Casimir, Hendrik (Brugt Gerhard)

(1909–2000) Dutch physicist: originated the ‘two-fluid’ model of superconductivity.

Casimir was educated at the universities of Leiden, Copenhagen and Zürich. He held a variety of research positions until, in 1942, he began a career with Philips. He became director of the Philips Research Laboratories in 1946.

Casimir’s papers cover aspects of theoretical physics, particularly low-temperature physics and superconductivity. W Meissner (1922– ) had examined some properties of superconductors, such as the expulsion of a magnetic field below the superconducting transition temperature (the Meissner effect). Casimir and C Gorter proposed in 1934 that two sorts of electrons exist, normal and superconducting, and used this to explain the relation between thermal and magnetic properties in superconductors. When and others produced the BCS theory it was clear that the two categories represented unpaired electrons and paired electrons (called Cooper pairs).

Casimir in 1948 predicted the effect named for him: an attractive force that occurs between two parallel conducting plates when they are about 10 –5 m apart. It was verified experimentally in 1958.