Extraterrestrial hypothesis

The extraterrestrial hypothesis (ETH) proposes that some unidentified flying objects (UFOs) are best explained as being physical spacecraft occupied by extraterrestrial life or non-human aliens from other planets visiting Earth. As yet, no evidence exists to support this hypothesis.

Origins of the term extraterrestrial hypothesis are unknown, but use in printed material on UFOs seems to date to at least the latter half of the 1960s. French ufologist Jacques Vallee used it in his 1966 book Challenge to science: the UFO enigma. It was used in a publication by French engineer Aimé Michel in 1967, by James E. McDonald in a symposium in March 1968 and again by McDonald and James Harder while testifying before the Congressional Committee on Science and Astronautics, in July 1968. Skeptic Philip J. Klass used it in his 1968 book UFOs--Identified. In 1969 physicist Edward Condon defined the "extraterrestrial hypothesis" or "ETH" as the "idea that some UFOs may be spacecraft sent to Earth from another civilization or space other than Earth, or on a planet associated with a more distant star," while presenting the findings of the much debated Condon Report. Some UFO historians credit Condon with popularizing the term and its abbreviation "ETH".

Although ETH is a comparatively new concept - one which owes a lot to the flying saucer sightings of the 1940s–1960s, its origins can be traced back to a number of earlier events such as the now discredited Martian canals and ancient Martian civilization promoted by astronomer Percival Lowell, popular culture including the writings of H. G. Wells and fellow science fiction pioneers such as Edgar Rice Burroughs, who likewise wrote of Martian civilizations, and even to the works of figures such as the Swedish philosopher, mystic and scientist Emanuel Swedenborg, who promoted a variety of unconventional views that linked other worlds to the afterlife.

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