Fermi paradox: a standalone construct

Enrico Fermi's 1950 lunchtime remark at Los Alamos, recounted by physicist Eric Jones in 1985, posed a plain question about extraterrestrial life: if the galaxy is old and vast and even a small fraction of its many stars host planets where technological civilizations arise, some should long ago have spread across it, so "Where is everybody?" The name and the first rigorous published argument came later, with Michael Hart's 1975 paper setting out why the complete absence of any observed extraterrestrial being or artifact on Earth is hard to reconcile with those expectations, unless such civilizations are rare, short-lived, or absent. The paradox is the tension between the high estimates for the number of communicating civilizations, of the kind tallied in the Drake equation, and the total lack of confirmed evidence or contact, a silence sometimes called the Great Silence. As a landmark it frames a large research program in astrobiology and the Search for Extraterrestrial Intelligence (SETI): each proposed resolution, from interstellar travel being impractical, to civilizations self-destructing, to Earth being deliberately unvisited, is a candidate answer to the one question rather than a rival meaning of the term. As Robert Gray noted in 2015, Fermi himself never published on the subject and the argument is not strictly a logical paradox, so the label is a historical convention for a well-defined problem.[1][2][3]

Unit

A named problem in astrobiology: the gap between the expected and the observed evidence of extraterrestrial civilizations

Recovery means

Not applicable

Measured by

Framed by contrasting probabilistic estimates of civilization counts, as in the Drake equation, against the null results of astronomical and radio searches (SETI)