Alan – Penn State Graduate Course in SETI

Reaction to Davies (2010): ”Nature Plus”

Davies, in this excerpt from his popular book The Eerie Silence, examines what we consider technology and how it may not necessarily apply to an advanced intelligence a thousand or even a million years ahead of us in terms of technological progression. He gives a definition of technology as “a mind, intelligence, or purpose blended with nature, which obeys the physical laws and harnesses them.” Therefore, technology is not distinct from nature in the sense that it is physically separate from nature, but is a part of and a higher form of it. It is “Nature-Plus.”

Classically, we recognized things as being artificial technology based on the organization and structure of its constituent parts, and its utility as a system. And also, such systems are macroscopic in scale. An example of such a system would be the modern personal computer, which is made of billions of transistors that come together to perform specific functions written in software, and which has occupies a physical volume on the scale of cubic decimeters. In fiction (and sometimes in bad science), there is a tendency to anthropomorphize the technology of an alien intelligence to follow our notions of machines. However, on the deeper level, he calls into question even the aforementioned characteristics of technology that we take for granted, and posits that an advanced technology would be like nothing we would understand. We can imagine (but not yet understand) a technology that doesn’t manifest or operate on the material level, or which is indistinct in form or topology, or which transcends our one temporal and three spatial dimensions, or which to us appears as bereft of function, or which does not appear to consist of discrete quanta. An example of such a technology in fiction would be the “sophon” of Cixin Liu’s Three Body Problem, an intelligent particle which can communicate instantaneously across interstellar distances and which is formed of a circuit system sketched onto a multi-dimensional manifold and collapsed to a point.

If such notions of technology were real and currently in operation, then our theories of how the universe works may be called into question. And so, we should ask, what exactly is it about technology that makes it distinguishable from nature? The question is loaded because we operate on the premise that the nature we observe is truly natural. That is, astrophysical phenomena are emergent properties of a universe governed by the laws of physics. This however, may not be the case. We can imagine scenarios where those phenomena that were thought to be natural turn out to be artificial. Then, any theory of how the universe or its constituents operates that was based on such an observation would be flawed. This is similar in vein to the Planetarium Hypothesis solution to the Fermi Paradox, which suggests that the universe we see is artificially constructed or designed in such a way to make us believe that it is self consistent (that is, until we can muster enough resolution to “lift the veil” so to speak, and discover that the universe is not as it seems).

I think this idea of “Nature-Plus” should be taken seriously by SETI scientists because it challenges the way we think about nature and may be an explanation for why searches based on conventional notions of technology and energy consumption have been unsuccessful. And I do indeed think that it is meaningful to search for astrophysical anomalies, because of the twofold benefit of performing novel science alongside a SETI search.

Reaction to Schwartz & Townes 1961

Following the theme of last week’s papers which took a look at alternatives to radio searches, this week’s papers focus on laser SETI in the optical and near-infrared. The first paper to discuss this possibility was Schwarz & Townes 1961, which was published just two years after Cocconi & Morrison motivated the radio SETI search in 1959. In an act of sheer clairvoyance (probably afforded by the fact that Townes won the Nobel prize for the discovery of lasers), the authors predicted a time when “maser apparati near the optical” technology would exist and be a viable alternative method of interstellar communication.

Notably, in our timeline, the discovery of lasers followed the development of radio communications; however, it seems that there is no necessary reason why this ought to be the case. One could imagine an ETI developing proficiency with lasers first, and hence use those as the primary means to signal to other ETI. Therefore, the abilty to detect a optical beams is an important addition in the ensemble of SETI search avenues.

To detect such a beam, the authors set two criteria: 1) that it produces enough photons per unit of area on the r eceiving end to be detectable (given the design of the detector and telescope), and 2) that it is distinguishable from the background. Given those criteria, they examined the possibility of whether or not an optical beam can be used to establish interstellar communications by testing two systems: 1) one which consists of a continuous 10kW beam at 5000A with a bandwith of 1Mhz and assuming a 200in reflector telescope, and 2) an array of 25 lasers like in part (1), but with an effective aperture of 4in. They conclude that in both cases that a signal carried on such a beam ought to be detectable to a distance 10ly given c. Earth 1960 technology. Of course, the technology of today is significantly more advanced than sixty years ago, so probably this estimate is highly underrated.

This paper is important because it was one of the first to offer a novel approach to the SETI problem (I believe the second after the Dyson 1960 paper). This paper’s predictions were vindicated by papers such as the other one for this week (Wright 2014) and others which actually conducted optical and NIR SETI searches. This paper laid the groundwork on which these subsequent additions build and helped frame our thinking about how a laser search ought to be conducted. Indeed, as we move further into the 21st century (only the second century of electronic technology on Earth) we are fastly transitioning to fiberoptical communication. Could it be that other societies also inevitably reach this conclusion as well (or at least transition through such a phase on a path of development to some even more advanced communication scheme)? Only a dedicated laser SETI search can attempt to answer those questions!

Reaction to Howard et al 2004

Continuing with the theme of optical SETI from last week, this week’s Howard et al (2004) paper discussed the results of an optical SETI experiment which searched for pulsed beacons around thousands of stars. Following with the other optical SETI papers we have encountered, the authors compare the merits of searches in the optical/NIR with searches for microwave/radio signals. If one’s figure of merit for the efficiency of technique is the signal-to-noise achieved for a fixed transmitter power, then optical methods are comparable to those of radio.

They further motivated this search by presenting the “Fundamental Theorem of Optical SETI”, which is a statement of the observation that even at our early stage of technology (Earth “2000”), we can already generate artificial optical pulses could appear to outshine the brightness of the Sun by a factor of 10^4. This follows a similar line of reasoning as the Schwarz & Townes paper from last time, which plausibly suggested that some ETIs would rapidly discover some form of optical interstellar communication and use it. However, in the case of Howard’s paper, the focus is on the search for pulsed beacons, which are unambiguous detections of alien laser signals (for which there are no possible astrophysical confounders or dopplegangers).

With similar avalanche photometer instruments at Harvard and Princeton, they began their campaign which would eventually consist of some 16,000 observations totalling 2400 hours of observing time spread over a five year baseline. They searched 6176 stars in their survey, of which only a handful of signals showed any promise as plausible artificial pulses (most were explained away as being stochastic in nature). Three triggers from HD 220077 were considered the most interesting, and were allotted many follow-up observations. Upon further investigation of those candidates, they found that their photon rate was consisten with Poisson noise and thus rule out the alien hypothesis. (Remember, it’s never aliens!) Another interesting pair of triggers from HIP 107395 was considered too ambiguous because of an asynchronicity between the Princeton and Harvard clocks.
This work was performed in fulfillment of Howard’s PhD thesis in astronomy; Andrew Howard is now a prominent exoplanetologist and astronomer, and so this work is a demonstration of SETI being firmly rooted as a part of astronomy and an example of the quality that SETI papers ought to strive for (that is, when it is taken seriously by astronomers and other scientists). It is also a good example of “Forensic” SETI done right, where the candidates were scrutinized on a case-by-case basis and all natural explanations were attempted to be exhausted before jumping to unsubstantiated conclusions (which contrasts with the approach of some other papers we have read this semester *cough* faces on Mars *cough*). Although the results were null, the study still placed valuable upper limits on the occurrence of beacons around nearby stars. Therefore, this paper serves as a template for how null results ought to be reported and makes a case for them to be published.

Reaction to Townes (1983) and Hippke & Forgan (2017): Alternative Frequencies for SETI

The theme between the Townes (1983) and Hippke & Forgan (2017) papers is that our SETI efforts should not be solely focused on searches in microwave and radio frequencies. These papers make the case that there are in fact equally viable if not superior alternatives to radio in both the infrared (IR) and X-ray portions of the electromagnetic spectrum, respectively. SETI experiments have been influenced by the precedent set by the earliest ideas in the field, which emphasized the radio search (and often near the 1.2-1.67GHz water hole). In fact, it was Cocconi and Morrison who gave us the idea that the most important factor when imagining interstellar communication systems is their efficiency in terms of photons per watt, which led them to pursue the radio search. However, with the development of new technologies and perspectives, it is clear that this narrow viewpoint misses out on a greater variety of possibilities.

These are examples of quality SETI papers because they attempt to expand our perspective and push boundaries. They remind us that we should be ever aware of falling into narrow-minded modes of thinking, and that when dealing with the perplexity of trying to predict the motivations and strategies of an ETI, we should stoically expect that we are wrong. They are also remarkable in their approach to the question. In the case of Townes, he thinks critically about the observational challenges of moving to the infrared and quantitatively compares the pros and cons of IR methods with those of microwave/radio. He is also cognizant of the fact that there are a lot of assumptions (which he makes explicit) made about the strategy of a transmitting ETI which we can only speculate about and limit the effectiveness of the IR search. On the other hand, Hippke & Forgan are motivated by the search of the global optimum for interstellar communication, which they decide ought to be in the X-ray near 1nm. In pursuit of this grail frequency, they examine a variety of astrophysical and observational difficulties which complicate communication, such as diffractive photon loss, interstellar extinction, and atmospheric transmission. In this way, both papers are firmly rooted in taking a classically quantitative and astronomical approach to SETI. This places these papers a tier higher than those which solely offer speculation on search strategies unsubstantiated by rigorous examinations of the merits of the alternative. Overall, the field benefits when scientists take SETI seriously and improve it by contributing to it with quality papers.

Reaction to Hippke 2017 (Non-EM Carriers): Is the SETI search too narrow-minded?

Since the conception of communications with extraterrestrial civilizations in the late fifties (Cocconi & Morrison 1959), the overwhelming majority of SETI endeavors have centered on electromagnetic communication systems, often in one narrow fraction of the entire spectrum. Hippke is aware of the potential shortcomings of such an approach and presents the possibility of alternatives, not just to microwave emission as in his previous work (Hippke 2017), but to electromagnetism as a medium for information carrying in general. In particular, he examines the merits and shortcomings of a variety of non-EM carriers such as electrons, protons, neutrinos, gravity waves, and occulting megastructures. Vetting based on energy efficiency and data rates, Hippke places these alternative channels in competition with EM-based communications. For transiting megastructures, Hippke fails to find a way for this method to be competitive when it comes to target communication with high data rates, and so tepidly dismisses them. He also quickly rules out charged particles, particles with short lifetimes, and heavy particles due to interstellar magnetism, longevity, and energy requirements, respectively. He is also critical of gravitational waves as a medium for signal carrying as their artificial production is extremely resource intensive and wasteful. Lastly he examines neutrino based communication, which fails due to issues with focusing when compared to photons and size requirements of detectors. All of his conclusions are based on current knowledge of physics, and so the possibility is open that with an improvement in knowledge, some of these avenues may potentially become viable again. He has framed this investigation to work within the confines of what is currently understood. With these limitations, he concludes that the best medium for point-to-point communications is still electromagnetic radiation, at around the 1nm scale. If the assumption of preference for speed is relaxed, then the best alternative would be inscribed matter, or probes carrying vast databases of information. This paper was a novel contribution to SETI because it is one of the first attempts at an exhaustive analysis of alternative modes of communication. Scientists can often times get caught up in the present paradigm, and so it is beneficial to get a fresh perspective on the issue from someone who is not formally scientifically trained and thus potentially not subject to the same prior perceptions. His conclusions also vindicate the thinking behind the Pioneer and Voyager plaques and records, since physical media transported on long timescales is shown to be one of the preferred methods of communication. The potential this paper had to to retroactively dismiss all of our previous SETI efforts as foolishly narrow-minded or misguided should not be discounted. While we will continue to perform SETI in the radio and microwave, we should always be open to the possibility of alternative means of communication, and at the very least entertain a more expanded search of the electromagnetic spectrum when designing future SETI surveys.

Reaction to Wright (2017) (Incomplete)

Humans have occupied the Earth for less than 0.1% of its total existence. Given the vastness of time and the incompleteness of the geologic record, is it possible that the Earth had independently produced another intelligent species in the remote past? By extension, given the lack of fullness of knowledge regarding the deep history of our solar system, could other worlds have been host to such intelligences? And if it is possible, is it a worthy endeavor to pursue answers to these questions? This is the situation presented to us by astronomer Jason Wright in his paper regarding the possibility of what he calls prior indigeneous intelligent species, that is, intelligences which arose organically (i.e., not from other star systems) within our own solar system.

For many modern astrobiologists, there is hope that extant or extinct life will be discovered on perhaps Mars or the moons of the gas giants, but Wright is distinct in his pursuit of the possibility of the development of a more complex lifeform in the solar system. He considers a variety of plausible lines of evidence we could follow to establish whether or not the Earth or any other body of the solar system could have harbored an intelligence in the distant past. In the case of the Earth, it is difficult to conceptualize a way for artifacts or other signatures could be preserved on lengths of time comparable to the age of the Earth, but one strong marker would be unnatural isotope ratios discovered in sedimentary layers indicative of nuclear activity. Since some radioactive atoms have half-lives of billions of years, their signal should still be active even given the eons. For other bodies, those with geologic activity and atmospheres tend to continually renew their surfaces wherease those without are at the very least impacted frequently by micrometeorites and infrequently by asteroids. This reduces the probability that any actual physical relicts would ever be detected. Also, relics in orbit would tend to decay or scatter or collide with other objects, and hence are unlikely to survive the temporal expanse.

Even with the apparent implausibility of any success, I would agree with the author and argue that there is a small place for this area of inquiry so long as it does not detract from the pursuit of more secure science. If indigenous species’ artifact searches can be performed in the background using data that is already acquired, then I feel that there is no harm in at least exhausting the possibilities.

The Dangers of Sensationalism

I am very critical of yellow journalism, especially when it comes to the topic of the burgeoning search for extraterrestrial intelligence. It seems that in order to draw more traffic to their domains, journalists are often incentivized to throw in more buzzwords or sensational misrepresentations of the primary message of their interviewees. In this department, Andersen’s article in The Atlantic fares moderately well in that he does not go headlong into sensation (though he does participate to some degree, as we shall see). The article provides decent exposition on the astronomical techniques used in the detection of exoplanets and an account of the events regarding Tabby’s star as they unfolded. My primary qualm with the presentation was that they emboldened and enlarged a paraphrase of a quote from Prof. Jason Wright, which seemed to distract from his main message (My secondary qualm is that in their last sentence they suggeste that Tabby’s star might see Earth transit, but the declination of Kepler field stars places them well beyond the range of the Earth transit zone). In the paragraph text, he says: “Aliens should always be the very last hypothesis you consider.” This is what most certainly, if any, should have been emboldened and enlarged. Instead they chose: “… it looked like [something] you might expect an alien civilization to build.” To the lay person who might only read the article in brief and without skeptically-trained eyes, they may come across this latter phrase and then go on to tell all their friends and family a false truth regarding Tabby’s Star due to this choice of emphasis. This is obviously dangerous to the representation of SETI and astronomy in general, and may tarnish the reputation of the field and the authors consulted. I would strongly admonish any deviation from a purely accurate representation of the ideas and phrases of a scientist, especially so in this area. Therefore, it is the role of the scientist to effectively explain the subtlety of their position to the journalist and the role of the journalist to reflect such a position with fidelity in the popular article.

Searching for Monoliths: When Science Fiction Informs Science Reality

In 1999, American satellites in orbit around the moon detected a strange magnetic anomaly emanating from within the crater designated Tycho. An early explanation for origin of the anomaly source was a ferrous meteorite, but that could not account for the strength of the produced magnetic field. A few years later in 2001, an expedition to the anomaly site was dispatched from the lunar base at Clavius. The team was led by astrophysicist and former chair of the US National Council of Astronautics, Dr. Heywood Floyd. The expedition revealed a structure, in more ways than one similar to a black box, with rectangular prismatic dimensions in the ratio of the squares of the first three nonzero natural numbers. This ratio held even when the distances were measured at the finest resolution afforded by modern instruments. Subsequent radioisotopic dating of the surrounding regolith implied that the structure had remained in place for some three million years, long before any lunar activity attributable to any human nation and in fact older than the genus \textit{Homo} itself. Given its age and unnatural design, scientists were led to conclude that the object is not of this world nor of this solar system, but actually an emissary of some advanced extraterrestrial civilization sent to monitor the development of the human race.

Does it sound like science fiction? The above story is indeed fictional and is actually lifted from the plot of 2001: A Space Odyssey, a film and novel by Stanley Kubrick and Arthur C. Clarke (which itself is influenced by Clarke’s earlier short story The Sentinel). However, this is fundamentally the type of object that SETI scientists are now seriously contemplating searching for! (As such, we should be mindful of the great ideas that have come to us from science fiction.) Setting aside great storytelling, one of the core ideas of this film was that the Earth had been visited in the remote past by an alien intelligence who established and left behind artifacts after their survey of the solar system was complete. Whether the artifacts were left deliberately or otherwise inadvertently is less important as is the fundamental question of whether or not it is possible for us to perform an exhaustive search for them. In 2013 (nonfiction timeline), Davies & Wagner suggested exactly this kind of search and also overviewed the kinds of strategies we might use to detect a variety of signatures which would suggest that the Moon had been visited in the remote past. These strategies revolve around searching through the Lunar Reconnaissance Orbiter (LRO) data, which offers high resolution imaging of the lunar surface. In this way, SETI science can “piggyback” off the gains of traditional science, which often acquires data that can dually be utilized for SETI purposes. (Imagine the difficulty of justifying a complete surface map of the Moon for the explicit purpose of searching for alien artifacts in a mission proposal to NASA!) With the LRO data, we are afforded the ability to search for 1-10m class objects which could be the detritus, message-carrier structures, habitats, or instruments of a past alien visitation.

This paper is the logical continuation of the Bracewell 1960 paper applied to the specific case of stationary (possibly perpetually ensconced by craters or more likely subterranean) artifacts on or near the surface of solar system bodies. (The original paper did not deal with this case, but focused more on probes in orbit, which was later expounded upon by Freitas 1983.) In my reaction to Bracewell, I suggested how a search for exposed artifacts on the surface of solar system bodies could be a feasible project given modern artificial item recognition software and machine learning algorithms. However, as the authors point out, there are difficulties with the lifetimes of exposed structures given that any region on the surface of the Moon, for example, is likely to be struck by impactors on vast geological timescales, releasing energies which no known materials would be immune to. This problem arises since the progenitor civilization is expected to be truly primordial given the expanses of cosmic time, and hence their probe is likely to be millions or possibly even billions of years old. Therefore, the artifacts would probably be buried and a subsurface search conducted with penetrating radar or by a human expedition is motivated for the future. For the present however, we are limited to “relatively” recently deposited surface objects which could have been picked up in the LRO survey maps. To process this vast amount of data presents another issue, since although it could be processed without automation, it would probably require tens of thousands of man-hours to sift through it all. The cost and upkeep of such an effort would obviously defeat the purpose of a low-cost, low-effort SETI search. In the case of automation however, machine learning algorithms are limited to identifying only those objects on which it is trained to identify. For example, a machine may be exquisitely capable of identifying particular geometrical shapes, but who is to say that an artifact need be perfectly geometrical? And what of partial or nearly complete obscuration by lunar regolith built up over time? The corner of a cubical object protruding from the ground would be missed by a machine trained to search for cubes. These many difficulties make the whole idea altogether less appealing. Until a general purpose artificial intelligence or serious effort of crowd-sourced volunteers can be employed on such a task, the completeness of the search will remain low. This should not be upsetting though, because as long as the search is incomplete there is still some chance for a positive detection. Who can say, perhaps Clarke and Kubrick will be vindicated some time within this century! (As a humorous aside, it was recounted by Clarke how the astronauts of Apollo 8 were tempted to radio back that they had seen an enigmatic black structure on the surface from orbit, but they decided that it would be in poor taste.) Nonetheless, it is clear that the search is on for evidence of alien artifacts within the solar system, a search that is certainly nowhere near over.

“Facing” Reality but Remaining Hopeful for Artifact SETI Within the Solar System: A Critical Analysis of the “Face on Mars”

Is it possible that a civilization could have existed on Mars long enough to monitor the development of the terrestrial species Homo sapiens, recognize its burgeoning intellect and future greatness, and so think to construct a replica of its face out of the geology of their world, all the while leaving no other evidence of their existence into the present era? Or alternatively, is it possible that the solar system has been visited by an extrasolar intelligence who studied the terrestrial biota remotely from the Martian surface for untold eons and thought to construct a human face on Mars, leaving no other traces? These are the kinds of solutions that one would have to invoke to explain the “Face on Mars” feature in the Cydonia region of Mars imaged by the Viking orbiter in 1976. In 1988, Carlotto performed an digital imagery analysis of this unusual feature in an attempt to preclude all unnatural explanations, which he at the end admits that he was unable to do. The complexity of these solutions brings to mind one of the truth assessment protocols utilized in science, the Occam’s Razor. If two competing theories to explain some natural phenomon are equally good, then the one that should be accepted is the one which makes less assumptions. While not universally applicable, it has historically and in many cases shown its effectiveness, as in, for example, the case of explaining the retrograde motions of heavenly bodies based on a heliocentric model rather than on a geocentric model with added epicycles. No, I think it is probably a lot easier to conclude that humans are exceptionally well-equipped with pattern recognition abilities, especially of the facial kind, and that we have anthropomorphically projected this face onto an otherwise completely natural geologic feature on the surface of Mars. In his 1995 book The Demon Haunted World, the astronomer Carl Sagan treated this exact possibility in a rather jocular manner:

“Occasionally, a vegetable or a pattern of wood grain or the hide of a cow resembles a human face. There was a celebrated eggplant that closely resembled Richard M. Nixon. What shall we deduce from this fact? Divine or extraterrestrial intervention? Republican meddling in eggplant genetics? No. We recognize that there are large numbers of eggplants in the world and that, given enough of them, sooner or later we’ll come upon one that looks like a human face, even a very particular human face.”

That is, there were and are a variety of other surface features on Mars and based on the stochastic nature of surface geomorphology it is plain to see that at least a few of them would have features that we would identify as potentially human. In fact, others have pointed out that there exists a multitude of other face-like features on Mars as well, but which did not, for unknown reasons, garner the same amount of attention and scrutiny as the one at Cydonia. The Cydonian face is probably just an example of human credulity and willingness to suspend traditional conventions in the domain of the apparently supernatural. Sagan further writes:

“There was an unfortunate dismissal of the feature by a project official as a trick of light and shadow, which prompted a later accusation that NASA was covering up the discovery of the millennium. A few engineers, computer specialists and others – some of them contract employees of NASA – worked on their own time digitally to enhance the image. Perhaps they hoped for stunning revelations. That’s permissible in science, even encouraged – as long as your standards of evidence are high. Some of them were fairly cautious and deserve to be commended for advancing the subject. Others were less restrained, deducing not only that the Face was a genuine, monumental sculpture of a human being, but claiming to find a city nearby with temples and fortifications. From spurious arguments, one writer announced that the monuments had a particular astronomical orientation – not now, though, but half a million years ago – from which it followed that the Cydonian wonders were erected in that remote epoch. But then how could the builders have been human? Half a million years ago, our
ancestors were busy mastering stone tools and fire. They did not have spaceships. . . Is the Face a remnant of a long-extinct human civilization? Were the builders originally from Earth or Mars? Could the Face have been sculpted by interstellar visitors stopping briefly on Mars? Was it left for us to discover? Might they also have come to Earth and initiated life here? Or at least human life? Were they, whoever they were, gods? Much fervent speculation is evoked.”

As is made clear by these ruminations, much conjecture and fanciful leaps of imagination must be invoked to explain the face when venturing outside of the mundane and routine. It was later shown in a subsequent orbital mission to Mars in 2001 that the Cydonian face had substantially eroded due to surface weathering and presently hardly resembles anything human. This paper is important because although it is a demonstration of our weakness and failure to remain steadfastly objective in the face (pun intended) of something of potentially grave importance, it does also show that our knowledge of the surfaces of solar system bodies is not exhaustive. We don’t know whether there could actually be an object in the solar system for whom the most plausible explanation is extraterrestrial in origin. Therefore, there is a place for SETI even within missions to bodies in our own solar system to establish conclusively whether or not our solar system has been visited by an extraterrestrial probe or emissary.

Reaction to Arnold (2005)

Is it possible that an advanced extraterrestrial intelligence (ETI) would have knowledge of the astronomical development of more primitive societies, and hence pre-emptively manufacture artificial megastructures around stars within their domain in an attempt to make their presence known? This is precisely the question that astronomer Luc Arnold sought to answer in his paper which laid down the groundwork for the idea that such structures would be detectable by modern astronomical instruments. Several years in advance of the deployment of the Kepler space observatory, a landmark mission which aimed to quantify the frequency of Earth-like planets orbiting Sun-like stars using a detection technique called “transit photometry,” Arnold posited that the high precision photometric monitoring of stars afforded by Kepler would be sufficient to distinguish between artificial structures embodying a variety of geometries and extrasolar planets, which are approximately spherical. If an ETI had the desire to reveal themselves, they would take advantage of the fact that societies with emerging science would perform routine astronomical observations of stars (in an attempt to detect worlds orbiting them) and hence place something less obviously natural in front of them! Arnold examined the possibility of three geometries of objects that may serve this purpose: a pure equilateral triangle, a double-screened object, and a series of screens on a louver. In all three cases, by subtracting the best fit circular aspect (assuredly that of a planet) from the artificial lightcurves of these geometries, the residuals were above the \textit{Kepler} photometric sensitivity and hence theoretically distinguishable. The louvre system may be actuated in such as a way that it could also convey information, and so Arnold quantified the effectiveness of a megastructure signaling system by examining its spatial data rate, which he showed to be comparable to that of laser (but without the requirements and shortcomings that come with laser signaling, such as precise knowledge of the system’s future position at the time of receipt). Therefore he concludes that such a signal system is feasible. However there are some problems that would have to be addressed, such as perhaps the scale of the engineering project. Even granting the alien intelligence the benefit of the doubt and ascribing to them an advanced knowledge of astroengineering, I still had a few concerns. Wouldn’t the triangle have to not significantly rotate along the transit arc in order to maintain its projected equilateral aspect from our vantage point? Would such an object be three-dimensional or 2D planar, and in either case, what would happen if it spun on its axis? One could imagine that these structures could be statites, objects that are stationary with respect to the host star supported by radiation pressure. If the triangle was composed of solar sail material, then every time it minimizes its aspect during rotation (i.e. when it is parallel to our line of sight) then wouldn’t it fall inward towards the star? Setting these problems aside, this is nonetheless a brave submission by Arnold and worth taking into consideration as more and more photometric data becomes available.