''Extraterrestrial Civilizations'' is a 1979 book by
Isaac Asimov
yi, יצחק אזימאװ
, birth_date =
, birth_place = Petrovichi, Russian SFSR
, spouse =
, relatives =
, children = 2
, death_date =
, death_place = Manhattan, New York City, U.S.
, nationality = Russian (1920–1922)Soviet (192 ...
, in which the author estimates the probability of there being intelligent
extraterrestrial
Extraterrestrial refers to any object or being beyond ( extra-) the planet Earth ( terrestrial). It is derived from the Latin words ''extra'' ("outside", "outwards") and ''terrestris'' ("earthly", "of or relating to the Earth"). It may be abbrevia ...
civilizations within the
Milky Way galaxy. This estimation is approached by progressively analyzing the requirements for
life
Life is a quality that distinguishes matter that has biological processes, such as signaling and self-sustaining processes, from that which does not, and is defined by the capacity for growth, reaction to stimuli, metabolism, energ ...
to exist.
Overview
The term "
Earth-like world" is prominent, in that the assumption is made that any world where life could evolve would have certain similarities to Earth, such as temperature ranges and gravity sufficient for an atmosphere to exist. Asimov begins with the estimated number of
star
A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
s in the galaxy, 300 billion.
This number is then reduced to 280 billion as stars without
planetary system
A planetary system is a set of gravitationally
In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interacti ...
s are discarded, and then furthermore reduced as more factors are taken into consideration. This process culminates in the statement that "the number of planets in our galaxy on which a technological civilization is now in being is roughly 530,000."
[The Internet Book Database of Fiction]
Extraterrestrial Civilizations
/ref>
See also
* Drake equation
References
Extraterrestrial Civilizations
1979 non-fiction books
{{astronomy-book-stub