Casimir, Hendrik Brugt Gerhard, << KAZ uh mihr, HEHN druhk brookt GAYR hahrt >> (1909-2000), a Dutch physicist, became widely known for his model of superconductivity and for the Casimir effect. Superconductivity is the ability of some materials to conduct electric current without resistance at extremely low temperatures. The Casimir effect is a force of attraction found to exist in a vacuum (empty space).
In 1934, Casimir and the Dutch physicist Cornelis Gorter published the two-fluid model of superconductivity. In this model, the electrons in a superconducting material are treated as “fluids.” One fluid consists of the electrons that travel along the material without resistance—the superconducting electrons. The other fluid consists of electrons that are not superconducting. The two-fluid model helped scientists to explain the observed properties of superconductors.
In 1948, Casimir published two important papers, one with the Dutch physicist Dirk Polder. The papers developed an idea that became known as the Casimir effect. The effect can be understood by envisioning two metallic plates in a vacuum. In classical physics, no force should exist between two plates, as long as they do not have an electromagnetic charge. But Casimir and Polder studied the problem using a type of nonclassical physics called quantum electrodynamics. He concluded that the small continuous energy changes in the vacuum could produce a force between the uncharged plates.
According to quantum electrodynamics, a vacuum is not entirely empty. Rather, it holds a constantly fluctuating swarm of virtual particles, each with a particular wavelength. The energy of these virtual particles gives the vacuum a quality called energy density. As the plates are moved extremely close together, only particles of certain wavelengths can exist between them. Casimir calculated that this would reduce the number of virtual particles between the plates, and thus reduce the energy density between them. The greater energy density outside the plates would therefore push the two plates together, creating a force of attraction between them. Scientists verified the Casimir effect in the late 1990’s.
Casimir was born on July 15, 1909, in the Hague, the Netherlands. He earned his Ph.D. degree in theoretical physics from the University of Leiden in 1931. Soon after, he began assisting the Austrian physicist Wolfgang Pauli, but he would return to the University of Leiden to teach after one year. In 1938, he became a professor at the university. In 1942, he moved to the Philips Research Laboratories in Eindhoven, the Netherlands, becoming co-director in 1946 and joining the board of directors 10 years later. He retired from Philips in 1972. Casimir’s work was widely celebrated, and he was honored with many awards and prizes, including many honorary Ph.D. degrees. He died on May 4, 2000, in Heeze, the Netherlands.
