Albert Einstein (March 14, 1879 - April 18, 1955) was a physicist and mathematician who proposed the theory of relativity. He also made major contributions to the development of quantum mechanics, statistical mechanics and cosmology, and is generally regarded as the most important physicist of the 20th century. He was awarded the 1921 Nobel Prize for Physics for his explanation of the photoelectric effect and "for his services to Theoretical Physics"; however, the announcement of the award was not made until a year later, in 1922. In 1999 Albert Einstein was named "Person of the Century" by Time Magazine. In popular culture, Einstein has become synonymous with someone of very high intelligence. His face is also one of the most recognizable the world-over. In his honor, a unit used in photochemistry was named after him. An einstein is equal to Avogadro's number times the energy of one photon of light. The chemical element Einsteinium is named after the scientist as well. Abram Joffe, in Einstein's biography, argues that Einstein was assisted by his wife Mileva Maric, who was a mathematician