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The ‘I Love Lucy’ Signal

As a fan of I Love Lucy since childhood, I’ve always been pleased that this show — and not, say, Milton Berle or Sid Caesar — is the one always referred to when talking about Earth being detected by other civilizations. And when I first thought about it, the idea that there was a detectable bubble of TV transmission forging out into the galaxy since Lucy’s first show in 1951 seemed completely wondrous. I Love Lucy is 60 light years from us now, or will be with this October’s anniversary of that first show. I’ve always wondered what extraterrestrials would make of Fred Mertz.

The film Contact mines the theme of stray transmissions from Earth, although in the case of Sagan’s story, it’s the transmissions from the 1936 Olympics in Berlin that trigger the detection and subsequent transmissions to Earth. A writer and music critic who I’ve known over the years once asked me about the expanding wavefront of Earthly transmissions, pondering how marvelous it would be to somehow get out in front of it and reacquire for the ‘first’ time some of the legendary performances of Arturo Toscanini with the NBC Symphony Orchestra, hopefully receiving them in better condition than the noisy kinescope versions that were used to preserve them.

Our Signals from Afar

Of course, getting out in front of the wavefront presents a bit of a problem — you’d have to travel faster than light. So let’s talk about something more realistic, which is the actual status of those interesting signals from the dawn of television. Here I’m drawing on James Benford’s presentation to the Royal Society meeting “Towards a Scientific and Societal Agenda on Extraterrestrial Life,” which convened last October in Britain and included a debate on extraterrestrial messaging that was sent to me in DVD form by Astronomy Now editor Keith Cooper. Benford looks at what an extraterrestrial civilization would be able to detect from Earth.

Remember, now, we’re talking about accidental signals, so-called ‘leakage’ radiation that was never intended as a directed signal. Benford goes to work on the math to ask whether installations like those we have on Earth would be able, if located around a nearby star, to pick up what we have been sending. The answer is no. A typical large radio telescope like the Parkes instrument in Australia could not, from a vantage near Alpha Centauri, see video footage from Earth. I’ll send you to the paper for the math (and I’ll post the link as soon as it’s available), but here’s his conclusion:

Picking up signals from commercial radio and television broadcasts is difficult. Because they are not intended to broadcast into space; broadcast antennas aim most of their transmitted power toward the surface. Most signal information is transmitted in bands on each side of the central frequency. What little detectable power reaches space is from many sources, not at the exact same frequencies, but in bands constrained by regulation by governments. Therefore, they are not coherent, so phase differences cause them to cancel each other out at great range.

What about over-the-horizon radars built during the Cold War? Much of their power was indeed radiated into space, but they have been replaced by frequency-hopping spread spectrum broadband radars that would likewise be undetectable by any technology like ours. The highest power emissions, it turns out, are those from interplanetary radars used for asteroid searches. But these signals are not directed at nearby stars, and Benford quantifies the issue using the specs of the Arecibo radar telescope. Again, I will hold off on the math, but the conclusion is that ‘there is a negligible chance of ETI noticing our asteroid search radars.’

Sending Earth’s ‘Wow’ Signal

So what would it take for an extraterrestrial civilization to notice us? Seth Shostak is on the record as saying that within a few hundred light years, clues to our existence could be picked up with an antenna the size of Chicago. Benford’s analysis shows that building such an antenna, given what we know of the present value of building an installation like the Square Kilometer Array, would run up a cost comparable to the entire GNP of planet Earth. If ETI were at our level of development, then, its entire science budget would be consumed by the project.

What about the future? Some proposed activities might flag our presence, but they would be hard to pin down:

We should be mindful also of the future possibilities for increased leakage from Earth due to beaming power for space industrial purposes, such as power transfer. Examples are transferring energy from Earth-to-space, space-to-Earth, and space-to-space using high power microwave beams… Microwave beams have been studied for propelling spacecraft for launch to orbit, orbit-raising, and launch from orbit into interplanetary and interstellar space. The power levels are ~GW with high directivity, so that isotropic radiated power W~1017 watts, would dwarf anything yet emitted into space. Observing such activities would appear to ETI as transient events.

Reception of Directed Transmissions

Moreover, the same techniques of quantitative analysis show that even directed messages like the Cosmic Call message from the Evpatoria site in the Ukraine would be detectable (and only at a low data rate of 100 bit/sec) out to just 19 years even if observed with a facility the size of the Square Kilometer Array. Detectability, Benford notes, depends on the bandwidth of the transmission. Low data rates can show that the signal is artificial but also carry little information, while high data rates require high bandwidth and suffer greatly from noise.

To detect a low-bit-rate signal, a number of additional factors must swing into play, including a predisposition to be looking at our system in the first place so that ETI would concentrate resources on that small patch of sky where our Sun is located. ETI would also have to guess the bit rate of the message, and would have to figure out that the message used binary frequency-shift keying instead of any other modulation method. All in all, these are tough requirements, though such a message could serve to flag a technological society:

The content of [Alexander] Zaitsev’s messages [from Evpatoria] will not be recoverable as messages by ETI if their radio telescopes are comparable to ours. To be observable, the receiving area must be greater than the SKA we’re contemplating building, and then only at low data rates.

Extending the messages by repeating, so they last hours, allows ETI to integrate the signal, and detect its presence at ranges of 100’s of light years. But that obliterates the message content, producing a recognizable pulse of energy. That could be taken by ETI as an undifferentiated energy source that could be artificial. But it cannot be characterized as a message.

We can’t know what technologies more advanced civilizations might bring to bear, but it’s helpful to get some constraints on the radiation leakage issue as they pertain to our own technology. A civilization anywhere near our own level of development should not, by Benford’s figures, be aware of our existence despite our television, radar and intentional messaging activities. That’s an interesting thought as we ponder our own failure, thus far, to find any trace of an extraterrestrial presence through SETI. The SETI search is clearly going to be long and arduous.

Benford goes on to argue that working out the parameters of future broadcasts and developing a database and top-level summary of Earth’s radio and laser signature should become standard practice, allowing us to calculate the possibilities for reception. All of this has implications for SETI and METI. About these, and the question of what kind of civilization might receive our signals, expect more in the coming week.

Addendum: The Benford and Billingham paper, “Costs and Difficulties of Large-Scale ‘Messaging’, and the Need for International Debate on Potential Risks,” is now available online.


Comments on this entry are closed.

  • Alex Tolley February 9, 2011, 12:06

    Isn’t this one of the reasons that SETI has an optical search program?

    This is one of the reasons for me, the Kepler results will be so interesting. If we are the most advanced civilization, then we would be building the lasers to pulse messages to targets. If Kepler showed that 10% of stars had potentially habitable worlds, we would need to direct pulses to 10% of stars. As we refine our techniques and actually detect life signatures on other worlds, we could reduce that fraction to most likely worlds.

    The problem for me is that the appearance of technological civilizations over time is likely to be random and highly spaced out in time. A directed beacon would therefore have to run for 10’s of millions of years to hope to catch the eye of a newly emergent civilization. For the first civilization, it seems to be faster to send smart machines to the target worlds. At 0.01c, every target in the galaxy could be reached within 10 million years. Therefore a machine, alive or dead should be somewhere in our solar system. Yet we haven’t seriously looked for monoliths yet…

  • Greg February 9, 2011, 12:14

    I’m curious, if there are solar sails proposed that are hundreds of miles in circumference, even a civilization slightly ahead of us could use one as a radio antennae, without breaking them.

  • Leonard February 9, 2011, 12:33

    “getting out in front of the wavefront presents a bit of a problem — you’d have to travel faster than light.” But, theorically speaking, is it possible that a higly reflective surface sends the waves back to earth? And (letting imagination run free here) could we, if such mirror-like artifact exists, point a telescope to it and see the surface of earth as it was, say, 50 years ago?

  • The Cosmist February 9, 2011, 17:28

    Alex Tolley you make a good point, which calls into question the whole SETI enterprise. The chances of any nearby civilization being anywhere near our technological level right now seems pretty remote. They’re either way beyond us and already know about us, they’re not interested in us, or they’re too primitive to detect our signals. It seems to me like SETI is based on some dubious and anthropocentric assumptions about extraterrestrial civilizations. Since we don’t really know what we’re looking for, we might as well put the resources into astronomical research and space exploration — our chances of randomly detecting another civilization that way may be better than actively seeking them out using the wrong methods.

  • arrowspace90 February 9, 2011, 18:51

    If we are counting on being seen and heard by civilizations similar to ours, the galaxy is in big trouble.

    As the poster above suggests, the galaxy is mappable by robots traveling at a tiny fraction of the speed of light. Von Newman (self replicating) machines have had plenty of time to survey the whole place several times.
    Even if the civilizations that built them are dead.
    So why are there no such machines puttering about? Why should EVERY advanced civilization be doomed? It’s not that we are having problems finding THEM, THEY should have found us by now.
    I don’t know much about this galaxy, but there would seem to be some major problems with it.

  • Astronist February 9, 2011, 20:03

    I agree with Alex Tolley and Cosmist. But would add the following: if we beam messages to sunlike stars for millions of years, we only get an answer if an intelligent species evolves at one of the targets. If for any reason we fail to make two-way contact, the radio or laser energy is totally wasted.

    But if we send probes such as Daedalus / Icarus, then (subject to the technology being reliable) within a century or two we are guaranteed data back on the contents of the planetary system, including much needed data on the presumptive large majority of systems which have microbiological life but not highly evolved intelligent life, and which we need to form a fuller picture of life in the Galaxy. An alien civilisation must be subject to this same logic.

    If we receive a signal from another star, it will be immediate evidence that an alien probe is active in our planetary system.

    Oxford, UK

  • mrG February 9, 2011, 20:23

    How about atmospheric detonation of nuclear bombs? Surely the EMP of these blasts, while cushioned by atmosphere from the surface of the earth, might raise some SETI alarms on Gliese? Could Colonel Bleep have been more prophetic than its creators imagined?

  • Doug M. February 9, 2011, 23:41

    There’s an interesting discussion of this over at James Nicoll’s blog:


    Doug M.

  • Adam February 9, 2011, 23:43

    Hi Paul

    So the Void gives ET a deaf-ear to our birth-cries? Maybe that’s a good thing. Perhaps we don’t want to be heard to be new arrivals on the Galactic stage.

  • Greg February 10, 2011, 1:34

    arrowspace90 said,
    “So why are there no such machines puttering about? Why should EVERY advanced civilization be doomed? It’s not that we are having problems finding THEM, THEY should have found us by now.”

    How do we know there hasn’t been. Life as we know it is pretty much a self-replicating machine. We may be over looking the very stuff we are used to seeing.

  • Rob Henry February 10, 2011, 6:16

    Given that so many have such faith in the SETI approach that much has been invested in it, and given that most of us harbour the improbable hope that they are right, it is interesting to ponder what criteria would validate them, other than a signal.

    The first and most obvious one is if interstellar travel is impossible in practice, under any reasonable circumstances, yet that seems all but ruled out, as readers on these pages would know.

    To me the best hope would be to find that our entire galaxy was seething with hazards up to a few hundred million years ago – to such an extent that higher land-based life could only begin evolving thereafter. It has been speculated that gamma ray bursters could perform this trick, but to me, something much more extreme needs to be indicated. I thus propose that, contrary to a vast weight of evidence, until recently the Milky Way was a quasar. Now we might be able to find that all technologically communicative life has arisen recently. Suddenly ideas such as Sagan’s percolation theory could work well enough to slow galactic colonisation below completion level over this new time frame. As for expanding waves of self-replicating robots, another argument way be able to slow their expansion just sufficiently here. Since each new wave of exploration must reduce the total return of interesting information that could be transmitted and received from previous waves, the home world of these probes could well loose interest in hurrying the process.

    The third option is the zoo hypothesis, were we could contact other entrapped civilisations, if not our keepers. Why they would let us contact each other after going to such elaborate lengths to avoid their own external influence in our affairs, I do not know, but who are we to second guess the workings of a stage III super civilisation.

  • Adam February 10, 2011, 7:26

    Hi All
    If we look at the economics of probing the Galaxy, to extend the trail blazed by the Benfords & co. in this series of papers, then how long will it take to build sufficient probes to reach the Galaxy? In a blog-post at “Project Icarus” I estimated a cost of at least several hundred billion per probe, for “Daedalus” class vehicles and several decades of effort. Perhaps the cost can be slashed ~100 fold so ~100 probes can be launched over ~20 years. Thus to probe every star takes ~20 billion years.

    Self-replicating probes have been mooted time and time again, but if we factor in the economics of actually receiving useful data, then eventually our probes will start reaching a range which overwhelms our ability to receive by the sheer multitude of stars being explored at once. I suspect a more organic, messy progress is more likely as a civilization spreads into the Galaxy via active means and passive observations will often prove easier than sending a probe, especially if gravity-lensing observatories prove feasible.

    Hmmm… That sounds like a paper, in abstract…

  • Joe P February 10, 2011, 16:32

    Look at how far our technology has progressed in the last hundred years or so.

    In the early part of the 20th century, an infrastructure developed around mass communications centered on radio and television signals that are broadcast. SETI assumes that this is the standard was ETs will communicate with us (intentionally or by chance interception). I know there are exceptions, but this has been the basic assumption.

    This broadcast technology reached its peak here on Earth until cable television started taking over. That was followed by satellite radio and television, and eventually streamed communication via TCP and UDP over the Internet.

    In another fifty years, will anything we are using for a data transfer resemble the current system?

    It seems to me that the use of radio and television EM waves for communication is a dead end. We move away from powerful broadcasts and more towards smaller, very weak (less than 5 watts) individual units (routers, cell phones, laptops and touch screen devices) that are harnessed together by a network of optical fiber.

    All this advancement has occurred in almost no time. If there are more advanced ETs out there, they probably would not bother listening or sending radio signals at all. Terribly limited and slower than light speed. Makes no sense for vast distances. If something like the Alcubierre drive is possible, then a small communication payload via that system is superior to waiting years and years for your EM based signal to get where you want it to go.

    Another thing is that we really don’t understand the mechanism behind the basic structure of the universe. What comes to mind is the supposed instantaneous link between entangled particles. I know that physicists have ruled out using such effects for FTL communication. However, history has shown that we are often surprised about the limitations of our theories.

  • Ron S February 10, 2011, 21:51

    Joe, are you criticizing SETI for not using technologies based on magic and arm waving?

  • darin February 11, 2011, 12:03

    This post reminded me of a suggestion given by a paper I read once (don’t remember the author) that we should be focusing our messaging/searching to those stars that would see the Earth as a transiting planet. Assuming that their technology is similar to ours (a big leap, of course), photometrically detecting the Earth is much easier than other methods (as proven by Kepler) and so those regions of sky have a somewhat larger probability of either listening or sending messages. It’s an easy and resonable way to narrow the amount of sky you have to search by a factor of ~100.

  • Keith Cooper February 11, 2011, 16:23

    Hi darin,
    I believe you’re talking about the SETI ecliptic search that was proposed a couple of years ago by Richard Conn Henry of Johns Hopkins University (and I think Paul has written about it on Centauri Dreams previously too). You’re right, any inhabitants of planets around stars in the ecliptic plane would see our Solar System edge-on, and see Earth transiting the Sun. We’ve been able to study atmospheres of exoplanets that we’ve found transiting their stars, so it’s not a stretch of the imagination to think that ET civilisations that see Earth transiting could study our atmosphere, find that it contains water vapour, oxygen, carbon dioxide etc, maybe even pollution, and deduce that it is not only inhabitable but perhaps also inhabited. So if they wanted to send signals into space, Earth would be a promising target. I think I’m right in saying that the SETI Institute are currently embarked on an ecliptic survey with the Allen Telescope Array. What this idea does show is that there are other ways that ET could possibly detect us without resorting to picking up our radio leakage.

  • Alexander Zaitsev February 12, 2011, 2:24

    The theory and practice of METI I have tried to state for the first time in the new Springer-Praxis book “SETI Past, Present, and Future”:

    Chapter 21.
    Alexander L. Zaitsev. METI: Messaging to Extra-Terrestrial Intelligence, pp. 399-428.

  • Alexander Zaitsev February 12, 2011, 2:32

    >Addendum: The Benford and Billingham paper, “Costs and Difficulties of
    >Large-Scale ‘Messaging’, and the Need for International Debate on Potential
    >Risks,” is now available online.

    The “References” of this paper has wrong url! The correct url of my paper is:


    My best,

  • Paul Gilster February 12, 2011, 10:44

    The new book Dr. Zaitsev references is Searching for Extraterrestrial Intelligence: SETI Past, Present, and Future, edited by Paul Shuch:


    I haven’t seen it yet (it was just published at the end of January), but it looks excellent. Here’s the Amazon description:

    This book is a collection of essays written by the very scientists and engineers who have led, and continue to lead, the scientific quest known as SETI, the search for extraterrestrial intelligence. Divided into three parts, the first section, ‘The Spirit of SETI Past’, written by the surviving pioneers of this then emerging discipline, reviews the major projects undertaken during the first 50 years of SETI science and the results of that research.

    In the second section, ‘The Spirit of SETI Present’, the present-day science and technology is discussed in detail, providing the technical background to contemporary SETI instruments, experiments, and analytical techniques, including the processing of the received signals to extract potential alien communications.

    In the third and final section, ‘The Spirit of SETI Future’, the book looks ahead to the possible directions that SETI will take in the next 50 years, addressing such important topics as interstellar message construction, the risks and assumptions of interstellar communications, when we might make contact, what aliens might look like and what is likely to happen in the aftermath of such a contact.

  • Alexander Zaitsev February 12, 2011, 16:24
  • Alexander Zaitsev February 12, 2011, 16:45

    P.S. to Paul:

    Do you know about 3rd IAA SETI Conference:


    My best,

  • Paul Gilster February 12, 2011, 16:54

    Yes, I believe Claudio Maccone has been working on the planning committee, and I see that you have as well. Wish I could be there! But thanks for the link, which lets our readers know about this interesting conference.

  • David February 12, 2011, 17:17

    The first season of “Amazing Stories” had an episode called “Fine Tuning” in which a kid builds a TV antenna strong enough to pick up alien transmissions, and he sees them doing their own alien version of I Love Lucy. You see, the aliens had been watching our version, and decided to make their own, and their TV signals were just now reaching us. Then the aliens come to Hollywood in hopes of meeting all the people they’ve been watching on TV. It’s worth watching if you can find it.

  • Paul Gilster February 12, 2011, 17:45

    David, that sounds wonderful!

  • ljk February 14, 2011, 0:00


    An Anomalous SETI Signal

    Credit & Copyright: SETI League

    Explanation: No one knows for sure what caused this signal. There is a slight possibility that it just might originate from an extraterrestrial intelligence. The bright colors on the blue background indicate that an anomalous signal was received here on Earth by a radio telescope involved in a Search for Extraterrestrial Intelligence (SETI).

    A search for these signals is ongoing by several groups including volunteer members of the SETI League. Time labels the vertical axis of the above plot, and frequency marks the horizontal axis. Although this strong signal was never positively identified, astronomers have identified in it many attributes characteristic of a more mundane and ultimately terrestrial origin.

    In this case, a leading possibility is that the signal originates from an unusual modulation between a GPS satellite and an unidentified Earth-based source. Many unusual signals from space remain unidentified. No signal has yet been strong enough or run long enough to be unambiguously identified as originating from an extraterrestrial intelligence.

  • ljk February 14, 2011, 1:08

    Costs and Difficulties of Large-Scale ‘Messaging’, and the Need for International Debate on Potential Risks

    Authors: John Billingham, James Benford

    (Submitted on 9 Feb 2011)

    Abstract: We advocate international consultations on societal and technical issues to address the risk problem, and a moratorium on future METI transmissions until such issues are resolved. Instead, we recommend continuing to conduct SETI by listening, with no innate risk, while using powerful new search systems to give a better total probability of detection of beacons and messages than METI for the same cost, and with no need for a long obligatory wait for a response.

    Realistically, beacons are costly. In light of recent work on the economics of contact by radio, we offer alternatives to the current standard of SETI searches. Historical leakage from Earth has been undetectable as messages for credible receiver systems. Transmissions (‘messages’) to date are faint and very unlikely to be detected, even by very nearby stars. Future space microwave and laser power systems will likely be more visible.

    Comments: 13 pages

    Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Earth and Planetary Astrophysics (astro-ph.EP)

    Cite as: arXiv:1102.1938v1 [astro-ph.IM]

    Submission history

    From: Gregory Benford [view email]

    [v1] Wed, 9 Feb 2011 18:48:56 GMT (380kb)


  • ljk February 14, 2011, 2:26

    Regarding the earlier comment about using nuclear explosions to attract attention in the galaxy, Guillermo A. Lemarchand had this to say on the subject in his 1992 paper titled “Detectability of Extraterrestrial Technological Activities”:

    Elliot estimated the distance at which the United States “Starfish” nuclear test could be detected by our present technology of X-ray detectors. Assuming that the energy of the explosion is equivalent to 1.4 megatons and that the X-ray pulse was equally intense in all directions, he found that this explosion should be detected from a distance of ~400 Astronomical Units, about ten times the radius of Pluto’s solar orbit.

    Supposing that all the terrestrial nuclear powers [3] pooled their nuclear weapons stockpiles to produce a single explosion in space (E~2×10 to the 4 power megatons). Considering that the X-ray pulse could be concentrated into a conical beam of about thirty degrees in angle with no loss of radiation, a typical terrestrial X-ray detector should be able to detect a signal from a distance of ~190 light years.

    3 – In 1989 the United States and the Soviet Union had almost 55,000 nuclear warheads with a combined destructive power of 15,500 megatons (Source: Bulletin of Atomic Scientist, 1990).

    Complete paper here:


    Andrei Sakharov, the Soviet father of the hydrogen bomb, had a plan to make some big explosions at the edge of the Sol system to attract ETIs’ attention.

    Read the fascinating details here:


  • ljk March 30, 2011, 9:19

    SETI: The transmission rate of radio communication and the signal’s detection

    Authors: P. A. Fridman

    (Submitted on 15 Feb 2011)

    Abstract: The transmission rate of communication between radio telescopes on Earth and extraterrestrial intelligence (ETI) has been calculated up to the distances 1000 light years. Phase-shift-keying (PSK) and frequency-shift keying (FSK) modulation schemes are both considered here. It has been demonstrated that M-ary FSK is advantageous in terms of energy.

    Narrow-band pulses scattered over the spectrum can be the probable signals of ETI and modern SETI spectrum analyzers are well suited to searching for these types of signals. Such signals can be detected using the Hough transform which is a dedicated tool for detecting patterns on an image. The time-frequency plane representing the power output of the spectrum analyzer during the search for ETI gives an image from which the Hough transform (HT) can detect signal patterns with frequency drift.

    Comments: 20 pages, 8 figures, submitted to Acta Astronautica

    Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

    Cite as: arXiv:1102.3332v1 [astro-ph.IM]

    Submission history

    From: Peter Fridman [view email]

    [v1] Tue, 15 Feb 2011 16:36:51 GMT (861kb)