Month: March 2018

The Virtues of Concreteness: An Argument for “Settlement”

Sofia’s Official SETI Definitions v0.1

Settlement: “a process by which an intelligent species spreads to new areas”*

I have a pet peeve about concreteness. I have been to a few conferences now, and an overarching theme I’ve noticed is that someone will have a fascinating concept, but be kind of dodgy when asked about how to directly apply their concept to real methodology.

As an example, the idea of “ecoscenography” was proposed at an art + science + education conference I attended a few years back. The thesis is that theatrical performances can be extremely wasteful – sets are constructed, used once, and then discarded, and the entire process is disproportionately and unnecessarily harmful to the environment. I was involved in theatre for a long time, and was really interested, so I talked to the speaker about implementation (Reusing simple set elements by repainting? Using more recycled materials? A sharing program between schools for costumes/props/set pieces?), and they kept insisting that we should keep it broad, it’s more of a philosophy, and not define any specific techniques. Well, to be frank, that sounds like a great way for your idea never to be of any use to anyone.

A more “concrete” illustration of the power of ecoscenography

I bring this up because I wanted to clarify a point brought up in Taxonomy and Jargon in SETI as an Interdisciplinary Field of Study (the white paper that I presented at DAI 2018). Some of my peers, in telling them about my presentation, argued that one of the less useful-sounding and more pedantic arguments in that talk was the distinction between “colonization” and “settlement”. Here are three arguments I ran into:

  1. We shouldn’t worry about offending / being politically correct to a species we haven’t met yet, that we may never discover the existence of!
  2. Putting a nice skin on the idea of “colonization” by calling it “settlement” is a little bit offensive in a way – it delegitimizes and hides the ugly parts of the analogous historical situations
  3. It doesn’t matter at all to the actual science of SETI and seems like a quibble over synonyms

Here’s my response to those arguments, after a few weeks of on and off pondering. This is not a paper about political correctness, either in its favour or against it. This is a paper that argues that the lack of precise and accurate terminology hinders the logistical workings of and the intellectual vibrancy/creativity of SETI more than in other fields, and we should recognize and take steps to fix that.

If I were as general as the talks that I berated for lack of concreteness in the earlier part of this post, I would leave it at that. But because I’m not, I want to take on this particular example.

The word “colonize”, according to Wikipedia, has some of the following connotations:

  • “a process by which a central system of power dominates the surrounding land and its components”
  • Comes from the Latin colere meaning “to inhabit”
  • Britain would consider new land as terra nullius (empty land) due to the absence of European farming techniques (regardless of the presence of other populations)
  • conflict between colonizers and local/native peoples
  • motivations being trade or “shorter-term exploitation of economic opportunities”
  • “absorbing and assimilating foreign people into the culture of the imperial country”
  • In science fiction, “sometimes more benign” – word is used very often

Here are some questions that this article brings up, for me (and, in parentheses, some search implications of each broken assumption):

(have I mentioned that I love Spore?)
Habitable worlds ripe for the picking… or not?
  • Why should we assume that an alien race would want to colonize in the first place? (searching for clusters of systems that have similar signatures becomes a poor search strategy)
  • What if ETI is NOT spreading for the purpose of resource acquisition and energy demand? (maybe black hole energy-farming is a bad thing to look for, shouldn’t look in places that humans would think are valuable (ex. asteroid belts), could be some underlying pattern in the spread based on religious/cultural/societal reasons behind it))
  • What if the ETI is conscious of their environment and co-exists with the surrounding land? (no technosignatures would appear during the spread)
  • What if the ETI is peaceful and co-exists with the inhabitants? (multiple different kinds of biosignatures or technosignatures could co-exist in a single area / N could be higher than one would calculate assuming “domination”)
  • What if the ETI puts von Neumann probes in systems for scientific or other purposes, but does not actually biologically inhabit it? (we shouldn’t just look at biologically-friendly environments like FGK stars)
  • What if a certain ETI has a very different idea of terra nullius? What if the presence of microbial life will limit the spread of an ETI because, to them, those environments are “already taken”? (we should look for technosignatures where there are no simple biosignatures already)
  • What if an ETI is a perfect, Sagan-esque archetype and lifts lesser species out of poverty/technological-infancy instead of causing conflict? (look for geographically-grouped, expanding technosignatures, rates of technological development become geographically dependent)
  • Is our acceptance of the more general, less problematic interpretation of “colonization” in SETI derived from our science fiction instead of our science? (we stick to a term that doesn’t make lexical sense based on stubbornness and end up making some of the other assumptions in this list)

The point of these questions isn’t that any particular suggestion I made is a good idea. A lot of them are not, or violate other fallacies (like the monocultural fallacy, for example). But it’s obvious that if we look closely at the relatively straightforward logical steps that follow from the dictionary definition of “colonization”, all sorts of SETI search strategies end up being implicitly excluded or assumed. Are we self-aware enough to say “well, I know what the word implies, but I wouldn’t let that affect my science in such obvious, drastic ways” and succeed in that quest? I don’t know about anyone else, but I don’t think I’m self-aware enough for that. I’m sure there are some assumptions hidden in here that I’ve missed. I am, after all, only human!

So in your next publication, dear reader, please use the word “settlement” instead of “colonization”. Your science will thank you.

To add an additional complication at the end of this blog post: I discovered that in biology, colonisation or colonization means “a process by which a species spreads to new areas”. This definition has the perfect lack of connotations that we’re looking for in SETI, and would be a strong argument to continue using the word. My response: SETI is a subset of astrobiology, so we will be interacting with people who DO use this definition. Most practitioners, however, will still have the historical connotations in their head (because that’s what we’ve been exposed to, socially, and humans aren’t very good at putting that sort of conditioning out of our heads). To get around this confusion, in SETI, we should take “settlement” to have the definition I posit at the top of the page.

Literally my first SETI paper

My opinion of this paper is completely biased by the fact that I’ve actually met David Kipping and that I read this paper back when it first went on the arxiv. This was my first exposure to SETI (beyond science fiction, if that counts) and I think it went well!

Kipping and Teachey postulate that a civilization (even the Earth) could use lasers in some interesting ways. They first suggest that a planet’s transit could be clocked, monochromatically, against a Kepler-like survey, without the need for much power (~30MW). Due to the Earth’s rotation, this would require multiple laser stations, but in the end, it would be doable. They then continue on to talk about clocking the signal at all wavelengths. This would be a bit more challenging, since many lasers at many different lasers would be required, and again these lasers would need to be placed around the planet, and the power requirement would increase by an order of magnitude, but a committed civilization could manage it. Both of these cloaking processes can be argued against since the planet would still be detectable via other detection methods (namely RV).

The last bit of cloaking they suggest involves the cloaking of biosignatures. A disequilibrium in an atmosphere (normally of oxygen) is a decent indication of life on a planet. These and other related absorption features are referred to as biosignatures. If lasers were emitted at these absorption features, then the planet would still be detected and noticed, but it would just not be studied much since it would be presumed uninhabitable. This is all, of course, under the assumption that other life out there is Earth-like, and that this Earth-like life would be looking for signatures similar to their life (Earth-like). Because of this Earth-like assumption, it is possibly that another civilization is already doing this for *their* biosignatures, we just don’t notice it though because we are looking for our biosignatures (also clouds are apparently all that we can see right now).

Lastly, the authors bring up the point that this laser method can be used not just to cloak, but also to signal existence. They briefly mention that the easiest way to get someone’s attention with this would be to cloak the transit’s ingress and egress, making the transit appear boxy and all around wrong.

Although this is a neat idea, it seems a little far fetched and specific to me. Sure, we have tons of data, so someone might as well look through for boxy transits (I think someone has already done this with Kepler data), but this seems so absurdly unlikely to happen. However, my thoughts on the likelihood of this completely come from the way I view humanity and our goals and motivations, so it’s just as possible that my thoughts of this being a waste are a minority in the galaxy.

Transiting exoplanets in SETI

I feel that it is quite appropriate for me to review this paper by David Kipping two days after we conducted an observation of 12 transiting Kepler planets from Green Bank Telescope in association with Breakthrough Listen, based on the principle outlined in this paper.

The paper talks about using lasers to cloak the presence of a planet during its transit. However, in this blog I shall not talk about a civilization trying to mask its presence but its attempts to broadcast itself. The paper proposes the principle of a temporal Schelling point in our search for ETI. The question often arises of the best time to search. Since there is no real special time, this paper suggests that the transit of an exoplanet around its host star could be one. If there is a beacon on the night side of the planet, then it would sweep out an arc as the planet revolves around its star. This beacon would be visible from our line of sight when the planet transits the star, if it is directly aimed at its sub – stellar point. This beacon if broadcast continuously would be visible to observers periodically with every transit. Doing this during a transit is an interesting proposition since transits allow for us to also measure the atmospheric composition of planets using spectroscopy. Further, in the near future we should be able to map the longitudinal heat profile as well as atmospheric composition of planets using phase curve spectroscopy. This would provide for definite clues of bio-signatures.

However, the beacon might not necessarily be on a planet which is inhabited by the ETI. The beacon can be on the closest planet, since that would have the highest probability for transiting in a randomly oriented system.

I think this paper is important in acknowledging the special place transits occupy in the optical astronomy, and subsequently extending it to SETI. Its ideas about a civilization using this phenomenon to hide its presence or beam out and advertise itself are novel, and can be one of the anomalies being considered in Wright et al. 2015 (GHat 4).

Playing Games with Lasers (Beaming Manhattan into the Void)

Everyone has been in a situation where they need to make themselves conspicuous. Proponents of SETI have often provided novel solutions to ensure an observer would readily identify their planet as one hosting life. The answer can be condensed to a basic principle: do something unnatural at the exact moment someone is observing you. David Kipping, an astronomer at Columbia University, who searches for planets and moons beyond our solar system, believes lasers can be used by ETI to serve as a beacon or mask a planet entirely. In a recent paper, Kipping and a graduate student argue that artificial transit profiles can be feasibly generated using laser emission. Unlike optical SETI, which focuses on pulses of light, Kipping believes the transit can be a useful signal to or cloak from Earth (see Movie 1).

Movie 1. Alex Teachey on Cloaking Planets
One of the co-authors of this paper sets out to describe how lasers could be used to cloak a transit. The timing of this video showed poor foresight (April Fool’s Day….). A secondary video by Alex provides answers to some common questions from YouTubers.

The use of transits in SETI goes back to the pre-Kepler days, when Luc Arnold first proposed distinguishing a transiting mega-structure from a natural body. Cloaking a planet requires many assumptions. Kipping ask us to consider an arbitrarily advanced civilization that discover all “nearby” habitable planets along their ecliptic plane. Kipping assumes the inhabitants would know which of these planets could observe their transits and, through some machinations privy only to ETI, such civilization would decide to prevent detection by these planets using the transit method. Kipping et. al. dismiss a previous suggestion of a mega-structure, arguing a powerful laser would be “technologically more feasible”. After performing a few calculations, Kipping et. al. argue a ~60 MW laser would serve as an optical, “broad-band” cloak and prevent detection from a mission such as Kepler. A laser, while monochromatic, could in theory serve to effectively mask a transit, as shown in Figure 1. Kipping et. al. argue that a laser array on the surface of a planet would be difficult and that instead ETI could place an array of lasers in space (colloquially known as a weapon). The authors aptly refuse to compare either solution. A similar and energetically cheaper alternative would be to use lasers to block out the absorption lines of biosignatures.

Figure 1. The Strange World of David Kipping
Both images are from Kipping et. al. 2016. On the left: Cloaking of a Transit Signal. The top panel shows the unaltered transit for various missions. The middle panel is the power profile of a 600 nm laser array designed to cloak the Earth. The bottom panel shows what an observer would detect. On the right: Using Transits as a Beacon.  The top panel shows the power profile of a laser array designed to broadcast the Earth. The bottom panel shows the transit signature an observer would detect. The laser makes for very unnatural signatures that distinguish it from orbiting planets.

In addition to cloaking, Kipping et. al. briefly discuss signaling via lasers. Broadcasting would be much cheaper, as it would not have to be broadband. The ingress and egress could be altered with lasers as shown in Figure 1. Another possibility, is to use lasers to etch intriguing patterns during the light curve. Kipping has stated:

You can make your transit look strange, have bumps and wiggles, maybe even the New York City skyline—whatever you want.

Savvy extraterrestrial scientists could use a deformed transit as a beacon to announce their existence (see Figure 2). By Kipping’s hypothesis, ETI no longer required planet-size megastructures, such as a rotating triangle or louvres, to produce unnatural transit signatures.

Figure 2. Laser Doodles
Going from top to bottom: (i) An unperturbed transit showing how a star dims slightly when an orbiting planet passes in front of it. (ii) A transit showing different shapes due to a laser array aimed toward an observer. This example shows the New York City skyline. (iii) The ideal beacon would be a square. This is a simple shape that would never occur naturally (yay limb darkening) and would require a laser only at ingress and egress.  Source: David Kipping

The reader is left with many questions and a sense of unease given all the assumptions. The ETI in question is apparently aware of all habitable planets in its ecliptic plane and capable of generating an array of lasers to block its transit. This is an act in vain if said planets use other techniques (i.e. direct imaging or radial velocity) to detect said planet. Kipping et. al. acknowledge this:

Transits are not the only method to discover planets and thus a truly xenophobic civilization may conclude that even a perfect and chromatic transit cloak would be ultimately defeated by observation of the planet using radial velocities. In this sense, the biocloak is perhaps the most effective strategy since certainly the transit and radial velocity measurements would appear compatible. However, even here, direct imaging would reveal a strong discrepancy in terms of the atmospheric interpretation and thus overcome the cloak.

A large part of this paper was to discuss how a transit could be cloaked, only to have that entire hypothesis appear to be an act in vain. The discussion on broadcasting with a strange transit signature is not fundamentally new. This blogger is left pondering the purpose of this paper. The authors themselves have dismissed the efficacy of cloaking and suggest we search for strange transits, something proposed by Arnold a decade earlier. Even if one were to assume cloaking to be efficient, SETI has predominantly concerned itself with civilizations indifferent to outside observers. After all, one could always invoke any arbitrary set of conditions or technology that would make a civilization impossible to detect. While the method of using lasers is novel, the rest of the paper reminds astronomers to search for strange transit signatures. Believe this requires strong priors and an indifference to all the assumptions. Kipping himself expects detections “on the order of a few dozen” and this blogger wishes him the best in his future endeavors.

How to halfway hide a planet (or make it obvious instead)

In Kipping & Teachey (2016), the possibility of using lasers to modify one’s planetary signature from a transiting exoplanet experiment is discussed.

Advanced civilizations may have several reasons for which they might want to modify their planetary signal. You can use lasers to make your transit either more or less remarkable, but it depends on the type of survey you are trying to adapt to. For broadband surveys like Kepler, it can be a lot easier. If you somehow knew the frequency band of the survey you were trying to hide from, you could use a monochromatic laser near the peak efficiency to effectively modify your planet’s signature. For example, we could hide Earth from a Kepler-like mission with ~30 MW of peak power for ~10 hours a year (the duration of our transit). It gets harder to completely hide a planet for missions that take spectra, as you need many lasers (at least a comparable amount to the number of frequency bins the survey uses) and they need to produce the entire spectrum of energy instead of focussing on the most efficient detector energy (which you probably wouldn’t know anyway). For the Earth, this would require ~250 MW of peak power. I don’t really see the point of doing this when the civilization would still probably find you based on RV data or orbital analyses of the rest of the planets in the system.

Something more interesting you can do is to just mask the atmosphere or even just the biosignatures so that Earth looks barren and uninteresting. This would take considerably less power (~1 MW for the atmosphere, or ~160 kW to mask a couple emission lines).

You could also use about 1/100th of the energy of any of these methods to modify only the begging and end of the transit to create an otherwise impossible transit shape. In this way, you could quite effectively broadcast the fact that there is life on your planet. I find it more likely that ETI would use lasers for this purpose than as a glorified invisibility cloak.

LASERS!!1!

 

Spin ‘er up, and call it alien!

Harwit describes a characteristic of photons that most, including this blog writer, did not know actually existed: orbital angular momentum. On top of this description, he also explains that we are able to incite large values of this momentum on photons ourselves and that we can (sort of) measure this value. Since nature doesn’t make photons with such high orbital angular momentum, such a detection would be an indication of artificial origin.

I happened to read this entire paper before realizing that the important bits were in Section 4.3, but oh well. The authors bring up interesting astrophysical applications aside from SETI, including probing a turbulent medium for inhomogeneities and studying different characteristics of black holes. According to the authors “radiation with high values of photon orbital angular momentum might have [significant advantages] for communication and quantum computing.” Apparently, taking this additional spin into considerations, one is able to encode more bits of information than previously (which makes sense given the additional degree of freedom). I think this paper is fantastic! It’s a good idea that is now

I must confess, this paper basically goes completely over my head, which I suppose could be formed as a sort of critique. I think it is important in science in general, but also in something as interdisciplinary as SETI to be clear in one’s writing and to lead the reading through all of your arguments, even if this means sometimes being repetitive or dumbing down your work. Although fields such as astronomy are marked by academics making things excessively convoluted to make them seem above the populace, I’d like to believe those days were over, and should have been over by 2003. Someone with a degree in physics or astronomy should be able to understand this paper, and although it could be my lack of coffee, Harwit should have written his paper at a more comprehendible level.

Given my lack of complete understanding of this paper and the fact that this paper is now 15 years old, most of my musing might not be all that interesting. For instance, how far have we actually progressed in this? Can we now readily inflict orbital spin on a photon and then detect it? Can we, with our current technology, encode messages in these photons, send them, and then later detect them?

A quick Google search has showed me that Wikipedia is, once again, a bro. Preliminary tests of radio and microwave photons showed that we are able to transmit 32 gigabits per second over the air, and 2.5 terabits of data per second through optical fibers. This is fantastic and amazing; this would revolutionize the telecommunications industry around the world! It reminds me of Artemis by Andy Weir, but with less mafia. Unfortunately, we have apparently not yet figured out how to reliably measure the orbital angular momentum. Since orbital angular momentum can have as many states as it wants, there is no device that can separate out more than two modes. A diffractive holographic filter is promising, but this idea is still being investigated.

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.

MASERS, LASERS, ETI, and other fun initialisms

A reoccurring thought while I read this paper was “What the hell are masers?” I just kind of assumed they would be defined *somewhere.* Well, they’re not. So here’s what masers are: “microwave amplification by stimulated emission of radiation.” So lasers, but specifically in the microwave. The acronym was coined in 1953 when the first maser (I think) was successfully operational. Later, an “optical maser” was successfully created in 1960. The optical maser was first envisioned in 1957, and the term LASER (*light* amplification by stimulated emission of radiation) was coined that same year. Apparently Charles H Townes made the first ammonia maser:

Given this information, it makes sense that Townes would look into additional uses for his optical maser (from now on, just laser). At the time, SETI was new and exciting (well new-ish; the idea of contacting ET species had existed for centuries), and was not weighed down by the “giggle factor” that it experiences today. An inventor could write a paper like this, and receive mostly positive support for the idea without anyone calling BS or science-fiction on the idea. This paper, I believe, marks the first discussion of contacting ET species with lasers and possibly detecting such signals. These ideas have now been integrated, and other papers written on them, but the first to propose it is always the coolest (right?). Townes computes that with modern (from 1961) technology, we could already detect specific laser signals, and postulates that with only a bit more time (and narrow-band optical receivers) other laser signals would have high enough signal-to-noise to be detected.

One last note is I enjoy how Schwartz and Townes end their paper. The paper is fairly technical and a nice proof of concept, but they end the paper with a quick SETI discussion, saying that searches should go beyond the waterhole, that UCE and IR are absorbed by most atmospheres (so not to really bother with those), but also that a civilization more advanced than our own could have technology that we currently rule out as unfeasible. I do appreciate this throw-in, since we only ever look for traces that could have potentially been left by humans, since we need to set restrictions to actually make a search, but it is nice to acknowledge that other civilizations could be unlike us, and therefore could be communicating in ways unimaginable to us.

A Way to Find Big ETI Laser Pointers

In Wright et al. (2014), a new, versatile optical SETI instrument is described that can search for direct evidence of interstellar communications via pulsed near-infrared signals. The article is in an SPIE (Society of Photo-Optical Instrumentation Engineers) conference proceedings paper and focuses heavily on the physical design of the detector and optics.

Modern high-powered lasers can easily outshine our Sun (for limited frequency ranges and times). As such, it is obvious that, if advanced ETI exists and wanted to communicate (or just broadcast its presence) specifically with us, it could easily do so with lasers. According to the article, the largest lasers on Earth are detectable with meter-class telescopes up to thousands of light years away. This is because, unlike radio signals, optical beams can be finely focused, providing a high received power flux for each amount of transmission energy.

Fast NIR pulses searches are an underexplored area not just for SETI, but for astronomy in general. Astrophysically-based nanosecond optical pulses are supposedly very rare, but this instrument is also planned to observed possible pulse sources such as pulsars, black holes, cataclysmic variables, gamma-ray bursters and active galactic nuclei.

The instrument works by utilizing commercial-off-the-shelf (COTS) products including NIR photon counters that, for the first time, can be very fast, wide bandwidth, high-gain, low noise and cheap. The light from the sky comes in and the NIR light gets split into two independent detectors (to help eliminate false positive detections) while the optical light goes to a guide camera so that they know that the telescope is pointed at the right place. Their setup is capable of recording the time of arrival of signals down to the nanosecond and it is planned to be used on the 1-meter Nickel telescope at Lick Observatory in California.

The first proposal for Optical SETI

This 1961 paper by R.N. Schwartz and Charles Townes, discusses using Optical Masers (Lasers) for communication across interstellar distances. I feel that it is worth noting that this falls closely on the Cocconi and Morrison paper of 1959 which first suggested the water-hole in the radio as the ideal place to look for, for intelligent extra terrestrial (ETI) civilization.

The authors talk about the recent discovery of ruby optical Masers  by Townes. Since the M in Masers is for Microwave, optical Masers, were soon called Lasers or Light Amplification by Simulated Emission of Radiation.

The authors consider using Optical Masers (Lasers) on two different systems and compare the two. One is a laser on a 200 inch telescope (like the 200 inch Hale Telescope), whereas the other is 25 individual 4 inch  telescopes with Lasers pointed in the same direction. They consider atmospheric seeing as a limiting factor and hence consider that the 25 individual small telescopes might be a better option. I think this paper was really advanced for its time, since 4 years after the launch of Sputnik (1957) it considers the use of Adaptive optics and space telescopes.

It also considers the detectability of Lasers using 1961 technology levels for laser power and detectability. The paper also talks about high resolution spectrometers which could spectrally resolve the laser and hence detect that this artificial beacon outshines the host star. This would be a hallmark of its artificial origins.

The paper concludes by noting that the water hole in the radio should not be the only region where we look for interstellar communication. It also mentions that an advanced ETI might develop capabilities that we have ruled out and consider impractical.

Optical SETI is not exactly a novel approach, but one that has not yet been pursued in earnest. There have been recent efforts by Andrew Howard, Shelley Wright, Nathaniel Tellis in this direction. We must take advantage of the vast resources that are plowed by the astronomical community in this direction and utilize the instruments, development and data sets that exist as a product of this.