An Expert Is A Person Who

Niels Bohr's son Hans recorded this as one of his father's characteristic remarks in his memoir chapter "My Father," published in Niels Bohr: His Life and Work As Seen By His Friends and Colleagues (1967, ed. S. Rozental). Werner Heisenberg also attributed the saying to Bohr in his 1969 memoir Der Teil und das Ganze. Bohr himself, in a 1949 essay on his debates with Albert Einstein, called it an "old saying" — suggesting he was passing on a received idea rather than coining one.