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SETI: Stiff Odds Against Eavesdropping

Take a look at the frequency range of our SETI searches and you’ll see that we are probing into new territory. Project Phoenix, which ran from 1995 to 2004, used radio telescopes at Arecibo, Parkes (NSW, Australia) and Green Bank (WV, USA), working in a frequency range of 1.2 to 3 GHz. The BETA project used a 26-meter radio telescope to examine the so-called ‘waterhole’ frequencies between 1400 and 1720 MHz, which seemed a likely place to look for an extraterrestrial beacon because this range covers an unusually quiet band of the electromagnetic spectrum between the hydrogen spectral line and the strongest hydroxyl line.

With the Allen Telescope Array coming online, we can look forward to a search of 250,000 stars in the ‘waterhole’ region, but new facilities like LOFAR (Low-Frequency Array) are pushing into the megahertz area in pursuit not only of SETI but also astrophysical studies of the early universe. LOFAR makes me think back to my shortwave radio days, tuning around these frequencies looking for hard to catch transmitters in places like the Falkland Islands (extremely difficult) or Tristan da Cunha (impossible unless you were based in South Africa). I often wondered about SETI at these frequencies and dismissed it as absurd. But that was then.

From Interference to Silence

The problem with LOFAR’s frequency range is that it runs into massive interference from many of the things our civilization does to emit radio signals, from radar to television stations. New technologies have come along that allow us to filter out this interference with great efficiency. But it’s undeniably true that we are radiating strongly in these wavelengths, so it’s an interesting question whether we might be able to pick up a civilization doing the same things by using LOFAR or the upcoming Square Kilometer Array (SKA), which some studies tell us could detect signals like those we produce at a distance of up to 300 light years.

A new paper by Duncan Forgan (University of Edinburgh) and Robert Nichol (Institute of Cosmology and Gravitation, Portsmouth, UK) looks at these possibilities in the context not only of technological capability but the likelihood of running into such radio leakage in the first place. The duo worked with Monte Carlo realization techniques, generating a catalog of planets which can develop life that evolves toward intelligence, and creating statistical populations of ETIs that develop at various times and locations. The resulting realizations are run multiple times and the resulting distributions averaged to quantify the uncertainty in the modeling process.

The connectivity calculations are approached in two ways, the first setting no maximum distance or time limits on communication — imagine a civilization that puts out detectable radio signals for the duration of its existence. The second, however, is more like us and it is deeply constrained. It tends to go quiet at these wavelengths rather quickly, just as our own civilization is doing. Here the distance assumption is 100 parsecs and the time that a civilization leaks radiation into space is reduced to about 100 years. As the authors note:

…we should think carefully about what we might expect the SKA to see. While humans are still leaking radio emission into the Galaxy, the extent of this emission has diminished. Technological improvements have reduced the transmission power required to broadcast, and the dawn of the digital age has begun to supersede traditional radio entirely. These events have occurred in just over 100 years, putting us on the path to becoming a “radio quiet” civilisation. If the Biological Copernican Principle is true (i.e. humans are not atypical as intelligent species), then what happens if all civilisations rapidly become radio quiet?

Human-like Cultures Hard to Find

The first scenario is easy to analyze, with cultures around various stars exchanging messages at the speed of light for the duration of their technological maturity. But the second scenario is grim. Connectivity reduces to virtually zero: Human-like civilizations have a probability of communication in the area of 10-7 under these constraints. We can play with the parameters by extending the observation period of a SKA-like installation from the 30 days used in these calculations to 10 years, in which case the probability of detection becomes 10-4. Assume 105 civilizations and a small number of detections become possible, although the likelihood of using a facility like SKA for 10 years of constant observations on a SETI project is slim.

If other civilizations behave like we do in terms of radio communications, then, we are not likely to find them with SKA. These considerations are not new, but the authors have updated the discussion by using the most recent predictions for the possible distribution of habitable planets and the sensitivity of the latest radio detection technologies. As the paper notes:

While the SKA remains an important instrument for SETI researchers, its abilities are limited to detecting civilisations that are at a less advanced state than Mankind, i.e. they must develop radio technology that remains radio-loud for a significant period of time. This strengthens the argument for a multi-wavelength approach to SETI, as radio-quiet civilisations may be optically loud, or detectable at some other energy scale…

The last point is the most important conclusion of the paper. Because the detection of radiation leakage from other civilizations at our current level of technology is unlikely, the multi-wavelength approach cited above is the best way to proceed. If accidental communications are off the table, we are probably looking for beacons, or else for signals deliberately beamed at us. Such a signal would demand a civilization far more advanced than our own, and in the latter case, one that was aware of our existence because it had developed a capability for optical or radio detections that we have yet to achieve.

The paper is Forgan and Nichol, “A Failure of Serendipity: The Square Kilometre Array will struggle to eavesdrop on Human-like ETI,” accepted for publication in the International Journal of Astrobiology and available as a preprint.


Comments on this entry are closed.

  • Tulse July 8, 2010, 10:31

    I’ll be a bit contrarian here — if detection of ET signals is so vastly unlikely to produce results, does it make any real scientific sense to spend the resources doing this, rather than on other more immediately useful space-related endeavours? Don’t get me wrong, I would be extremely excited and delighted if we did receive a signal from the stars, and I think it would be perhaps the most significant event in our species history. But with those detection probabilities, SETI seems more like the activity of a cargo cult than real science.

  • Bounty July 8, 2010, 12:58

    Do you have some examples of the types of accidental detectable signals we have been sending out that will soon be ‘gone?’ It seems like there is a big jump from every radio civilization able to connect, to everyone is quiet except for a few super advanced beacon civilizations. Do we need every television station active in order to be ‘noisy,’ or would just one do? Basically I’m thinking of simple ‘beacons.’

  • Thomas Hair July 8, 2010, 13:15

    I must disagree with the entire premise that our civilization is going radio quiet. We are only going radio communications quiet. The need for powerful radars will continue whether they be for tracking aircraft, spacecraft, or afternoon thunderstorms. The Cobra Dane radar on Shemya Island in the Aluetians could be detected by a SKA thousands of light years away…and it conveniently broadcasts in the water hole at tight bandwidths as do most other powerful search radars. I suspect our first detection will probably come from just such a source.

  • Chris T July 8, 2010, 14:41

    This is precisely why I’ve moved to the opinion that passive SETI is a waste of time. Much better to spend resources on advancing active approaches, such as planet hunting.

  • NS July 8, 2010, 15:04

    To Tulse, the more expensive instruments used for SETI (including the ATA, LOFAR, and SKA) also gather data for other astronomical projects. The resources dedicated exclusively to SETI are small.

    I think Thomas Hair is right that other advanced civilizations (if any) will be doing things, like scanning for asteroids or communicating with deep space probes, that we might intercept. Unfortunately these would appear to us as transient events and wouldn’t be verifiable. Current SETI searches all require a long-lasting detection for verification.

  • Thomas Hair July 8, 2010, 16:00

    NS is right, many will be transients, but some of the most powerful we transmit, for example, are part of the always operational US Space Surveillance Network of phased array radars operating world-wide. Each radar constantly scans a sector of the sky electronically many times per second (as opposed to a traditional rotating radar) to track earth-orbiting and near earth objects. In this circumstance, as seen from light years away, each transients would last for tens of minutes only to be replaced by a new transient at a slightly different frequency.

    Additionally, after reading the entire submission of Forge and Nichol I was a bit taken aback by the N-peak value in their conclusion. A Monte Carlo simulation’s results are only as good as its underlying assumptions…and I humbly submit that their 100 years to radio quiet is way off because I know of no one in the field of satellite/aircraft/weather/etc tracking who would make the claim that we will be switching off the tracking radars anytime soon.

  • Administrator July 8, 2010, 18:02

    Thomas Hair writes:

    I know of no one in the field of satellite/aircraft/weather/etc tracking who would make the claim that we will be switching off the tracking radars anytime soon.

    As indeed we had better not, given their value in the detection of near-Earth objects.

  • Michael Simmons July 8, 2010, 19:24

    How do intelligent civilisations communicate with their colonies at high bandwidth both with in solar systems and across star systems?
    Could that be picked up?

    If they have large, exposed to space, colonies then those will need to detect incoming asteroids etc. Hence powerful radars of some kind.

    In my opinion the best chance of us making contact with another intelligent with our technology is to rapidly cycle short high powered directional transmissions at millions of nearby stars (via a phased array?). The odds are much higher of a more advance race being able to pick that up, using equipment made for some other purpose, than us picking up them.

    We have had radio for what, 150 years. Wait until that’s a million or so years.
    Given cosmic time scales its incredibly unlikely they are going to be at the same stage as us. Chances are they will be millions if not hundred of millions of years ahead of us.

    If intelligent civilisations never migrate of their home world, fibre their entire planet and live that way for millions and millions of years , then yes we probably won’t find them.

  • Interstellar Bill July 9, 2010, 3:12

    A civilization could go from first spaceflight to a full Dyson swarm in a few thousand years, far less than the one-way comm times to most of the Galaxy. If you want to look for leakage, a K-II would be a beacon even at 99.999% efficiency.
    Such a Swarm would soon be spreading seeds to neighboring stars, especially the most luminous ones (for Swarms 10,000 times larger than Sol’s). Conventional SETI implicitly assumes this never happens, with stasis the unanimous norm, basically sidestepping Fermi’s original question. That question’s latest corollaries are ‘Where are the Dyson Swarms?’ and my favorite, ‘Are some galaxies Sub-Luminous because they’re actually being Swarmed as we watch?’

    The vastness of time is even more daunting than that of space. SETI also has to assume that most ET civilizations are far older than ours, which is reasonable given that ETs would necessarily implement near-immortality for themselves. But this conflicts with SETI’s implicit assumption of civilizational stasis, which immortals would find utterly boring.

    Between the Scylla of space-vastness and the Charybdis of time-vastness, how can SETI find its way? Finding ET at the small distances we can cover could only happen at ET-probability levels that would also produce millions of Swarmed Galaxies. It’s an all-or-nothing alternative (no ETs or trillions), while SETI needs an impossible, in-between self-contradictory scenario–‘Just one little ET, that’s all.’ Every ET in the entire history of the cosmos has to have taken the Oath of Stasis and the Vow of Renunciation of Astro-Engineering, yet the ones within our range will be broadcasting helpful leakage signals. Fat chance of that.

    ‘Twould thus be prudent to have other astronomy-uses for the SETI data. SETI’s only reasonable prospect is continued failure, even after we get giant antennas and telescopes in space. But we do have to listen, just in case that Big Thrill does come.

  • philw1776 July 9, 2010, 13:38

    Yes, passive SETI’s prospects have dimmed at an exponential rate faster than our search and detection capabilities have grown. The outlook by all execpt the rabid has grown more sanguine as we’ve had time to reflect on the actual probabilities. I’m much more pessimistic now than in the 60s and believe that we’re the only technical civilization in and surrounding the Virgo cluster at the best. Still, not to look (OSETI) or listen at all would be foolish. The money and resources for SETI are small enough to continue at this modest rate of expansion of capabilities. What if all we ‘know’ is really, really off base?

  • Ron S July 9, 2010, 20:22

    While it is necessary to make a whole raft of assumptions when calculating the probability of success with any SETI effort, it is regrettably the best we can do when making decisions on whether to spend the time and effort doing so. To me, that makes proposals like that by Loeb to piggyback SETI on LOFAR (which we’ve discussed here before, and the present paper references) attractive since the added cost is modest.

    One point that I think is worth criticizing in the present paper is that it does not deal with second-orders effects. It correctly notes that there is only one planet known to be making detectable “stray” transmissions (Earth), but does not then take into accounts that this impacts the probability of SETI success. For example, if a more-advanced ETI that has gone radio quiet (a questionable assumption) it does not mean that they do not listen. If they do listen and they hear us, they may then decide to transmit to us, directly, to see if and how we respond. Radio silence does not imply passivity.

    This of course reduces the distance of a detectable ETI to perhaps no more than 30 ly since truly high-power microwave transmitters only really came online after WW-II. They might nevertheless then choose to transmit to us in optical or neutrinos or something else that strikes their fancy, to determine our technological gradient by measuring how long it takes us to notice and deal with their chosen form of signal. ETI will likely be more clever at this game than we can imagine.

    I’m not saying this is the case, but only shows that any set of assumptions tends to unreasonably narrow the intentions and capabilities of ETI, us, or both.

  • Greg July 10, 2010, 21:08

    The one problem I see with this study is that it’s based on our current world technology level. If and when we branch out to the rest of the solar system I would think we would see an increase in radio communication. Also any young “colony” would be more resource dependent, basically low to no manufacturing industry established, which would imply that their technology levels would be lower than on their home world, and more likely using older radio technologies. This should extend the time a civilization is radio “noisy”. The fascinating thing is, based on our ability to detect radio signals we could then determine the development level of a civilization. Of course this all is speculation if in the next 50 years we develop cheap neutrino communications.

  • ljk July 6, 2011, 23:31

    Square Kilometer Array telescope may help make contact with aliens

    by Staff Writers

    Canberra (XNA) Jul 06, 2011

    The Square Kilometer Array (SKA), the world’s most powerful radio telescope in development, may help make contact with aliens, if there is any, Australia’s leading astronomer Fred Watson said on Tuesday.

    The SKA is a global collaboration of 20 countries, which is aimed to provide answers to fundamental questions about origin and evolution of the Universe.

    It will be able to survey the sky more than 10,000 times faster than ever before. With receiving stations extending out to distance of 3,000 km from a concentrated central core, it will continue radio astronomy’s tradition of providing the highest resolution images in all astronomy.

    Professor Watson, astronomer in charge at the Australian Astronomical Observatory at Coonabarabran in New South Wales, said the SKA will reveal more about the origins of the universe.

    “It’s about asking the big questions,” The Australia Associated Press quoted Professor Watson as saying Tuesday.

    Full article here:


  • ljk May 25, 2012, 16:41


    SKA, the World’s Largest Telescope Will Be Built at Two Sites

    by Nancy Atkinson on May 25, 2012

    In an anticipated great compromise, South Africa and Australia will share their sites for the Square Kilometre Array telescope, the world’s largest and most sensitive radio telescope. Both sites were competing to win the $2 billion contract for the SKA, which is hoped shed light on how the Universe began, why it is expanding and whether there is any other life beyond our planet.

    “We have decided on a dual site approach,” said SKA board chairman John Womersley, following a meeting of the SKA organisation’s members. “This position was reached after very careful consideration of information gathered from extensive investigations at both candidate sites.”

    An SKA press release said the majority of the members were in favor of a dual-site implementation model for SKA. The members noted the report from the SKA Site Advisory Committee that both sites were well suited to hosting the SKA and that the report provided justification for the relative advantages and disadvantages of both locations, but that they identified Southern Africa as the preferred site. The members also received advice from the working group set up to look at dual site options.

    Therefore, the majority of SKA dishes in Phase 1 will be built in South Africa, combined with MeerKAT, a seven-dish prototype interferometer array built by South Africa, where 190 dishes will be added. 60 dishes will be added to the Australian Square Kilometre Array Pathfinder (ASKAP) array in Australia, as well as a large number of omni-directional dipole antennas. This will give the Australian site a wide-field survey capability, whereas South Africa will be able to look deeply into a narrow part of the sky.

    Three antenna types, high frequency dishes and mid and low frequency aperture arrays, will be used by the SKA to provide continuous frequency coverage from 70 MHz to 10 GHz. Combining the signals from all the antennas will create a telescope with a collecting area equivalent to a dish with an area of about one square kilometer.

    All the dishes and the mid frequency aperture arrays for Phase II of the SKA will be built in Southern Africa while the low frequency aperture array antennas for Phase I and II will be built in Australia.

    “It’s a distinct possibility that we’ll discover a new type of astronomical object,” CSIRO SKA Director Brian Boyle told Universe Today in interview earlier this year. “History has shown that every time we’ve gone to a new astronomical wavelength domain, we pick up new objects.” An example of that is the discovery of pulsars in radio

    At the lowest frequencies, the SKA will be looking for red-shifted hydrogen, looking at the very earliest events of our Universe. At highest frequencies will look for things like pulsars or even pre-biotic molecules in space. The array will also be very effective in looking for transient events like supernovae or gamma ray bursts.

    “The placement of the array will give it a phenomenally wide field of view, between 30 and 100 square degrees,” Boyle said. “It is hoped to provide the first all-sky survey at phenomenal depths at these wavelengths, which can then be compared with other all-sky surveys done at optical wavelengths.”

    One downside of splitting the frequencies between the two sites is that some of the science may suffer. One of the original science requirements of the SKA was to look at the same piece of the sky at the same time in different frequencies. Boyle said there is not much common sky between the two locations.

    Another is cost for having redundant computing and networking capabilities, not cheap for the remote areas where both sites are located.

    But the dual-site approach solves political issues, and the SKA press release says the arrangement “will deliver more science and will maximize on investments already made by both Australia and South Africa.”

    Womersley said that in this approach “Science is the winner,” and by building on existing pilot projects in both countries, the SKA will be made even more powerful.

    Additionally, technology is sure to get a boost, as the SKA project will drive technology development in antennas, data transport, software and computing, and power.

    Additionally, the SKA members say the influence of the SKA project extends beyond radio astronomy.

    “The design, construction and operation of the SKA have the potential to impact skills development, employment and economic growth in science, engineering and associated industries, not only in the host countries but in all partner countries,” said their press release.

  • Tim December 14, 2012, 18:54

    I’d tend to be a contrarian here to many of the views expressed. My opinion is that eavesdropping type SETI might be the ONLY realistic way of detecting and making use of other intelligent civilizations in the universe during a certain period in their technological development, and a lot more effort should actually be directed here. There are two main reasons. One is the very real possibility of the short duration in time for which an intelligent civilization will emit decipherable narrow-band emissions (we are already using broad band emissions for many of our communications). Radio communications we know lasted for about at least 100 years in our time, and maybe we can estimate detectable radio signals about 1000 years. After that, we just don’t know. Civilization may naturally self destruct or develop no interest in space being able to create at that point their own virtual worlds and lay low, or be too intelligent to care about less advanced life. Self-destruction seems highly likely, as we ourselves are extremely close to the precipice. The second reason is very practical… a really comprehensive eavesdropping expecting to pick up a hundred or so early technological civilizations by the Drake Equation would produce very valuable information as well as new technologies. We’d have a pretty good idea that either aliens don’t exist and maybe treasure our own lives more, and we wouldn’t have to waste future resources…..OR, we’d know they do exist and have get useful statistical information on their frequency and durations, early technological information to improve our own world, and learn to avoid possible calamities and unforeseen problem, by example, even if those civilizations have long since disappeared.
    I think with the recent discovery of many stars holding planets, an Appollo type eavesdropping endeavor would be well worth the money and could have huge payoffs and possibly be even essential for our survival as a species. I am not holding out for any superhuman benevolent race to help us out. We should take advantage of what is available with early technological civilizations who have discovered radio.
    Unfortunately, even the Allen array is not sensitive enough only able to pick up GW sources within 40 light years. If the average radio station on earth puts out 10’s of kW, this will not do. We certainly have the technology to build large radiotelescopes on the far side of the moon to accomplish eavesdropping detection of 10kW stations in our galaxy and nearby galaxies. It would be trillions of dollars, but within a world budget and I feel worth the expense. Poking around for superbright signals from supposedlly more advanced civilizations seems to be making too many assumptions.