THE PRINCIPLE OF MEDIOCRITY

CHAPTER 8C

THE PRINCIPLE OF MEDIOCRITY

Even apart from the wisdom of making contact, we have seen why assuming the principle of mediocrity serves the opponents of SETI well. SETI depends on the possible transmission of signals by extraterrestrials. That is the extent of the search: To listen to the universe with radio telescopes in the hope that an artificial combination of pulses may be identified. And then, of course, we would try to decipher such a signal and perhaps to respond, thereby initiating the most extraordinary communication in the history of the human species. That is the program of SETI. Now, to show the urgency of the matter, the principle of mediocrity is invoked: There may well be a whole club of civilizations out there, and with just a little effort we might be able to join them. But if we assume the principle of mediocrity very literally, and consider the age of the galaxy, we must wonder why the extraterrestrials are not here.

Quite apart from such concerns, this principle deserves examination. Let us begin with the motivation for invoking it. What could we have learned from the Copernican revolution in the first place? Surely not that we are average. At best that we had no reason to assert that we are special. This is not the same as to say that we are not special, for it may well turn out that we are, even if we have no reason at this time to think so. I may have no reason to assert that the respectable looking man walking by my window is a criminal, even though perchance he might indeed be one. At most, then, we should simply gain a healthy skepticism about claims of human privilege.

Moreover, although we have now reasons to believe that the sun is an average star and that the Earth is not the center of the universe, we cannot say that we have similar reasons about our own standing in the realm of life. In the one relevant aspect--intelligence--we are clearly not average in the domain that we have been able to observe.

The principle of mediocrity is prompted, I suspect, by the notion that our belief that the Earth was the center of the universe and that we were the pinnacle of creation sprung from some primitive anthropocentric view of the world later reinforced by religion. Remove the notion of man at the center of things, and it becomes imperative to face up to our average nature. But however convenient for their religion, our ancestors did have good reasons for thinking that the Earth was the center of the universe. It took a lot of ingenuity and good timing to overcome devastating objections to the idea of the motion of the Earth (cf. the treatment of the Tower Argument in Chapter 3). Nor did they think that the Earth was at the center of the universe because it was special in any commendable way. On the contrary, the heavens were eternal, and unchanging, our example of perfection. Change and corruption could take place only in the lowly Earth. Copernicus himself resurrected the Pythagorean claim that the sun should be at the center of the universe since it was obviously so much nobler a body than the Earth.

The existence of extraterrestrial intelligence should thus be discussed without the burden of the principle of mediocrity. On the other hand, the principle of mediocrity cannot be used by the opponents of SETI either. The arguments against ETIs can no longer assume that if there are any, they should be so strikingly similar to us that we can make reliable, quasi-probabilistic guesses about them based on intuitions about ourselves. To be acceptable, the arguments must include a wide range of considerations from biology and space science. With this in mind, we need to explore two questions at both ends of the issue. First: how is it possible that ETIs exist but we have no evidence for them? As we have seen, the answer to this first question is that ETIs may exist without our knowing about them. And second: what events or processes could make it possible for our technological civilization to be the only one in the galaxy?

But before we embark on the task of answering this second question, it is useful to cast a critical eye on some practices that reflect on the field of SETI. One of them is the use of what some proponents of SETI call "subjective probability," which they think it permits them to arrive at their rosy conclusions about the chances for the existence of ETI. According to T. Fine, the subjective interpretation of probability "maintains that probability statements are derived through a largely unassisted process of introspection and are then applied to the selection of optimal decisions or acts."[1] Furthermore this subjective view "encourages the holder to fully use his informal judgment, beliefs, experience in arriving at probability estimates."[2] Although personal, such estimates are presumably not arbitrary because "there are reasonable axioms of internal consistency between assessments and constraints that force the user to learn from experience in a reasonably explicit way."[3]

This view of probability, together with the principle of mediocrity, has indeed encouraged some SETI enthusiasts to make highly optimistic pronouncements about the likelihood of planets with life, intelligence and technological civilizations, based on the fact that the Earth has life, intelligence and a technological civilization. But can these scientists justify what amounts to giving a statistical distribution from only one case?

If I think it is likely that I will survive intact a jump from the Golden Gate Bridge because I cannot believe that harm can come to me at this stage of my life, my estimate will be as wrong as it is arbitrary. Nonetheless the constraints of the experience (serious injury or death) will most definitely be inconsistent with my assessment. And if I do survive, such inconsistency will force me to learn a valuable lesson. Even so the arbitrariness of my initial assessment is not thereby removed.

The intuition behind subjective probability is that a scientist who has already learned from experience, and who is in a situation to which his expertise is relevant, may come up with reliable hunches as to what is the right action to take. Indeed we may measure such probability by determining how much he is willing to bet on a course of action over its alternatives. I think that this notion of probability has serious problems even under the best of circumstances. But in any event it does not apply in the case of SETI. On this subject we have learned nothing from experience because we have had no experience to learn from, nor can we use our expertise about the Earth because our theories are not yet developed enough to make decent guesses about how representative the Earth is. In a few years we are likely to, if we continue to increase the sophistication of telescopes in orbit. We may begin by detecting terrestrial planets at the right distance from their suns to have liquid water; and then we might be lucky enough to find one or more such planets with the right spectrum in their atmosphere (e.g., appropriate percentages of oxygen, methane, etc.) to make us believe that we have detected the “signature” of life. But so far we do not quite have instrumentation that refined. And we do not know if, once we have it, we will ever find such planets.

A related misuse of probability comes in the practice of splitting the difference. The optimist will use his subjective probability to estimate that in every mature planetary system there will be at least one planet with life (the probability of life is one), the pessimist will say that the probability is zero because life could have arisen only on Earth. And then there are those congenial types who declare that the truth must fall somewhere in between, and so decide that a probability of one half (or one fourth or one sixteenth) is a "conservative" or "reasonable" estimate.

Imagine, however, that I am given a photograph of a building that could be either Fort Knox or an empty warehouse, and that I am asked to estimate how much wealth that building contains. Suppose that I know that there are 200 billion dollars in gold in Fort Knox. And now, since I have no idea which building it is, I split the difference and estimate that there are 100 billion dollars in it. Whichever building it turns out to be, my estimate will be off by 100 billion, not a small mistake. In the case of ETI our estimates of probability should be based on our knowledge of the universe, not on reaching a compromise between the uneducated guesses of interested parties. As space science advances, we will have more insightful things to say about the chances for extraterrestrial life. For extraterrestrial intelligence we will have to take a few additional steps.

To see what those steps are, in the next posting I will discuss briefly the second question listed above: What events or processes would make it possible for our technological civilization to be the only one in the galaxy?

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[1] T. Fine, “Nature of Probability Statements in Discussions of the Prevalence of Extraterrestrial Intelligence,” in C. Sagan, Communication with Extraterrestrial Intelligence, The MIT Press, 1973, p. 360

[2] Ibid.

[3] Ibid.

THE SEARCH FOR EXTRATERRESTRIAL INTELLIGENCE

CHAPTER 8a

THE SEARCH FOR EXTRATERRESTRIAL INTELLIGENCE

Are we alone in the universe? Is it really possible that no sentient being on a faraway planet ever contemplated the stars and felt awe? That only humans ever wondered about the nature of the universe, or pondered whether similar beings might be asking similar questions? In the view of some people it is extremely parochial to suppose that we are alone – one more instance of the syndrome that once made us believe that the Earth was the center of the universe. According to those people, we have no more reason now to believe that we must be the pinnacle of creation than we had once upon a time to believe that the Earth was so special.

Thus begins the reasoning that takes them to the conclusion that extraterrestrial intelligences (ETI) are likely to exist, a presupposition without which the search for them (SETI) would make little sense. This does not mean, however, that the proponents of SETI advocate the building of starships at all. Indeed, many of its practitioners believe that star travel is not very likely, at least not for a very long time. They urge instead that we scan the skies for the radio signals of other advanced species.

Success in their mission is seen by SETI proponents as of such extraordinary importance that at some point they proposed Project Cyclops, a very elaborate, and expensive, arrays of radio telescopes to carry it out. Their proposals were not received with much sympathy by those who control the purse strings, and thus over the years they had to content themselves with ever meager levels of support (from tens of billions for the proposed Cyclops[1] to less than two million per year in actual funding, and then to nothing). But what seemed like a deplorable situation to them appeared far too exorbitant to opponents of SETI. For in the view of such opponents, the very foundation of SETI, that extraterrestrial intelligence probably exists, was not only unwarranted but preposterous. U.S. Senator William Proxmire gave the program his Golden Fleece Award, for the most inane waste of taxpayers’ money. Eventually NASA cut SETI of its budget altogether. But the program lives on, bolstered by the privately-funded SETI Institute and by the ingenuity and good will of many contributing scientists.

Ironically, the opposition to SETI is buttressed by the key assumption of the SETI proponents themselves: Carl Sagan’s so-called "Principle of Mediocrity."[2] The Principle of Mediocrity asserts that the sun is a typical star in having a planet like the Earth in which life could arise, that terrestrial life is typical in having produced intelligence, and that human intelligence is typical in giving rise to a technological civilization.

Presumably Copernicus taught us humility when he argued that the Earth was not privileged but average, and later astronomy reinforced the lesson by discovering that the sun itself was merely an average star in an average galaxy. By extending the Copernican lesson, the reasoning goes, we should learn to be humble about our own position in the scheme of life. The principle of mediocrity thus purports to recognize that humanity and the conditions that have brought it about are pretty much average. In their arguments, the opponents of SETI stretch this principle slightly to add that a technological civilization is typically expansionist. As a result they are able to produce a variety of "impossibility proofs" against the existence of extraterrestrial intelligence.

In the pages that follow I will examine the justification of SETI in light of this controversy. This examination, I trust, will lead naturally to a discussion of some of the important philosophical assumptions made by SETI in estimating our ability to communicate with ETIs if they exist, a very interesting issue in its own right. Let me begin with a brief account of the reasons for optimism with respect to SETI. I will then proceed with an explanation of how such optimism actually sets up the impossibility proofs.

MOTIVATION FOR SETI

First there is the incredibly large number of stars. This galaxy alone contains over 100 billion, and there may be at least 100 billion galaxies. We do not know how many of those stars have planetary systems, but most theories of star formation would encourage us to believe that planets are rather common, at least in the average stars of what is called the Main Sequence (of star evolution) such as our own Sun. As we saw in Chapter 5, this optimism has been born out by the recent discovery of over 200 Jupiter-planets and a few rocky (“terrestrial”) planets around other stars, as well as by the very credible evidence for forming planetary systems around young stars.

All this has some very convenient aspects for SETI. One is that the average stars may live longer than ten billion years. Since it has taken about four and half billion years to produce a technological civilization on this planet, it is encouraging to know that the stars that live long enough are also the ones most likely to have planets in the first place.

From here on matters generally become far more speculative. Those who are in the business of making probability estimates for SETI often use the so-called "Drake Equation" (named after Frank Drake, the contemporary astronomer who first proposed it). According to this equation, the number of intelligent civilizations in this galaxy is equal to the product of the rate of star formation, the percentage of favorable stars, the number of planets around such stars, the fraction of Earth-like planets among those, the fraction of such planets in which life begins, the fraction of planets with life in which intelligence develops, and then the number of planets with intelligence in which technological civilizations arise. This product is then multiplied by the average longevity of a technological civilization.

We believe that in this galaxy the rate of star formation is about twenty per year. And the existence of other planets is now established, although not the rate of planet formation. But as we progress through Drake's equation, the estimates are not as well grounded. This situation does not prevent SETI enthusiasts from assigning optimistic probabilities to every factor. One often hears, for example, that once life begins on a planet, intelligence is very likely to result eventually. Such optimism surely deserves examination.

Impossibility Proofs: A Summary

The most interesting impossibility proof against the existence of ETIs is the famous question by Enrico Fermi, which assumed an early version of Sagan’s Principle of Mediocrity: “Where are they?” With such good omens for the existence of ETIs, they should be everywhere, including our own solar system, watching us, making contact with us, and so on. But we don’t see them, hear them, or in any other way detect them. This of course assumes also that all the talk about UFOs, alien abductions, and the like is a delusion, or at best an illusion. So, if aliens do exist, they should be all over the place, but we have no trace of them; therefore, they do not exist.

SETI proponents like Bernard Oliver, however, argued that the reason we don’t see them is because star trekking takes too long, since the distances between solar systems are so vast. So no one can really be expected to undertake such a trip. That is why we need to resort to electromagnetic signals as a means to search for ETIs, as well as a means for communicating with them if we ever find them.

We have seen in the previous two postings why Oliver’s case is not as good as he might have thought. We cannot rule out the possibility of travel between the stars, either by traveling space colonies, or by ships that approach the speed of light. It is also physically possible, as we have seen, that warp engines might actually allow us to go faster than light (cf. Alcubierre[3]). Nevertheless we cannot affirm it either. This result weakens the impossibility proof some, but not completely: It still manages to cast serious doubt upon the existence of very advanced civilizations.

Some opponents of SETI have brushed Oliver’s response aside for a different reason. Even if star trekking takes too long for living things, an advanced civilization could still send self-reproducing machines to report about every interesting solar system, including ours. All they need do is send one. Once it gets to the backyard of another star, it will make copies of itself, which will then move on to other stars and do likewise. This self-reproducing probes will reproduce and cover any galaxy, give or take a few million years, the way a bacteria culture ends up taking over a petri dish. Thus Fermi’s question arises all over again: “Where are they?”

I do not believe that this impossibility proof succeeds. It is based on John von Neumann’s “proof” for the possibility of self-reproducing automata. I make two main points against such proof as the basis for exploring the galaxy in the fashion considered here. The first is that the conditions that make von Neumann’s proof plausible are not likely to be met under the exigencies of exploration. The second is that von Neumann assumes that a genome is like a computer program, and I think that such an assumption is unwarranted. I then criticize some clever proposals to apply von Neumann’s ideas to interstellar exploration (e.g. with space probes based on collections of nanorobots). Unfortunately I will have to ask my readers’ forgiveness for not providing the details of my arguments. As it turns out, such details will appear in my contribution to a book on imaging outer space that will be published in December. I promised the editor, Prof. Alexander Geppert, that I would not post the article, since the publisher would be naturally upset were my chapter to appear in this blog right before the publication of the book.

I will, however, provide a little plug for the book, since it is likely to interest most of you (I do not share in the profits). The title of my chapter is “Self-Reproducing Automata and the Impossibility of SETI.” The title of the book is Imagining Outer Space, and the editor is Alexander C. T. Geppert, as I said. The publisher will be Palgrave MacMillan

You can find out more information about the volume by clicking on this link:

http://www.palgrave.com/products/title.aspx?PID=364196

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[1] For a descripton of Cyclops see Bernard Oliver’s description in Carl Sagan, ed., Communication with Extraterrestrial Intelligence, MIT Press, 1973, pp. 279-301. The report on the project was published by NASA: CR 11445.

[2] Carl Sagan, Pale Blue Dot, Random House, 1994, pp. 39, 372-73.

[3] It seems that I left out the reference to Alcubierre’s seminal paper in my previous posting. It is as follows: Miguel Alcubierre (1994): "The Warp Drive: Hyper-Fast Travel within General Relativity". Classical and Quantum Gravity, 11: L73-L77.