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SETI: Don’t Expect an Alien Sitcom

Since we’ve kicked around the idea of searching for SETI signals in the television bands (as noted in a previous story on Abraham Loeb and the Mileura Wide-Field Array), it’s interesting to note Seth Shostak’s thoughts on the subject. Because although planet Earth has been broadcasting TV signals for some time now, our transmissions are unlikely to be received at any great distance. And that makes a search for accidental TV-like emissions even from relatively nearby stars problematic.

Shostak imagines a civilization 55 light years away hoping to pick up I Love Lucy from Earth. He notes that the non-directional TV signal, assuming a million watts of transmitter power, will reach this distant world “…with a power density of about 0.3 million million million million millionths of a watt per square meter…” And because only a third of the transmission power is in the carrier signal — the most readily detected part of the transmission — even that number is too high.

It’s possible to run these numbers against a new facility, the Low-Frequency Array (LOFAR) now being built in Europe for radio astronomy work. At VHF television frequencies, LOFAR will have an effective collecting area similar to that of the Arecibo dish. Says Shostak:

That’s big. That’s brawny. But not brawny enough. In our SETI experiments at Arecibo, we could find a signal if it were about 0.1 million million million millionths of a watt per square meter. That number, you will notice if you count up the words, is a million times bigger than the “I Love Lucy” carrier at 55 light-years. The aliens’ LOFAR would be inadequate to detect the broadcast by a factor of a million, a not entirely negligible amount. Simply stated: LOFAR couldn’t hear it.

That’s bad news for our hopes of picking up extraneous signals from a technological civilization. It doesn’t disqualify these frequencies from SETI study, but does imply that if we were to find something interesting, it probably wouldn’t be an extraterrestrial sitcom. If any readers have references to other work on the strength of such signals at interstellar distances, please let me know. It’s a question that bears on how visible our own culture is at the distance of nearby stars. The answer may well be that despite I Love Lucy, we’re still all but undetectible.

Comments on this entry are closed.

  • Ron S November 11, 2006, 19:36

    I found Shostak’s points to on beaming, carrier power & detection, and duration of the “broadcast age” to be correct. What puzzled me was that he started from scratch with his own quantitative analysis and did not specifically address Loeb’s analysis. That’s an odd critique since we’re left guessing if he found something wrong in Loeb’s reasoning or if he even read the paper. Allowing 20 db of long-term integration enhancement, and blindly assuming that they are using the same detection bandwidth, it seems they’re 20+ db apart in their positions, which would pull the 55 ly range back to 5.5 ly. That’s a lot!

    No, I have not attempted to do my own analysis so I can’t say judge who is right and who is wrong. However the calculation is, in its basics, straight-forward enough using well-known path loss formulae. There shouldn’t be this much disagreement.

  • Alexander Zaitsev November 12, 2006, 3:41

    The duration of such non-directional TV transmission is very, very shot.

    Now we, terrestrials, use GeO (Geostationary Orbit) exactly for directional TV transmission, and non-directional TV transmission era sunk into oblivion…

    Besides, in order to hope to detect Alien signals, we must treat with respect to those who transmit. See “Searching for Extraterrestrial Idiots?” at:

    http://www.setileague.org/editor/idiots.htm

    My best,
    Alexander.

  • Administrator November 12, 2006, 10:25

    Ron’s point seems like a strong one to me, which is why I’d like to see some further work on how such signals travel.

    And yes, as Dr. Zaitsev says, we’re moving deeply into the era of direction transmission of TV, gradually going silent from an accidental leakage perspective (at least, in the TV bands). Non-directional broadcasting of TV seems to have a short lifetime as we all move to cable and other options.

  • Adam November 12, 2006, 15:40

    Hi All

    I think radio SETI will have much more chance of detection of ETI spacecraft than leaky TV transmissions. If ET uses magnetic-sails or their equivalent to deccelerate then such plasma interactions will generate terawatts of power, much of it as radio. And highly relativistic vehicles will beam the radiated energy in a cone concentrated in their direction of motion, potentially giving us advanced notice of an imminent arrival – something we might observe if there’s a covert base in the Kuiper Belt.

  • Ron S November 12, 2006, 16:38

    Hmmm. Yes it’s possible there is, now, an ET spacecraft decelerating towards us and using radiation to do so. My gut reaction tells me this is less likely than detecting broadcast leakage, but certainly easier to detect. Both are unlikely. While the deceleration radiation should be easy enough to detect, it can be masked pretty easily, though not entirely eliminated. Radiate in a hollow cone pattern with a simple conical shield ahead of the craft, and make the radiation broadband so its power spectrum is weaker and looks like noise. This might be done simply to avoid annoying us rather than to hide from us.

    Repeating part of what I said in the earlier Loeb thread, if their analysis is correct and reasonably inexpensive, seems like a good idea to piggyback this experiment on top of MWA.

  • Adam November 13, 2006, 4:00

    Hi Ron

    The TV leakage detection experiment definitely has to go ahead, no doubt about it. A lot will be learnt by doing so.

    But the starship I was describing wasn’t using radiation to deccelerate, but magnetic drag as it moves through the ISM. By itself a mag-sail radiates isotropically, but at relativistic speeds an isotropic radiation field in the co-moving reference frame looks like it has been ‘beamed’ to ‘stationary’ orbservers. This is actually the main process behind the beaming emission of gamma-ray bursts – highly relativistic thermalised plasmas crashing into a surrounding nebula will emit in narrow cones.

    Regardless of the emission physics I doubt any “cloaking” of terawatts of radio energy would be possible.

    Adam

  • Ron S November 13, 2006, 19:32

    Adam,

    Sorry that I misunderstand you. In fact after I made my comment I realized that I had no idea where the craft’s energy for the deceleration radiation was coming from! Thanks for the clarification.

    I understand your point about relativistic ‘beaming’. Without belaboring the point, since I don’t know precisely in what manner the energy is being radiated, it still seems to me that a very small (as in small solid angle) ‘shield’ in the direction of travel could mask direct radiation. This of course excludes effects of diffraction and ability of the shield to absorb little energy so it doesn’t vaporize. Even with relativistic beaming you could still maintain a bit of a radiation-free cone.

    Even terawatts as far as the Kuiper belt could appear as a modest amount of noise with some shielding, moderate beamwidth ,and with a broad spectrum. The remaining noise could be falsely interpretted as stellar noise from the craft’s home star since it would be collinear with the craft.

  • Adam November 13, 2006, 21:03

    Hi Ron

    Good point about confusing a starship source of radiation with the origin point, presumably a star. I guess any ship not from a star should be seen as suspicious – they’re trying to cover their origin.

    Adam

  • ljk January 9, 2007, 12:21

    Eavesdropping on the Universe

    Seattle, WA – Astronomers have proposed an improved method of searching for intelligent extraterrestrial life using instruments like one now under construction in Australia. The Low Frequency Demonstrator (LFD) of the Mileura Wide-Field Array (MWA), a facility for radio astronomy, theoretically could detect Earth-like civilizations around any of the 1,000 nearest stars.

    “Soon, we may be eavesdropping on signals from Galactic civilizations,” says theorist Avi Loeb of the Harvard-Smithsonian Center for Astrophysics (CfA). “This is the first time in history that humans will be capable of finding a civilization like ours among the stars.”

    Loeb will present his findings on Wednesday, January 10, in a press conference at the American Astronomical Society meeting in Seattle, Wash.

    http://cfa-www.harvard.edu/press/pr0701.html

  • Ron S January 9, 2007, 14:55

    From how the press release is written it looks like Loeb’s proposal has not yet been approved or quashed.

  • ljk February 10, 2008, 23:49

    LOFAR-UK White Paper: A Science case for UK involvement in LOFAR

    Authors: P. N. Best, the LOFAR-UK Consortium

    (Submitted on 8 Feb 2008)

    Abstract: LOFAR, the Low-Frequency Array, is a next-generation software-driven radio telescope operating between 30 and 240MHz, currently under construction by ASTRON in the Netherlands. This low frequency radio band is one of the few largely unexplored regions of the electromagnetic spectrum.

    The sensitivity and angular resolution offered by LOFAR will be two to three orders of magnitude better than existing telescopes, and as such it will open up this new window on the Universe. LOFAR will impact on a broad range of astrophysics, from cosmology to solar system studies.

    There is growing European involvement in LOFAR, driven by the need to add stations far from the main core in order to improve angular resolution. LOFAR-UK is a project aimed at cementing UK participation in LOFAR via the operation of four stations within the UK. LOFAR-UK ground stations will allow LOFAR observations to reach sub-arcsecond scales at the highest frequencies, and as a result will also improve the (confusion-limited) sensitivity limit of the telescope for deep surveys.

    LOFAR-UK will achieve involvement for UK astronomers in a world-leading science facility operating in the immediate future. It will allow the UK to build up important scientific and technical expertise in `next generation’ radio astronomy in preparation for the Square Kilometre Array (SKA), and will play an important role in broadening the UK community that has an interest in radio astronomy.

    This White Paper outlines the strategic importance to the UK astronomy community of gaining involvement in the LOFAR project, the scientific interests of UK researchers in using the telescope, and the technical challenges that will need to be overcome [abridged].

    Comments: 86 pages. To constrain file-size, many figures are reduced resolution or attached as separate jpg files. A version with all full-resolution figures included is available at this http URL

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0802.1186v1 [astro-ph]

    Submission history

    From: Philip Best [view email]

    [v1] Fri, 8 Feb 2008 17:28:34 GMT (1916kb)

    http://arxiv.org/abs/0802.1186

  • ljk April 3, 2008, 15:17

    Europe-wide radio net in aliens search

    http://www.guardian.co.uk/science/2008/mar/30/spaceexploration.spacetechnology

    Project will pick up clues from space on possible extraterrestrials
    and data on the early universe

    Robin McKie, science editor The Observer, Sunday March 30 2008

    This article appeared in the Observer on Sunday March 30 2008 on
    p27 of the News section. It was last updated at 12:04 on April 01 2008.

    Scientists are finalising plans to link radio wave detectors in five countries and create a device sensitive enough to pick up signals from worlds the other side of the galaxy.

    By connecting banks of detectors in fields across Britain, France, Holland, Sweden and Germany, astronomers aim to create a radio telescope that will have the accuracy of a machine the size of Europe. They believe it could solve some of the universe’s most important secrets – including the discovery of radio broadcasts from intelligent extraterrestrials.

    ‘This system works by collecting radio waves over a range of frequencies,’ said cosmologist Robert Nichol of Portsmouth University. ‘These can then be analysed using arrays of computers which can identify patterns from the data streaming from our detectors.

    ‘Some of these signals will reveal information about the early universe, for example. However, broadcasts by alien intelligences would also be revealed by our computers because we will, primarily, be collecting radio signals. Signals that have regular patterns will give themselves away as the possible handiwork of extraterrestrials. Such work is a bonus, however. The main work of the system is basic research,’ added Nichol.

    The project – known as Lofar (low frequency array) – was launched in Holland several years ago, but has attracted the attention of other European astronomers. All have agreed to build their own banks of detectors, which can then be linked to those in Holland. Britain is committed to building one set, while requests for money for another three have been put to research councils.

    Several sites for Britain’s first array are being considered, although most scientists expect it to be built at Jodrell Bank in Cheshire, where the giant radio dish is threatened with closure because of funding cuts. By building the Lofar antenna, which represents the future of radio astronomy, ground-breaking research can continue at the site, say scientists.

    Lofar arrays exploit the fact that metals pick up radio waves and convert them into weak electric signals. In the past, dishes were pointed at heavenly objects so that their radio waves could be focused on a central receiver and generate a signal strong enough to be analysed.

    Lofar uses a very different approach. ‘Instead of moving a huge dish around the sky and pointing it at a star or galaxy or nebula, you simply cover a field with sheets of metal. The metal will pick up radio waves from all over the sky,’ said Nichol, who this month was awarded a €50,000 Marie Curie prize by the European Union for his research. ‘You then analyse these with banks of computers and, by carefully writing your software, you can pinpoint the object you want to study.

    ‘The crucial point is that the more arrays you have, the more radio waves you collect, so Lofar becomes more sensitive. And if you have arrays far apart from each other, you can resolve distant objects with greater and greater precision.’

    In other words, instead of using complex hardware to target objects in the sky, astronomers will exploit highly sophisticated 21st-century computer software to select and study their targets. Thus the steerable radio telescope at Jodrell Bank could be replaced by a series of metal plates the size of a football pitch.

    ‘We will be looking for all sorts of different things with Lofar,’ added Nichol. ‘We will make surveys of the skies to look for unexpected events; for things that go bump in the night, as it were. We will also be able to study the universe’s childhood years. We know a lot about the Big Bang, when the universe was created 13 billion years ago, and a lot about it now. But its early childhood years, around 500 million years after the Big Bang, remain a mystery.

    ‘Why and how did stars form out of atoms that then permeated the cosmos? Lofar will help us work that out.’

    Other scientists, including Lyndsay Fletcher at Glasgow University, intend to use Lofar to study objects much nearer to home, such as the Sun. ‘Radio emissions pour from the Sun at all sorts of frequencies, each characteristic of a different physical process that is going on inside it,’ said Fletcher. ‘Lofar will give us a completely new method for understanding what goes on inside our own Sun.’

  • ljk May 29, 2008, 14:30

    LOFAR Transients and the Radio Sky Monitor

    Authors: Rob Fender (Amsterdam and Southampton), Ralph Wijers (Amsterdam), Ben Stappers (Manchester), the LOFAR Transients Key Science Project

    (Submitted on 28 May 2008)

    Abstract: The study of transient and variable low-frequency radio sources is a key goal for LOFAR, with an extremely broad science case ranging from relativistic jets sources to pulsars, exoplanets, radio bursts at cosmological distances, the identification of gravitational wave sources and even SETI. In this paper we will very briefly summarize the science of the LOFAR Transients key science project, will outline the capabilities of LOFAR for transient studies, and introduce the LOFAR Radio Sky Monitor, a proposed mode in which LOFAR regularly scans 2 pi radians of sky.

    Comments: In “Bursts, Pulses and Flickering: wide-field monitoring of the dynamic radio sky”, Tzioumis, Lazio & Fender (Eds), Proceedings of Science, 2007

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0805.4349v1 [astro-ph]

    Submission history

    From: Rob Fender [view email]

    [v1] Wed, 28 May 2008 13:36:24 GMT (781kb)

    http://arxiv.org/abs/0805.4349

  • ljk June 4, 2008, 8:03

    Gravitational lens surveys with LOFAR

    Authors: Olaf Wucknitz (1,2), Mike Garrett (3) ((1) AIfA, Bonn; (2) JIVE, Dwingeloo; (3) ASTRON, Dwingeloo)

    (Submitted on 3 Jun 2008)

    Abstract: Deep surveys planned as a Key Science Project of LOFAR provide completely new opportunities for gravitational lens searches. For the first time do large-scale surveys reach the resolution required for a direct selection of lens candidates using morphological criteria. We briefly describe the strategies that we will use to exploit this potential. The long baselines of an international E-LOFAR are essential for this project.

    Comments: Poster presented at the conference “From planets to dark energy: The modern radio Universe” in Manchester, October 2007. Proceedings contribution and original poster also available from this http URL

    Subjects: Astrophysics (astro-ph)

    Report number: PoS(MRU)142

    Cite as: arXiv:0806.0494v1 [astro-ph]

    Submission history

    From: Olaf Wucknitz [view email]

    [v1] Tue, 3 Jun 2008 10:59:57 GMT (316kb,D)

    http://arxiv.org/abs/0806.0494

  • ljk June 10, 2008, 13:16

    LOFAR telescope used in search for extraterrestrial life

    “ASTRON is researching the potential role of the LOFAR
    telescope in the Search for ExtraTerrestrial Intelligence (SETI).

    This initiative has been taken by Professor Michael Garrett,
    General Director of ASTRON and professor of radio techniques
    in astronomy at Leiden University in the Netherlands.

    Researchers from all over the world will contribute to this effort
    to find ways in which LOFAR can be used in the search for
    extraterrestrial life.”

    http://www.spaceref.com/news/viewpr.html?pid=25619