Space signals are transmissions conducted in various ways in an effort to establish contact with a hypothetical extraterrestrial intelligence. Communication with extraterrestrial intelligence (CETI) focuses on composing and deciphering messages that could theoretically be understood by a non-terrestrial technological civilization.
The first international conference to discuss the various problems for making contact with extraterrestrial intelligence was held September 1971 in Soviet Armenia. The conference was a gathering of specialists working in a wide variety of fields in physics and astronomy. Freeman Dyson, Philip Morrison, and Charles Townes were among the American participants; their Russian counterparts were of comparable distinction. The conference was jointly organized by the US National Academy of Sciences (with assistance from the US National Science Foundation) and the USSR Academy of Sciences. Scientists from several other countries also participated.
Critical thinking problems related to establishing contact with hypothetical extraterrestrial civilizations were discussed in detail at the conference. Particular attention was devoted to the following questions: the plurality of planetary systems in the universe, the origin of life on Earth, the possibility of life arising on cosmic bodies, the origin and evolution of intelligence, the origin and development of technological civilizations, problems in searching for intelligent signals or for evidence of astroengineering activities, and the problems and possible consequences of establishing contact with extraterrestrial civilizations. These discussions are fully presented in the book, Communication with Extraterrestrial Intelligence.