11 Extraterrestrial Intelligent Life 11.1 Future of Mankind The questions “Why don’t we have contact with extraterrestrial intelligent life?” and “How will mankind evolve in the near future?” are intimately connected. Clearly, civilizations that are far behind our technological state would not be capable of communicating with us. But even societies more advanced than us would have difficulties in making contact, as radio waves or spacecraft take a long time to cross the huge distances in our galaxy. In addition, such advanced societies might no longer exist. They could have fallen victim to external or internal dangers, or they might not wish to communicate with us. The only way to gain some insights into the possible dangers afflicting extraterrestrial intelligent societies and their likely mode of behavior is to consider our own future development, because these civilizations are expected to have gone through our own technological state long ago. Major developments Although it is very speculative to predict the likely evolution of human society, it is impossible to overlook three current developments that have particularly far-reaching consequences for our future: the advances in information technology, the conquest of space, and the mastering of the biological world. In less than a quarter of a century, computers have mutated from specialized machines for some scientists to universal and absolutely essential tools in manufacture, process management, administration, commerce, communication, education, and recreation. Because of their usefulness, these machines have modified everyone’s lives both at work and at home, and we no longer want to live without them. They allow us an almost instant contact with millions of people and databases around the world, and they permit access to the remotest places on Earth. There is little doubt that this progress in information technology will continue by making computers even more sophisticated and intelligent. They could be viewed as evolving external organs of our body, which greatly help to improve our interaction with the environment and other human beings. The second, easily foreseeable development in the near future is the conquest of the solar system. One of the greatest current endeavors in space is the construction of the International Space Station (ISS), where we can study the effect of weightlessness on humans, and explore industrial applications in zero gravity and space manufacturing. The ISS can serve as a gateway for the many missions to the Moon, Mars, comets, asteroids that are planned. Asteroids are particularly interesting thanks to their rich mineral resources that could be mined and used for industrial purposes. Manned missions to the Moon and Mars, as they are already in discussion, face the problem of how to obtain the large amounts of rocket fuel necessary for the return flight to Earth. The only logical way is to manufacture it in space, since it is prohibitively expensive to carry it along from Earth. For this aim water ice is most important because, with the help of solar or nuclear energy, it can be split by electrolysis into hydrogen and oxygen Astrobiology: 11 Extraterrestrial Intelligent Life 11-1 S.V. Berdyugina, University of Freiburg for rocket fuel. It makes sense to locally process resources collected in space because it is very expensive (in terms of fuel) to transport material up from Earth’s surface. Sending goods down to Earth e.g. from a space station is however cheap and relatively easy. It is thus only a question of time until semi-permanent or permanent settlements in space or on the Moon are established. The mastering of the biological world can also have huge impacts on humans. In this area ethical questions and responsible research are of particular importance. It is in principle only a matter of time until the DNA sequence of practically all important organisms will be known and the function of their genes understood. This will eventually not only revolutionize medicine, but also allow us to understand what life is, and reveal how biological organisms carry out the manufacture of chemical compounds and body parts, how memory and information processing works, the way in which immunological warfare is conducted against internal and external enemies, and even how conscious thought arises. It becomes then even feasible to construct androids with self-conscious, non-biological brains, although the consequences are difficult to foresee and have to be carefully considered. Dangers for Mankind While the conquest of space and the mastering of the biological world are revolutionary and exciting foreseeable developments, there are other prospects that portray a much more sinister future for mankind. It has been suggested that an explanation for our lack of contact with extraterrestrial intelligent societies is that they no longer exist. This view believes that, due to disastrous external or internal events, every intelligent civilization will invariably come to a sudden end, perhaps soon after it reaches our technological stage and long before it can conduct extensive interstellar travel. But how likely is this scenario? Clearly, it is not possible to imagine all the many dangers that an advanced intelligent civilization will face. However, some external and internal dangers that threaten the survival of mankind can be foreseen, and one may ponder ways to avoid them. Figure 1: The extinction intensity of marine animal genera over the past 550 million years. Astrobiology: 11 Extraterrestrial Intelligent Life 11-2 S.V. Berdyugina, University of Freiburg Earth’s history shows several episodes of mass extinction, which illustrate external dangers. Figure 1 shows the extinction intensity deduced from the changes in numbers of marine animal genera in the fossil record over the past 550 million years. Episodes of massive volcanism, impacts of comets or asteroids, supernova or gamma ray events, global glaciations, and attack by deadly bacteria or viruses have all been proposed as possible causes for such events. External dangers are not likely to be fatal to life and intelligent life on Earth. Despite the continuous presence of these threats and mass extinctions, life as such always survived and adjusted to new situations. The conquest of space and the foundation of space colonies will lessen external dangers even more because mankind would be spread out over larger distances and would only be subject to catastrophes concerning the whole solar system (or the galaxy once we can conduct interstellar travel). If our absence of contact with extraterrestrial beings can indeed be attributed to a fatal destruction, it therefore must be the internal dangers that are the most formidable. Indeed, this is also what one is forced to conclude when looking at our own past and present history. Over the past few millennia there has been a clear progress in the amount of destruction that man has caused and that mankind is capable of doing. While man-made irreversible environmental damage might be still seen as a somewhat external threat, it is the likelihood of uncontrollable inventions, and particularly the possibility of deliberate man-made destruction that poses the most dangerous threat to the survival of mankind. Indeed, the greatest danger to mankind and the only one that is presently known to be absolutely life-threatening is deliberate global destruction. Over the last centuries the number of war dead strongly increased. Already now, we could in principle eliminate mankind with our weapons of mass destruction. But it is not only war that constitutes the great danger; it is the mounting concentration of power put into the hands of a few individuals. Weapons of mass destruction could be found in the possession of fundamentalists, revolutionaries, dictators, bosses of criminal organizations, and of insane individuals. These internal dangers, which arise from ourselves, are particularly worrying, since mankind is faced with an incessant and unstoppable development toward more knowledge, and consequently vastly greater power. In view of the achievements of past centuries, what will we know in a few hundred or a few thousand years? With mankind set in its present ways, it is clear that before long our world is heading for a nightmare of possible destruction. How can we control this irrationality and irresponsibility? Only if we learn how to solidly control these destructive tendencies will mankind be able to survive even the next few centuries. 11.2 Number of Extraterrestrial Societies In our search for extraterrestrial intelligent life, looking for Earth-like planets is only the first step. The next step is to consider the probability of the formation of life − and particularly of intelligent life − on such planets. It was the American radio astronomer Astrobiology: 11 Extraterrestrial Intelligent Life 11-3 S.V. Berdyugina, University of Freiburg Frank Drake, who in 1961 first suggested that the number of intelligent societies in our galaxy can be inferred, starting with an estimated frequency of Earthlike planets. He proposed a formula in which the total likelihood is expressed as a product of the individual probabilities for the various necessary conditions. This formula, henceforth called the Drake formula, roughly estimates the total number N of communicating extraterrestrial civilizations in our galaxy as the following product: NNfnfffLL SPELIC/ S . Here NS is the number of stars in the galaxy suitable for life, fP is the fraction of such stars which have planets, nE is the number of Earth-like planets which orbit in the habitable zone for each star, fL is the fraction of planets on which life develops, fI is the fraction of planets on which life evolves into intelligent life, fC is the fraction of civilizations which engage in radio communications, L is the lifetime of communicating societies, and LS is the time-span over which Earth-like planets and their parent stars have formed in the galaxy. Note that for an existing communicating society the fraction L/LS represents the likelihood that it can be detected.