Month: April 2018

SETI: A Fantasy Land

In his spare time, theoretical physicist, cosmologist, and astrobiologist Paul Davies exerts his role as an author. As his Amazon page describes, he has written at least twelve published books often on some existential question about life (or the dearth of life) in the Universe as informed by science. Davies has claimed he seeks to “bring the message of science and religion to the people” and, being a physics savant, was awarded funds from the Templeton foundation to support his research on “the natures of time and consciousness and extraterrestrial life”. One of his more recent books, The Eerie Silence, overlaps with his research interests and can be described as intellectually provocative.

Figure 1. Above is a popular image of what an alien would look like. Science fiction and pop culture have spawned this image as the most likely visage of ETI. The source is The Eerie Silence.

Davie’s book discusses SETI, focusing on its implications and assumptions. He dismisses the entrenched cliché of aliens (see Figure 1), as crafted by science fiction and movies. The end of chapter six and the entirety of chapter seven, “Alien Magic”, seek to question an important premise in SETI: that we know what we are looking for and it is something we can readily distinguish. Absent exotica, SETI seems a plausible and fruitful, albeit onerous, endeavor. The epigraph at the beginning of chapter seven is borrowed from Arthur Clarke and states “any sufficiently advanced technology would be indistinguishable from magic.” Davies describes the conundrum for a proponent of SETI:

If we were to encounter alien technology far superior to our own, would we even realize what it was? Think how a laser or a radio would seem to a tribe of rainforest dwellers who have never been in contact with the outside world. Now imagine a technology a million or more years in advance of ours: it might well appear miraculous to us. All of which presents new SETI with a serious problem. How can we look for signatures of alien technology when we have no idea how it would be manifested? In the previous chapter I suggested some ways in which an advanced civilization spreading across the galaxy might leave traces of its activity. But all the examples I gave were based on extrapolations of twenty-first-century human physics, and so are tainted by anthropocentrism. Suppose that alien technology is based on principles that are completely beyond the ken of our best scientists?

Figure 2. Above is a whimsical depiction of energy extraction from a rotating black hole seen in The Eerie Silence. A truck can be thrown into a black hole and ejected with more energy than it originally had thanks to the conservation of angular momentum.

At the end of chapter six, Davies presents the reader various exotic astrophysical objects that have yet to be discovered, but have been theorized by scientists. This includes magnetic monopoles, which could be recombined with the opposite monopole to produce energy that would dwarf a hydrogen bomb, and cosmic strings, which have been proposed as sources of fast radio bursts. Davies casually mentions one possible hypothesis for the apparent lack of these objects is the sequestration by a super civilization, but as he notes “the hypothesis that aliens are the correct explanation for the anomalous absence of something is only as good as the prior probability of an alien super-civilization in the first place”. His discussion of these objects brings into focus our current understanding of physics. Davies mentions an example, from John Wheeler, of what ETI could do to satisfy its energy needs (see Figure 2) while baffling humans:

Wheeler dreamed up the amusing scenario [in] which trucks containing industrial waste are dropped on a carefully calculated trajectory towards the spinning black hole. […] The trucks spill out their contents in such a way that the waste is devoured by the black hole. For certain trajectories, the empty trucks get propelled away from the ergosphere at high speed, zooming off with more mass-energy than the laden trucks originally had going in. Ultimately the additional energy has to come from somewhere, and in fact it comes from the rotational energy of the hole; every time the trick with the trucks is performed, the black hole’s angular speed drops a bit. The good times will not last for ever – eventually all the rotational energy will be extracted and the civilization will be obliged to decamp elsewhere. But at present human levels of energy consumption, a black hole could meet our energy needs for at least a trillion trillion years.

This is where Davies coins the phrase “nature-plus”. With our arguably limited understanding of the Universe, it becomes necessary to look past familiar proxies, such as energy or resource usage, to limit the bias from human understanding. Davies asks the reader to consider technology that:

  • is not made of matter,
  • has no fixed size or shape,
  • has no well-defined boundaries or topology,
  • is dynamical on all scales of space and time or, conversely, does not appear to do anything at all that we can discern, and
  • does not consist of discrete, separate things; rather it is a system, or a subtle higher-level correlation of things.

This emphasizes there may exist incomprehensible technology that operates on levels indiscernible to a human. Davies surmises that:

Technology is, in the broadest sense, mind or intelligence or purpose blending with nature. Importantly, technological devices don’t subjugate nature; the devices still obey the laws of physics. Technology harnesses the laws; it does not override them. […] Truly advanced alien technology might manifest itself by an entirely new form of whole–part interrelationship. And just as quantum weirdness is uncovered only with very special apparatus, so alien technology might go unobserved and unsuspected, because we are not viewing it with the equivalent of… well, a Bose–Einstein condensate beam-splitting interferometer.

However, while we may not completely understand the Universe, there exist certain laws that we can be fairly sure of, notably the second law of thermodynamics and the maximum speed of light. Davies uses these laws to dismiss science fiction, such as a quantum vacuum drive (violates the second law of thermodynamics) and levitation (violates the law of gravitation). To this blogger, this chapter by Davies discusses one of the unsettling things about SETI: its apparent indifference to its existential problems. While astrobiology can rely on our understanding of the biochemistry of terrestrial life (particularly bacteria), SETI is limited to humanity’s machinations. SETI experiments have varying levels of assumptions and most palatable are the parasitic searches focusing on Dysonian SETI. Once cultural assumptions come into play, SETI quickly devolves into fantasy. While a given experiment may be a null result, if it explores a subset of an infinite-dimensional manifold then it is scientifically useless. SETI should proceed but should take caution to limit itself to experiments where a scientific result can say something informative. To this blogger, a reasonable way to search for life would be to start with unintelligent life within our own Solar System, then work together as a scientific community towards extraterrestrial intelligence.

Spooky Soundlessness

The Eerie Silence by Paul Davies (2010) is a popular science book which “explores the possibilities of intelligent extraterrestrial life, and its potential consequences” (Wikipedia).

The reading we were provided included the end of Chapter 6 “Evidence for a Galactic Diaspora” and the beginning of Chapter 7 “Alien Magic”.

At the end of chapter 6, Davies focuses on how ETI may be responsible for the lack of certain high-energy objects that have been predicted by theoretical physicists but have remained elusive. Most grand unified theories (models where the electromagnetic, strong and weak forces can merge at extremely high temperatures) require a magnetic monopole. These particles would have extremely high mass energies, so maybe ETI is scooping all of them up and annihilating them whenever it needs more energy. Don’t know what to do with that possibility, but I guess it could be true.

At the beginning of chapter 7, Davies talks about alien technology. It is possible that alien technology will be just that, alien. We may not be able to distinguish what it does or even that it is technology at all. Becuase of this, Davies wants technology to be known as “nature-plus”. Technology does now break the laws of nature, it simply arranges pieces of it together in a way to harness these laws to do a useful function (like break rocks, or in the case of art, inspire/express emotion). He suggests that we should avoid our own human biases in trying to think of what ETI may want/is capable of. That being said, the known laws of physics should be used as a basis, because without them, there is only speculation as to what ETI can do, which would be both endless and pointless.

That is a good point to keep in mind I think. It is hard to work in a field where you have only a limited idea of the capabilities and desires of what you are searching for (there might be a connection here to USA/USSR trying to figure each other out during the cold war, but even then they had a lot more information on each other than we have on ETI), but it is still important to not lose sight of reality. We may not like that we only know what we know now, but we just have to live with it and do the best we can. That’s all we can (and should) do.

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).

How to look for something that isn’t there

A common artifact searched for in looking for ETI is Dyson spheres, or some other megastructure whose purpose is to collect energy from the star. This structure was first suggested by Dyson 1961, but later expanded on by Kardashev 1964. Kardashev suggested that civilizations could be categorized into three different types, depending on the quantity of resources collected: a type I civilization would gather resources from their planet, type II from their star, and type III from their galaxy. Kardashev 1964, and later Annis 1999, and even later (sort of) Villaroel et al. 2016 argued that these different stages of civilizations could potentially be discovered! If a civilization were to harvest all of the energy from their star, then we would no longer see them (in the visible; the heat would dissipate as IR, leading to searches for this waste heat).

Villaroel et al. looked for disappearing stars. They compared data from Sloan and from archived data, looking for sources that were present in the latter but no longer there for the former. In essence, looking for disappearing stars. In the end, they found one potential candidate.

I said earlier that they sort of argued that this was a method for detecting other civilizations. I say “sort of” because they didn’t directly mention it. The thought is there, that this is a way to look for ETI, but the reasoning behind why ETI would cause a star to disappear is not mentioned. I’m sure there are a number of explanations that sci-fi fanatics could list, and maybe the authors did not want to potentially embarrass themselves by playing sci-fi author? Nonetheless, I’m not really sure, short of a Dyson swarm, what would cause a star to vanish. Feeding it to a BH?

That being said, I am becoming a fan of “parasitic” SETI searches. There is something about only needing to pay for time (not receivers or data) that really seems great to me! The data are already there, so why not go for it?

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.

Finding life from spectra, but not your typical way

Lin et al. (2104) identify pollutants such as chlorofluorocarbons in the Earth’s atmosphere that would be detectable using JWST on other planets. In particular, they find that the time dedicated to an atmosphere with other potential biosignatures would be sufficient to constrain the levels of these CFCs, so the search can be parasitic, in a sense.

I think this is a great idea! As I come across ideas for artefact SETI, especially parasitic ones, I get more excited about the prospects for the field. Two major issues facing SETI are the lifetime of a technological civilization and funding. Both of these are, if not solved, greatly minimized by artefact SETI.

With that being said, I fear such a search for CFCs will flop. Even though the timescales of CFCs and excess carbon are large (especially compared to the age of human technology), I don’t have much faith in atmospheric measurements. I know that JWST will improve all of our current measurements, but from what I remember it will only be useful for large or close planets. All of the studies on exoplanet atmospheres have returned one result: clouds. I don’t expect this to change by much, but hopefully we’ll get a spectrum that isn’t flat! I do agree with the authors that since this data will already be gathered and analyzed for biosignatures, it might as well be analyzed for CFC absorption. The worst that happens if we find such absorption is that chemists/geologists/biologists publish ways that CFCs can be produced in the absence of intelligent life, which will further our understanding (and maybe will lead us to ways of removing the CFCs in our atmosphere!).

The one issue I have with this paper is the white dwarf thing. In the beginning, the authors say that they will only look at planets around white dwarfs, but say that their results “are generalizable to other telescopes and planetary systems.” I understand their arguments for a white dwarf, in that they provide better contrast, they could be the same temperature as the Sun, and they have very long lifetimes, but as of now (2018), we have yet to find a single planet around a white dwarf. I just feel they should have expanded their discussion to include all stars, and if they wanted the low contrast, then just M dwarfs. I personally don’t have enough background to state whether the absorption features from CFCs in an atmosphere around an Earth-like planet around an FGKM star would be visible. I wish this information had been provided by the authors in this paper.

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.

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.

 

 

Searching for Humans around White Dwarfs

One of the primary tasks in astrobiology is to detect biomarkers. Lin et al, in a recent paper, argue that industrial pollutants could be used in lieu of biomarkers to detect life on other planets. The unexpected twist in their hypothesis: they propose to observe old white dwarfs. They argue it is possible to look for pollutants from an industrialized society with technology comparable to ours. According to the authors, the ideal pollutant to detect would be specific chlorofluorocarbons (CFCs).

Lin et al begin by motivating their choice of host star. Following previous work by Loeb and Agol, they cite three reasons to favor these stars:

  • white dwarfs have long-lived habitable zones as they are at the end of stellar evolution,
  • the similarity in size of the white dwarf and an Earth-like planet should give the best contrast between the planet’s atmospheric transmission spectrum and the stellar background, and
  • after a few billion years, a white dwarf at the Sun’s effective surface temperature should have a spectrum similar to the Sun, creating a comparable habitable zone, albeit much closer to the star

Lin et al mention that habitable planets could plausibly form debris of the stellar remnant. In short, a white dwarf could host an Earth-like planet at ~0.01 AU. If we further assume there is an anthropogenic civilization on said planet, they could industrialize and produce pollutants. The authors argue the ideal pollutants would be CFC-11 and CFC-14. CFCs have short lifetimes in the atmosphere (at most a few thousand years) and largely produced unnaturally, at least on Earth. There may be volcanic and fumarolic CFCs, but these are appreciably lower in concentration. The estimated time for this measurement would be on the order of day with JWST, which the authors argue could be used to simultaneous detect a spectral edge, be it natural or artificial. The simulations of spectra are shown in Figure 1.

Figure 1. Above are the spectral windows used for detecting CFCs and select molecules used in this paper. The top row shows the combined transmission spectrum. The orange segments are expanded below to highlight where CFCs and other molecules have significant lines. In each zoomed segment, the black represents the contribution from the most significant components of Earth’s atmosphere. Lin et al argue the highlighted regions make good regions to observe for pollutants caused by an Earth-like civilization around a white dwarf.

This blogger is in awe at the assumptions going into this paper. The notion of white dwarfs around planets, while not new, invokes various questions of habitability. If we assume the planet existed before the stellar remnant emerged, how could it survive and retain its orbit? If we assume the planet forms from stellar ejecta, would the metallicity allow for the formation of a rocky planet? “Polluted” white dwarfs do exist and have evidence of debris disks, but as of yet no bona fide planet has been detected around a white dwarf. If we ignore that assumption, the issue of detectability persists and the choice of a cultural signal (a pollutant). CFCs are particularly heavy and would require an observation to probe beneath a significant amount of atmosphere. Furthermore, if in the outer atmosphere, UV radiation would readily destroy CFCs. The required resolution of 3000 is the estimate from JWST documentation but it may be much less at these particular windows. Lin et al assume the civilization must develop like Earth and cause an excess (more than ten times our currently level) of pollutants while refusing to control said emissions. Too many assumptions go into this argument for it to be a viable SETI experiment (i.e. a direct JWST proposal).