supposed societies of rational beings in other planetary systems who have attained or surpassed the level of development of human society.
The presence of life on earth and the materialist under-standing of life’s origin and development, as well as the existence of an infinite number of other planetary systems, give grounds for inferring the possibility of life originating in other regions of the universe. Equally indisputable is the inference that the development of living matter to highly organized forms—the origin of extraterrestrial civilizations—is possible. On the basis of this general proposition and proceeding from the fact of the proximity of Mars and Venus to the earth, the presence of atmospheres on them, and other factors, the existence of civilizations even on these planets was once considered fairly probable. The development of astronautics led to the appearance of hypotheses, and some-times even categorical statements, of visits to the earth by intelligent beings from other worlds. By means of such visits, attempts were made to explain the existence of ancient monuments and to interpret ancient legends, including those in the Bible. Many “witnesses” of such visits to the earth in our time have appeared as well as observers of “flying saucers” and “unidentified flying objects” associated with extraterrestrial civilizations. However, as a rule, all these “facts” have received an entirely terrestrial explanation and some of them proved to be deliberate deceit.
The results of studies of physical conditions on various planets carried out in the middle of the 20th century have led to the conclusion that it is impossible for highly organized life to exist on the planets of the solar system; it is conjectured that life in primitive forms can exist only on Mars. Evaluation of the physical conditions in the surroundings of many stars close to the sun possessing planetary systems has greatly reduced the probability of the origin and development of life in these planetary systems as well. The existence of “ecospheres”—regions in which (under appropriate conditions) life could develop—is now attributed to only a small number of stars.
The technical difficulties in realizing the idea of interstellar flights, the great duration of such flights, and the appraisal of the effectiveness of other forms of exchange of information between hypothetical extraterrestrial civilizations have led to efforts to seek such information in various regions of the electromagnetic spectrum. One of the hypotheses upon which such searches are based amounts to the fact that the development of technology, population growth, society’s needs, and a striving for the optimal exploitation of the material and energy resources of the planets and of the central star would necessarily lead to the inevitable reconstruction of the planetary system itself, for example, to the construction of a gigantic sphere from the material of planets and asteroids that would encompass the star at some optimal distance. The internal surface of this reconstructed world would accumulate all of the star’s radiation, while the outer surface would radiate in the infrared range. The task of finding such a civilization might begin with the discovery of localized sources of infrared radiation.
The problem of the existence of extraterrestrial civilizations belongs to the category of extremely probable hypotheses not yet confirmed by experimental facts. One can assume that the distribution of extraterrestrial civilizations in the universe is small just as is the probability of the earth’s being visited by newcomers from other worlds. Further progress in astronautics and the study of radiation coming from the universe should either give evidence of the existence of such civilizations or further reduce the probability of their discovery. The discovery of any traces of intelligent activity on the moon would constitute irrefutable evidence that in the past the solar system (and the earth, in particular) was visited by representatives of other civilizations. The study of Mars may yield experimental data on the origin and development of living matter under conditions different from those on earth, and the discovery of radiation containing intelligent information would confirm the presence of civilized worlds and indicate the direction in which to look for them.