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Wolf 359: Of Gravitational Lensing and Galactic Networks

If self-reproducing probes have ever been turned loose in the Milky Way, they may well have spread throughout the galaxy. Our planet is 4.6 billion years old, but the galaxy’s age is 13 billion, offering plenty of time for this spread. A number of papers have explored the concept, including work by Frank Tipler, who in 1980 argued that even at the speed of current spacecraft, the galaxy could be completely explored within 300 million years. Because we had found no evidence of such probes, Tipler concluded that extraterrestrial technological civilizations did not exist.

Robert Freitas also explored the consequences of self-reproducing probes in that same year, reaching similar conclusions about how quickly they would spread, although not buying Tipler’s ultimate conclusion. It’s interesting that Freitas went to work on looking for evidence, reasoning that halo orbits around the Lagrangian points might be one place to search. He was, to my knowledge, the first to use the term SETA — Search for Extraterrestrial Artifacts — which has now come into common use, and is currently under examination by Jim Benford in his work on ‘lurkers.’

A new paper from Michaël Gillon (University of Liège) and Artem Burdanov (Massachusetts Institute of Technology) has now appeared that follows the implications of self-reproduction and technology, tying them to a more specific search regimen. Conversant with the work of Von Eshleman as well as Claudio Maccone, the authors ask whether using the gravitational lens offered by a star wouldn’t make the most reasonable method for ETI communications. The Sun’s huge magnifications, bending light from objects behind it as seen from a relay somewhere beyond its 550 AU lensing distance, could enable participation in a network that functioned on a galactic scale.

You probably remember Gillon as the man who led the team that discovered TRAPPIST-1’s planets. Back in 2014, he began his exploration of gravitational lensing and communications with the publication of a paper titled “A novel SETI strategy targeting the solar focal regions of the most nearby stars.” Accepting the idea that self-reproducing probes could spread through the galaxy in a span of hundreds of millions of years, the author opened the question of detectability. He drew on Maccone’s insight that links enabled by gravitational lensing could allow data-rich communications between two stars at extremely low power. It is in this 2014 paper that Gillon first proposes looking for leakage in traffic between star systems.

A civilization that has spread throughout the galaxy might set up such relays around any stars useful as network nodes. This would turn conventional SETI on its head. Rather than scanning for radio or optical signals from other stellar systems, we consider intercepting ongoing traffic between another star and the relay in our own system. A fully colonized galaxy, so the thinking goes, should have a relay around at least one nearby star.

Thus the term Focal Interstellar Communication Devices (FICDs), examples of which could be present in our own Solar System and perhaps in the focal regions of nearby stars. Several studies have already appeared on a strategy of performing intense multi-spectral monitoring of these focal regions in the hopes of snagging communication leakage from such a network. Gillon and Burdanov focus on a specific FICD. They identify Wolf 359, an M-dwarf that is the third closest stellar system to our own, as a prime candidate to receive a signal from a local FICD, and implement an optical search.

Why Wolf 359? Ponder this:

…detecting the FICD emission to a nearby star can only be done if the observer is within one of these narrow beams, putting a stringent geometrical constraint on the project concept. For an Earth-based observer, this means that the Earth’s minimum impact parameter has to be close to 1 as seen from the FICD, and thus also from the targeted nearby star. In other words, the Earth has to be a transiting (or nearly transiting) planet for one of the nearest stars to give this SETI concept a chance of success, so the target star has to be very close to the ecliptic plane. With its nearly circular orbit and its semi-major axis 215 times larger than the solar radius, the Earth has a mean transit probability < 0.5% for any random star of the solar neighborhood.

Image: An artist’s depiction of an active red dwarf star like Wolf 359 orbited by a planet. Credit: David A. Aguilar.

In other words, because the Earth transits the Sun as seen from Wolf 359, our planet would pass through any communication beam between the star and a local probe once per orbit. Thus a signal to Wolf 359 from an FICD in our Sun’s gravitational lensing region could in principle be detected. Gillon and Burdanov put the idea to the test using the TRAPPIST-South and SPECULOOS Southern Observatory in Chile, in a search “sensitive enough to detect constant emission with emitting power as small as 1W.”

The result: No detections. This could indicate that no probes exist within the Solar System using these methods, or at least that such a probe did not transmit during the observations. Indeed, the list of hypotheses to explain a null result is so large that no conclusion can be drawn. No detection simply means no detection.

But the observations lead us further to consider the spectral range of possible emissions from FICD to star. This is going to change depending on the star. Remember that using gravitational lensing to enable communications forces the receiver to face the host star, blocking its light with some kind of occulter (or perhaps a coronagraph) while enabling the signal to be received. Gillon and Burdanov note that Wolf 359 is a flare star with strong coronal activity, one with significant emission of X-ray and extreme ultraviolet light. The authors determine ‘a spectral zone of minimal emission’ that becomes interesting as a communications channel. Here let’s turn back to the paper, for this zone may be a better place to look:

While the very low emission of late-type M-dwarfs in this spectral range could be an issue for prebiotic chemistry on habitable planets (Rimmer et al. 2018), it could represent a nice spectral ’sweet spot’ for a GL-based communication to a late M-dwarf like Wolf 359 or TRAPPIST-1. Another advantage of using this wavelength range instead of the optical range is the improved emission rate, thanks to the narrower laser beams… These considerations suggest that the spectral ranges 300-920nm and 400-950nm probed by the TRAPPIST-South and SPECULOOS South observations could not correspond to the optimal spectral range for a GL-based communication [gravitational lensing] from the solar system to Wolf 359. The 150-250 nm spectral range could represent a more optimal spectral range for such GL-based interstellar communication to a cold and active late-type M-dwarf like Wolf-359.

Image: This is Figure 2 from the paper. Caption: Illustration showing the geometry of the hypothesized communication link from the solar system to the Wolf 359 system. The distances and stellar sizes are not to scale. Wolf 359 is shown at 3 different positions. Position 1 corresponds to the time of the emission of the photons that we receive from it now. Position 2 corresponds to its current position. Position 3 corresponds to the time it will receive the photons emitted now by the FICD. Credit: Gillon & Burdanov.

Probing this spectral range would require a space-based instrument, but it would be interesting to target these frequencies in a reproduction of the Wolf 359 observations. This paper recounts the first attempt to detect optical messages emitted from the Solar System to this star, and as such seems intended primarily as a way to shake out observing methods and explore how gravitational lens-based networking could be observed.

The paper is Gillon & Burdanov, “Search for an alien communication from the Solar System to a neighbor star,” submitted to Monthly Notices of the Royal Astronomical Society (preprint). Gillon’s 2014 paper is “ “A novel SETI strategy targeting the solar focal regions of the most nearby stars,” Acta Astronautica Vol. 94, Issue 2 (February 2014), 629-633 (abstract).


Comments on this entry are closed.

  • Alex Tolley November 26, 2021, 11:37

    As the authors cite Kaltenegger’s paper on Earth as a transiting planet, there are 2000 possible stars that could have relays at the SGL. That is plenty of possible search effort.

    The problem I have with this paper, as with the Kaltenegger paper, is that it is constrained by current techniques. In the Gillon paper, it assumes that there must be a node at the Earth’s SGL, and in addition it can only possibly be detected if the communicating star sees the Earth as a transit planet of our sun. There could be many such nodes at 550+ AU from the sun, but all of them in alignments with other stars.

    It is equivalent to aliens on Earth trying to detect our microwave transmissions by finding spots between 2 dish transmitters. They would miss the vast majority of our communications. It is a “Let’s see if we get lucky” strategy.

    If there is a node at our SGL, it will not likely be a node to simply act as a booster or router, but rather it will be a receiver for a [Bracewell/Lurker] probe in our system. Depending on the location of the probe, there must be a spherical search space that is much smaller than one with a 550+ AU radius. Jim Benford has argued for a probe to be located relatively near the Earth, perhaps on the Moon, or in an orbit near Earth. If on the Moon, one of out lunar orbiters could pick up a transmission being sent to any node located in a spherical surface of the 550 AU radius, although I would suggest his strategy of looking for the local probe directly makes more sense in this case.

    In summary, there has to be so many assumptions about the need for nodes, their locations, and their activity that it is an extremely low probability that we could detect any transmission to or from these nodes even if they exist. [We are back to looking for black cats in unlit cellars that are probably not even there. Sure, bring a flashlight and look, but it is probably better to wait for some other sign of activity before searching.]

    Wolf 357 is less than 10 ly away. If it was in communication with a probe in our system, its node knows of our technological presence. If there is any intelligence in the local probe or node, ET might want to direct a message at us. Wouldn’t bright laser flashes (or some other artificial pattern in the star’s light emissions) be a good signal, especially as TESS is monitoring all the nearby stars? Unless we get some unambiguous signal, we will continue to add to the number of reasons to explain the Fermi Question. Nearby smart, active communication nodes and probes eliminates the “ETI is many thousands of ly away and therefore…[X]”. If ETI is as godlike as the fictional Dave Bowman/HALman, then they don’t need communication nodes either. We would be like ants wondering why we cannot detect the alien pheromone signals.

  • Ron S. November 26, 2021, 14:20

    Considering the high proper motion of stars relative to each other and the exquisite aiming and sunshades required this would be a bizarrely complicated and high maintenance network. I find it difficult to take too seriously. I suppose it’s worth some effort to test, but a negative result won’t help us to conclude anything.

    • Alex Tolley November 26, 2021, 23:36

      You raise a good point about the need to track the foci to maintain the connection. This requires constant fuel expenditure unless there is a way to harness the star’s energy to steer. While it saves transmission energy, it also incurs energy costs to maintain node alignment. It might not even be possible to constantly realign nodes for the whole network that might be required if the nodes must be accurately placed. It seems to me that to prevent this, the nodes can be fixed, but they must transmit and receive data from a number of sub-nodes that must do the steering to maintain connections to prevent the network from becoming very brittle. IOW, a local network on the 550 AU radius sphere handles the local position changes and absorbs the position changes. Replicated at each star in the network ensures that the connections between stars stays operational, while also maintaining the low signaling energy costs.

    • Antonio November 27, 2021, 6:34

      I don’t see the point in their strategy either. Since stars move, the probe would soon be out of focus for communication with another star. The only sensible communication system would be to have a huge swarm beyond 550 AU, so that frequently some probe would be on focus. But, given the existence of such huge swarm, astronomers on Earth don’t need to observe a particular star like Wolf 359, they can point to almost wherever they want to search for probes.

  • Mike Serfas November 26, 2021, 16:28

    Does photonic matter have relevance for SETI (or SETA)? I have seen stories like http://www.sci-news.com/physics/new-kind-photonic-matter-05737.html that give me the impression that Earthlings are just about ready to package photons together in bundles – which would imply the ability to encode a “book” of information in a single packet of light that is either received or missed. A 10% chance of receiving a communication would seem vastly preferable to receiving 10% of the bits of a communication.

    I also have a vague impression that cosmic rays are still imperfectly understood and characterized, to the point where if one in a hundred were actually a packet of smaller photons moving together, maybe no one has noticed?

    • Robin Datta November 27, 2021, 1:13

      Yes, Mr. Wright, the message may be unrecognizably drowned in noise but someone with the right technological winnow may yet be able to separate the wheat from the chaff. I once had a shortwave radio with Single Side Band: it was quite remarkable how a message emerged as the SSB was increased.

  • Andrei November 26, 2021, 16:53

    When I have an idea, I often consider that someone else thought along the same lines. That certainly is true for Tipler and Freitas.
    So yes, perhaps we should be happy that there has not been another civ sending out VonNeumann machines, else we might have found ourselves in a system where the other planets already been consumed.
    That do not completely exclude that such civs do exist, one could imagine one case in which one civ build such machines, and another oppose the practice by sending out killer bots – eventually creating an interstellar ‘ecology’ which prevents the bots from the first civ to reach more than a local bubble of space.
    This only on the conditions where any the civs have a moderate long technological age, extremely long lived ones with any kind of outreach or advanced tech would eventually start such projects that they would be detectable also from a huge distance. (Neither that we’ve done any targeted search for such.)
    In any case, this is one interesting suggestion. If one interstellar network exist, either an active one, or stations and equipment that still exist from one civ that no longer is active. Perhaps as lotus eaters in virtual realities. I think it’s work looking. As such a communication relay would be a reason they for such a civ to visit also nearby stars, either physically or more likely – via automated construction machinery.

  • henry cordova November 26, 2021, 17:40

    I’m not sure I understand the geometrical reasoning behind this concept. Please correct me if I have missed something.

    A transmitter relay station has been placed in our solar system by an ancient civilization a long time ago. This device is transmitting to a nearby dwarf star (Wolf 359) , using our sun as a gravitational lens to focus a beam aimed at the dwarf (or at the point where the dwarf will be when the beam gets there!). Presumably, this is part of some trans-galactic communications network established long ago, and either the local transmitter or the Wolf 359 receiver, or both, are relays in this system.

    I presume this geometry would work regardless of where on the celestial sphere the receiver is located, so the requirement that the receiver be located near the ecliptic is simply because that is the only way the Earth would be in a position to intercept the signal.

    There could be thousands of potential targets all over the sky for this signal, but since we can’t fly around the solar system checking them all, only those stars on or near the ecliptic (Wolf 359 would see Earth transiting the Sun once a year) would be favorably placed for us to eavesdrop.

    If my reasoning is correct, 6 months later, I presume the Earth would pass through the point in its orbit opposite Wolf 359 and be able to intercept transmissions from Wolf 359 to the local FICD.

    I have my suspicions about this effort. Supposedly, nearby stars in the orbital plane of the Earth would have to be focusing their attention on Sol because they have a relay station here, out in the far reaches of our own Oort cloud.

    • Robin Datta November 27, 2021, 0:54

      Yes, Mr. Cordova, if one star is well below the ecliptic, and the other well above, with Sol in the straight line between the two, the each of FICDs at Sol (one on each side of Sol to receive the amplified signal from the star behind Sol) would have to be well away from the ecliptic of Sol to be aligned with the star and Sol.

  • Jeff Wright November 26, 2021, 18:35

    Could the “WOW” signal have been the result of Earth passing through-or just nicking-a focal line between two systems? They see a signal drop out, where we are the radio of a car that just passed a saddle of two mountains where a snippet of a song was audible for only a moment. So I suggest rewinding the clock such that we look for two star systems that Earth was dead between the moment ‘Wow’ was heard. If Ouamuamua or Teton also come from this focal line…so much the better. Put a probe in that line to act as a linesmans handset to eavesdrop.

    • Robin Datta November 27, 2021, 0:56

      Mr. Wright: WOW! That’s a good idea!

    • henry cordova November 27, 2021, 1:33

      Its always possible. The sun flies around the galaxy at hundreds of km/s, and all the stars in its vicinity also have superimposed on that their own proper motions. If ET is transmitting a navigational beacon, planetary defense radar, communications link or some other tight beam, we would only intercept it for a very short time. They would not be aiming at us, so the beam would flash by us very briefly and we would be illuminated by it for a very short time. Just how long would be determined by distances, beam footprint, relative motions, etc, but the flash would probably be on the order of a few seconds or minutes. No gravitational lensing need be involved.

      I’ve always thought that there was a good chance that’s exactly what the WOW was. Of course, if that was the case, you would never get a confirmation signal no matter how long you listened at the same point of origin. Accidental beam interceptions are probably very rare, and we would probably miss most of them because we would very likely not be looking that way when they flashed by. But they cannot be ruled out.

      • Jeff Wright November 27, 2021, 23:03

        We need to chart focal lines…like spider webs.

    • torque_xtr November 28, 2021, 8:53

      Maybe a search through GAIA data could show if there was some precise alignment of stars at the moment. If there are two stars linked by SGR relays and located in line with Solar system, and one of them passed exactly in front of another from “Wow” receiver vantage point, then signals would be extremely amplified by the strong lensing. The main objection is strong and non-uniform refraction of radio waves in stellar coronae. Maybe some radio transmission by SGL is possible, but definitely only with much greater focal lengths than the minimum (550 AU for the Sun). Optical bands (IR+Vis+UV) in SGL communications have all advantages over radio – greater bandwidth, greater gain, less distortions…

      There is a natural mechanism that could generate ‘Wow’-type signals by (possibly maser?) emissions from cometary tails, https://planetary-science.org/wp-content/uploads/2017/06/Paris_WAS_103_02.pdf. This far, this is my favorite one despite objections. Since the signal, paradigm shifted towards optical bands as more effective means of transmission, and a narrow radio band which could be contaminated by all kinds of natural hydrogen emission is poor choice for a comm band anyway.
      For a beacon signal, I would choose hydrogen or some other common line, multiplied or divided by some common irrational constant, like pi or e, so that the line does not interfere with anything natural (within reasonable Doppler range) and cannot be mimicked by any natural process.

  • Michael Fidler November 26, 2021, 22:37

    Instead of going to all this trouble…

    David Kipping’s Terrascope telescope:



    Or Uranusscope or Neptunescope, I’m sure any alien races and their AI probes would know which planets atmosphere would work best for a relay.

    The big point, at Neptune’s distance it would be able to reach the whole celestial sphere with little light from the dim Sun lit surface of Neptune.

    What may work better is Triton’s or Pluto’s atmosphere…

    Neptune’s Moon Triton ‘Flashes’ During Star Occultation.


    On the Possibility of Using the Earth as an Atmospheric Lens.


    • Mike Serfas November 27, 2021, 16:52

      Neptune, Triton, stars get brighter… in addition to being pleased and amazed to see an atmospheric lens work, I also, at long last, now understand the lyrics from Astronomy Domine. :)

    • Michael Fidler November 28, 2021, 10:16

      It seems to me that if anything interstellar civilization’s would be oriented toward fitting into the galactic ecology. Instead of flying around looking for stellar focal points they would use the closet and easiest form of antenna which would be planet or moons atmospheres. Titan huge nitrogen atmosphere would make an excellent lens, the question is where to place the reciever/transmitter in a stable orbit that could hold it stare long enough? The Sun’s movement, Saturn’s movement, Titan’s movement and the recievers movement. The coordinates for here and at the reciever would be the first data sent and changes as time proceeds would be calculated. The actual beam should be some what easy to capture…

      Saturn’s and the rest of the Solar system orbits are perpendicular to the disc of the galaxy so signals sent would be more or less north and south of our cardinal points to where most of the galactic civilizations exist.

      • Alex Tolley November 28, 2021, 14:26

        Using planetary atmospheres and long orbits might actually solve a lot of problems. You get much of the low energy gain, but also using short laser pulses, the possibility of firing short messages at many target nodes. The problem of synchronizing alignment can be solved, at least partially, by having many such nodes in the same orbit and in orbits with different declinations. Think of the swarms we are putting up now in LEO as precursors. The interstellar communication satellites would just be at higher orbits around their planets. This would be cheaper and easier to service.

        An even fancier idea is to construct an Dyson sphere around the planet at the needed radius (perhaps more like a lattice) that is transparent to the communication wavelength, and studded with many millions of transmitter/receivers which will receive the communications, in a network to ensure that the signal is pieced together from a number of receivers as the sending node drifts.

        Because there are so many receivers, each able to handle a portion of any message, the structure could handle very many source messages and transmit to many target systems as well. If messages were sent as short, 1) of the target receivers received the the message that could be sent on to the next node or relayed within the system.

        • Michael Fidler November 28, 2021, 21:32

          After thinking about my last comment, the north south transmissions would not be correct, but transmissions would be along the milky way and especial toward the galactic center in Sagittarius.

          The possibility of FTL or Longitudinal (Electric/Scalar) Waves transmissions would negate all of this since they pass thru everything, so how could it be focused??? Black holes, White holes, White dwarfs – or Longitudinal holes, now that’s a good question…

          But back to known physics, if Elon Musk and the other 20 some internet satellite constellations fill the sky we will be living in a Dyson sphere! Maybe that’s why the Russians did the antisatellite test, to clear an altitude for its own constellation! ;-}

          • Alex Tolley November 29, 2021, 11:51

            Rather than worry about focusing different types of waves, I would stick to em waves we know about. While the SGL will focus all em radiation, atmospheres will only do so for those that are refracted by the atmosphere. This limits planetary atmospheres to focusing mid-range wavelengths like visible light and IR. This seems like a plus to me as these have far higher frequencies than radio waves and therefore can transmit far more information per unit of time. If we look at all possible atmospheres, which wavelengths are optimal to minimize absorption losses across all these atmospheres? This might help us direct the search for such signals if they exist.

            ASAT-produced fragment streams are like trying to poison your neighbor’s well, only to find you have poisoned the aquifer your own well uses too. :(

          • Michael Fidler December 14, 2021, 10:47

            Satellite operators criticize “extreme” megaconstellation filings
            by Jeff Foust — December 14, 2021

            The best known of such filings is one by the government of Rwanda with the International Telecommunication Union (ITU) in September, which proposed two constellations with a combined 327,230 satellites. Rwanda has launched to date a single satellite, a three-unit cubesat called RwaSat-1 in 2019.


  • Brenda Kalt November 27, 2021, 9:49

    We send out probes to obtain information. What kind of information could a civilization gain from self-replicating Von Neumann probes that consume their environment?

    • Henry Cordova November 27, 2021, 13:13

      You have a point.

      Besides, we don’t need to develop self-replicating technology. We already have it: people. They are cheap, self-maintaining, versatile, capable, robust… and expendable.

      DNA solved that problem a long time ago.

      The only issue is that they have an annoying habit of altering their initial programming. However, there is every reason to suspect von Neumann machines might have the exact same problem.

  • torque_xtr November 28, 2021, 6:25

    Another option is to look closely at a sample of nearly aligned stars in our skies. If there is something going between them, and we are in the line, we have better chance of intercepting something than by all-sky listening. Especially if we could observe from a caustic, a line of exact alignment of barycenters of both systems.

    Old red dwarfs or white dwarfs are especially good, the latter because of smaller focal lengths (and thus, intra-relay processing times), and debris disks which could serve as raw materials for buiding relays. Since SGL relaying does not require much signal power, the luminosity of the host star is not as crucial as the uniformity of it’s gravitational field and availability of raw baterial. For the laser signals, receiver has to maintain position within meters of current caustic, and fast rotation and/or strong convection in the lensing star could ruin the signal gain.

    This goes in line with a local precursor mission to our own solar gravitational lens observations. If there are a billion stars in Gaia catalog, then average separation between well-characterized stars is around half-arcminute. Surely there are some stars which form close alignment as seen from Earth, and make *exact* alignment from some POV in the inner solar system, at some point of time (because of proper motion). A spacecrast launched into caustic-intercepting trajectory could make unique observations of lensed stellar system (the farther one) and double as possible detector of ultra-narrow emissions indicating communications between SGL relays.

    There is a magnificent sci-fi novel, “Rose and Worm” by Robert Ibatullin, which describes a complex and slow-evolving galactic society based on SGL communications (sadly, AFAIK, no English translations yet)

  • Michael Gillon November 28, 2021, 18:35

    Hi folks,

    First, let me thank you, Paul, for this nice summary of our paper!

    After having read the interesting comments, I would like to clarify why we picked Wolf 359 as target for this search. This selection is not random, it is based on the assumption that the ‘galactic network’ has a node-less neighbor-to-neighbor infrastructure. This communication infrastructure is highly used by the cells of multicellular organisms : neighbor cells are always ‘chatting’ to each other through chemical and physical means, which enable them to ‘sense’ their environment and to react smoothly to any local stress/stimulus without having to wait for a remote ‘node’ to receive their message, take a decision, and send back an instruction.
    To illustrate the advantage of this infrastructure in a ‘galactic network’, let’s imagine the following situation (echoing some of the comments above). In a given system, the probes replication process has gone wrong, and the ‘mutated’ offsprings tend to have anomalous behaviors. If the situation has to be reported to a decision node very far away, the reaction could come very late, too late to contain it. Oppositely, if the information reaches all neighbor stars, they could react much more quickly while relying the information to the whole network. The biological equivalent situation could be a cell that becomes cancerous. If its cancerous nature is noticed by its neighbor cells and that they trigger a proper response (e.g. kill the abnormal cell), the situation would have much more chance to remain contained than if a reaction has to wait for a remote ‘decision node’ to be informed and react.

    So in this assumption, neighbor stars are always chatting to each other. This does not preclude the existence of local and even central decision nodes (our nervous system is a good example of a communication network that mixes neighbor-to-neighbor and node infrastructure). Now, if we take the Sun, its probes should thus discuss with the N nearest stars, N being a relatively small number > 1. In this scenario, a communication with Wolf 359, the third nearest star system, can thus be expected. Unlike the Centauri system (1st nearest) and Barnard’s star (2nd nearest), Wolf 359 lies in the ecliptic, and so the Earth should transit the Sun as seen from the FICD once per orbit, passing in the FICD’s communication beam. During that crossing, an Earth-bound telescope observing in the right spectral range the FICD’s coordinates could detect it as a transient source that would disappear after the crossing and come back one year later.

    Note that our paper has now a third co-author, Jason Wright from Penn State University. We will post soon a new version of the draft on astroph in which we explored the possibility that the FICD could be composed of ‘out-of-focus’ lasers located much closer to the Sun than the SGL. Such a location would diminish the efficiency of the interstellar communication, but it would still be much more efficient than a classical (i.e. unlensed) communication strategy. Furthermore, the decrease of the efficiency would be more than compensated by the larger solar flux, resulting in more energy for communication and motions. Indeed, it seems natural to assume that the FICD would use a solar sail for keeping the same radial position to the Sun and for its azimuthal corrective motions. What is cool with this scenario is that if the FICD components are closer than ~50 au from the Sun, we could maybe detect them directly in reflected light (imagery) even if they are not in the ecliptic. Basing on this fact, we initiated a search for out-of-focus FICDs on the 10 nearest stars (and on TRAPPIST-1, just for fun).

    For the record, this SETI project came to my mind after having read Manifold: Space from Stephen Baxter, in which alien Van Neumann probes use the Sun as a gravitational lens.

    All the best,

    • Paul Gilster November 28, 2021, 20:47

      Thanks so much for your comments, Dr. Gillon. What a pleasure to have you here. By the way, I read Manifold:Space myself when it first came out, a provocative work indeed, but I had no idea it inspired this project. Fascinating.

    • Alex Tolley November 29, 2021, 12:08

      The biological equivalent situation could be a cell that becomes cancerous. If its cancerous nature is noticed by its neighbor cells and that they trigger a proper response (e.g. kill the abnormal cell), the situation would have much more chance to remain contained than if a reaction has to wait for a remote ‘decision node’ to be informed and react.

      This is a poor analogy. The various immune cells are not located nearby the cancerous cells, but rather in tissues farther away. In the case of new pathogens, their detection, and creation of new antibodies, are achieved in distant organs, such as a the lymph glands (which is why you feel for any swelling in those glands to determine if a fever is due to infection).

      I am not clear why the internet model of updating routing tables with packet routing around broken routers isn’t the more direct analogy for the interstellar network.

      • Michael Gillon November 29, 2021, 18:03

        Yes, I know how the immune system works. This was exactly my point, i.e. that the response to a cell going wild could be much more efficient if it was noticed and killed or at least reported by its neighbors, instead of having to rely on the noticing and reaction of remote specialised cells. I just wanted to illustrate with a biological example how a neighbor-to-neighbor nodeless architecture could be more efficient than a mono- or multi-mode architecture like the one of our immune system. But I concur that my wording was confusing! In my defense, English is not my mother language :)

    • Steve Muise November 29, 2021, 14:50

      “In a given system, the probes replication process has gone wrong, and the ‘mutated’ offsprings tend to have anomalous behaviors. If the situation has to be reported to a decision node very far away, the reaction could come very late, too late to contain it. Oppositely, if the information reaches all neighbor stars, they could react much more quickly while relying the information to the whole network.”

      There is a better biological analogy that could be used: the digital version of telomeres that would restrict the number of times a probe could reproduce, thereby limiting the chances of a reproduction error leading to anomalous behavior. If the builders restrict each probe to reproducing, say, 4 times the odds of a copy error are greatly reduced.

  • ljk December 2, 2021, 12:30

    I wonder if this conflict affected the local gravity fields of this system…


    Or should I say will? :^)