Annis (1999) Summary

This paper presents an empirical way to find type 3 Kardashev civilizations, which is to identify outliers in the Tully-Fisher relation for spiral galaxies and in the fundamental plane for elliptical galaxies.

The author begins by arguing that it is possible to observe galaxy scale interruption of starlight. Then the author derives the scaling relation for galaxies argues that the scatter seen in empirical data around the scaling relation is as low as 10 percent.

This tight relation could be used to identify outlier galaxies which have very low surface brightness, probably with a infrared excess if the type 3 Kardashev civilizations use technologies such as Dyson sphere.

Then the author describes the empirical effort to find such outliers in 31 spiral galaxies and 106 elliptical galaxies. However, no significant outlier has been detected in those galaxies. The author argues that this could be due to setting a too strict cut on the surface brightness deviation. Newer samples could reduce the cut down to 50 percent. However, the author leaves it for another time. Further, the author discusses the limitation of photographic plates not being able to detect low surface brightness galaxies which could give us biases towards regular galaxies than galaxies harnessed by type 3 Kardeshev civilizations.

Finally, the author discusses how long it would take for a type 3 Kardashev civilization to rise and the upper limit is 304 billion years which is much longer than the age of the universe. There are several reasons which could lower this upper limit. First, the sample is incomplete and they do not have any very low surface brightness galaxies. Second, not all type 3 Kardashev civilizations have to be star-fed. They could harness other types of energy such as dark matter and dark energy. Third, the time for those civilizations to develop may be much shorter than 10 billion years. One thing I do not understand is that why it is an upper limit than a lower limit because if those civilizations do not exist, the upper limit should be infinite.

The Case for Artifact SETI

Olaf Stapledon’s 1937 science-fiction novel, Star Maker, pushed the imagination by featuring an advanced civilization that built a spherical shell around its host star to capture the radiation and meet its energy requirements. This spherical shell would later become known as a Dyson sphere (see Figure 1), after the astrophysicist who contemplated the mid-IR excess such an object would release. While the concept originated in fiction, it has since gained a niche as a potential alien mega-structure that could be observed. It also emphasizes that the search for extraterrestrial intelligence (SETI) is difficult due to the limitations of our imagination. While SETI is fundamentally a search for a society capable and willing to communicate, there exist other approaches that make the SETI more feasible and draw on the concept of waste-heat from alien activities, such as the Dyson sphere. Jason Wright and fellow scientists recently published a four-part series to motivate and present the Glimpsing Heat from Alien Technologies (G-HAT or Ĝ) survey. Wright et. al. argue the sensitivity of a waste-heat search would be greatest for a civilization which satisfies a physicist’s definition of intelligent life. This defined ETI as a species that (i) “processes resources and energy to produce more of itself” and (ii) “overcome[s] local resource limitations through the application of energy”. They surmise that “if a species is spacefaring, then its level of intelligence is such that there is no practical resource limitation that it cannot overcome, except that of energy”. The authors note there may be other intelligent life excluded by this definition of intelligent life, but argue such a society would not be easily detected through the Ĝ survey.

Dyson (not the vacuum)!
Figure 1: An artists depiction of a Dyson sphere. It can be considered a swarm of steerable energy collectors. Most cases assume it is at roughly 1 AU around a Sun-like star. The Ĝ survey aims to discover the excess IR radiation from such a structure (if it exists). Source: New Scientist, Mark Garlick/Science Photo Library

The first paper introduces the philosophies of SETI, with particular emphasis on the Hart argument that the dearth of ETI encounters implies we must be the first intelligent species in our galaxy. Hart stated there were four categories of solutions to this problem: (i) physical, (ii) sociological, (iii) temporal, and (iv) ETI has visited, but he denounced each solution and conclude we were alone in our galaxy. Wright et. al. review each of the categories with insights from our current understanding of astrophysics and reinforce the temporal and sociological reasons presented by Hart. An order-of-magnitude calculation show a colony of ships traveling at 10-4 c (comparable to the velocity of Voyager 2 or Pioneer) in a rotating disk (i.e. our galaxy) should populate the Milky Way in at most a billion years. With regards to the extinction theories, the authors aptly note this must hold for all colonies of a civilization that has spread throughout its galaxy. A species confined to one planet can go extinct but as long as there is a self-sufficient colony somewhere away from a gamma ray burst or interstellar war (anything lethal), the species can always repopulate the galaxy. The authors state that sustainability arguments do not hold because, before all stars are colonized, there is no limit in the relevant resource (stars) and there is no reason galactic hegemony must be explicitly driven by a lack of resources.

While Hart’s argument was pessimistic, it only considered one galaxy. Therefore, if each galaxy is considered to be an “independent realization” of his experiment, there could exist galaxy-spanning ETIs. Wright et. al. then describe the previous searches for Dyson spheres and discuss the promise of NASA’s Wide-Field Infrared Explorer (WISE). Wright has stated that “WISE was launched by NASA for pure, natural astrophysics; it just happened to be perfect Dyson sphere finder.” In the case of a Dyson sphere, if a star were perfectly encased by a shell at roughly 1 AU, the resulting spectrum could be approximated with a few-hundred-Kelvin blackbody. The results of searching for this heat-waste, this artifact of ETI activity, would at worst put an upper limit on alien activity.

The Ĝ survey strives to address some of the issues inherent in typical SETI, namely the assumption that ETI is emitting a signal amenable to radio detection. Instead of forcing ETI to behave this way, artifact SETI seeks to detect the thermodynamic consequences of galactic-scale colonization. In this first paper, the Wright et. al. briefly note something like the Ĝ survey will be “hard pressed to prove that an unusual source is artificial”. IR observations are prone to contamination from dust and must be disentangled form other, astrophysical processes. The survey analyzed roughly 100,000 galaxies to determine the reddest sources and concluded “no galaxies resolved by WISE contain galaxy-spanning supercivilizations with energy supplies greater than 85% of the starlight in the galaxy”. Others have introduced possible corrections to the treatment of data, but nothing so far suggests galaxy-spanning civilizations exist.

Movie 1: Above is a video showing KIC 8462852 and a possible alien mega-structure (around the 1:00 mark) explaining the decrease in flux. Source: The Washington Post

While the Ĝ survey is more scientific and data driven than conventional SETI, it is important to carefully vet candidates and, at the very least, apply the law of parsimony. One such example of artifact SETI gone awry is KIC 8462852 (see Movie 1). Perhaps to Wright’s chagrin, he has been “credited” with fomenting the idea that an alien mega-structure is to blame for the dips in KIC 8462852 (see here and especially here). Additional observations suggest optically thin dust may cause the dips. The biggest damage is to the credibility of SETI, as it degrades the science behind these papers to nothing more than a form of sensational pseudoscience. The support from the Templeton Foundation, often criticized as having a history of supporting controversial and speculative research (see here for physicist’s opinion), is another issue that may affect the credibility of the Ĝ survey. Regardless of one’s prior on SETI, Dyson provides some keen insight:

“If there are any real aliens, they are likely to behave in ways that we never imagined. The WISE result shows that the aliens did not follow one particular path. That is good to know. But it still leaves a huge variety of other paths open. The failure of one guess does not mean that we should stop looking for aliens.”

This blogger, while having concerns with SETI as a whole, firmly believes more research should be done with both conventional SETI and artifact SETI. Until there is more data, it is unscientific to completely reject the premise of SETI, however flawed its premise may be.

Dyson Spheres: Fiction or Fantasy? (definitely not vacuums)

I don’t mean to just flat-out say that Dyson Spheres are impossible (even though they are). Instead, I separate their possibility into two categories: “fiction” and “fantasy.” Here,  fantasy is something thought up by the imaginative yet impossible (think wizards and dragons) but fiction is something thought up that *could* be real. Maybe.

In 1960, Dyson wrote an article (letter?) to Science, stating a fun mind experiment that he had come up with: that advanced civilizations could build a “biosphere” (later called a Dyson sphere) around their star out of some outside matter (e.g. Jupiter), successfully harnessing all of the power of the star and solving over-population problems. This biosphere would block radiation from the star to outside viewers, except in the IR. Therefore, Dyson argued, we should begin a search for objects with strong IR emission and not much else.

It’s hard to discuss this paper without mentioning some of the published responses he received and his rebuttal to them, mostly because some other people basically mentioned my arguments to this idea nearly 58 years ago. Maddox points out that a Dyson sphere is physically impossible. To keep this shell in orbit around the Sun at any distance in the Habitable Zone would require some force counteracting gravity and pushing outwards on the sphere. In stars, this is radiation pressure. Maddox points out that radiation pressure wouldn’t really work, but doesn’t go into any specifics beyond that (it was only a short response). I wonder if there is any material strong enough that we know of or even theorize that would maintain its structure, so that the rigidity itself was counteracting gravity. Probably not, but still fun to think about. Dyson counters that by biosphere he imagined was obviously not whole as that would be impossible, but instead made of “a loose collection or swarm of objects traveling independent orbits around the star.” Wait, what? So even though it is a sphere, it’s not actually a sphere. But it is a lot of artificial bodies around the star..would that be bodies going the same velocity so having the same semi-major axis? Or are people just going to build a bunch of planets with different inclinations to fully cover a sphere? I can understand what s sphere around a star would look like, and agree that it probably is not mechanically possible, but I cannot figure out how “a loose collection or swarm of objects” would work at all. Personally, I feel this clarification terribly backfired. I had also always thought of and heard of Dyson spheres as being, well, spheres, so it seems that this clarification wasn’t read or remembered by most anyways.

Anderson then argues that such a sphere could not even be constructed. Since it would take so long to construct (several thousand years), there is basically no way that a civilization would bother continuing it. Sure, they could start, but after a few generations someone would come up with a better solution to over-population or for energy usage that would require so much less work and time. He argues that the only way this could work would be to go all Brave New World and condition people to accept the continuation of the project, in which case people could just be conditioned reproduce at sustainable rates! I completely agree with this argument, although I’m not sure how relevant it is to Dyson’s paper. It is true that a Dyson sphere is so unlikely to be produced that no civilization would do it, but Dyson spheres themselves aren’t really possible, so this seems like a waste of ink. I, however, do not agree with Anderson’s conclusion that “astronomical discovery of infrared sources won’t prove anything about the inhabitants of other planets.” I mostly don’t agree with this because we have no way of knowing for sure what we can learn from an IR signature until we actually start looking at them. Only slightly related to this, we can *detect* planets using their IR signatures (kind of, direct imaging in the IR is easier due to the slightly less horrible contrast issues); besides, as Maddox pointed out, an IR search would still be astronomically valuable, even if it wouldn’t lead to the discovery of Dyson spheres.

I personally believe that Dyson spheres under the definition of a solid sphere somehow encasing a star are impossible. The sheer force required to keep the sphere together would be insane, and no civilization would bother putting that much time and money into such a feet (we can’t even get funding to put man back on the Moon!). I can see the appeal of a Dyson sphere as it would lead to plenty of space for people and solar panels and such, but I don’t think it would solve over-population problems nor do I think anyone would bother making it.

Dyson Sphere

Compared to the Cocconi and Morrison’s proposal to search for radio signals in the nearby stars. Dyson (1960) pointed out it was also useful to look at infrared signals at 10 microns radiated by his hypothesized Dyson sphere. He argued much more advanced civilizations would have built thin shells around their host stars to more efficiently harvest the energy of the host star.

He argued the Malthusian pressure would drive some of the advanced civilizations to build such a sphere to catch up with the exponential population growth. Additionally, he also argued that the such a sphere would have similar orbit size as the Earth and same temperature as well so that we could possibly detect it at the 10 microns which was also transparent to the Earth atmosphere.

I do not really understand how he concluded that the temperature of the sphere would be at the same temperature as the Earth. Would not the energy harvesting efficiency be much higher if the sphere was radiating at a much lower effective temperature. It seems to me that his conclusion about the temperature of the sphere came from our understanding of the Earth and it was 10 microns which was also transparent to the Earth atmosphere made him draw the conclusion that we should observe at 10 microns.

In the later reply letter, he clarified the idea of Dyson sphere to not being a solid sphere which was physically impossible to build but a swarm of objects traveling on independent orbits around their host star. He also admitted whether the alien civilizations obeyed the Malthusian principle or not was a question of taste. Finally, he argued that even if we did not find any aliens, the search for intense infrared signals could help us identify interesting astronomical objects.

Dyson and the Beginnings of Artifact SETI

In Dyson (1960), the beginnings of a new type of SETI is proposed that has significantly fewer behavioral and technological assumptions about ETI (Wright 2014). If ETI does exist and use a large amount of energy, they will likely be utilizing starlight as an easily accessible energy source and be indirectly converting it into IR radiation. The search for this IR radiation is proposed to complement the existing searches for communication.

Dyson argues that if exponential population and technology growth is sustained for a couple millennia, a civilization could use on the order of a Jupiter mass’s worth of material to construct a spherical shell around the Sun (using only 800 years worth of solar energy!). This is followed by the bold statement that “One should expect that, within a few thousand years of its entering the stage of industrial development, any intelligent species should be found occupying an artificial biosphere which completely surrounds its parent star.” Finally, he notes that the thermal emission of these shells will be in the IR range and that ground telescopes will be able to detect them through the atmosphere.

A popular idea that resulted from this paper was that of a Dyson sphere, a hypothetical megastructure that completely encloses a host star, capturing all of its energy. It is sometimes postulated that the sphere is not only used to capture energy, but to also serve as a space for habitation, where life can live on the inner surface of the sphere. If one was constructed with a radius of 1 AU around out Sun, there would be more livable space than half a billion Earths! There are several problems with this implementation, namely, there is no material we know of that could withstand thepressure imposed by the star’s gravity. Additionally, there would be no effective gravity imparted by the shell on anything in its interior, so there would be nothing holding anything to the interior surface and the shell could drift into the star over time.

The Dyson Sphere has remained a prevalent idea in popular culture to this day, with appearances in many forms of science fiction media (including the television show Star Trek: The Next Generation and the grand strategy videogame Stellaris)

In Stellaris, you can spend an inordinate amount of resources constructing this mega structure. Realistically, it turns all rocky planets and moons in the system into frozen or barren worlds. Unrealistically, the amount of energy provided does not vary between different star types. Tsk tsk developers.


3 Types, 3 Questions

This week, I wanted to talk about Kardashev (1964) because I naturally started doing a lot of follow-up as I read. The famous idea that was first proposed in this paper was the classification of civilizations by the amount of energy they consume, as summarized below:

Type I: Earth-level, consuming 4 * 10^19 erg/s

Type II: Full-star usage (a la Dyson spheres), consuming 4 * 10^33 erg/s

Type III: Full-galaxy usage, consuming 4 * 10^44 erg/s

I had three questions that popped up over the course of reading the paper.

  1. Has the definition of Type I always been the same over time?
  2. Did we keep up with Kardashev’s energy growth rate predictions?
  3. Whatever became of CTA-21 and CTA-102?

I’ll tackle these one at a time.

  1. In my memory, when I’ve heard about the Kardashev scale before, humanity was said to be at a Kardashev 0.7 or so, which is a pretty long way from a Kardashev I (because the scale is not linear). The argument that I read (I believe in the book Physics of the Impossible by Michio Kaku*) is that a Kardashev I civilization uses an amount of energy equal to the amount of starlight falling on the planet’s surface. A quick glance at the Wikipedia page confirms that interpretation. But, as I mentioned above, Kardashev defined it as being the amount of power that Earth was using in 1964, at the time the paper was written. So when did the flip in definition happen? Turns out this shift was the fault of the ever-present Carl Sagan. His standardization of the scale with a logarithmic power formula allows values other than I, II, and III and allows a more generalizable formulation (versus Kardavshev’s Earth-centric standards). It’s amazing to me that a redefinition happening a decade after the original paper has caught hold so strongly.
  2. Since it has been over 50 years since this paper was written, I was curious to see if we had kept up to Kardashev’s proposed growth rate of 3-4% a year, starting at 4 * 10^19 erg/s. After a long 10 minutes of trying to figure out why my simple exponential growth rate equations were wrong (ergs/second not ergs/year, past-Me), I got an answer of ~6.5 * 10^27 to ~1.3 * 10^28 erg using his values (using 3% and 4% growth respectively). The actual current value is 3.9 * 10^27 erg, so while Kardashev’s predictions were optimistic by a factor of 2-3, they weren’t really that far off. That’s honestly pretty impressive, at least to me (perhaps an economist would say that this is an easy problem, but it isn’t quite intuitive to me). Will it continue at this rate, or will we level off in some logistic-like function? That’s the question, isn’t it? But at least so far, we’re on track with Kardashev’s prediction.
  3. After some research on CTA-21 and CTA-102, it looks like (predictably) they were both false alarms. CTA-102, according to a quick Wikipedia, is identified as a very-variable quasar with extremely luminous “blazar states”. This is a great example of how objects of interest to SETI (at least in the context of artifact SETI) are going to invariably be interesting to the rest of astronomy, and should be valued for that reason. Meanwhile, both objects had an entire article in the NYT written on them by none other than Isaac Asimov. A quick scan on Google Scholar suggests that it too is just a quasar, though a less extreme example than CTA-102.

*This book was my “eureka” moment about wanting to be a physicist/astronomer. I picked it up on a whim when my seventh grade book club got to go to the local book store for a mini-field trip. After finishing it, I decided that I wanted to go into physics, and I haven’t looked back since.

Earth to ET, come in ET

On November 16, 1974, the Arecibo radio telescope in Puerto Rico sent out a message to the stars (specifically those in M13, a cluster 25000ly away). This message, in binary, was the first emission from Earth with the intent of someone else receiving it. And here it is:

Isn’t that sexy? For those of you who can’t read binary and/or have no idea how to break this code (probably most everyone on this planet), the message is decoded into groups of 23 characters, leaving 73 groups. The authors explain that because these numbers are prime, this would clearly be the right way to interpret this. Personally, I would never get there. I wouldn’t think there to be any significance in the number of characters per line, or what have you. Once you know how many characters should go into each line, this looks a little bit more like something that could be interpreted:

This personally reminds me of Christmas sweaters, nonograms, or the early Atari games, but there is meaning to it. The first line indicates the numbers 1 through 10 in binary. Apparently the numbers 8, 9, and 10 are too large, so they are written differently? I’m not sure I really understand that even with a decent explanation from the authors, which makes me believe that anyone trying to decipher this would have an even more difficult time (I suppose they could just be remarkably more clever than I).

After these numbers, there is a “description of fundamental terrestrial biochemistry.” Although I can pretend to see the 1-10 numbers, I have no idea where they biochemistry stuff is (apparently lines 12-30). First comes the numbers 1, 6, 7, 8, and 15, indicated the elements H, C, N, O, and P. These elements are required for life as we know it (although some might argue the importance of other elements). After these numbers are chemical formulae of molecules or radicals (the paper doesn’t say which ones). Included in here are the structures of the molecules that make up DNA, in the structure of a double helix, and the number 4 billion to indicate the number of molecular pairs (adenine-thymine or guanine-cytosine) in DNA in a single chromosome.

Below all this is a representation of a human! We are bipedal with arms and a head. This comes with the number 14, indicated that the human is about 14 units tall. The units are (apparently obviously) the wavelength of the original transmission.

Below the human is a schematic of the solar system; the big blob is the Sun, then all nine [at the time] planets. The length of each bar is a semi- indication of the planetary size, and the third dot from the Sun is us! It is slightly placed out of plane, in an attempt to indicate that that planet is where humans reside. I would interpret it as the planet’s inclination, but that’s okay.

Below our solar system is a drawing of Arecibo. I would never guess this, but that’s what it is. This drawing is accompanied by the size of the telescope, my guess is with the hope that any response would take into consideration our limitations and make sure that we could actually hear them.

This message was put together by numerous people, and is quite creative to say the least. That being said, I am extremely doubtful that this message could be interpreted! For starters, the only way I could make heads or tales of it was from the picture directly, and that was after the whole 27-73 thing was implemented. But what if the receivers only caught part of the transmission? It took 169 seconds to send, so it is possible that only a minute or less would be received if the receiver was not pointed at Earth for the entirety of the message. With only part of the message, there is nothing to indicate where each line starts or how long it should be. In addition to all this, it would take a lot of brain power to decipher all of it. Sure, some of it could be understood without much time, but to get all of the message would take work and prior knowledge. This all assumes that whomever receives this thinks in a way similar to how we do, and what is to say that they way we think is normal? What’s to say that clearly it is logical that the first line is just numbers, and then straight from numbers we switch to chemistry?

I do wonder, assuming that the recipient of this deciphered it, what the odds are for misinterpretation, and what the consequences of this would be. It would certainly be amusing (to read about, not to experience), if the compounds were interpreted as a cry for help, and some lovely civilization prepared them all and brought them to us in quantities large enough for our population (4 billion at the time). What if they thought that each of our chromosomes needed these compounds for each of the 4 billion people? Imagine an entire fleet of interstellar (or intergalactic) ships coming to our rescue in 50,000 years with buckets and buckets full of thymine (I don’t think you can just store that in a bucket).

I also wonder if a group of humans could decipher this. If we just gave this message in binary (we could also just send it via radio, but I’m not sure that would be picked up) to a group of intelligent, multi-disciplinary people, would they be able to pull out all of this information? This seems like an important sanity check (to me) for any METI that we do end up sending out. If we humans can’t decipher our own messages, with the culture and knowledge that went into its making, then why would anyone else out there be able to decipher it?

With all this being said, I should note that the people who sent this message did not really expect it to be received or answered, that this was just a proof of concept of the current technological capabilities. So whether or not this message is received, understood, correctly interpreted, or responded to isn’t all that important.

Arecibo 1974 – Interstellar telegram or PR gimmick?

In this article I shall delve into whether Message Extra-Terrestrial Intelligence (METI) is a smart idea or not. I  seek to discuss and question whether the message broadcasted by Arecibo in 1974 was meant to reach out to another civilization, or was it just a PR gimmick?

Arecibo Observatory

The Arecibo Observatory, in Puerto Rico (USA) is a 305 m (1000 ft) radio telescope. It is the most powerful non military radio transmitter that mankind possesses. In 1974, it was used to broadcast a narrow-band signal ( ~ 10 MHz) at  2380 MHz towards the globular cluster Messier 13.  M 13 is a globular cluster in the constellation of Hercules and is at a distance of about 22000 light years. Globular clusters are some of the oldest objects in the known Universe and hence harbour a stable host environment for an intelligent life form to develop, say as opposed to a Star Forming Region.

The message contained 1679 (73 x 23) bits (0s and 1s) and was supposed to be a cheat sheet for alien civilizations to infer our presence and know more about humans and the fundamentals of our existence.  Further, the signal was barycentric corrected (motion of the Earth around the Sun) to ensure that the frequency received is not modulated due to this motion. It contained the following information  (taken from Wikipedia) –

  1. The numbers one (1) to ten (10) (white)
  2. The atomic numbers of the elements hydrogen, carbon, nitrogen, oxygen, and phosphorus, which make up deoxyribonucleic acid (DNA) (purple)
  3. The formulas for the sugars and bases in the nucleotides of DNA (green)
  4. The number of nucleotides in DNA, and a graphic of the double helix structure of DNA (white & blue)
  5. A graphic figure of a human, the dimension (physical height) of an average man, and the human population of Earth (red, blue/white, & white respectively)
  6. A graphic of the Solar System indicating which of the planets the message is coming from (yellow)
  7. A graphic of the Arecibo radio telescope and the dimension (the physical diameter) of the transmitting antenna dish (purple, white, & blue)

The Arecibo message represented pictorially  in a grid of 73 x 23 with colour added for clarity. Courtesy: Wikipedia


The intensity of the transmitted signal was such, that is would outshine the Sun by a factor of 10 billion (10^7). The intensity, narrow-band and the prime number factors should be enough to clue in the listener to the signal’s artificial origin. A fact that can be further confirmed by the contents of the signal.

Thus, it seems that the message was formulated and broadcasted to serve as an announcement of our place in the Universe. That being said, as has been clearly articulated at the end of NAIC STAFF, 1974: the target (why not M4, at one third the distance), the frequency (2380 MHz and not the waterhole frequency), and the duration of the message (only 169 seconds) clearly indicate that the message was not meant to initiate interstellar dialogue. Further they also mention that a serious attempt to initiate such a discourse should come from an international consensus of nations and not unilateral action. Rather I believe, that the broadcast was a technology demonstrator for the newly upgraded radio transmitter (funded by the National Science Foundation – NSF) . It was meant to garner public support towards funding scientific pursuit.


Considering that it was not really meant as an attempt to initiate interstellar dialogue, is it justified to classify it along with METI (Messaging to ET intelligence) ?






Searching for Ozma!

Princess Ozma?
No.   Project Ozma








The PSU SETI class with the Project Ozma 85ft telescope.


In his 1960 article for Physics Today, Frank Donald Drake (1930 – Now) discusses the rationale for searching for extra-terrestrial (ET) intelligent civilizations using radio surveys, and after doing so describes Project Ozma. Further, he lays the groundwork to quantify the probability of finding intelligent life, which was later formalized as the ‘Drake Equation’.

Project Ozma conducted at Green Bank using the 26 m (85 ft) diameter radio telescope, was one of the first SETI (Search for Extra-Terrestrial Intelligence) experiments to search for intelligent transmissions of ET origin. It included observations of Tau Ceti and Epsilon Eridani, two stars spectrally similar to the Sun. With the exception of a false alarm due to a secret military project, the project did not yield any significant signal from these two stars.

Drake starts off by discussing how later generation stars contain not only Hydrogen and Helium but also metals. These metals (heavier elements) are required to form solid bodies like planets. Further, the formation of planets assuages the angular momentum problem in a cloud of condensing gas. Sun and other stars like the Sun have relatively slow rotational periods. This rotational period does not conserve the initial angular momentum and hence leads to a discrepancy. This can be solved by the introduction of secondary bodies like planets or binary stars, to which the gas cloud transfers angular momentum as it slows down. Drake suggests that as high as 60 percent of stars should harbour planetary systems.

Establishing heuristic arguments for their existence, Drake goes on to hypothesize whether life can arise on these extra solar planetary systems. He then cites the Urey – Miller experiment, which managed to successfully create amino acids in the laboratory using gases like ammonia, methane, hydrogen and water vapour and an electric discharge (simulating the early atmosphere and a lightning discharge). Amino acids are the building blocks of proteins which are the key ingredients for life. Therefore, the oceans were the harbinger of early life, which after about 5 billion years of evolution led to intelligent civilization. Drawing parallels to the origin and evolution of  life on Earth, he postulates the fact that since life would take so long (5 Gyrs) to develop and achieve intelligent civilization one can discount non main – sequence stars and those which have relatively short life spans (stars much larger than the Sun).

Another consequence of the comparison to life on Earth is the hypothesis that life needs liquid water to develop, due to which the planet (if it has water on it), cannot be too cold or too hot. This leads to existence of a narrow band around the star a planet can orbit – The Habitable zone. Being much closer, or much farther would lead to the vapourisation or freezing of water, respectively.

To search for such life on Earth – like planets around Sun – like stars, the use of narrow – band transmission in the radio is suggested. Discovery, and subsequent contact with such a civilization would likely be in the vicinity of the 1420 MHz region of the radio spectrum. This would be because it corresponds to the 21 cm Hydrogen line spin transition in neutral Hydrogen, a spectral feature that should be known to an intelligent life form. Also, in this region the cosmic noise signal is negligible making it easier to transfer signal at cosmic distances. On the other hand, even if we want to actively seek out ET intelligence this would be the appropriate EM region to seek communication in, since there is a greater possibility of such civilization having radio telescopes tuned and actively searching in this region of the spectrum.

Thus Drake lays the justification for Project Ozma where he searches in this radio band around two Sun -like stars (for princess Ozma?) . He concludes by stating the goal (of finding ET  intelligence) justifies the amount of effort required to carry out this work, and with the hope that in the near future, the search will be successful.

The Groundbreaking Project Ozma

This article was written by Frank Drake (of Drake equation fame) in 1961 and was published in Physics Today. It described the planning and execution of the first completed radio SETI observing program in history, the whimsically named Project Ozma. It also included a good deal of justification for why we might expect to find ETI out there – necessarily so, as this was the first project of its kind. Results? No aliens around Tau Ceti and Epsilon Eridani are broadcasting at the little slice of frequencies that were searched.

The search itself targeted 2 stars with 150 hours of radio observing time at Green Bank (I’ll admit, I’m jealous). They focused on the area around the 21-cm line. Since this paper, the 21-cm line became the most popular Schelling Point in frequency space, with the argument that the spin-flip frequency of hydrogen (the most abundant element in the universe) had to be the simplest universal watering hole. Whether that’s actually true, well, it’s hard to say – we human scientists agree that it seems like a promising place to search, but we’re not looking for human scientists out there.

Grab Bag Thoughts:

  • Now, of course, we know of thousands of exoplanets, but I appreciate the careful skepticism with which the idea was treated back before we had the instruments and evidence that we have today. Also, it’s amazing to me that the smallest extrasolar objects we’d detected at the time were apparently 10X Jupiter’s mass.
  • Neither of Drake’s “two helpful points” (a 5 billion year constraint, and a “ecosphere”/habitable zone/liquid water argument) are bad starting places – after all, we only have one data point to go off of. They do, however, seem anthropocentric (or maybe just simplistic) in hindsight. Then again, I suppose I have to keep in mind that the ideas and the search itself were novel at the time – hence the reason this was assigned!
  • On first read, the idea of a “group of intercommunicating civilizations” seemed a little far-fetched to me – we know nothing about the politics/society/mindsets of potential civilizations, so imagining a ton of independently arising civilizations that are all curious, cheery, and helpful seems a little optimistic. It was interesting how prevalent this idea seemed to be (Cocconi and Morrison imagined that they “look forward patiently to answering signals from the Sun” and Bracewell thought they were “probably already linked together into an existing galaxy-wide chain of communication”). But once I’d read Sagan’s argument from Sagan and Newman 1982 (I’ll talk about it in more depth in a future post), I could see the first justification for the popularity of this idea; in a nutshell, civilizations will be subject to a Darwinian evolution that will only preserve those that are not aggressive and intent upon colonization. Comprehensive explanation? Maybe not. But food for thought.
  • In light of some of the later papers in the semester, Drake’s rigorous scientific search for intelligent/sentient/communicative life seems very grounded and so much better than the general state of the literature in the decades to come. Is it coincidence that passions seemed to get inflamed about the subject in those following decades during funding struggles (a la Garber 1999) and after those original, perhaps a little too airy, early papers? Searching for sentient life has so many benefits that searching for non-sentient life does not (in the form of unintentional or intentional technosignatures) and I wish we had more evidence yay or nay in the form of searches like this one.

~ Less Relevant Coda – How Poorly Things Age ~

Much of what caught my eye while reading this paper wasn’t directly related to the scientific content but rather some (now) obvious faux pas.

  • Citations! Where are the citations?! It took me forever to figure out who Calvin was and what he did! Answer: if he was Dr. Melvin Calvin (my best guess) he was part of the Berkeley physics department back in the 1960s (go bears), Director of the Laboratory of Chemical Biodynamics at LBL, and won the 1961 Nobel Prize for Chemistry (according to the LBL website)
  • The “Harpsichord Maker with a Ph.D. in Physics” job posting is just a goldmine. Prize goes to “Men with appropriate advance degrees, preferably a Ph.D., are invited to…”. Intellectually, I know that’s just how it was back then, but it’s startling to read it now.