Do we know what we do not know?

This article is based on pages 133 – 152 of Paul Davies `s book Eerie Silence. The extract builds upon the third law of Arthur C. Clarke, that “Any sufficiently advanced technology is indistinguishable from magic.” It discusses the principle for SETI artifact searches.

There are various structures / particles postulated by the fundamental theories of physics which have not been observed experimentally. Few of the examples cited in the passage are magnetic monopoles, dark matter particle and cosmic string. An example given is that the paucity of these could be due to exploitation of this structures / particles by a hyper – advanced ET civilization for energy production.

Moving on from here, the author builds on the ‘nature plus’ theme for ET. Basically how ET could manifest itself as the next step after nature and thus not stand out obviously like a sore thumb, but as an extension of the abilities and phenomenon seen naturally. He gives the example of a scenario from Roger Penrose about dumping waste into a black hole to harness its rotational kinetic energy.

Another important point made is that it is quite possible, perhaps even likely that ET manifests itself in a manner unfathomable to us. The example given is of lasers. For someone from a few centuries ago, lasers would not seem like a man – made thing and would seem like a weird (then inexplicable) naturally occurring phenomenon. On a similar note, potential ET technology could be right in our face but its artificial origins undetectable to us.

The last thing he covers is how the ‘laws of Physics’, which in theory are set in stone, are not really. They are only sacrosanct as far our current measurement capabilities are concerned. For example, ether was accepted till Michelson – Morley proved it otherwise. Newtonian gravity was good enough till observations began diverging from it and could no longer be explained by simple theory. Therefore the laws of Physics which we let govern us in our search for ET, might fundamentally be incomplete.

I think the point of this article is not to cast a gloomy note over our search for ET, but just to say that we do not know what we don’t know. Our knowledge and understanding of the ‘known’ Universe is severely lacking. Therefore, 1) we should not consider our search for ET exhaustive even if we plough through a major portion of the cosmic haystack unsuccessfully; 2) always be open to and on the watch for anomalies in observational data (similar to the point made in GHat 4).

Technosignatures in exoplanet atmospheres

In this post I shall discuss two articles – Lin et al. 2014, and Lingam and Loeb 2017. The premise of both these articles is the distinction between biosignatures and technosignatures. The two terms are discussed in this paper by Jason Wright. Biosignatures in this case refer to evidence for life found  in the transmission and reflection spectra of exoplanetary atmospheres (review of biosignatures by Schwieterman et al. 2017). Technosignatures refer to signs of intelligent civilization. In the SETI context it can be communication, megastructures, and pollution.

The article by Lin et al 2014 posits the existence of absorption features corresponding to organohalogens, and more specifically chlorofluorocarbons (CFCs). The existence of these chemicals which are not produced naturally would require an intelligent civilization. They posit that  a civilization with 10x our CFC levels would be detectable by the James Webb Space Telescope (JWST) with ~ 1 day of integration time.  I do have objections to their assumptions – an anthropocentric industrial and polluting model; habitable planet around white dwarf. Further how sustainable would 10x CFC levels be. However, despite that I found this interesting since it shows that within an order of magnitude we could detect such a planet with prolonged use of today’s technology (JWST).

The article by Lingam and Loeb, instead of considering polluting features, looks for ‘spectral edges’ from the harvesting of stellar energy by either photovoltaic cells or vegetation. The presence of vegetation on a planet would impart a red edge (infrared) due to expelled heat. Similarly, silicon photovoltaic cells cause a peak  in the extreme UV. This peak if indubitable, and confirmed without any other natural explanation would signify the existence of large photovoltaic farms deployed to harness stellar energy. This would also be an unmistakable technosignature.

The advent of new instruments like JWST and perhaps ARIEL are taking us into the era, where search for technosignatures can be achieved by optical and NIR spectroscopy. Since the instrumentation is being built and developed for finding Earth like planets in their habitable zones, along with characterization of atmospheres; SETI stands to gain in its search for technosignatures by piggybacking on this progress.



SETI Jargon

In this post I shall discuss the white paper written by Jason Wright on the need for SETI to adopt standard terminology. The paper argues about the need for such an approach. In the era of advances in astrobiology, we need to find the right synergy between the two fields, and how SETI is rightfully a subset of astrobiology since it is also looking for signatures of life (biology) around celestial bodies.

The field of exoplanets has rapidly grown since the first discovery of an exoplanet around a star in 1995 [51 Pegasi b]. With advances in engineering and instrumentation we are slowly approaching the domain where we can detect the presence of an Earth like planet around a Sun like star in its habitable zone [Kasting 1991]. In tandem with this process of discovery,  the characterization of exoplanetary atmosphere and climate has also progressed using spectroscopy techniques; attempts have been made to detect biosignatures in these spectra of exoplanets.

Closer home, we also have ‘potentially’ habitable objects, which could  have harboured life in the past, or might have life in the present as well. Solar system bodies like Europa, Enceladus and Mars, are intriguing objects which might have the right conditions to sustain (or have sustained) life.

Astrobiology is generally touted to be limited to this search for biosignatures. However, as mentioned in the introduction, it must include not only biosignatures, but also technosignatures or signs of intelligent (advanced technologically) life.

A unified jargon is important in a diverse and interdisciplinary field like SETI which involves contributions and discourse from not only astronomers, but also engineers, anthropologists, linguists,  and potentially cryptologists. The paper by cites the example of Artifact SETI, and how it should be an umbrella term for various kinds of searches.

An example of this that I have encountered (a situation nowhere as close to as significant as  in SETI, however representative nonetheless), is when I tried to understand radio astronomer jargon in order to derive the relation between transmitter bandwidth and the sensitivity of a receiver. Being involved with optical and NIR astronomy, I am completely alien to radio astronomy. Despite both the fields being subsets of astronomy and governed by the same laws of Physics, there exist a large number of differences in how they measure and quantify similar parameters.  It would have been very useful if they used the same terminology or in the least had some kind of a guide to bridge the two.

Now, if we take this situation and extrapolate it to collaborations between the sciences and humanities, this problem gets severely exacerbated.  Hence, I think the framework adopted by this paper is necessary, and one that should be worked on as the field of SETI grows and involves collaborations from other fields and subjects.

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).

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.



Townes 1983

This article by Charles Townes from 1983 discusses the optimum frequency we should use to listen at for ETI. It discusses how all the previous SETI searches have focussed in the microwave due to the obsession with the water – hole and the potential ‘fallacy’ of this obsession. It must be noted that this article was written in 1983, before many of the technological advancements of the 21st century.

The author talks about how the diffraction limit affects observations, and the advantage of directed observations over a beamed observation. It also suggests that the transmitter might want to correct for barycentric movement to ensure that the signal is in the ‘rest frame’, and then the receiver could correct for their respective motion. I believe this drift is an important factor that needs to be taken into account when we decide the bandwidth of future SETI searches (cue: Sofia’s project).

To differentiate between the microwave and the infrared, the author compares the detectors available and the background contributions in the two domains. Since the diffraction limited solid angle is different in the two regimes, the background plays a higher role in the microwave and radio.

The suggestions of the paper have aged though since photon counters are no longer the most sensitive means of detecting optical and IR light. It does not extrapolate into the future for potential telescope primary sizes, however the detector assumptions made have fallen way by the side due to advancements in the field.

All that being said, I believe this paper is important as it is the first one which goads us to not be myopic and consider looking outside the water-hole (21cm) for communication with ET.






What happens when we find them?

This paper by Forgan et al. (2016) talks about the protocol that needs to be followed if  when we find extra terrestrial intelligence. To understand the need for this, one only needs to look at the commotion and media frenzy caused by Tabby’s star and Oumuamua.

The existence and search for ET has always been a favourite of popular media, simply because it catches the eye of the general public. It is a topic that attracts people from all age groups irrespective of their age group. The question of whether we are alone in the Universe is one of the fundamental questions that transcends Astronomy and science, and goes into philosophy and anthropology. It starts delving into the arena of religious beliefs and the anthropocentric view that biases us.

Considering the above, it is important to understand the importance of the search for ET. Any kind of media coverage of this topic is almost guaranteed to get good viewership / readership. Therefore any researcher associated with this field must tread very lightly and be cautious about any kinds of claims made or results published, which even REMOTELY can be interpreted to imply the existence or our successful detection of ET.  This does not mean that one must hide their research or not go public with it, for fear of rebuke. However, as the article discusses, there should be a framework that is followed before a search is conducted and transparency, once it is done and the data has been analyzed, and results obtained.

The article further lays forth a possible path to follow to release the data and clue in the media as to the results and the need for independent verification. Another step that the authors alluded to, is that an international consensus must be built. Currently the only body which has such a mandate is the United Nations. Within the United Nations, perhaps UNESCO? It could get interesting, albeit tricky if the UNESCO is tasked with building up an international opinion and charting a path forward. Namely because the United States of America has decided to withdraw from UNESCO as a member starting 2019.

Going by the past record and partisanship in the UN, it could be problematic for all the nations to reach a consensus. Since, any kind of interaction with an alien civilization could have far reaching consequences for all of humanity today and in the future, it is something that should definitely involve all the stakeholders, or at least their chosen representatives. We still divide the Earth with borders, however Space cannot be (at least not yet). Its contents and inhabitants (?) affect all of humanity. Could the answer be  Asgardia?


Rio 2.0

The Rio scale first introduced in 2010 by Almár & Tarter to quantify the significance of a potential ET detection. It was named so (Rio) since it was first presented at a conference in Rio de Janeiro. The scale “…was designed for communicating with the public as to ‘how excited’ they should be regarding a signal.” With the initial version (v1.0) of the scale being bound between 0 and 15, v1.1 and the version proposed by Duncan Forgan v2.0 scale between 0 and 10.

With Rio v2.0, the authors of this article seek to provide a quick and objective way to quantify a potential ‘detection’. This calculation examines the ET significance of the signal and if there is a possibility to establish 2 – way communication. Further, this value is convolved with the authenticity of the signal – basically whether the signal can have a potential anthropocentric or instrumental source, if it can be studied / observed again, and potential sources of bias in the detection.

They also provide a web based interface to calculate the score for a discovery by answering a handful of questions (here). I believe such a framework is useful to weed out news of detections which are better to not be proclaimed (example: the Face on Mars). This also helps since any news regarding this field can get sensationalized really easily and hence needs to be ‘curated’ better.


Artificial illumination around Kuiper Belt objects

In this article by Loeb and Turner (2012), they propose the search for artificial illumination around Kuiper Belt objects on the outskirts of the Solar System. This would be a search for technologically advanced ET in our vicinity.

As one can see when flying at night during take off or descent into a big city, humans like to lengthen the duration of the ‘daylight’ using artificial light sources of lighting. Since our circadian rhythms have evolved to sleep when the Sun goes down, our eyes are not sensitive enough in low light conditions (night). Therefore, we try to illuminate our surroundings using fire and electricity for us to extend the hours we can work / recreate (or do anything), apart from sleeping. Since we as a species are very wasteful with little to no collective foresight, most of our sources of illumination are such that a huge fraction of the light they produce is wasted and radiated out into space. Below is an image which shows what the night sky looks like over various points on the Earth’s surface. This is an image created by piecing together numerous snapshots by NASA.

Earth at night. Credit: NASA

In this article, the authors propose a search for similar lighting around Kuiper belt objects (KBOs). Why KBOs? Perhaps since we have already looked at the moons of Jupiter and Saturn to rule out such ‘city’ sized illumination. However, I do not see the utility of such a search.

  1. A KBO at about 50 AU would experience about 0.04% the Solar Flux we receive on Earth. Would sunlight really be an efficient source of energy for a civilization there? What are the alternatives? Chemical or fossil energy also relies on a primary energy source which is Sun in the Earth’s case. An advanced civilization cannot directly start using nuclear energy. Therefore, barring solar energy, there is no energy source that a primitive life form can utilize and evolve along. Even if one argues that the amount of sunlight is sufficient for species to thrive (like deep in the ocean) or caves on Earth, then the question arises can it sustain an intelligent civilization like humanity with a power hungry ‘brain’?
  2. Moving on, if we argue that evolution is the mode by which life forms and transforms into intelligent life; then why will a ET civilization need bright Earth like lighting during their night time? Humans do not have night lights around their homes and cities which are 2500 (50AU ^2) brighter than our daylight. Our rods and cones will just saturate and perhaps even get damaged under such intense illumination.
  3. Further,  from our line of sight (Earth) the KBO will ALWAYS have day time. Since the side facing us is to a good approximation, the side facing the Sun. Unless they want to artificially brighten their day side, we will not be seeing anything.

Therefore to summarize my arguments against such a search are  –

  1. Plausibility of evolution of intelligent life on a KBO.
  2. The need for such bright light for an ET on KBO.
  3. We are always seeing the day side of a KBO from Earth.

Hence, I think such a search should not be conducted. Some of these points are mentioned in the conclusion of the paper, and it is correct that we cannot predict the nature of another civilization or its biology. However, the basic laws of Physics and Chemistry are universal.

Is the 9 dimensional haystack enough?

In this post I shall build upon some of the discussion from  Paul Davies (2013).  The article describes a search effort which uses data from the Lunar Reconnaissance Orbiter. They attempt to use data from this satellite with a resolution of about 50 cm/pixel, to find artifacts of ET on the Moon.

An important consideration in this search is the size of the data set that needs to be sifted through. The complete data set is expected to contain about a million frames of 500 Megabytes each, which translates to about 500 Terabytes in all. The search is for something left behind accidentally or on purpose by alien civilizations, a la  Transformers: Dark of the Moon (but mostly smaller?).

The challenge over here is that it is simply to numerous for a human or groups of humans to go over the entire data set manually, and the computer algorithms being used are not necessarily primed to look for signatures or anomalies highlighting the artificial origin. Another example of this is the Kepler mission. It has looked at more than 100,000 stars. A great search technique to find Dyson swarms, or other hallmarks of advanced ET civilization in orbit around a star. The periodic dip if caused not by a planet, but a irregular (non spherical structure) would encode information about its structure, in the residuals.  As has been discussed in Wright et al. (2016), there are a number of anomalies in exoplanet science which might be from astrophysical phenomenon or possibly from an advanced ET civilization. If we find more than one such anomaly in a system, it would be difficult to attribute it to natural sources.

Therefore, from a SETI point of view there is a LOT of information in these giant data sets from missions like Kepler, TESS, LSST, among others. Citizen Science initiatives do help in this by using human cognitive abilities in pattern recognition to pick out these anomalies and outliers; arguably better than any computer can do.  However, when it comes to automated pipelines, we should quantify their efficacy.

The point I would like to make here, is that in the era where we are transcending the radio region of the electromagnetic spectrum into the optical and infrared, we must make use of these existing big astrophysical missions and include them in our quantification of the search volume probed for ET.  However, I propose that we must add a 10th dimension to this haystack which quantifies the ability of our data pipeline to retrieve these signals IF we were to receive them. By this I mean, if there is a pipeline which is analyzing an existing database to find anomalies, the completeness fraction of that pipeline should also be quantified. By inserting artificial signals into the data, and counting the ones we retrieve, this can be done. However, that is an overtly simplistic view of this problem. This is not an easy task since we do not know the nature of these signals and can hence only hypothesize and to a certain extent – guess.

This way we could include Kepler, and other such missions in our search volume (volume searched by all SETI projects so far) using their actual efficiency and not a mere theoretical one.  This 10th dimension fraction should ideally be close to unity for most searches, however as mentioned in the paragraph above, in the absence of knowledge about the nature of the signal we can only hypothesize using our current understanding of Physics.


Addendum: 2018 – 04 – 30

After further research and work on the 9-dimensional haystack , I realize that in the original Haystack proposed by Jill Tarter in 2010, this ability to retrieve potential signals from the data is exactly what she meant in the modulation axis.

9 suffices. Phew!