Fermi paradox
The physicist Enrico Fermi first asked the question in an informal discussion in 1950. A paper by Michael H. Hart in 1975 made scientists more curious and they began to study the question in more detail. This is why some people call it the Fermi–Hart paradox. Other common names for the same phenomenon are Fermi's question ("Where are they?"), the Fermi Problem, the Great Silence, and silentium universi (Latin for "the silence of the universe"; the misspelling silencium universi is also common).