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SETI Requires a Skeptical Reappraisal


Peter Schenkel

Skeptical Inquirer Volume 30.3, May / June 2006

Early SETI efforts were marked by overly optimistic estimates of the probable number of extraterrestrial civilizations in our galaxy. In light of new findings and insights, it seems appropriate to put excessive euphoria to rest and to take a more down-to-earth view. Earth may be more special, and intelligence much rarer, in the universe than previously thought.

The possible existence of extraterrestrial intelligence (ETI) has always stirred the imagination of man. Greek philosophers speculated about it. Giordano Bruno was burnt on the stake in Rome in 1600, mainly because positing the likelihood of other inhabited worlds in the universe. Kant and Laplace were also convinced of the multiplicity of worlds similar to ours. In the latter part of the nineteenth-century Flammarion charmed vast circles with his books on the plurality of habitable worlds. But all these ideas were mainly philosophical considerations or pure speculations. It was only in the second half of the twentieth- century that the Search for Extraterrestrial Intelligence (SETI) became a scientifically underpinned endeavor. Since the late 1950s distinguished scientists have conducted research, attempting to receive intelligent signals or messages from space via radio-telescopes. Hundreds of amateur astronomers, members of the SETI-League in dozens of countries, are scanning the sky, trying to detect evidence of intelligent life elsewhere in our galaxy. SETI pioneers, such as Frank Drake and Carl Sagan, held the stance that the Milky Way is teeming with a large number of advanced civilizations. However, the many search projects to date have not succeeded, and this daring prediction remains unverified. New scientific insights suggest the need for a more cautious approach and a revision of the overly optimistic considerations.

The standard argument for the existence of a multiplicity of intelligent life runs like this: There are about 200 to 300 billion stars in our galaxy and probably hundreds of millions, maybe even billions of planets in our galaxy. Many of these planets are likely to be located in the so-called “habitable zone” in relation with their star, enjoying-as Earth-favorable conditions for the evolution of life. The physical laws, known to us, apply also to the cosmos, and far-away stellar formations are composed of the same elements as our solar system. Therefore, it is assumed, many should possess water and a stable atmosphere, considered to be basic requisites for the development of life. Such planets must have experienced geological and biological processes similar to those on Earth, leading to the development of primitive life organisms. Then, in the course of time, following a similar course of Darwin’s theory of natural selection, these evolved into more complex forms, some eventually developing cognitive capacities and-as in our case-higher intelligence.

In other words, it is maintained, our solar system, Earth, and its evolution are not exceptional cases, but something very common in our Milky Way galaxy. Consequently it must be populated by a huge number of extraterrestrial civilizations, many of them older and more advanced than ours.

Considering the enormous number of stars and planets, these seem like fair and legitimate assumptions. It indeed appears unlikely that intelligence should have evolved only on our planet. If many of these civilizations are scientifically and technologically superior to us, contact with them would give mankind a boost in many ways.

These optimistic views are based mainly on the famous Drake formula N=RfpnefifjfeL. It considers the formation of stars in the galaxy, the fraction of stars with planetary systems, the number of planets ecologically suited for life, the fraction of these planets, on which life and intelligent life evolves, and those reaching a communicative stage and the length of time of technical civilizations. On the basis of this formula it was estimated that a million advanced civilizations probably exist in the galaxy. The nearest one should be at a distance of about 200 to 300 light-years from Earth. German astronomer Sebastian von Hoerner estimated a number between ten thousand and ten million such civilizations.

But because of many new insights and results of research in a number of scientific fields, ranging from paleontology, geology, biology to astronomy, I believe this formula is incomplete and must be revised. The early optimistic estimates are no longer tenable. A more realistic and sober view is required.

I by no means intend to discredit SETI; the search for extraterrestrial intelligent life is a legitimate scientific endeavor. But it seems prudent to demystify this interesting subject, and to reformulate its claims on a new level, free of the romantic flair that adorns it.

Years ago, I readily admit, I myself was quite taken in by the allegations that intelligence is a very common phenomenon in the galaxy. In books, articles, and on radio and television I advocated the idea that our world, beset by problems, could learn a lot from a civilization more advanced than ours. But, in the meantime, I became convinced that a more skeptical attitude would do reality better justice. There are probably only a few such civilizations in the galaxy, if any at all. The following considerations buttress this rather pessimistic appraisal.

First of all, since project OZMA I in 1959 by Frank Drake, about a hundred radio-magnetic and other searches were conducted in the U.S. and in other countries, and a considerable part of our sky was scanned thoroughly and repeatedly, but it remained disappointingly silent. In forty-six years not a single artificial intelligent signal or message from outer space was received. Some specialists try to downplay this negative result, arguing that so far only a small part of the entire spectrum has been covered, and that more time and more sophisticated equipment is required for arriving at a definite conclusion. Technological and economic criteria may thwart the possibility of extraterrestrial civilizations beaming signals into space over long stretches of time, without knowing where to direct their signals. Or, they may use communication methods unknown to us. Another explanation is that advanced ETI may lack interest in contacting other intelligences, especially those less developed. The argument of the Russian rocket expert Konstantin Tsiolkovski is often quoted: “Absence of evidence is not evidence of absence.”

But neither of these arguments, which attempt to explain why we have not received a single intelligent signal from space-is convincing. True, future search projects may strike pay dirt and register the reception of a signal of verified artificial origin. But as long as no such evidence is forthcoming, the possibility of achieving success must be considered remote. If a hundred searches were unsuccessful, it is fair to deduce that estimates of a million or many thousands ETI are unsustainable propositions. As long as no breakthrough occurs, the probability of contact with ETI is near to zero. The argument that advanced extraterrestrials may not be interested in contact with other intelligences is also-as I will show-highly implausible.

Second, as recent research results demonstrate, many more factors and conditions than those considered by the Drake formula need to be taken into account. The geologist Peter D. Ward and the astronomer Donald Brownlee present in their book Rare Earth a series of such aspects, which turn the optimistic estimates of ETI upside down.

According to their reasoning, the old assumption that our solar system and Earth are quite common phenomena in the galaxy needs profound revision. On the contrary, the new insights suggest, we are much more special than thought. The evolution of life forms and eventually of intelligent life on Earth was due to a large number of very special conditions and developments, many of a coincidental nature. I'll mention only some that seem particularly important: The age, size, and composition of our sun, the location of Earth and inclination of its axis to it, the existence of water, a stable oxygen-rich atmosphere and temperature over long periods of time-factors considered essential for the evolution of life-and the development of a carbon-based chemistry. Furthermore an active interior and the existence of plate tectonics form the majestic mountain ridges like the Alps, the Himalayas and the Andes, creating different ecological conditions, propitious for the proliferation of a great variety of species. Also the existence of the Moon, Jupiter, and Saturn (as shields for the bombardment of comets and meteorites during the early stages of Earth). Also the repeated climatic changes, long ice ages, and especially the numerous and quite fortuitous catastrophes, causing the extinction of many species, like the one 65 millions years ago, which led to the disappearance of dinosaurs, but opened the way for more diversified and complex life forms.

Though first primitive life forms on Earth, the prokaryotic bacteria, evolved relatively rapidly, only about 500 million years after the cooling off of Earth’s crust and the end of the dense bombardment of meteorites and comets, they were the only lifeforms during the first two billion years of Earth’s 4.6-billion-year history. Mammals-including apes and man-developed much later, only after the extinction of the dinosaurs 65 million years ago. The first human-like being, the Proconsul, emerged in the Miocene Period, just about 18 million years ago. The Australopithecus, our antecessor, dates only 5 to 6 million years. In other words, it took almost 4 billion years, or more than 96 percent of the age of Earth, for intelligence to evolve-an awfully long time, even on the cosmic clock.

In this regard we should note also the caveat of the distinguished biologist Ernst Mayr, who underscored the enormous complexity of human DNA and RNA and their functions for the production of proteins, the basic building blocks of life. He estimated that the likelihood that similar biological developments may have occurred elsewhere in the universe was nil.

The upshot of these considerations is the following: Because of the very special geological, biological, and other conditions which propitiated the evolution of life and intelligence on Earth, similar developments in our galaxy are probably very rare. Primitive life forms, Ward and Brownlee conclude, may exist on planets of other stellar systems, but intelligent life, as ours, is probably very rare, if it exists at all.

Third is the so called “Fermi Paradox” another powerful reason suggesting a skeptical evaluation of the multiplicity of intelligence in the galaxy. Italian physicist Enrico Fermi posed the annoying question, “If so many highly developed ETIs are out there, as SETI specialists claim, why haven't they contacted us?” I already expressed great doubt about some of the explanations given to this paradox. Here I need to focus on two more. The first refers to the supposed lack of interest of advanced aliens to establish contact with other intelligent beings. This argument seems to me particularly untrustworthy. I refer to a Norwegian book, which explains why the Vikings undertook dangerous voyages to far-away coasts in precarious vessels. “One reason,” it says, “is fame, another curiosity, and a third, gain!” If the Vikings, driven by the desire to discover the unknown, reached America a thousand years ago with a primitive technology, if we-furthermore-a still scientifically and technically young civilization, search for primitive life on other planets of the solar system and their moons, it is incredible that higher developed extraterrestrial intelligences would not be spurred by likewise interests and yearnings. One of the fundamental traits of intelligence is its unquenchable intellectual curiosity and urge to penetrate the unknown. Elder civilizations, our peers in every respect, must be imbued by the same daring and scrutinizing spirit, because if they are not, they could not have achieved their advanced standards.

A second argument often posited is that distances between stars are too great for interstellar travel. But this explanation also stands on shaky ground. Even our scientifically and technically adolescent civilization is exploring space and sending probes-the Voyager crafts-which someday may reach other stellar systems. We are still far from achieving velocities, near the velocity of light, necessary for interstellar travel. But some scientists predict that in 200 or 300 years, maybe even earlier, we are likely to master low “c” velocities, and once we reach them our civilization will send manned exploratory expeditions to the nearest stars. Automatic unmanned craft may be the initial attempts. But I am convinced that nothing will impede the desire of man to see other worlds with his own eyes, to touch their soil and to perform research that unmanned probes would not be able to perform. Evidently, civilizations tens of thousands or millions of years in our advance will have reached near c velocities, and they will be able to explore a considerable part of the galaxy. Advanced ETI civilizations would engage in such explorations not only out of scientific curiosity, but in their own interest, for instance for spreading out and finding new habitats for their growing population, or because of the need to abandon their planet due to hazards from their star, and also because with the help of other civilizations it may confront dangers, lurking in the universe, more successfully than alone. The Fermi Paradox should therefore put us on guard, and foster a sound skepticism. Lack of interest in meeting a civilization such as ours is the least plausible reason why we have not heard from ETI.

A little mental experiment illustrates this point. Carl Sagan held once that intelligent aliens would visit Earth at least once every thousand years. But such visits have not taken place. Even extending this period to a million years, we fare no better. Let us assume an extraterrestrial craft landed on Earth any time during the era of the dinosaurs, lasting about 140 million years. It is only logical to assume the aliens would have returned at reasonable intervals to study our world and these fascinating animals, but also to find out if any one of them evolved the capability of reasoning, higher math, and building a civilization. There would have been reason for much surmise. According to paleontologists, Drake stresses, the dinosaur sauronithoides was endowed with such a potential. It was a dinosaur resembling a bird of our size and weight and possessing a mass of brain well above average, and, Drake speculates, if it had survived for an additional ten or twenty million years, it might have evolved into the first intelligent being on Earth. But it didn't happen, because the dinosaurs went extinct due to a cosmic catastrophe. When Homo australopithecus, then Homo faber and habilis, and lastly Homo sapiens evolved, shouldn't that have provoked on the part of visiting extraterrestrials a high level of interest? But no such visits are recorded. Only a few mythological, undocumented and highly suspect accounts of alleged visiting aliens exist. It is fair to assume, if advanced aliens had visited Earth during the past 200 million or, at least, during the past 16 million years, they would have left some durable, indestructible and recognizable mark, probably on the moon. But nothing has been detected. The most likely explanation? No such visits took place! There are no advanced extraterrestrial civilizations anywhere in our vicinity. If they existed, they already would have responded to our world’s television signals, reaching some 60 light-years into space-another reason invalidating the claim that our galaxy is teeming with intelligence.

Another argument supporting the skeptical point of view sustained here is the fact that none of the detected planets around other stars comes close to having conditions apt for creating and sustaining life. Since Michel Mayor’s Swiss group discovered the first planet outside our solar system around the star 51 Pegasi ten years ago, about 130 other planets have been identified within a distance of 200 light-years. Research results show that most are of gaseous composition, some many times the size of Jupiter, some very close to their stars, very hot and with extremely rapid orbital cycles. So far, not one presents conditions favorable for the development of even the most primitive forms of life, not to speak of more complex species. Again it may be argued that only a very tiny fraction of planets were surveyed and future research might strike upon a suitable candidate. This may well be, and I would certainly welcome it. But so far the evidence fails to nourish optimistic expectations. The conditions in our universe are not as favorable for the evolution of life as optimists like to think.

Even if water or fossils of microorganisms should be found underneath the surface of Mars, the importance of such a finding for the theory of a multiplicity of inhabited worlds would be insignificant. Some astronomers think that Titan, the famous moon of Saturn, may have an ocean, possibly of methane. Primitive life forms may exist in it, but this remains to be seen. Even if it does, the evolutionary path from such primitive forms to complex life as human beings is-as we have seen-a long one, studded with a unique sequence of chance and catastrophes.

I am not claiming that we are probably the only intelligent species in our galaxy. Nor do I suggest that SETI activities are a waste of time and money. Though, so far, they have failed to obtain evidence for the existence of ETI, they enrich man’s knowledge about the cosmos in many ways. They helped develop sophisticated search techniques, and they contribute decisively to the perception of man’s cosmic destiny. Carl Sagan and Frank Drake, the two most distinguished pioneers of SETI, did groundbreaking work. That their efforts and those of other dedicated SETI experts on behalf of this great cause are tinged with a dash of too optimistic expectation is understandable and profoundly human.

However, in the interest of science and sound skepticism, I believe it is time to take the new findings and insights into account, to dampen excessive SETI euphoria and to adopt a more pragmatic and down-to-earth stand, compatible with facts. We should quietly admit that the early estimates-that there may be a million, a hundred thousand, or ten thousand advanced extraterrestrial civilizations in our galaxy-may no longer be tenable. There might not be a hundred, not even ten such civilizations. The optimistic estimates were fraught with too many imponderables and speculative appraisals. What is required is to make contact with a single extraterrestrial intelligence, obtaining irrefutable, thoroughly verified evidence, either via electromagnetic or optical waves or via physical contact, that we are not the only intelligent species in the cosmos. Maybe an alien spacecraft, attracted by our signals, will decide to visit us some day, as I surmised in my novel Contact: Are We Ready For It? I would be the first one to react to such a contact event with great delight and satisfaction. The knowledge that we are not alone in the vast realm of the cosmos, and that it will be possible to establish a fruitful dialogue with other, possibly more advanced intelligent beings would mark the biggest event in human history. It would open the door to fantastic perspectives.

But SETI activities so far do not justify this hope. They recommend a more realistic and sober view. Considering the negative search results, the creation of excessive expectations is only grist to the mill of the naysayers-for instance, members of Congress who question the scientific standing of SETI, imputing to it wishful thinking, and denying it financial support. This absolutely negative approach to SETI is certainly wrong, because contrary to the UFO hoax, SETI (as UCLA space scientist Mark Moldwin [2004] stressed in a recent issue of this magazine) is based on solid scientific premises and considerations. But exaggerated estimates fail to conform to realities, as they are seen today, tending to backfire and create disappointment and a turning away from this fascinating scientific endeavor. The dream of mankind to find brethren in space may yet be fulfilled. If it is not, man should not feel sorry for his uniqueness. Rather that circumstance should boost the gratitude for his existence and his sense of responsibility for making the most of it.


Peter Schenkel

Peter Schenkel is a retired political scientist and author of many books, among them three on extraterrestrial intelligence: ETI: A Challenge for Change, The Message from Yon and Contact: Are We Ready For It? Schenkel is primarily interested in the question of what contact with advanced aliens would mean to mankind. He is a member of the Interplanetary Society and Chairman of the group Prociencia in Ecuador.