Student Blog Entries – Page 13 – Penn State Graduate Course in SETI

Hart: There is no ETI therefore there should be no SETI

Hart (1975) is about asserting why the author believes that there are no other intelligent civilizations in our galaxy. That essentially makes this paper about addressing the Fermi Paradox.

The entire article is written about refuting different explanations for the fact that “there are no intelligent beings from outer space on Earth now”, which he puts into four categories: physical, sociological, and temporal as well as those that say that we have been visited, but the visitors are no longer here.

The paper makes its case by attacking each type of explanation individually. Physical explanations are refuted by providing some examples of future possibilities for long distance space travel and saying a sufficiently advanced civilization could figure it out. Sociological explanations aren’t valid unless they apply to all civilizations for the entirety of their existences. Temporal explanations are addressed by stating that it would be a mighty coincidence that a galaxy colonizing civilization evolved less than a million years ago (<0.1% of our galaxy’s age). The last category is address with a mixture of arguments from the temporal and sociological section.

Finally, anyone saying that the main fact is actually false and that aliens are here is wrong because few astronomers believe that. This point is added on at the end and I find it childish. I don’t really see the point of bringing up the possibility of the main fact being wrong if it is not going to be properly addressed.

This paper is interesting because it is the first paper that is openly against spending resources on SETI.

I feel like the paper takes a lot of logical liberties in order to make its point. Importantly, his conclusion is that there are no intelligent civilizations in our galaxy, and I think he means currently. When he makes his arguments against sociological explanations, he talks about how cultures change over millennia, so any intelligent civilization would eventually start venturing out to find us, but a critical point he never mentions (at any point in the paper) is that we don’t know how long intelligent civilizations last. A lot of his arguments (eventually their technology will advance, their cultures will change, their colonization borders will grow) fall apart when dealing with technological civilizations that only last a thousand years or so.

Tipler Needs to Chill

“A Brief History of the Extraterrestrial Intelligence Concept” by Frank Tipler is a meta-paper about (or more appropriately, against) SETI as a funded endeavor. The author assigns three different characteristics to the philosophy of SETI-proponents throughout time: plenitude (the belief that Earth is not a special location: in current parlance, the principle of mediocrity), infinite cosmos, and a lack of a sense of history. It is this last point that he seems to try to prove in the paper, going through the ideas of philosophers for and against SETI from Greek times onwards.

There is certainly a place for a discussion of 2000 years of theology and philosophy about whether we are the only intelligent life in the universe. We can stand on the shoulders of all of this work that has come before us, and not worry about uselessly retreading the same ideological ground. That’s a sound and fair reason to be familiar with the long literature. However, using the existence of the literature itself as a counter-argument seems unfounded and rather mean-spirited.

Of course, as one of the slandered SETI-proponents, I had a pretty strong negative reaction to the paper. I felt that the Hart (1975) paper, equally pessimistic, actually engaged the issue with quantitative calculations and a scientific basis. I know that this paper was assigned to let us see the full spectrum of arguments and beliefs about ETI, positive and negative, and for that, it certainly has value. But I strongly disagree with the line of evidence that Tipler chose.

Tipler claims that those in favor of SETI are “always willing to suspend the physics of their day.” But in his conclusion, he points out that there have been scientific advances in the previous two decades which lend credence to SETI: the nebular hypothesis, the Urey-Miller experiment, the development of radio astronomy, and the steady-state theory of the universe. And then he disregards all of these ideas before really engaging with them, ending his paper by stating that the “philosophical and theological beliefs are the main motivations for the belief in ETI”.

In addition, I would contest that going through the history this way provides both pro-SETI and anti-SETI arguments, the pro-SETI ones being played down in this particular paper. For example, the reoccurrence of the idea of ‘plenitude’ throughout history is interesting and good to be aware of… but calling it a flaw of current SETI practitioners seems a bit silly when, again and again, it’s been correct (we aren’t the center of the universe, or solar system, or galaxy, or universe…). Is that a replacement for evidence? Of course not. But if we’re engaging in a philosophical discourse, it’s a reasonable fact to bring up.

Celestial spheres — 19th century woodcut (colorized) – “Fantastic Depiction of the Solar System” – in which some guy sticks his head out of the sphere of stars surrounding the Earth. Because of course all the stars are just on a celestial sphere surrounding the Earth. Why would they want to be anywhere else?

More politically, and less scientifically, the fact that SETI has been in the (European/Western/white/male*) public consciousness for so long is perhaps a reason to pursue it, instead of an argument against it. We’ve wanted to know the answers for so long, but now we have the tools to do so – does that not bring value of its own, divorced from any scientific results or merit?

Being aware of one’s biases is important, especially if you’re doing calculations that will a) later affect actual, observational work and b) can be heavily skewed by coming in with priors (looking at you, Drake Equation). Post-discussion, I am a little more accepting that there is a place for this paper. But only a little.

*someday, I would love to do a review of the history of the idea of extraterrestrial intelligence in other cultures – I’ll add it to the list!

Reaction to Tipler (1981)

In this brief document, Tipler reviews the history and development of the question of the plurality of worlds/extraterrestrial intelligence (ETI), from the earliest Greek thinkers through to the modern scientific era. This “meta” paper aims to justify the conclusion that the modern proliferation and acceptance of the ETI question is a consequence of developments in philosophical, theological, and empirical reasoning that been made throughout the centuries. He constructs a temporal chain linking advancements in thinking on the subject (supported by direct quotations of the primary sources), revised and modified with each new generation, that continues through to the current time. This paper is relevant to our discussion of SETI because it is one of few which attempt to comprehensively depict the status of thinking regarding the ETI question throughout history. In particular, the Greeks were separated into two schools, those who subscribed to plurality and plenitude, and those who objected; the Stoics, Pythagoreans, and Epicureans fell into the former camp, whereas the Platonists and Aristotelians the latter. Since the cosmology of Aristotle was highly influential on the thought of the medieval scholars, the early Church Doctors concluded the concept of plurality to be antithetical to Christian theology. Not until the time of the Copernican Revolution and the emergence of the Principle of Mediocrity did the idea that other worlds could be inhabited reemerge, and when it finally did, it did so with great force. One interesting feature of the history that this blogger did not as of yet know was the opinion held by the early Darwinists through to the modern evolutionary biologists, which turns out to be a pessimistic one on the grounds of the improbable series of millions of mutations which are requisite for the development of human-level intelligence. Tipler concludes the history at the end of the 20th century, when feelings regarding the ETI are positive due to advances in radio communication technology, theories of stellar and planetary formation and abiogenesis, and the contemporary cosmology which supported the thesis. Since this paper is not really a scientific paper in itself, but rather an exploration of the history of scientific and pre-scientific thought on the matter, it is fitting that a subsequent paper, to be written either presently or at some future point, should contain a continued account of the ETI question by way of a comprehensive treatment of SETI developments through the 21st century.

Why we might be the first (according to Hart)

In 1975, Hart published his paper “An Explanation for the Absence of Extraterrestrials on Earth,” where he methodically presents every well-known explanation for this (below) and then presents his own explanation: that mankind on our Earth is the first civilization in our Galaxy.

First, let me say that I appreciate this paper. I did not find any logical fallacies or leaps in an attempt to justify what he claimed. Instead, everything seemed well thought-out and matched with diction appropriate to his stance: that given the paucity of evidence and lack of other theories that sufficiently support this paucity, we should accept the last explanation (that we are the first).

As mentioned before, Hart methodically goes through possible explanations for why there are currently no creatures from other planets on Earth (he does mention that this could be wrong, but is improbable). The top explanations for this include physical explanations (space travel is infeasible), sociological explanations (the culture of the civilization does not want to visit other civilizations), temporal explanations (the civilizations will visit us but have yet to arrive because space travel takes time), and simply that others have visited us before but decided not to stay. Each of these theories is introduced, explained, and then debunked. As a spoiler alert, any explanation of why there are currently no alien species on Earth would have to hold for all civilizations that arise, and for the lifetime of these civilizations.

Space travel is in fact possible. This paper was published after the moon landing, so even at that time, Hart knew that humans could at least go to the moon. Any problems dealing with space travel can be overcome with technological advances or even just enough time and money.

Hart sufficiently (in my mind) eliminated sociological explanations completely. The unwillingness to explore or visit places (something not really seen in our society today) could be derived from culture or religion, but it is something that is most likely fluid with time; this unwillingness would be challenged over time with new generations. Even if thousands and thousands of generations of a civilization are in fact against visiting others, this outlook could not possibly be held (for forever) by every single civilization.

Temporal explanations are also dismissed quickly (dismissed as unlikely but plausible); even though space travel takes time, it would take us only 650,000 years to traverse the Galaxy. For this explanation to satisfy the fact that no alien species are currently on Earth, the first civilization with the desire and ability to travel space would have required 10 Gyr to arise AND for our civilization to arise as second about 1Myr later. Because of the unlikeliness of both of these being true, Hart dismisses this argument as possible, but highly unlikely.

Lastly, the theory that other species did visit but are no longer here is dismissed in the same why sociological explanations were eliminated. Although plausible for this to be true for one civilization, it is unlikely that all civilizations that visited decided to leave and never return (or died here, or died before being able to return).

Since there is no adequate explanation for why there are currently no alien species on Earth, Hart concludes that we are probably the first civilization in our Galaxy.

I personally enjoyed this paper mostly due to the lack of logical leaps and bounds. That being said, I think the conclusion is a bit pessimistic. Since we can’t really prove a negative (that there are no other civilizations) and since finding intelligent life would be amazing, we might as well keep looking! Hart includes in this conclusion that “an extensive search for radio messages from other civilizations is probably a waste of time and money,” which I completely disagree with (I might be biased). I think there is merit to these searches beyond just looking for aliens; they lead to valuable data and technologies, and even lead to some people joining the fields of astronomy and astrobiology.

Mediocrity and its Complex Relationship to ETI

Arguments for or against SETI rarely invoke the theological and philosophical evolution behind such reasoning. Tipler, in his 1981 article, presents an historical approach to the concepts of extraterrestrial intelligence (ETI). The debates and arguments for or against ETI periodically reappear throughout history, albeit slightly refashioned to reflect the principles of any contemporaneous philosophical movement. Tipler introduces two related philosophies: the principle of plenitude and the plurality of worlds. The principle of plenitude surmises that what can exist must exist, such that the Universe contains all forms of existence and intelligent life must exist in elsewhere. The plurality of worlds describes the Universe as infinite, producing an indefinite number of worlds which may harbor life. Tipler then provides the historical evolution of these ideas discussing the Greco-Roman debates, the Copernican revolution, the scholasticism of the Medieval period, the Enlightened support for the plurality of worlds, and finally the scientific view of these philosophies.

Of particular interest was to see the evolution of the concept of the plurality of worlds. Prior to the Copernican revolution, the Ptolemaic Universe reigned supreme and the plurality of worlds meant an infinite number of self-contained Universes with a central Earth. Tipler mentions that despite having the physics wrong, this particular thought is akin to the modern support of ETI by the principle of mediocrity. The principle of mediocrity states that we are not special in the Universe such that, given the existence of life on Earth, life exists in other Earth-like planets in the Universe. The Christian argument against ETI was also intriguing. St. Augustine wrote that the uniqueness of Christ meant there was no other intelligent life, else they would have a separate Christ for such a world. St. Thomas Aquinas argued that God was perfect; which was inconsistent with the plurality of worlds as this would be an act in vain if similar worlds existed and an act of imperfection if dissimilar worlds existed. It was not until the nineteenth century that the plurality of worlds was used to argue for ETI and against Christianity, as seen by the excerpt from Thomas Paine’s Age of Reason.

The post-nineteenth century pervasiveness of the plurality of worlds should be viewed through a critical scientific lens. It was through the scientific understanding of the geological, biological, and chemical evolution of the Earth that the principle of plenitude was rejected. Tipler repeats the arguments of William Whewell and Alfred Wallace, which were aligned with that of evolutionary biologists in that they argued the Earth was uninhabited for most of its history and, to our knowledge, the conditions for life and natural selection are incompatible with harsh environments elsewhere. Tipler, unfortunately, does not muse over the fact that a post-Enlightened society would use the plurality of worlds to fuel the imagination and foment the idea that humans are not alone in the Universe (i.e. It Came From Outer Space or the spoof, It Came From Planet Earth). Most surprising to this blogger was that modern evolutionists argued against ETI while physicists and theologists appeared to have no issues with it. While the scientific community, with achievements such as the development of radio communication and the Miller experiment, may have cemented the belief in the plurality of worlds and the search for ETI, the larger biological and chemical considerations appeared to be ignored during the late twentieth century. Despite the support the principle of mediocrity provides ETI, it is imperative to address all scientific concerns regarding ETI. Perhaps it is no surprise that astrobiology has recently developed to as a response to the complex scientific nature of the search for ETI.

Searching for 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 Sagan petition

In this brief one page petition, astronomer Carl Sagan (1934 – 1996) makes the case to begin a world wide coordinated program to search for signals from advanced civilizations. He mobilizes the support of numerous scientists across nations who have given this issue thought, some of whom have worked on it upwards of 20 years.

This petition seeks to galvanize support and financial assistance for the cause of establishing such a coordinated search. It also lays forth an interesting point about how noise and terrestrial contamination in the radio frequency is a growing problem and with further development of technology this would only worsen. Further, Sagan seeks to rebuke the extrapolation which decries the existence of extraterrestrial intelligence in the Milky Way galaxy due to the apparent absence of any signatures of such origin in the Solar System.

Such a ‘call to arms’ by a prominent astronomer and public scientific figure (Carl Sagan) is significant in its own right, only to be bolstered by the supported it garnered from the leading scientific minds of its time. I feel an effort such as this is more symbolic, and is meant to lobby for funding from the unsympathetic national funding agencies of the time.

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.

The Origin of Bracewell Probes

Bracewell (1960) asks the following question: How will civilizations of equal or greater intelligence try to initiate communication with nearby, unknown civilizations. He mostly elaborates on this by following semi-informal chains of thought. He argues that it is unlikely that they are running megawatt level transmitters pointed towards every nearby star that could possibly be hosting (or nurturing future) intelligent life. He instead argues that it is more feasible to search for life by sending out a swarm of armored, radio-transmitting probes to rapidly explore the nearby stellar neighborhood and a selection of further, promising target stars.

I think some of his reasoning is flawed here as one of his arguments against the interstellar transmitters is that they have a “dependence on our ingenuity in selecting the right star and the right wavelength”. It seems like he is suggesting that his probe swarm is a better idea than using a single transmitter. I would agree, but I think the swarm would be more comparable to using a network of many transmitters. Maybe the cost of building and maintaining thousands of transmitters continuously pointed at all of the targets is significant, but I would imagine the cost of launching thousands of autonomous probes would be pretty high as well.

He postulates that if there are already several advanced civilizations that know about each other, they will be connected and communicating, so we would only find evidence of the nearest community that is looking for us.

It is noted that by looking for probes within our own solar system we are in a way looking for signs that there are any advanced civilizations capable of reaching us. A cool idea. The probe within our solar system might only be a listener that reports back to home base via a star to star relay system.

This paper seems to have significance due to its documentation of several novel communication ideas and its introduction of extraterrestrial civilization network ideas.

Reaction to Bracewell (1960)

This paper describes a new search method and suggests a Schelling point for contacting extraterrestrial civilizations through detection of their emissaries in our solar system. Bracewell discusses the difficulty with maintaining an array of radio transmitters beaming signals to all nearby star systems in the style of Cocconi & Morrison (1959). The method for handling this problem is primarily thought-based. Bracewell argues that it would be more feasible to send probes to each system and wait for the emergence of a radio-capable technology in that system before relaying such information back to the advanced civilization. They further argue that due to the difficulties with sending macroscopic objects across interstellar distances, it would be worthwhile to outfit such a probe with advanced communicative and computational capabilities. This paper is novel for the suggestion that such “Bracewell” probes may exist and that it may be in our interest to search for evidence of them in our own solar system. He concludes that a null detection of such a probe would constitute evidence that either such probes are unfeasible or that the superior community is at such a distance that the possibility of successful contact with us is low. They admit the possibility of longer-lived, sustained civilizations which have bypassed the low mean lifespan they determine from their probability experiment. If we limit the search for Bracewell probes to simply searching for an object in the solar system with radio emission, it may be possible at some point in time to deem the search complete. However, advanced civilizations may have access to technologies which are unknown or undetectable to us, which would make their detection impossible to our instruments, thereby leading to an un-ending search with no definitive conclusion. Therefore, even in our modernity we cannot dislodge the primary idea of this paper. The obvious follow up to this paper would be targeted observational searches for the aforementioned radio emissions emerging anomalously and unnaturally within our own solar system. A Herculean project for the future would be a surface mapping of the majority of macroscopic objects in orbit around the Sun at high resolution and then employing machine-learning algorithms to hunt for sedentary, exposed Bracewell probes of perfect geometric dimension.