Scientific literature and
science fiction have put forward various models of the ways in which extraterrestrial and human civilizations might interact. Their predictions range widely, from sophisticated civilizations that could advance human civilization in many areas to imperial powers that might draw upon the forces necessary to subjugate humanity. Some theories suggest that an extraterrestrial civilization could be advanced enough to dispense with biology, living instead inside of advanced computers. and how much human and extraterrestrial biologies have in common. These factors may govern the quantity and type of dialogue that can take place. In the case of communication using electromagnetic signals, the long silence between the reception of one message and another would mean that the content of any message would particularly affect the consequences of contact , as would the extent of mutual comprehension. Concerning probes, a study suggested the first
interstellar probe to is not likely to be the civilization's earliest (e.g. the ones sent first) but a more advanced one as (at least) the departure speed is thought to (likely) improve for at least some duration per each
civilization, which e.g. may have implications for the type of probes to expect and the impacts of any probes sent earlier.
Friendly civilizations Many writers have speculated on the ways in which a friendly civilization might interact with humankind.
Albert Harrison, a professor emeritus of psychology at the University of California, Davis, thought that a highly advanced civilization might teach humanity such things as a physical
theory of everything, how to use
zero-point energy, or how to travel
faster than light. They suggest that collaboration with such a civilization could initially be in the arts and humanities before moving to the hard sciences, and even that artists may spearhead collaboration. Seth D. Baum, of the Global Catastrophic Risk Institute, and others consider that the greater longevity of cooperative civilizations in comparison to uncooperative and aggressive ones might render extraterrestrial civilizations in general more likely to aid humanity. Futurist
Allen Tough suggests that an extremely advanced extraterrestrial civilization, recalling its own past of war and plunder and knowing that it possesses superweapons that could destroy it, would be likely to try to help humans rather than to destroy them. He identifies three approaches that a friendly civilization might take to help humanity: According to Tough, it is unlikely that the avoidance of immediate dangers and prevention of future catastrophes would be conducted through radio, as these tasks would demand constant surveillance and quick action. However, a friendly civilization may calibrate its contact with humanity in such a way as to minimize unintended consequences. this is known as the
zoo hypothesis.
Hostile civilizations Science fiction often depicts humans successfully repelling
alien invasions, but scientists more often take the view that an extraterrestrial civilization with sufficient power to reach the Earth would be able
to destroy human civilization or humanity with minimal effort. Operations that are enormous on a human scale, such as destroying all major population centers on a planet, bombarding a planet with deadly
neutron radiation, or even traveling to another planetary system in order to lay waste to it, may be important tools for a hostile civilization. Deardorff speculates that a small proportion of the intelligent life forms in the galaxy may be aggressive, but the actual aggressiveness or benevolence of the civilizations would cover a wide spectrum, with some civilizations "policing" others. As among humans, civilizations may not be homogeneous and contain different factions or subgroups. According to Harrison and Dick, hostile extraterrestrial life may indeed be rare in the Universe, just as belligerent and autocratic nations on Earth have been the ones that lasted for the shortest periods of time, and humanity is seeing a shift away from these characteristics in its own sociopolitical systems.
Seth Shostak, an astronomer at the SETI Institute, disagrees, stating that the finite quantity of resources in the galaxy would cultivate aggression in any intelligent species, and that an explorer civilization that would want to contact humanity would be aggressive. Similarly,
Ragbir Bhathal claimed that since the laws of evolution would be the same on another habitable planet as they are on Earth, an extremely advanced extraterrestrial civilization may have the motivation to colonize humanity in a similar manner to the
European colonization of much of the rest of the world. Disputing these analyses,
David Brin states that while an extraterrestrial civilization may have an imperative to act for no benefit to itself, it would be naïve to suggest that such a trait would be prevalent throughout the galaxy. Brin points to the fact that in many moral systems on Earth, such as the Aztec or Carthaginian one, non-military killing has been accepted and even "exalted" by society, and further mentions that such acts are not confined to humans but can be found throughout the animal kingdom. because "any civilization that has the ability to travel between the stars can already pick up our accidental radio and TV leakage" at a distance of several hundred light-years. The easiest or most likely artificial signals from Earth to be
detectable are brief pulses transmitted by
anti-ballistic missile (ABM) early-warning and space-surveillance radars during the
Cold War and later astronomical and military radars. Unlike the earliest and conventional radio- and television-broadcasting which has been claimed to be undetectable at short distances, such signals could be detected also from relatively distant receiver stations in certain regions. Politicians have also commented on the likely human reaction to contact with hostile species. In a 1987 speech at the 42d Session of the
United Nations General Assembly,
Ronald Reagan said, "I occasionally think how quickly our differences worldwide would vanish if we were facing an alien threat from outside this world."
Equally advanced and more advanced civilizations .|alt=A Dyson sphere
Robert Freitas speculated in 1978 that the technological advancement and energy usage of a civilization, measured either relative to another civilization or in absolute terms by its rating on the
Kardashev scale, may play an important role in the result of extraterrestrial contact. Given the infeasibility of interstellar space flight for civilizations at a technological level similar to that of humanity, interactions between such civilizations would have to take place by radio. Because of the long transit times of radio waves between stars, such interactions would not lead to the establishment of diplomatic relations, nor any significant future interaction at all, between the two civilizations. Freitas expected that such interactions would be carefully planned by the more advanced civilization to avoid mass societal shock for humanity. For similar reasons, such civilizations would not readily give humanity the knowledge required to build such devices. Whether an advanced extraterrestrial civilization would send humanity a decipherable message is a matter of debate in itself. Sagan argued that a highly advanced extraterrestrial civilization would bear in mind that they were communicating with a relatively primitive one and therefore would try to ensure that the receiving civilization would be able to understand the message.
Marvin Minsky believed that aliens might think similarly to humans because of shared constraints, permitting communication. Arguing against this view, astronomer Guillermo Lemarchand stated that an advanced civilization would probably encrypt a message with high information content, such as an
Encyclopædia Galactica, in order to ensure that only other ethically advanced civilizations would be able to understand it. "There's going to be a lot of guesswork in trying to interpret another civilization," he told
Science Friday, adding that "in some ways, any message we get from an extraterrestrial will be like a cosmic
Rorschach ink blot test."
Interstellar groups of civilizations Given the age of the galaxy, Harrison surmises that "galactic clubs" might exist, groupings of civilizations from across the galaxy. Such clubs could begin as loose confederations or alliances, eventually developing into powerful unions of many civilizations. Whether a broad spectrum of civilizations from many places in the galaxy would even be able to cooperate is disputed by Michaud, who states that civilizations with huge differences in the technologies and resources at their command "may not consider themselves even remotely equal". It is unlikely that humanity would meet the basic requirements for membership at its current low level of technological advancement. through analysis of the
Sloan Digital Sky Survey database,
Douglas Vakoch doubted their explanation for their findings, noting that it would be unusual for all of these stars to pulse at exactly the same frequency unless they were part of a coordinated network: "If you take a step back," he said, "that would mean you have 234 independent stars that all decided to transmit the exact same way." Michaud suggests that an interstellar grouping of civilizations might take the form of an empire, which need not necessarily be a force for evil, but may provide for peace and security throughout its jurisdiction. Owing to the distances between the stars, such an empire would not necessarily maintain control solely by military force, but may rather tolerate local cultures and institutions to the extent that these would not pose a threat to the central imperial authority. This contrasts with the classic Kardashev Type III civilization, which has access to the energy output of an entire galaxy and is not subject to any limits on its future expansion. Tough speculates that the enormous amount of energy required to achieve such speeds under currently proposed mechanisms means that robotic probes traveling at conventional speeds will still have an advantage for various applications. needing only about 1 tonne of exotic mass-energy to move a spacecraft at 10 times the speed of light, in contrast to previous estimates that stated that only a Jupiter-mass object would contain sufficient energy to power a faster-than-light spacecraft. According to Tough, an extraterrestrial civilization might want to send various types of information to humanity by means of artifacts, such as an
Encyclopædia Galactica, containing the wisdom of countless extraterrestrial cultures, or perhaps an invitation to engage in diplomacy with them. A civilization that sees itself on the brink of decline might use the abilities it still possesses to send probes throughout the galaxy, with its cultures, values, religions, sciences, technologies, and laws, so that these may not die along with the civilization itself. Freitas points out that probes, unlike the interstellar radio waves commonly targeted by SETI searches, could store information for long, perhaps geological, timescales, Moreover, the use of small robotic probes with widely distributed beacons in individual systems, rather than a small number of powerful, centralized beacons, would provide a security advantage to the civilization using them. Rather than revealing the location of a radio beacon powerful enough to signal the whole galaxy and risk such a powerful device being compromised, decentralized beacons installed on robotic probes need not reveal any information that an extraterrestrial civilization prefers others not to have. Given the age of the Milky Way galaxy, an ancient extraterrestrial civilization may have existed and sent probes to the Solar System millions or even billions of years before the evolution of
Homo sapiens. Thus, a probe sent may have been nonfunctional for millions of years before humans learn of its existence. Such a "dead" probe would not pose an imminent threat to humanity, but would prove that interstellar flight is possible. However, if an active probe were to be discovered, humans would react much more strongly than they would to the discovery of a probe that has long since ceased to function. ==Further implications of contact==