a few EM-tech rabbit trails around for others to follow.

But, there could be a very good reason why they wouldn’t. If their civilization advanced from only being able to detect interstellar EM signals to using whatever future-tech interstellar communications technique they now employ within, say, a couple of hundred years, they may not think its worth the effort to send out EM signals. They might believe that any civilization worth its salt would progress past the EM-only stage within a very short period of time, in historical terms.

That could be especially true if FTL communications was possible in some way. Why send a message that will get there 1000 years after the target civilization has made contact by FTL means? (It might still be necessary if there is no obvious path from our current knowledge to the future-tech they employ, of course).

Tulse September 21, 2009 at 14:52

Some advanced cultures might use more “exotic” signaling media, but if intelligent life is indeed common in the universe, wouldn’t we expect to run across the more “basic” EM signals of a culture such as ours? If ETs exist, surely not all of them are communicating via sources we can’t detect?

tacitus September 21, 2009 at 15:38

Some advanced cultures might use more “exotic” signaling media, but if intelligent life is indeed common in the universe, wouldn’t we expect to run across the more “basic” EM signals of a culture such as ours? If ETs exist, surely not all of them are communicating via sources we can’t detect?

If the exotic signaling technology is only a few decades or a couple of centuries beyond that of basic EM technology in development terms, then it’s entirely plausible that more advanced civilizations would think it isn’t worth bothering with the old technology, especially if they’ve had the exotic technology for, say, 10,000 years already.

For selfish reasons (i.e. I’d like to see contact in my lifetime) I hope that’s not the case, but it’s easy to forget how short a 100 years is in terms of the broad sweep of history. It may turn out that our ability to ETI signals via EM and only EM lasts a very short period of time. Just think how many technologies have already come and gone within the last 100 years.

Tulse September 21, 2009 at 16:01

It may turn out that our ability to ETI signals via EM and only EM lasts a very short period of time. Just think how many technologies have already come and gone within the last 100 years.

Right, but this doesn’t necessarily solve the dilemma, as it doesn’t account for how many ETI cultures we should expect, and thus how many might currently be at the stage of using detectable EM. At the very least, if one says that there are no cultures we could detect that are using EM, that puts an upper limit on how many such cultures there could be. Presumably the probability of detecting an ETI via EM is determined both by how long a culture uses EM and how many cultures there are. If ETIs are very common, then even if each specific civilization uses EM for a brief time, we should be able to detect a civilization that has yet to pass through that stage. The silence tells us something about how common ETIs might be.

tacitus September 21, 2009 at 18:09

Tulse, I think it depends on how long the EM-tech window. Assuming the more exotic, more suitable technology does exist, if the EM window is only a few hundred years, you would probably need a very large number of alien civilizations to exist before you could expect to make even one detection. That would mean the upper limit could still be high enough for other factors (like the question of why we haven’t already been contacted yet) to come into play.

Of course, we won’t know what is reasonable to expect for a long, long time yet, unless we do quicky discover the intragalactic internet backbone technology. One can always dream!

Steven R. Martin September 21, 2009 at 22:00

You know, the far side of the moon would be a perfect station for a continuous signal. A SNAP module might give you a quarter century or more of continuous power. Perhaps a low-cost project to launch on a Falcon 9?

Tulse September 21, 2009 at 22:04

Good points, tacitus — I presume that someone more mathematically inclined than me could actually calculate what the density of civilizations would have to be for a given EM “window” and level of signal detectability.

Also, presumably detectability would relate to the power of the EM signal, and it may very well be that once the tech is advanced enough to produce extremely powerful EM signals, detectable by us over large galactic distances, it will also be so advanced as to make other, more desirable communications methods/media available. So we might not even expect to see any EM signal except from fairly close by, since we’d never even be able to detect a contemporary EM “window” of more distant ETIs.

Wayne Farmer September 22, 2009 at 0:42

It occurs to me that a highly capable civilization wishing to construct an interstellar beacon could modulate the emissions of a star. A large shutter could work as a transmitter while orbiting a star either by modulating its transparency (producing any desired transmission waveform), or by simply rotating while remaining opaque (producing a sinusoidal transmission waveform). Let’s hope our Kepler mission won’t miss an eclipsing “planet” that exhibits an odd periodic transparency while occulting its sun.

Wayne Farmer September 22, 2009 at 0:56

Ah – I see that Morrison had a similar idea in the 60′s: http://www.coseti.org/lemarch1.htm .

spaceman September 22, 2009 at 2:53

Is there really any reason to expect that we will stop or at least replace EM communication technology with a style of communication based on different physics? Obviously we are biased in favor of EM singaling, but aren’t other non-EM methods of communication more cumbersome and less technically complex? Or, perhaps advanced extraterrestrial civilizations use EM for communication amongst themselves on their home world but for some reason chose another method such as neutrinos for interstellar communication.

djlactin September 22, 2009 at 9:27

I recently read a novel (Titan, by Ben Bova) that included a very interesting ‘inverse’ of the METI concept. In it, sentient beings had seeded Saturn’s rings with self-replicating nano…. er … ‘things’ that emitted a signal each time Saturn’s moons reached a specified configuration. The characters in were considering mining the rings for water, but decided not to do so when the nano-whatsits were discovered. However, such a system would be very useful: it could signal the advent of a planet-faring civilization by CEASING. The system would also be coward-friendly by completely hiding the location of the seeders.

ljk September 22, 2009 at 10:40

French scientist Luc Arnold has discussed the possibility of advanced ETI
using very large geometric structures in space that transit their suns and
make clear to anyone who observes such a transit that the object is in
fact not natural.

At present, while we can detect when a large exoplanet passes in front of
its star due to the small dip in luminosity during the event, we are not at a
point where we can tell things like actual shapes. Of course a more advanced
species may have very large space-based telescopes that can resolve them.

Then again, we are starting to detect certain elements and molecules in the
worlds of other star systems. Perhaps we will be able to detect elements in
such structures that would provide another way to confirm that they are
artificial in nature. If a space-faring species uses their sun as a dumping
ground for nuclear and other kinds of artificial waste, that might be
detectable by us as well.

The details of this idea plus his papers on looking for biosignatures on
exoplanets may be found on his Web site here:

http://www.obs-hp.fr/%7Elarnold/homepage.html

Regarding the building of a SETI outpost on the lunar farside: While it would be
an excellent idea, if NASA does not get the funding and support it needs to keep
its manned lunar exploration plans going, that plan is going to have to wait for
a long time, as even the other nations that might be able or want to do such
things are nowhere near ready for a lunar base of any sort for at least the next
two decades or more.

I even read an article not too long ago about carving the planetoid Ceres into
a giant set of radio telescopes for SETI and other forms of radio astronomy,
but that also isn’t going to happen until well after we start moving out of Low
Earth Orbit (LEO) on a permanent basis.

As for ETI using communications methods very different from what most of
our current SETI projects are trying to find, it is certainly plausible that
other species, especially very sophisticated ones that can move about the
galaxy, might use communications technologies way above ours. However,
I tend to put this in the same category as hoping warp drives and cosmic
wormholes will get us to Alpha Centauri and way beyond: Not impossible,
but not likely any time in our near future.

They certainly show how imaginative we are and they help us think outside
the box, but as for getting us to another star system for finding a real ETI
signature, they probably will not be happening in the relatively short term.

Let us be honest here: If Kardashev Type 2 or 3 societies use neutrino
beams or muons to talk amongst its members and neighbors across the galaxy,
we probably won’t be on their party lines. Even if we did intercept one of their
transmissions somehow, those who run the few neutrino observatories and
particle accelerators on this planet are not looking for alien signatures as
part of their jobs. They would likely reject such a possibility in any event
due to their training plus the genuine fear of ridicule or worse from their
colleagues. Mainstream SETI still has enough strikes going against it even
in 2009 without adding more to the fringe factor.

So yes, highly advanced aliens or just alien aliens in general might have
abandoned radio and even lasers long ago, or never picked them up to
begin with, and now search and talk with others in the galaxy using methods
we either only know of in theory or cannot even imagine at all. But while it
is fun to speculate and something seredipitous may come out of such out of
the box thinking, exotic communications methods we won’t have a handle
on for many years or more doesn’t do our current SETI programs a lot of
good now and in the near future.

As has been stated in recent threads on this subject, the kinds of ETI we have
the best chances of finding at present are ones who are not too dissimilar from
humanity. This means that the odds are better placed in favor of them using
communications methods we are familiar with such as radio and lasers. This
will also have the advantage of us having a chance of comprehending them,
unlike a Matroiskha Brain or other form of Artilect that would think many
times faster and larger than us and would not even be organic.

I know I will probably hear the lamp post story analogy for saying the above,
but we are not going to have starships or giant gamma ray detectors on the
Moon any time soon, so we need to work with what we have or we won’t have
any SETI program at all. And I definitely recall not too long ago that SETI
in even radio form was struggling for survival. The attitude taken towards
SETI in the film Contact, which was made in 1997, was quite typical of the
mainstream science community and general public.

If we keep harping on what might be some day instead of focusing on what we
do have – especially in this global economy – we will be back to the days of
sporadic and token SETI projects or even less.

By all means, please do not stop speculating on SETI and alien life, but we
need to stop wishing about esoteric ways of doing such things or hoping that
some benevolent intelligences will come to “save” us and get into the
business of making these things happen for real with real physics and
real technologies. Or they will remain science fiction or fantasy forever.

Jon Lomberg has provided in this thread some practical methods to go about
detecting beings which we may be able to understand and communicate with.
This is a very good place to start the necessary sustainable SETI programs
we must have if we ever want to have a realistic chance of finding out if we
are alone in the Universe or not.

M. D. Van Norman September 22, 2009 at 12:05

Why announce your presence at all? Doing so is fraught with almost unimaginable risk.

tacitus September 22, 2009 at 22:12

M.D., you need to read some of the comments on these and other METI related threads. Simply put, any alien civilization capable of doing us harm (i.e. getting to Earth) almost certainly already knows we’re here anyway. Earth is easily detectable from hundreds of light years away with the right technology, as is the impact our technology has had on it. So broadcasting messages extremely unlikely to add much to whatever risk we currently face from others who would wish to do us harm.

John Hunt September 23, 2009 at 2:30

Unless intelligent civilizations routinely go extinct, they are bound to progress technologically to very advanced levels. In a relatively short period of time they should be able to make themselves stand out like the proverbial “sore thumb”. ljk mentions different means of affecting their starlight. I would add that they could also do the equivalent of this. IF they wanted to, they could make themselves known to us. I don’t buy the idea that advanced civilizations are unable to.

Humanity is facing existential threats from several directions. I think it therefore somewhat less likely that ETs are sitting on their “hands” until we develop FTL propulsion, figure out their frequency or mode of communication, etc. If we go extinct, they just lost a bit of diversity. Also, the longer that they don’t contact us and show us how to solve all our problems, the more guilty they are for failing to stop our suffering.

So I lean towards the idea that they don’t exist. That’s the easiest explanation. But it is improbable that, after billions of years and gazillions of exoplanets, that we just happened to be the first within a billion light-years.

Since, we seem to be fairly close to (by routine way of course) developing our own self-replicating existential threats and since we seem far from establishing a human colony at interstellar distances, the idea of universal self-extinction seems fairly plausible to me.

So, I predict that all attempts to detect advanced civilizations will fail. And broadcasting info about us will also be pointless because all other civilizations will destroy themselves while not being at a level where they will be able to detect our signals.

The only solution would be to use this understanding to pursue an unusual and successful course which no other intelligent civilization has gone. My guess as to what this course might be would be to intentionally demonstrate a contained existential threat so as to shock the powers-that-be into radical funding of interstellar travel and to suppress potentially dangerous technology so as to buy us more time for the interstellar mission.

ljk September 23, 2009 at 10:31

Replying to John Hunt’s post of September 23, 2009 at 2:30 (my comments
are marked with >):

Unless intelligent civilizations routinely go extinct, they are bound to progress technologically to very advanced levels. In a relatively short period of time they should be able to make themselves stand out like the proverbial “sore thumb”. ljk mentions different means of affecting their starlight. I would add that they could also do the equivalent of this. IF they wanted to, they could make themselves known to us. I don’t buy the idea that advanced civilizations are unable to.

> I don’t think it is a question of advanced ETI being unable to let the Universe
> know they exist or humanity in particular so much as whether they WANT to
> alert the Cosmos to their presence or not. And I do have trouble finding many
> valid reasons for a high-level intelligence wanting to deliberately contact us.

Humanity is facing existential threats from several directions. I think it therefore somewhat less likely that ETs are sitting on their “hands” until we develop FTL propulsion, figure out their frequency or mode of communication, etc. If we go extinct, they just lost a bit of diversity. Also, the longer that they don’t contact us and show us how to solve all our problems, the more guilty they are for failing to stop our suffering.

> What is the difference between genuine suffering where it is detrimental to
> the survival of a species and actual growing pains where one is struggling but
> it is towards acieving a higher and better goal? Would an alien species be
> able to recognize if we needed “help” or not? Would we WANT a non-human
> culture telling us how to live and act? Would we do the same for others in the
> galaxy? Would we even know how or recognize to help an alien?

So I lean towards the idea that they don’t exist. That’s the easiest explanation. But it is improbable that, after billions of years and gazillions of exoplanets, that we just happened to be the first within a billion light-years.

> Star Trek and Star Wars have done a disservice to the way people think
> about the size of the galaxy and the Universe. Space is BIG – really, really big.
> Not only would it be difficult for us to recognize an ETI civilization somewhere
> in the Milky Way, but our current state of science is designed to reject outright
> anything that appears artificial in favor of a more natural (non-intelligent
> explanation. That is a good policy overall, of course, but it will also keep us
> from recognizing and accepting evidence of ETI out there for quite a while.

> When we have directly explored a good portion of the galaxy and have found
> nothing obviously intelligent, then perhaps we can say we are alone at least in
> terms of anything galactically local. Otherwise it is WAY too early make such
> a declaration at our level of SETI and science in general.

Since, we seem to be fairly close to (by routine way of course) developing our own self-replicating existential threats and since we seem far from establishing a human colony at interstellar distances, the idea of universal self-extinction seems fairly plausible to me.

> Extinction, yes. A literally universal policy? Not so sure. Hey, I thought
> we would have been destroyed by nuclear war long before now, but we are
> still here. I know the threat is hardly gone, but we have thousands fewer
> nuclear weapons than we did at their peak in the Cold War of 55,000 bombs
> between the USA and USSR.

So, I predict that all attempts to detect advanced civilizations will fail. And broadcasting info about us will also be pointless because all other civilizations will destroy themselves while not being at a level where they will be able to detect our signals.

> Way too premature and just plain pessimistic, yikes!

The only solution would be to use this understanding to pursue an unusual and successful course which no other intelligent civilization has gone. My guess as to what this course might be would be to intentionally demonstrate a contained existential threat so as to shock the powers-that-be into radical funding of interstellar travel and to suppress potentially dangerous technology so as to buy us more time for the interstellar mission.

> You mean like turn Jupiter into a star as the Monolith aliens did in 2010?
> I don’t know, we’re talking politicians here. Maybe if you threatened their
> paychecks and perks, you might get a quick reaction. Otherwise threats of
> the nature you are talking about only seem to have short-term benefits.
> Take 9/11 for example: Everyone was buddy-buddy for a while, but life
>went back to politics and greed and hatred as usual in short order.

> I think we need to stick with honest, non-threatening approaches. They may
> still take longer, but humans tend to have bad reactions to be tricked or
> threatened and could outright reject what otherwise might happen given time.

> In David Grinspoon’s book Lonely Planets, he reveals that Carl Sagan was once
> asked to participate in a plan to pretend that aliens had been detected in order
> to boost SETI funding and unite the world. Sagan wisely rejected the idea as he
> felt once the ruse was reveald the backlash would be far worse than not finding
> any real aliens.

Tulse September 23, 2009 at 10:32

“Simply put, any alien civilization capable of doing us harm (i.e. getting to Earth) almost certainly already knows we’re here anyway. ”

Right, that may be why it’s not an added risk for us to broadcast, but it may explain why other civilizations aren’t. If there are indeed cultures out there capable of inflicting harm on an interstellar level, why would another interstellar culture risk advertising its existence?

In other words, maybe the heavens are silent not because there’s no one out there, but because everyone is scared.

After all, camouflage and concealment is very common in non-predatory organisms. In the case of interstellar civilizations, where it may not be possible to size up one’s potential predator until too late, the prudent thing for any civilization to do, no matter how powerful, is stay quiet.

ASJ September 23, 2009 at 12:19

If the galaxy were laced with automated monitoring stations (fleets of super-Voyager spacecraft), the message that “something is happening on planet Earth” has already been sent to their “data collection central”. These monitoring stations would be designed with long operating life, low energy usage and maximum opportunities for close approaches to interesting targets as requirements. Of course, contact with such a monitoring station will depend on its programming, or our ability to rendezvous with of these stations as it breezes past the Solar System.

tacitus September 23, 2009 at 14:54

Right, that may be why it’s not an added risk for us to broadcast, but it may explain why other civilizations aren’t.

I don’t know why it would be more of a risk for others than to us. They still have to live on habitable planets and the signature of life, if not the signature of technology, would be well-nigh impossible to mask.

I guess you could envision some Borg-like species that predates on the artifices of a technological civilization, but I would think it’s much more likely that a predatory species would target any habitable planet it came across, whether or not there is intelligence there. If habitable planets are rare, then it won’t matter how much you hide your presence. If habitable planets are commonplace, perhaps advertising your presence would actually allow the predators to avoid conflict and focus on the easy pickings.

I think, in the end, any advanced civilization will realize that attempting to hide is futile. Perhaps they might be reticent until they have confirmed that there are no nearby threats (within, say, 1000 light years), but as their own capabilities advance they will probably realize that any civilization just a few thousand years ahead of them (peanuts in cosmic terms) will have the technology to complete a pretty comprehensive survey of their part of the galaxy (von Neumann probes, etc) anyway.

It’s all complete speculation, of course, and the worrywarts will always point out that we don’t know what the psychological make up of an intelligent alien species would be like. Suffice to say that I don’t find the majority of the darker scenarios painted terribly credible. The galaxy is simply too big and spread out for the same type of conflicts over resources and conquest that we’ve seen historically here on Earth. And given that is highly unlikely that civilizations will arise at the same time, it’s not likely that two civilizations will share the same needs or wants anyway.

tacitus September 23, 2009 at 16:15

If the galaxy were laced with automated monitoring stations (fleets of super-Voyager spacecraft), the message that “something is happening on planet Earth” has already been sent to their “data collection central”.

Indeed, and it could still be thousands of years before home base has been notified and has responded to the message. That leads some to believe that if such monitoring stations exist, they will be highly autonomous, endowed with enough AI to determine what action it should take under different circumstances. Thus if the main imperative was to contact all new technological civilizations as they make their way into space for the first time, there would be no need to delay the hundreds or thousands of years it could take to communicate with its home planet.

But then… we ain’t heard anything yet… :-)

ASJ September 23, 2009 at 20:26

“But then… we ain’t heard anything yet… :-)”

Earth would have long been listed in a database as a planet with carbon-based life forms. The Solar System would be flagged for routine investigation at each flyby of opportunity. If super-Voyagers flew by Earth in the last 10,000 years, signatures of organized habitation along certain river valleys would have been noted. Large structures would have been detected in the last 4000 years. Road networks and cities in the last 2000 years. Their equivalent of Vela satellites may just now be detecting gamma rays from atmospheric nuclear tests.

The primary goal of this galactic Voyager fleet would be to collect and
distribute information to its network of “subscribers”. Self-protection and concealment would be a high priority. Any attempt to contact Earth would be in the nature of a test. Becoming a galactic network “subscriber” ourselves may be a long process, gaining admission only after we survive the next 10,000+ years and agree to contribute to the fleet-building project.

Ronald September 24, 2009 at 4:30

I hate to be a party-pooper, but I think I agree with John Hunt (23 Sept., 2:30) and the last part of Tacitus (September 23, 2009 at 14:54):

Even if advanced intelligence exists anywhere in our galaxy it must be so rare that it is highly unlikely that some kind of innate ‘cosmic caution’ would have developed by nature.

Fact is that in the billions of years of our planet’s history and among the multiple millions of species, there have only been a handful with higher intelligence and ‘self-awareness’ and only one with intelligence leading to a civilization. This leads one to the strong suggestion that such intelligence is not an example of convergent evolution (i.e. similar challenges leading to similar natural solutions in form and function, e.g. wings, legs, heart, respiratory system, eyes) but rather a extreme exception, a fluke.

Add to this the likelihood that a budding intelligence has a very realistic chance to go extinct long before reaching any technological level or even something we could call civilization. There have been several branches of humanoids, but we are the only survivors. And even our own species has developed civilization and technology only recently.

I think the main problem is not an advanced civilization exterminating itself, but rather an intelligence going extinct long before ever reaching technological civilization.

We may have to face the stark reality, that our galaxy (and other similar ones, such as Andromeda) may be filled with potentially suitable planets, even teeming with various biological lifeforms, but with no or virtually no other advanced civilization.

I myself would be overjoyed if we just found the unambiguous biosignature of another earthlike planet with a biosphere, any biosphere.

Ronald September 24, 2009 at 4:41

Further to my previous comment; the Star Wars series, though of course being mainly fun instead of science based, has one trait, which I always liked as a fundamental idea: the scene is strongly dominated by humans, most of the intelligent beings are simply humans and many if not most of the inhabited planets in that galaxy are inhabited by humans (and it seems that they don’t even know their true origin!).
This might some day be the real picture of our own galaxy: we may become the ‘aliens’ ourselves, even diverging and diversifying as we disperse, and only very occasionally (rarely) encountering some kind of other intelligence in some stage of development.
Not a bad prospect, I would say.

Athena Andreadis September 24, 2009 at 10:32

Although I detest Star Wars for reasons I explain in my article We Must Love One Another or Die in Strange Horizons, I agree with the central point of Ron’s post: If we undertake long-term stellar travel and planetary settlement, we will speciate inevitably and relatively quickly (compared to standard “unforced” evolutionary rates) because of the unique circumstances of each starship or habitable planet. I have discussed this development in the last segment of my Aliens series, Making Aliens 6: The Descendants.

ljk September 24, 2009 at 10:54

Ronald said:

“Even if advanced intelligence exists anywhere in our galaxy it must be so rare that it is highly unlikely that some kind of innate ‘cosmic caution’ would have developed by nature.

“Fact is that in the billions of years of our planet’s history and among the multiple millions of species, there have only been a handful with higher intelligence and ’self-awareness’ and only one with intelligence leading to a civilization.”

We have ONE data point to go on, Earth and its inhabitants. Science always
needs multiple data points before it can start coming to certain conclusions.
Thus our need for SETI, limited as it has been and still is.

Intelligent societies may not be terribly obvious around every sun as we
thought and hoped in the early days of SETI, but there is so much of the
Milky Way galaxy alone that we have yet to explore in any depth.

Look at the situation with exoplanets: We know of just over 300 after
twenty years of searching for them (I am including the pulsar planets).
Astronomers estimate there are hundreds of billions of planetary systems
in our galaxy alone that we know nothing about yet. Of the few hundred
alien worlds that we do know about, most of them are not like the ones
in our solar system (most astronomers did not expect super Jovian type
worlds to be orbiting their suns in a matter of days or less as one example).

So just imagine what is out there in terms of life that is so much harder to see
in our current situation. It is just way too early for us to make such declarations
about who and what is or is not out there.

Athena Andreadis September 24, 2009 at 14:32

I want to add several clauses to Larry’s reply. In the last half-century we have been progressively attaining technologies that allow us to essentially walk from the left to the right of the Drake “equation”. We have detected solar systems, we have detected Jupiter-size planets, we just began to detect Earth-size ones… so it will be a matter of time before we become able to detect biological and, who knows, cultural signatures.

For detecting physical/chemical activity, the advantage is that we know these follow universal rules; also, we’re directly or indirectly familiar with their “exotic” variations. That doesn’t hold true for biology, since we’re still limited to our single sample. And the same caveat holds even more strongly for cultural signatures. The sole unambiguous footprint would be a concrete artifact — like Clarke’s black monolith, or McDevitt’s Enceladus ammonia ice sculpture.

Ronald September 24, 2009 at 15:08

@ljk, September 24, 2009 at 10:54:

“We have ONE data point to go on, Earth and its inhabitants”.

I sure agree that we have only one data point as an example of a living planet, which is a very poor sample indeed.

However, I dare argue that when it comes to data sampling with regard to intelligence, our sample is vastly greater: millions of species over eons of time and various environmental conditions.

And yet, only one advanced intelligence.

It is this which is so strongly suggestive that intelligence is not a logical outcome of evolution given specific conditions (convergent evolution), such as long necks, strong legs or wings, but rather an extremely unusual (and expensive and risky) strategy for survival. Life has proven to do perfectly well without it. One positive thing we can say about is is that, once it arises and manages to surpass a certain threshold, it can develop very quickly.

What could we compare it to? A highly unusual but handy trait that occurs at most once or a few times only in the lifetime of a planet, such as … ?

I am definitely not asserting that there could not be other advanced intelligences and civilizations in our galaxy, but I do suggest that these are probably exceedingly rare for the above-mentioned reasons.

amphiox September 24, 2009 at 16:09

Ronald, while your argument is logical, it is equally logical to argue that since 100% of all known biospheres older than 3.5 billion years have produced an intelligent, technological species with the desire to explore and communicate, to search for and send messages to the stars, which has not destroyed itself despite numerous self-destructive tendencies, we should expect that ALL habitable planets of a certain age will have an intelligent civilization either contemplating or attempting a METI or SETI program, and ALL of them will survive long enough to start sending and listening for signals.

Both lines of argument are equally valid with the available data, which is what we get with an N of 1.

tacitus September 24, 2009 at 16:33

Larry, I certainly agree it’s far too early to give up on hunt for other intelligent life, and I am optimistic that there some out there to be discovered eventually (just not likely in our lifetime), but we do have to deal with the fact that unless we’re in some type of Prime Directive-style quarantine, it is a concern that no one has contacted us so far.

Assuming there is no quarantine in force around Earth, one can only conclude that technological civilizations much be rare in our galaxy since absent some insurmountable problem with achieving interstellar travel, it would only take one of them to advance perhaps just a few thousand years ahead of where we are before they were able to undertake a comprehensive survey of the galaxy. 12 billion years is a long time to go without some form of advanced intelligence to arise before ours.

Perhaps it’s just a matter of time. If there isn’t a permanent presence in all solar systems (or at least the likely candidates for life to evolve) then may be it will take a few thousand years for them to catch up with us if we are now deemed ready for contact, of course.

I tend to think one of two scenarios is true — either we are one of a very rare cases where intelligence has evolved to point of technological prowess, or intelligence is commonplace and we are being monitored and/or being left to our own devices. (But no, I don’t believe in UFOs or alien abductions!). When I’m pessimistic, I think the former is more likely, but when I’m optimistic, the latter, since I think that’s our best chance of making contact in my lifetime.

I don’t know. Thinking about all the possible permutations is enough to make one’s head spin! Thankfully, whatever the reality, our curiosity will certainly lead us to make as full and detailed a survey of our neighboring star systems anyway, to give us at least a slightly better idea of what we are dealing with. I am still hopeful that we will catch our first glimpse of another Earth-like planet within the next two decades, and it will be exciting to see what type of planet it reveals.

Ronald September 25, 2009 at 3:38

@Amphiox; without wanting to drag this discussion detail out too long, I disagree: the sample size is indeed N = 1 with regard to planet/biosphere. However, the sample size is xx million when it comes to species and intelligence.

Regarding convergent evolution and inevitability: I would agree with you and ljk if higher intelligence was something that pops up regularly among various (and very different) lifeforms under certain environmental circumstances over time (such as wings, eyes, legs, long necks, gills, etc. etc.). Similar solutions for similar challenges.
However, we just do not see that happen for inteligence, or at least not for high intelligence such as ours (exceptionally large brain cortex etc.). Apparently then, ‘nature’ can also solve similar challenges without it and it is not a logical outcome of evolution under certain conditions.

The one thing that gives some hope, however, is that tendency toward higher intelligence (including self-awareness, complex behavior and communication, maybe even some language) also seems to occur among cetaceans, elephants, certain birds (parrots, crows), …, though we have no idea how far this would develop and whether this would ever lead to something like ‘civilization’.

So I may still be wrong after all. Please correct me :-)

ljk September 25, 2009 at 13:15

There has been more than one intelligent species on Earth, and I do not mean
just any ol’ creature with a brain.

There have been at least 15 versions of homo sapiens in the last 5 million years
or so. We just happen to be the current survivors.

And there was a very recent article on how certain higher organisms on this
planet such as whales and primates have cognitive abilities similar to the way
we humans think in terms of planning ahead and deciding which of several
possible actions will have the best outcome.

And we have known for quite a while now that humans are hardly the only
terrestrial beings who use tools for a variety of reasons. That old chestnut
which folks once used to differentiate us from the animals is long out of style.

So maybe we haven’t found (or recognize) an extraterrestrial intelligence yet,
but we do have modern evidence that humans are not the only “smart” ones
on the block.

Next we need to stop assuming that just because there could be other intelligences
in the galaxy that they all know about Earth and humanity and have nothing better
to do than get our attention or pay us a visit in person. I would not be at all
surprised if other young species who first become aware of the Cosmos ask the
same thing of their potential neighbors as well.

Ronald September 25, 2009 at 15:19

@ljk:
“There have been at least 15 versions of homo sapiens in the last 5 million years or so. We just happen to be the current survivors. ”

Well, that is hardly encouraging and in fact confirms my concerns: all within one and the same lineage (Homo) and even of those all but one species perished before reaching techno civilization level.

“(…) certain higher organisms on this planet such as whales and primates have cognitive abilities similar to the way we humans think in terms of planning ahead and deciding (…)”

Now, that *is* encouraging.

Ron S September 25, 2009 at 23:56

I’ve been tied up for some time and just returned to skim through some of the comment threads. I will venture just one thought:

No matter how many assumptions you pile on top of one another they will never add up to so much as one fact.

(This is not to be confused with calculus where the addition of an infinite sum of infinitesimals can add up to a real number!)

M. D. Van Norman September 27, 2009 at 4:03

The danger of broadcast is probably not the well-established interstellar civilization—though that’s a big assumption in itself—but rather the outcasts of that civilization. The best time to exploit a less advanced civilization is just when it’s beginning to develop its own interplanetary infrastructure but still incapable of defending itself against even one hostile starship.

tacitus September 27, 2009 at 17:30

My assessment of the risks of broadcast are not based on the assumed altruism of any aliens, either their main players or the outcasts. It’s purely down to how visible Earth already is as a planet harboring life and eventually, as the light cone extends, technology.

If the danger lies within a few dozen light years then all bets are off. Any interstellar-capable civilization will almost certainly have detailed images of Earth including the night-time illumination which is a dead give-away regarding our presence.

Once you’re out to, say 500-1000 light years then perhaps detection is that much harder, but the sheer distance is much more of a buffer from any expeditionary force the aliens might launch. If they waited until they detected signs of industry in the light spectrum then we would have at least many centuries in which to advance our own technologies.

I’m short of time otherwise I would go into more detail, but suffice to say that any deliberate beacon is unlikely to increase the risks of attack from hostile aliens by very much at all.

ljk September 28, 2009 at 7:58

M. D. Van Norman said on September 27, 2009 at 4:03

“The danger of broadcast is probably not the well-established interstellar civilization—though that’s a big assumption in itself—but rather the outcasts of that civilization. The best time to exploit a less advanced civilization is just when it’s beginning to develop its own interplanetary infrastructure but still incapable of defending itself against even one hostile starship.”

I am willing to bet that the first human explorers who leave our
Sol system for the wider galaxy will be those who are unhappy with
current human society or need to leave for reasons other than pure
scientific exploration.

I can imagine some cult group or band of missionaries escaping the
Sol system and becoming our first “ambassadors” to the stars. Just
imagine them running into a group of ETI with similar motives.

Who knows, maybe they will find mutual understanding with each
others situation and get along. Let’s hope they don’t decide to team
up and go a-conquering.

ljk September 28, 2009 at 13:04

Expanding upon my sentiments above, I think another question that is not
always considered first is, while we naturally worry about unknown beings
dwelling in the galaxy that might be a threat to humanity and other species,
perhaps we should consider the distinct possibility that the main character
in the Pogo comic strip once uttered, that “we have met the enemy and he
is us.”

I know we are stuck on that one annoying data point (Earth life), but just about
every creature living on our world (and we assume we all began and evolved
on this planet) competes with every other life form to survive long enough to
reproduce. Most of it is not done out of evil or even willful intent beyond the
fact that all organisms need a certain amount of room and resources to grow
and carry on their DNA. If something interferes with it, a typical creature
either flees from the danger to find a safe location or it defends itself to live.
Either that or one becomes the aggressor in a similar motive of survival.

Perhaps just as we hope and assume some alien beings are benign and
cooperative, there may also be worlds where the life has developed that is
also cooperative rather than in constant conflict for survival. However,
perhaps such beings are not terribly diverse as Earth life is, or perhaps
they were once diverse but all that is left are the few winners who finally
learned how to get along and tolerate each other. This applies to intelligent
species as well as animalistic ones.

Are there worlds out there were only a few species dominate their planets
or whatever place they live upon? Or do all worlds start with a few simple
species that turn into many different kinds over time that do a complex
combination of cooperation and competition? Are we the norm? All I can
think of is how we used to assume most other planetary systems would
resemble ours, but most of the 300-plus that we know of so far don’t look
much like ours at all. Will this also apply to alien life and explain at least
in part our lack of a successful SETI project so far?

It is probably a sad joke to assume humanity could ever be considered a
threat to the makeup and stability of the Universe as a whole, but might we
be the dreaded enemy many people tend to fear to at least our closer
sections of the Milky Way galaxy?

Suppose we do start seeing spaceships leave our Sol system not filled with
brave, noble astronauts or rational and hyperintelligent machine-based
beings, but groups of humans not terribly different from what has existed
on Earth since well before written history: People who think existence is
better out beyond the Oort Cloud or groups who feel too oppressed to stay
anywhere near the current bulk of human society. Or perhaps groups who
feel it is their divinely-inspired duty to spread their beliefs to what they
consider the great unwashed of the galaxy.

M. D. Van Norman September 28, 2009 at 17:03

Tacitus, I agree with your overall assessment. Given interstellar distances, the risk is probably always very low, but I don’t think it can be dismissed entirely. It would also neatly explain why we haven’t spotted any beacons.

However, to get anthropic, we humans are probably first on the scene, so there have been no beacons to spot.

Adam September 30, 2009 at 5:34

Radio is so passe

http://arxiv.org/abs/0909.4554

Submarine neutrino communication
Authors: Patrick Huber
(Submitted on 25 Sep 2009)

Abstract: We discuss the possibility to use a high energy neutrino beam from a muon storage ring to provide one way communication with a submerged submarine. Neutrino interactions produce muons which can be detected either, directly when they pass through the submarine or by their emission of Cerenkov light in sea water, which, in turn, can be exploited with sensitive photo detectors. Due to the very high neutrino flux from a muon storage ring, it is sufficient to mount either detection system directly onto the hull of the submersible. The achievable data transfer rates compare favorable with existing technologies and do allow for a communication at the usual speed and depth of submarines.

drpayton December 27, 2009 at 5:47

I believe that all possibilities are true.considering the fact that we do not know what is true then we must hope for the best and prepair for the worst. It pains me to consider that we r alone but it must be done. Hopefully the opposite is true and we can embark on a glorious mission of stellar travel… But we may only find ourselves searching deeper and deeper until we have forgotten where the journey begain.

Brandon April 7, 2010 at 15:10

What if we could block the light of the sun from going in a certain direction (not in our direction; we need that light/heat :P)? It seems to me that if any beings were looking for life like ours, the first thing they’d see is our star. If we could block out that light at irregular intervals (so it wasn’t mistaken for a planet passing by), maybe it would get seen.

Administrator April 7, 2010 at 16:41

Brandon, Luc Arnold has done some interesting work along these lines:

http://www.centauri-dreams.org/?p=434

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