Response to Benford (2010)

This story made for a fantastic (albeit slightly out of order) finale to my experience in this SETI class. Several different story lines are captured within this one brief encounter described in the story. I also love the first line – “the best is the enemy of the good” – and firmly believe that this is an important philosophy to keep in mind while doing science.

Beyond being an extremely entertaining story, the article touches on a fundamental theme of SETI: what seems obvious to us may not be universally so, and, no matter how we try, we are unable to decouple our thoughts and ideas from the human perspective. Try as we might to search for “obvious” signals of extraterrestrial origin, it is entirely possible that some extraterrestrial intelligence is, in their own way, screaming their greetings to us and we are simply blind to the significance of the signal.

Response to Townes (1983)

Townes raises the question of where in the electromagnetic spectrum should the search for extraterrestrial intelligence be conducted? While SETI has historically been radio-centric (especially at the time this paper was published), the author suggests that certain assumptions are required to arrive at the conclusion of the radio as the optimal region to search. If these assumptions are appropriately relaxed, one could argue that the infrared is an equally viable part of the spectrum to search for signals of extraterrestrial origin.

One aspect that must be considered in choosing the optimal spectral region is the power requirements of the transmission. This depends on whether the signal is isotropic or beamed, which, of course, we can only guess. A second point that must be considered is the technology of the transmitter and, more broadly, the technology of the transmitting civilization as a whole. In particular, it is conceivable that other forms of communication technology could be dominate on a distant world, e.g., lasers. This relates directly to the suggestion by Schwartz & Townes (1961) to search for nanosecond light pulses in the optical.

Ultimately, the authors recognize that the optimal SETI search would be include efforts across the electromagnetic spectrum. After all, arguing for one particular spectral region over another involves making a set of assumptions that could turn out to be false.

Response to Declaration of SETI Principles

The International Academy of Astronautics (IAA) compile a set of principles to guide the Search for Extraterrestrial Intelligence (SETI). SETI inherently concerns the entire world, especially in the case of a positive detection, so extensive thought must be lent to ensuring SETI efforts are conducted in an ethical and scientifically collaborative manner.

In many ways, though, this document appears to raise more questions than it answers. For example, the last point regarding post-detection conduct could (and should!) trigger a storm of debate, garnering expert advice in fields such as communications, law, ethics, and anthropology (among many others.) While it is important that these guidelines have been put in place by the IAA, it is equally important to establish some sort of platform for discussing the questions raised by these guidelines.

Response to Villarroel, Imaz, and Bergstedt (2016)

This paper discusses the value of conducting a search for extraterrestrial intelligence by searching for seemingly impossible astrophysical phenomena. The advantage of this approach is two-fold: in the absence of discovering an extraterrestrial civilization, it may be possible to uncover unknown exotic physics or astrophysical processes.

The specific goal of this study is to query the sky for “disappearing stars” – the idea being that advanced civilizations around these stars could either be harnessing the stellar energy (which would then be re-radiated as waste heat) or intentionally cloaking themselves. This task is accomplished by cross-matching the United State Naval Observatory B1.0 catalog (USNO-B1.0) and the Sloan Digital Sky Survey (SDSS). Objects of interest include those which appear in USNO-B1.0 but not in SDSS, and, if confirmed, would identify stars that have disappeared over the decade lag between these two surveys.

An initial query yields several thousand candidates – stars appearing in USNO-B1.o but not in SDSS. However, this could occur for a variety of reasons significantly more mundane than an advanced extraterrestrial civilization, e.g., diffraction spikes or image artifacts in the SDSS frames which cause the SDSS pipeline to overlook the star. A visual inspection of the initial list of candidates reduces the target sample to 148 objects.

These 148 candidates must be combed for false positives (appears in the USNO-B1.0 catalog when it should not) and false negatives (appears in SDSS, but is not detected.) Most of the candidates fall into the former case, where no object appears in the images that were used to generate the USNO-B1.o catalog. A large fraction also fall into the latter case, where the stars are present in the SDSS frames but the coordinates between the two systems do not agree. In the end, one suspicious candidate is identified. It appears in two separate images used for generating the USNO-B1.o catalog, but cannot be found in the SDSS images.

This study is very good in the sense that it reports the null result as an upper limit. It starts with a clearly stated problem, addresses the problem in a clear way, and translates the result into an upper limit. As acknowledged by the authors, the study critically suffers by probing only a small fraction of the sky, and by probing only a short period of time (~10 years) during which the star could have disappeared. The authors look forward with great anticipation to larger surveys (e.g., GAIA and LSST) that could extend this search to much larger scales. They also suggest that much of this work could be efficiently accomplished by employing citizen science, which has proven itself extremely beneficial to other astronomical projects.

Response to Lin, Abad, and Loeb (2014)

The authors suggest that observations of exoplanet atmospheres could detect signatures of runaway industrial pollution. While discussion of exoplanet atmospheres has primarily focused on the detection of biosignatures, the authors argue for the feasibility of detecting other atmospheric absorption features that may be indicative of intelligent life.

Two considerations must be lent in determining the optimal pollution signature: the feature must be strong and have little to no natural sources. They rule out methane and nitrous oxide, as both of these have natural sources. The authors identify two strong candidates, both of which are chlorofluorocarbons (CFC-11 and CFC-14). Both have strong absorption features in the mid-infrared (~10 micron) and are broad (~0.3 micron.) Both have the potential to be confused with other common features (methane and nitrous oxide for CFC-14, ozone and hydrogen dioxide for CFC-11) though the problem is more severe for CFC-14. Observations in the near-infrared (2-5 micron) can help to mitigate the ambiguity by enabling constraints on methane and nitrous oxide abundances.

The authors estimate that around 1.5 days of total integration time would be sufficient to detect either of these pollution signatures (if they were present at 10x the terrestrial level.) They propose an observing strategy that evaluates the strength of a candidate exoplanet in real-time. The first few hours of integration time should enable a preliminary detection of typical biosignatures. Additional hours could yield ambiguous tracers of runaway industrial revolution (e.g., methane and nitrous oxide.) If both of the aforementioned signatures are detected, additional integration time would enable the detection of the chlorofluorocarbons discussed here; if, instead, the first several hours of integration time do not detect biosignatures, the target could be abandoned.

I am uncertain about how anthropocentric this study might be. Is it likely that an advanced extraterrestrial civilization would use the same fuel sources as us (and therefore have the same pollutants?) Or would their fuel sources be dictated by resource availability, which could be vastly different from our environment? Is it feasible to predict other likely fuel sources (and pollutant signatures) and could these other features be detected with reasonable integration times?

Response to Wright (2018)

This paper argues for an interdisciplinary approach to SETI, building on other recent suggestions (e.g., Dysonian SETI (Bradbury 2011)). Special consideration must be given to how best to facilitate this interdisciplinary approach, particularly in the vocabulary used to discuss this broadened SETI perspective. Academic/industrial subfields are so deeply entrenched in their own jargon and vocabulary that the general language used to describe SETI needs to take each relevant subfield into account.

Two contrasting views have recently arisen with respect to how SETI is / should be approached. These are commonly referred to as “orthodox SETI”, which focuses on the detection of extraterrestrial communications, and “Dysonian SETI”, which focuses on the secondary effects that advanced civilizations have on their environments. The optimal SETI approach is likely some combination of these two mindsets, and, regardless of what approach is taken, the broad umbrella term of “SETI” should capture both viewpoints.

Several relevant fields discussed here that should be included in an interdisciplinary approach to SETI are: radio astronomy, infrared/optical astronomy, exoplanets, Earth system science, game theory, social sciences, anthropology, galactic astrophysics, stellar astrophysics, time-domain astronomy, computer science, multi-messenger astronomy, planetary science, media/communications, law, and political science. It rapidly becomes obvious why implementing such an interdisciplinary approach can be challenging. It will require a great deal of effort by practitioners of SETI, as they will have to master (or, at least, grasp deeply) the concepts in all other relevant fields in order to appropriately apply those concepts within a broader framework.

The author suggests a structure that could be used to organize the various SETI efforts. First, they argue that SETI is most certainly a subfield of astrobiology. Where astrobiology is primarily focused on the discovery of extraterrestrial life, SETI narrows this focus by restricting it to intelligent extraterrestrial life. This search has the added bonus that intelligent signals are likely to be much more obvious, and obviously artificial, than their unintelligent counterparts. Within SETI, efforts can be broadly classified as either communication SETI or artifact SETI, though the lines between these two are often blurred.

Overall, special care must be taken (particularly with respect to vocabulary) to facilitate a sustainable interdisciplinary approach to SETI.

Response to Schwartz and Townes (1961)

The authors propose the use of optical/near-IR masers as an alternative to radio transmissions for the purposes of searching for extraterrestrial intelligences (ETIs). In that way, they are suggesting new search methods.

As of 1961 (when this paper was published), the “[development of maser oscillators in the optical/near-IR spectral region which would allow transmission across several light-years]” was on the horizon. Interestingly, the authors state that such masers could have been thoroughly developed even 30 years earlier, suggesting that other ETIs may have pursued such avenues (as opposed to radio transmission).

Technology in 1961 suggested that the continuous operation of high power masers was entirely within the realm of possibility, and the outlook has only brightened in the years since then. One issue relates to the directability of such a maser, and the authors suggest that the problem can be overcome by employing masers in tandem with optical systems. They recommend a coordinated system of 25 masers as the optimal configuration.

There are two important factors that must be considered when evaluating the detectability of a maser signal: (1) it must produce a sufficiently large photon flux and (2) it must be distinguishable from the astronomical background. The authors argue that the first condition can be easily satisfied, and, again, the outlook has only become more optimistic over the past half century. The second condition requires more consideration. Due to the small separation between Earth and the Sun, it is likely that a maser signal cannot be spatially separated from the light of the host star around which the signal is originating. The authors suggest transmitting far away from the peak energy output of the Sun (~5000 Angstrom), i.e., either the extreme violet (shortward of ~2000 Angstrom) or in the near-IR. The former choice suffers from limited atmospheric transmission, while the latter suffers more from the diffraction limit at longer wavelengths (if such a limit is applicable for the system being employed). The authors also suggest transmitting in strong absorption features, e.g., the Ca II H or K lines. Since 1961, our knowledge of stellar populations and corresponding exoplanet systems has greatly improved, so perhaps it is more useful to optimize the transmission interval for a typical M dwarf (as opposed to the Sun, which is a G dwarf).

This study proposes a very novel idea. When considering how to find an ETI (and by extension, in trying to envision how they might attempt interstellar communication) it is important to broaden our perspective and consider all possibilities.

Response to “It’s Never Aliens – until It Is”

This article discusses several recent examples of “supernatural” phenomena that are not easily explained. Some interpret these events as evidence for intelligent extraterrestrial civilizations, but most(?) people are extremely hesitant to jump to that conclusion. The author suggests that these “pessimists” are really just trying to maintain a high standard for what might constitute incontrovertible evidence for the existence of extraterrestrial intelligences. This paper was assigned, because it contributes to the overall discussion of how SETI programs and results are interpreted, in particular, with regard to framing the public debate.

Three recent examples are discussed in detail. The first is the case of the bizarre light curve of KIC 8462852, while shows several strange dips in brightness. While initially lacking a satisfactory natural explanation, the strange dips in brightness are now attributed to dust. This explanation was reached in part due to the wavelength dependence of the brightness changes, mimicking the behavior of dust.

The second example is that of Oumaumau, the strange, needle-shaped object that passed through our solar system. The existence of interstellar comets is widely accepted, but the absence of a diffuse tail (caused by melting ice on the comet) initially seemed counter to the comet explanation. Upon closer inspection, the ice seems to be locked up under a red, radiation-hardened surface of carbon-rich molecules. The object was also targeted by radio telescopes which detected no radio emission.

The final example discussed here was recent, declassified videos showing encounters with bizarre flying objects. In two cases, the UFOs are seen to defy the principles of aerodynamics and to seemingly exceed the speed of sound without producing a sonic boom. An interesting point is raised: if these encounters truly captured UFOs, then the number of such encounters could be expected to increase with the total imaging capacity of the world. While the latter has exploded over the last ~30 years, we still have (at best) blurry and ambiguous footage of UFO encounters.

The author suggests that the process of conducting SETI experiments and engaging in related discussion is intimately linked with the future and fate of humanity. This point of view champions SETI efforts, even though the endeavors themselves may produce null results.

Response to Kipping & Teachey (2016)

The authors take the perspective of an extraterrestrial intelligence (ETI) located around a different star and consider the signals they might transmit while they are transiting (i.e., to other ETIs lying in their ecliptic which might view their transit). In some ways, this paper proposes Schelling points; however, they explore two wildly contrasting motives for the types of signals they might transmit, one of which is completely against the nature of Schelling points. One point they stress is the complement of these methods to traditional radio SETI efforts and the importance of taking a multiwavelength approach to SETI searches.

In this paper, the authors suggest that lasers can be used to adjust the nature of the signal an external observer might receive while watching the transmitting planet transit their host star. In particular, they suggest that lasers can be used to either (a) mask certain pieces of information encoded in the transit signal or (b) alter the transit signal in a way that is clearly non-physical (and therefore broadcasting their existence to other hypothetical ETIs). They explore the power requirements necessary for each case and conclude that the technologies are entirely feasible, especially if we assume that the supposed ETI employing these methods is more advanced than our own.

They first discuss the possibility of using lasers to disguise their transit signal. In one case, they seek to entirely mask the transit signal by transmitting power that perfectly offsets the deficit (of starlight) produced by the transit. They note that to accomplish this over all wavelengths (or an appropriately large range) is considerably more difficult, but could be feasible for sufficiently advanced civilizations. In a second case, they consider blocking only the biosignatures of their planet. For example, if oxygen were present in the planet’s atmosphere, it would produce absorption features during the transit which could conceivably be detected by an external observer. One interesting caveat of this viewpoint, though, is that certain biosignatures may be somewhat unique to the ETI in question!

They next take an alternate perspective and imagine that the transmitting ETI wishes to broadcast their existence and intelligence to potential observers. The authors suggest that the most effective way to accomplish this task is to create an obviously non-physical transit signal; in particular, they recommend masking the ingress and egress of the transit, a signature for which no known physical explanation can be invoked.

This study is really interesting and creative, but it seems like they take two entirely opposing viewpoints in the two cases they explore. In one, they imagine that the supposed ETI is hoping to mask its existence, while in the other, they imagine intentional broadcasting of their existence and intelligence. I suppose it is useful to explore all possibilities when imaging hypothetical ETIs, but it seems a bit contradictory and, in the former case, almost like xenopsychology.

Response to “Seeing the Beautiful Intelligence of Microbes”

I especially enjoyed this reading, because it comes from a vastly different perspective than the majority of the other readings we have done for this course. In particular, it encourages an expanded view of what intelligence and awareness can mean, opposing the common SETI pitfall of an overly-anthropocentric perspective. This paper is not specifically explicitly related to SETI, but contributes a valuable scientific perspective to the broad question of extraterrestrial intelligence.

The authors discuss the collective behavior of individual cell organisms and present a variety of examples where the cells work together in a group (biofilm) in intelligent ways. The cells within a biofilm often differentiate to perform a variety of functions that serve to benefit the collective group. For example, the cells in some biofilms organize themselves in elegant structures so as to maximize oxygen intake and waste release. Other biofilms expand out in spiral or filamentary patterns to explore the surrounding environment for nutrients. These explorations sometimes leave behind a slimey residue, effectively “marking” the path and building a collective memory of areas that are rich in nutrients or areas that should be to avoided.

While this concept of life is very different from what likely first comes to mind as intelligent or aware, there are a number of reasons why such a form of intelligence may flourish. The authors suggest that the betterment of the whole may outweigh the sacrifices of its individual members. Additionally, the differentiation of tasks could allow for individual benefits to go along with the sacrifices. For example, cells on the outer part of a biofilm may have to divide frequently for growth, but may have the best access to oxygen, while cells on the inner part may have to release spores to seed new biofilms, but may enjoy longer lifetimes than their counterparts on the outer reaches.

It is important to keep an open mind about what extraterrestrial intelligence may be like as we conduct our search for its evidence. Making overly strong assumptions about the nature of a supposed extraterrestrial intelligence (in particular, its similarity to us) may lead us to overlook signatures that we are not receptive to finding.