Are we alone?

Are we alone, and do we care?

by Massimo Pigliucci

“Until they come to see us from their planet, I wait patiently. I hear them saying: Don’t call us, we’ll call you.”
(Marlene Dietrich, Marlene Dietrich’s ABC)



Next to the question “where do we come from?” undoubtedly the one investigating the possibility of someone else being “out there” is the most philosophically intriguing, and it certainly is even more frustrating for a mind inclined toward scientific inquiry. Possibly humans started asking this question since they looked up at the stars for the first time, but more likely we thought of ET only much later, after we realized that stars and planets were likely to be worlds like our own Sun and Earth. In Western society for a long period it was the Church’s dogma that the celestial spheres could not be inhabited by anything less perfect than angels, and many lost their lives at the stakes for daring to question such an assumption, Giordano Bruno (1548-1600) being the most famous example. Fortunately, today not only scientists, but writers and movie directors can freely speculate on what life would be on another planet, what we would do in encountering another form of life, and how boldly we would go about the whole business.

The story of the modern SETI (search for extraterrestrial intelligence) has been recanted in several places (e.g., Casti 1989) , and I will not repeat here the details of the daring enterprise of Frank Drake, the radioastronomer who started Project Ozma, the first such attempt back in 1960; or how we came about to send the only radio message ever consciously broadcast to potential extraterrestrial listeners from the Arecibo radiotelescope in 1974. Current, more sophisticated and faster searches are going on thanks mostly to private funding. Depending on their outcome, this whole discussion might be totally irrelevant any day, or perhaps remain forever as current as it is now (the secret wish of every writer, yet the nightmare of the scientist).

What I would like to focus on here instead are the following points: first, how do we approach the question of the existence of extraterrestrial life from a rational, scientific standpoint? Second, how come that some parties involved in the debate take it as a given that the answer is positive, while others are equally unmovable from an uncompromisingly negative perspective? Third, does it make sense that we are mostly trying to listen, instead of broadcasting? And, are our feeble attempts at taking the initiative a realistic scientific enterprise, or little more than a good topic for party conversation? Fourth, is the whole enterprise worth our attention and, especially, money?

Is it a scientific problem? The omnipresent Drake equation

Is the pursuit of ET a scientific question, or should we leave it to philosophers, religious authorities, or better yet, the writers of Star Trek and 2001? One of the cardinal points of the scientific method as expounded by Descartes (1637) is that any broad question such as this has first to be broken in several components. This process of atomization, or reductionism, has of course limits of its own (e.g., Brandon 1996) . Yet, it has been incredibly successful in all realms of modern science and technology, and it is still our best bet to attack any complex problem. But how does one partition the search for extraterrestrial intelligence into digestible bites? There is a lot of contention about this point, but I am afraid that any serious discussion of the topic just cannot avoid considering in detail the famous (some would say infamous) “Drake equation”. This equation was proposed by the same Frank Drake who initiated the experimental approach to the problem of SETI, as a way to pin down the difficulties of considering the question from a theoretical viewpoint. So, here it goes:

                                                                    (eq. 1)

where: N is the number of advanced communicating civilizations in our galaxy; R is the per year rate of formation of stars in the Milky Way; f_p is the proportion of those stars that have planetary systems; n_e is the number of planets in a given system having conditions suitable for the origin of life; f_l is the probability of life actually originating on one of these planets; f_i is the probability that that life will evolve to the status of “intelligent”; f_c is the likelihood that that intelligent life will also be able to communicate outside its solar system; and L is the time in years that ET actually spends trying to communicate. As Casti pointed out (1989) , all major scientific disciplines are involved or called into action by the equation, from physics and astronomy, to geology and biology, to technology and social sciences.

            Before we can briefly discuss what do we actually know, or can guess, about each term in the Drake equation, let me raise one very serious criticism to its current form. The multiplication signs interspersed among the quantities are equivalent to one powerful and very dubious assumption: that each term is independent of the others. In probability theory, the only time one is allowed to multiply two fractions or likelihood estimates is when the two events to which they refer happen independently of each other. For example, if you flip a coin twice, the probability to get “head” at the first attempt is half, i.e., 0.50. The probability to get “head” the second time is still 0.50, because the coin doesn’t have a “memory” of what happened in the previous trial. In other words, the second outcome is not influenced by the first one in any manner. Therefore, the two events are independent, and we can simply multiply their probabilities to obtain the joint likelihood that the ensemble of the two trials will yield “head” in both cases: P = 0.5 * 0.5 = 0.25. But what if the two events are not independent? What if the outcome of the first one somehow influences the result of the second one? For example, let us assume that we are dealing a hand of poker. The probability that the first card handed out be an ace is four out of 52 (because there are four aces in a deck of 52 cards). Now, what is the probability that the second card is also an ace? It is 3/51, because there are 51 cards left, and only three of them are aces. In order to determine the probability of the second event, however, we had to know what the first one was. If, for example, the first card had been a five, then the probability of getting an ace as a second card would have been higher, 4/51 to be precise. This because there would still be 51 cards left in the deck, but now four, not three of them were aces. It is clear that the probability of the second event depends on the outcome of the first one; in statistical terms, we are dealing with conditional probabilities.

Now, it is conceivable that some of the terms in the Drake equation are indeed independent from each other. For example, the galaxy-wide rate of formation of new stars and the likelihood for a given star to have a planetary system are probably not connected to each other. On the other hand, the number of planets suitable to host life and the likelihood that life actually originates on one of these planets must be intimately connected, since they both depend on the parameters of the planet’s orbit in relation to the type of star it orbits around (but they are not one and the same, because the fact that a planet could host life does not necessarily imply that it will). Therefore, the Drake equation should be rewritten accounting for the lack of independence of some of its terms:

                                                              (eq. 2)

This particular version embodies a different set of assumptions from Drake’s. Namely, the terms f_c through f_p are assumed to be hierarchically nested within each other (the | indicates conditional probability), with the likelihood of the next term being dependent on the previous one; R and L, on the other hand, are considered independent of each other and of the nested set of conditional probabilities. Obviously, one could come up with yet another model, embedding a distinct set of assumptions. My point is that this source of variation (and discussion) in the Drake equation has not being extensively explored.

Now we can turn to the discussion of each single term, with the understanding that its actual value may in fact be directly connected to the value of other terms as exemplified in equation 2. I shall not attempt to actually attach numbers, or even ranges, to these variables. Few people have tried, and the variation in the guesses is so vast that the particular numbers proposed become meaningless. What is important, on the other hand, is to arrive at least to a qualitative judgment of the order of magnitude of these parameters. If any of these terms turns out to be too small, the final product of the Drake equation would be a number very close to zero (although we know that it has to be at least one, since we exist!). Also notice that in the following discussion I will refer to a kind of life similar to our own, that is based on carbon, or at most on silicon under the proper temperature/pressure conditions. There may be something out there that “it is life, Jim, but not as we know it”, as Mr. Spock would have pointed out in Star Trek, but we are in no position to speculate scientifically about it, and such a possibility is best left to pure science fiction, at least at the moment.

f_p, the probability that a given star forms a planetary system. This used to be pretty much an unknown quantity in astrophysics, simply because the only star with an actual planetary system we knew about is our own sun. It is true that theoretical models of the formation of planetary systems have been devised (e.g., Wuchterl 1991) , and that they can be used to define theoretical boundaries for the actual number. But to a skeptic, convincing empirical evidence is a must, and the first experimental confirmation of the existence of other planetary bodies outside our own solar system came only very recently. However, now we know for sure of the existence of several extrasolar planets (Bennett et al. 1999) , there is no doubt that this term of the equation is far from being zero.

All these planets have been identified in the proximity of our own star, because current telescopes are not powerful enough to reveal any at all at greater distances, even if they existed. This is good news for SETI, since it implies that planets may indeed be abundant in our galaxy (or at least, in our corner of the galaxy). The downside of these recent discoveries is that all the planets so far confirmed orbiting nearby stars are giants, often larger than “our” gaseous giants, Jupiter and Saturn. In fact, some of them are so large that certain astronomers have questioned if the concept of planet can reasonably be stretched that far. Then again, the reason we uncovered only the giants among interstellar planets is once more because of the limited power of our telescopes, and does not imply that smaller, Earth-like and presumably more life-friendly planets do not exist. Also, the recent discovery of conditions that may be suitable to the development of life on the largest satellites of the solar giant planets (Hiscox 1999) is certainly another reason for optimism. All things considered, I would be willing to bet that f_p is indeed not so minuscule to endanger the credibility of SETI projects.

n_e, the number of planets in a given system characterized by an environment capable of sustaining life. Well, here - as for several other terms in the equation - we really have only a sample size of one to go by. Even though we know of other planets in different star systems, and even though we know something about the physical characteristics of the stars they orbit around (temperature, chemical composition, mass), we still have no way to know how likely it is that the candidate planets will be of the right type and at the right distance from the central star.

As far as we can tell from our knowledge of biology and physiology, an Earth-like life form is more likely to develop on a solid than on a gaseous planet, it requires an atmosphere, and a fairly limited range of temperatures. But these are vague conditions which can be fulfilled not just by a planet like the Earth or Mars, but by satellites around giant planets, such as some of the Medicean satellites orbiting around Jupiter, or perhaps by Titan around Saturn. The argument has been made that there is a fairly restricted “belt” around a star within which a planet will be at a safe distance so not too be too hot, while at the same time receiving enough energy not to freeze. In our solar system, Venus is clearly outside such a belt, being too close to the Sun, while the jury is still out about Mars. In any case, the space between Venus and Mars (with the Earth in between) is certainly not... astronomical, thereby casting doubts on the likelihood of this set of circumstances happening frequently in the galaxy. But the distance and amplitude of the safe zone depends entirely on the type of star, its mass, and its age, so it is not that simple to generalize from our very limited direct experience. Furthermore, if indeed satellites of larger planets outside the belt can also be considered likely candidates to host life, then the argument becomes less cogent and the likelihood of this parameter being much larger than zero increases considerably. All in all, I think that even if n_e is relatively small, the astounding number of star systems in our galaxy will probably make it large enough not to nullify the product of the Drake equation.

f_l, the likelihood that life will originate on a given planet. Again, we run here into the problem that our empirical evidence is limited to a unitary sample size, our own case. The origin of life on Earth is in itself largely a mystery, still only scratched at the surface by modern science; therefore, attempting to generalize from a single case that we understand very little is hazardous to say the least. The only point we can make is that our fossil record here on Earth indicates that life did originate very early, soon after the planet’s crust was cold enough to allow any complex chemical compound to exist in a semi-stable form. So, when given the opportunity, life apparently sprang out of the primordial soup or pizza with little hesitation (although we have only vague ideas about how this happened). And this is the best we can estimate would happen anywhere else, since there is no particular reason to think otherwise.

f_i, the probability that life will evolve intelligence. Of course, what constitutes intelligence is in and of itself a very controversial question. And how much intelligence do we need from ET, anyway? Once more, one can point to the only example we have available directly, that is evolution of “intelligent” life on Earth. If we define intelligence in a broad sense, as a general problem-solving ability, we have several independent examples of its evolution on our planet. Cephalopods (squids, octopuses), for example have evolved a very complex central nervous system that makes them capable of refined movements and of solving simple tasks. That ability clearly evolved independently of the type of intelligence that we find in vertebrates, and in fact, the evolution of birds, mammals, dinosaurs, and reptiles, although phylogenetically connected to some extent, shows the independent or repeated appearance of several features that we consider hallmarks of “higher” intelligence. In general, intelligence seems to be associated to a predatory life style, probably because of the necessity that such a life style carries for a large brain capable of coordinating the multifaceted information and responses involved in successfully capturing a prey (Futuyma 1998) . My feeling is that a variety of evolutionary scenarios may favor the occurrence of intelligent life forms as a generalized strategy to enhance Darwinian fitness, and that therefore the magnitude of f_i may be moderate, but not dangerously small.

f_c, the likelihood that an intelligent life form will become technological and be able to communicate over interstellar distances. Currently, there is no reasonable way to even estimate the order of magnitude of this entry in the equation. Obviously, there is only one species that has reached technological levels and is actually able to communicate with creatures from other star systems that we know of, good old Homo sapiens. But this may have been the result of historical accidents, or due to the fact that we are so competitive and destructive that other primates simply didn’t have a chance (Tattersall 2000) . As a cautionary statement, on the other hand, it did take more than three and half billion years for natural selection to produce the atomic bomb as an epiphenomenon of human evolution, not exactly a fast track for technologically-bent intelligence (unless someone is willing to submit the idea that that’s the real reason for the extinction of the dinosaurs...). This is the first of the terms in the Drake equation that may really be vanishingly small, and that certainly requires completely new approaches to be presented. Any bright idea, anyone?

R, the rate of formation of stars in the Milky Way. It is a large galaxy (more than 200 billion stars), and astronomers know of several places, such as the Orion Nebula, in which stars are being formed as we speak. The Hubble telescope is providing fascinating new insights into the process of stellar formation, and I do not see anything in the astronomical literature to indicate that we should be pessimistic about the value of R.

L, the time during which a technological culture tries to communicate with the external world. This is the second term of the equation that we simply have to label with a question mark. Judging from our own example (see below), L would be incredibly small, at least up until now. But the situation may change even for us, and we literally just started to play the galactic game. A technological society has to have not just the means, but also the curiosity and will to do it. We, for example, do have the technology to reach the nearest stars (contrary to popular belief). But it would take so much energy and investment of resources, both material and in terms of commitment, that simply it is not happening. And we certainly cannot bet that an alien psychology will be driven by the same sense of innate curiosity which is one of the best characteristics of at least some human beings. Nevertheless, as in the case of f_c, this is bound to be philosophical speculation, if not down right science fiction, at least for now.

Overall, it seems to me that most of the terms of the Drake equation can be reasonably assumed to be either large or moderate, and certainly not minuscule. The exceptions are represented by the two terms dealing with the characteristics of technological societies, of which our science knows the least, and that should be the focus of renewed investigation.

In discussing the Drake equation, it is often said that the best guess we can make is to assume that whatever happened on Earth is typical of the rest of the galaxy. This has been somewhat scornfully nicknamed the “principle of mediocrity” by John Casti (1989) . However, Casti himself gives the best rationale for it. If we consider the problem from a statistical standpoint (after all, most terms in the equation are probabilities), basic statistics teaches us that with a sample size of n=1, the best estimate of the mean of the population at large is exactly that single value. True, with a larger sample size we may find that our first observation was an atypical outlier, but the farthest an outlier is from the true mean, the less likely it is to occur at all, and therefore the least probable it is that it will occur in your sample, however small. (The statistically savvy reader will have noticed that I am assuming a normal, bell-shaped distribution of the parameters in the Drake equation. This may itself not be true, but normal distributions are remarkably... normal in nature!)

There is another good reason to trust the principle of mediocrity, at least provisionally: history. Every time humans have thought and seriously believed that they were something absolutely special and out of the ordinary, they have set themselves up for a soar disillusionment. Copernicus (1543) was the one who wiped us out of the center of the universe, and Darwin (1859) inflicted another blow by directly linking us by descent to every other form of life on the planet, including bacteria and amoebae. I really don’t see any reason to think that we are any more special than the guy next door, wherever she will turn out to be.

Given the uncertainties outlined above, is there a point in the Drake equation? Well, yes and no. No, in the sense that it isn’t really an “equation” in the usual scientific sense of the term. Currently, we cannot solve the equation even to an approximate degree, either by analytic or by computer simulation methods. Yes, in the sense that it is a formidable tool for getting a grip of this overwhelming problem. At least, it is a way to fix our ideas on a concrete, albeit incredibly difficult, subset of problems related to our general quest for ET. It seems to me that the answer to our preliminary question, is SETI a scientifically legitimate problem, is a qualified “yes”. It is indeed a problem that can be broken down in smaller parts, and there is a possibility for us to experiment or otherwise gain knowledge on all of these parts. But we’re still in the very preliminary rounds of the game.

Why do scientists disagree on SETI?

This question deals more with scientists’ attitudes and characters than with science per se. But we all know that science is to some extent a social enterprise, affected by the vagaries of human nature (Kuhn 1970) . Therefore, it makes sense to ask why is it that we encounter a full spectrum of reactions and positions about the SETI enterprise among scientists.

First of all, most practicing scientists simply do not devote any professional time to the problem. This is very likely not a reflection of the importance of the question, but rather a result of the difficulty in making any headway. The best quality of a scientist is curiosity, but a close second is pragmatism. Especially in this modern era of competitive universities, costly laboratories, and ever decreasing public funding for science, the first thing that graduate students learn from their advisors is not to pick a topic for their dissertation that will not surely give them publishable results within the following few years. This publish or perish attitude is arguably a major plague of the modern scientific enterprise, and it certainly is worth a separate discussion in and of itself. Its main result may be a huge amount of practical or focused knowledge, but a dearth of wide-ranging studies which, after all, are those that entice any curious mind to become a scientist in the first place. As for SETI, I think this is the main reason so little effort and money is being spent on it. It certainly is not a matter of lack of potential payoff. Whomever will get the first positive evidence of intelligent life outside our planet can count on an immediate Nobel prize, as well as to claim a place in the pantheon of people who shaped our cultural history, right next to Galileo, Newton, or Einstein.

Among the scientists who have ever pronounced themselves on the subject, two extreme views prevail. On the one hand we have the ultraconservatives, who claim that the likely answer to the question of how many civilizations exist in the Milky Way is: just one, and no need to look further than your mirror. At the opposite end of the spectrum are the overly liberal, the people who think that the galaxy swarms with other cultures and that we are just about to enter the galactic yellow pages, more or less a la Star Trek. Certainly Drake, as well as Carl Sagan, belong to this latter category. Their enthusiasm is as contagious as it is tenuously founded (see our discussion above). The best that can be said about these pro-ET scientists is that they keep the dream alive, which is not a small feat in this dreamless age.

On the other hand, I think the negativists really have little redeeming qualities. From a strict scientific viewpoint they are probably as naive (or at least, they have as little support) as their optimistic counterparts. And as far as curiosity goes, they would gladly shut down the whole enterprise so to have a few more cents to spend on sequencing one more genome or on smashing atoms in ever smaller pieces. The best (or worst) example of this sort is a scientist for whom I otherwise have the utmost respect: the Italian Enrico Fermi. The story goes that Fermi was asked about SETI in 1950, at a lunch at Los Alamos National Labs. One of the people present at the gathering apparently claimed that ET must exist in some form or another. Fermi’s laconic reply was “then were are they?” This anecdote has ever since been celebrated as ‘Fermi’s paradox’. Let’s analyze this supposed mortal blow to the quest for extraterrestrial intelligence.

The core (and in fact, the whole) of the paradox rests on the observation that - so far - we have not been visited by ETs. Ergo, ET does not exist. By the same token, of course, if you have not suffered from a deadly disease, the virus that causes it does not exist! Or, since the Aztecs weren’t aware of the existence of Spaniards for most of their history, they shouldn’t have to be afraid of being suddenly slaughtered... Fermi’s paradox is one of the most silly manifestations of anthropocentrism that I have ever come across. It amounts to say that if anything important is going on in the galaxy, we’re bound to know about it! Moreover, by applying the same logic, anybody else out there can safely conclude that there is no such thing as the human race, because they are not currently (or have ever) been visited by us. I hope the logical fallacy of the argument is plainly evident at this point, so that we can dismiss one of the few mistakes of Fermi’s career [1].

If everybody is listening, is anybody transmitting?

Ever since I got interested in SETI I wondered about a simple fact: we are spending quite a bit of energy, time, and finances while listening to possible extraterrestrial signals. But we only broadcast one such message from Arecibo in 1974. And the occasion was simply the celebration of the completion of that giant of radiotelescopes, i.e., more of a cute publicity stunt than a serious scientific attempt.

Furthermore, the Arecibo signal was probably sent on the wrong frequency, directed at the wrong target, and only sent once. That is, we violated every single precept of our own guidelines for uncovering ETs. As far as the frequency is concerned, the Arecibo signal was transmitted at 2380 MHz, probably because of convenience factors related to the available hardware (which was not designed for SETI). But according to a famous article by Morrison and Cocconi (1959) , the “ideal” frequency is actually much lower, centered around 1420 MHz. This is known as the “waterhole”, a low background noise region of the spectrum between the frequencies of interstellar hydrogen (H) and hydroxyl radical (OH) (whence the name, H + OH produce H₂O, that is water). Morrison and Cocconi’s reasoning was that such a choice would come ‘natural’ for most civilizations (even those whose evolution has not been linked with water) simply because of the extreme convenience of that band, and because it is associated to the frequency of the most abundant element in the universe, namely, hydrogen. Yet, when it came down to take the initiative and actually put into practice what Cocconi and Morrison suggested, mere convenience got the best of our logical arguments (no surprise there, is it?).

What about the target? Bad choice indeed. By the reasoning we put forth when we discussed the Drake equation, and by general acceptance in the SETI community, we should target sun-like stars. It is not that we know for sure that other types of stars cannot harbor planetary systems carrying life, but we do know for sure that at least in one case this kind of star does carry life. Well, the chosen target of the Arecibo message was a very dense globular star cluster known as M13, in the constellation of Hercules. Even though numerically it may have seemed a good choice (M13 is made of 300,000 stars), the distance and type of stars make it a good bet that we wont’ get any answer at all. First of all, M13 is about 25,000 light-years from Earth, which means that the Arecibo signal will be there in the year 26,974 (and we would have to wait until at least the year 51,974 for an answer, assuming the ETs are prompt). Second, most stars in M13 are not of solar type. Furthermore, these stars are so densely packed in a relatively small amount of space that they must exert an incredibly strong gravitational attraction onto each other, with the likely result that any planetary system either never had a chance to form, or has by now been crushed in a chaotic gravitational game.

Finally, we only sent the Arecibo message once. This is again contrary to any rational thinking. If we received a message, even one that can hardly qualify as “natural”, but we got only one instance of it with no repetition, we would have to relegate it to the ocean of scientific curiosities. In fact, such an event has probably occurred. I am referring to the “Wow” signal received in 1977 at Ohio State University. The signal was received on all 50 channels then being scanned, and its intensity was so far above background radiation to immediately qualify it as a very good SETI candidate. Except, the signal never repeated itself, it was never observed by any independent observatory, and it is now part of the SETI folklore, not of the annals of great scientific discoveries. It may indeed be an inevitable limitation of the scientific method that scientists can deal effectively only with repeatable phenomena, but that we ourselves would consciously play such an ignominious trick on the poor inhabitants of M13 is beyond excuse.

With all its defects (and notice that I haven’t even gotten into the details of how the message was in fact put together), the Arecibo signal is nevertheless the only attempt at radio contact ever purposely enacted by human beings. It seems that the prevalent reasoning in the SETI community is that it is more “cost effective” to listen than to broadcast. I rather suspect that this is yet another situation in which good old selfish human nature emerges. After all, should we get some, any, information from outer space, we would benefit immensely - if not from a practical standpoint, certainly from a scientific and philosophical one. But what’s the advantage to us of broadcasting our knowledge or existence to the rest of the universe? Of course, we can only hope that that particular human trait is not widespread throughout the galaxy, or we may be in a crowded galaxy and never hear a fly go by.

Is the bang worth our buck?

The ultimate question about any scientific enterprise seems to be: is it worth it? Now, unlike in many other realms of human experience, “worth” in science is not measured only in terms of vile hard cash. Don’t get me wrong, especially in the latter part of the 20^th century scientists are very much aware of the difficulty of raising funds for anything, and they therefore have to look uncomfortably closely to what their chronically meager purse can afford. Nevertheless, scientific worth is a compound measure in which several quantities weigh together. First and foremost, scientists have to agree that the question to be pursued is indeed a scientific question. Mind you, not just an interesting question, but one that can - at least potentially - be answered scientifically. There are plenty of fascinating questions out there, but many simply do not lend themselves to the rigors of the scientific method (for example, what was there before the Big Bang? Or, what where Neanderthal people’s feeling after the death of one of their own?). Second, even if the question is answerable in principle, is it likely that a significant contribution can be made within a few years to a few decades? This is important because most research grants do not last more than five years, which is also the life span of a graduate student’s tenure in a university. As I pointed out above, modern scientific research proceeds by tackling “bite-size” questions, which constitute the best material for a PhD thesis or a grant proposal. Alas, few scientists today could afford a lifetime project such as the one that brought Darwin to formulate the theory of evolution by natural selection, or which finally brought us the solution to the infamous Fermat’s theorem (Cipra 1993) . Third, assuming that the question is addressable in a relatively short period of time, what do we gain by doing so? To put it into another fashion, how would the solution of this particular riddle further our intellectual growth, or even merely augment our material welfare?

I think the answer to the first question is a definite yes, as I have tried to show at the beginning of this essay. SETI is indeed a scientific enterprise. It is no different in kind from the search for a new subatomic particle, or the attempts to detect black holes. Sure, it is in theory possible that there is no ET, or that we do not have the means to find them, but that sort of uncertainty is a normal component of scientific discoveries. The only science that proceeds with the certainty of positive results is rather boring and trivial (though often not devoid of practical value, like the purification of a new antibiotic, contrasted with the discovery of antibiotics). We do have good reasons to think that extraterrestrial civilizations are out there, and we do have a variety of tools to investigate their presence.

Is ET a bite that can be chewed by a graduate student or a tenure-track faculty? Clearly not. Unfortunately, no scientific journal would accept a paper that reported that, well, after five years of searching at 1420 MHz we found no intelligent communication from the Andromeda galaxy. Is there a way around this difficulty? Piggybacking, of course: the key is to set up SETI programs that can produce side results worth paying for. For example, a search around the “water hole” frequency could yield a detailed map of the distribution of interstellar hydrogen and hydroxyl radicals in selected regions of space. This information would be simultaneously valuable for astro-chemists while potentially lead to our first interplanetary “hello!” This example is not that far-fetched. Many scientists (including myself) actually use this strategy every day: get funding for projects that are “reasonable” (i.e., they have predictable outcomes), while diverting some of the money and energy to more high risk enterprises. Why? Because if one of these enterprises should turn into a home run, its payoff would be much greater than the minor investment one has made on it (sort of like winning the lottery while buying a low cost ticket once in a while - you don’t plan to buy your next home with it, but if it happens...).

A very clever example of how SETI can proceed with little spending is provided by the current incarnation of it at the University of California Berkeley, known as SETI@home (http://setiathome.ssl.berkeley.edu/). Not only they are using data that are being collected by the Arecibo radiotelescope for other purposes and scanning them for signs of extra-terrestrial intelligence, but they are making millions of personal computers worldwide performing the complex and endless task of analyzing such data! The problem is complex and the solution brilliant: the data incoming from the telescope constitute an endless stream, and the analyses to be carried out to accurately search for non-natural signals are very elaborate. The computer time required for such task would be prohibitive even for a highly funded scientific enterprise. Therefore, the scientists at SETI@home have designed a program that works like a screen saver on your personal computer and that anybody can download from the project’s web site. But the program is much more than a screen saver: whenever your computer is idle, it starts a set of calculations on small packages of data that from time to time the program itself down- and up-loads from the SETI server. At the time I am writing my computer has already performed more than 9000 hours of calculations for SETI. The inducement to PC users all over the world is the thrill of participating in one of the potentially most far-reaching enterprises of modern science, and of course the (astronomically small) probability of actually finding the right signal.

All of the above notwithstanding, what would the payoff of a positive SETI program actually be? Well, let me start by stating what it probably would not be. ET will probably not solve humanity’s problems, will not cure cancer or AIDS, nor tell us how to stop wars or avoid environmental suicide. Why should they, and how could they? Probably several of our problems are just that, our. It is very unlikely that what we experience as cancer and AIDS would exist in a different part of the galaxy, where the local life forms would have evolved for billions of years under different circumstances from those prevalent on Earth. What about possibly more universal questions such as the threat of global environmental collapse (which possibly, but not surely, a technological society would sooner or later have to face)? For one thing, the problem may be universal, but the solution would probably turn out to be contingent on the particular resources, as well as on idiosyncratic sociological and psychological factors. Furthermore, if our own efforts at interstellar communication are any guide, the most likely kind of message we may hope to receive is just an elaborate “hello there!” It would simply be very costly to send a much longer, information-rich message. And what purpose would it serve from the ET’s perspective? Finally, since the possibility of a radio dialogue is basically nil because of the vast interstellar distances and the finite speed of radio signals, there would be no point in hoping for a prolonged Q&A session across the galaxy. (Of course, all this assumes that the actual contact would occur along lines foreseen by current SETI researchers. There is always the remote possibility that we will find a completely new medium which could overcome some of these difficulties)

            What we would get out of the knowledge that ET is really out there is, however, far from negligible. First of all, we would have the answer to a fundamental biological question: is life a rare, or a widespread phenomenon in the universe? This would constitute a giant leap forward for biology, together with offering new clues about the origin of life itself, perhaps one of the most persistent and involving questions of modern science. Second, ET would bring a fatal blow to that perversion of modern cosmology known as the “anthropic principle”, that is the idea that the universe is custom-made to allow for the evolution of humans (for a detailed critique see: Stenger 1996; Stenger 1999) . If ET exists we would be forced to conclude that others share the dubious distinction of having zillions of galaxies and stars brought into existence just to make sense of their everyday ramblings about the universe. Thirdly, the discovery of ET would be one of those once-in-a-long-while scientific results capable of influencing a larger portion of the human experience, including philosophy, religion, and our perception of humankind’s place in the universe. Whoever will confirm the existence of extraterrestrial intelligences will demolish any remnants of irrational pride that Homo sapiens may still harbor. We would know that the same mindless process that originated us has also produced other similar creatures, possibly in turn deluded about some central role they played in the universe. At least up to the moment they received an unnatural signal from a small planet orbiting a perfectly average star at the periphery of a rather ordinary galaxy. As the immortal Monty Python song (from The Meaning of Life) goes:

Just remember that you’re standing on a planet that’s evolving

and revolving at 900 miles an hour,

that’s orbiting at 19 miles a second, so it’s reckoned,

a sun that is the source of all our power.

The sun and you and me and all the stars that we can see,

are moving at a million miles a day

in an outer spiral arm, at 40,000 miles an hour,

of the galaxy we call the Milky Way

...

So remember when you’re feeling very small and insecure

how amazingly unlikely is your birth

and pray that there’s intelligent life somewhere up in space

because there’s bugger all down here on earth.

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[1] Incidentally, I took a biophysics course with Dr. Mario Ageno, one of Fermi’s students. He told us an amusing story which occurred when Ageno was taking one of Fermi’s classes. Fermi submitted to his students that every scientist publishes something of which he will later be ashamed. One of the attendees then asked where did Fermi published his questionable material. To which the physicist replied that he was being honest, but not stupid, and that it would be up to the student to find out...