**Born:** Ulm, Germany. **Died:** Princeton, USA.

Albert Einstein was a very famous scientist; he was mostly famous for his theory of Relativity. In 1894 Einstein’s family moved to Milan and Einstein decided officially to relinquish his German citizenship in favor of Swiss. In 1895 Einstein failed an examination that would have allowed him to study for a diploma as an electrical engineer at Zurich. After attending secondary school at Aarau, Einstein returned (1896) to the Zurich Polytechnic, graduating (1900) as a secondary school teacher of mathematics and physics.

He worked at the patent office in Bern from 1902 to 1909 and while there he completed an astonishing range of theoretical physics publications, written in his spare time without the benefit of close contact with scientific literature or colleagues. Einstein earned a doctorate from the University of Zurich in 1905. In 1908 he became a lecturer at the University of Bern, the following year becoming professor of physics at the University of Zurich.

By 1909 Einstein was recognized as a leading scientific thinker. After holding chairs in Prague and Zurich he advanced (1914) to a prestigious post at the Kaiser-Wilhelm Gesellschaft in Berlin. From this time he never taught a university courses. Einstein remained on the staff at Berlin until 1933, from which time until his death he held a research position at the Institute for Advanced Study in Princeton.

In the first of three papers (1905) Einstein examined the phenomenon discovered by Max Planck, according to which electromagnetic energy seemed to be emitted from radiating objects in discrete quantities. The energy of these quanta was directly proportional to the frequency of the radiation. This seemed at odds with the classical electromagnetic theory, based on Maxwell’s equations and the laws of thermodynamics which assumed that electromagnetic energy consisted of waves which could contain any small amount of energy. Einstein used Planck’s quantum hypothesis to describe the electromagnetic radiation of light.

Einstein’s second 1905 paper proposed what is today called the special theory of relativity. He based his new theory on a reinterpretation of the classical principle of relativity, namely that the laws of physics had to have the same form in any frame of reference. As a second fundamental hypothesis, Einstein assumed that the speed of light remained constant in all frames of reference, as required by Maxwell’s theory.

Later in 1905 Einstein showed how mass and energy were equivalent. Einstein was not the first to propose all the components of special theory of relativity. His contribution is unifying important parts of classical mechanics and Maxwell’s electrodynamics. The third of Einstein’s papers of 1905 concerned statistical mechanics, a field of that had been studied by Ludwig Boltzmann and Josiah Gibbs.

After 1905 Einstein continued working in the areas described above. He made important contributions to quantum theory, but he sought to extend the special theory of relativity to phenomena involving acceleration. The key appeared in 1907 with the principle of equivalence, in which gravitational acceleration was held to be indistinguishable from acceleration caused by mechanical forces. Gravitational mass was therefore identical with inertial mass.

By 1911 Einstein was able to make preliminary predictions about how a ray of light from a distant star, passing near the Sun, would appear to be bent slightly, in the direction of the Sun. About 1912, Einstein began a new phase of his gravitational research, with the help of his mathematician friend Marcel Grossmann, by expressing his work in terms of the tensor calculus of Tullio Levi-Civita and Gregorio Ricci-Curbastro. Einstein called his new work the general theory of relativity. After a number of false starts he published, late in 1915, the definitive version of general theory.

When British eclipse expeditions in 1919 confirmed his predictions, Einstein was idolized by the popular press. Einstein returned to Germany in 1914 but did not reapply for German citizenship. Einstein received the Nobel Prize in 1921 but not for relativity rather for his 1905 work on the photoelectric effect. He worked at Princeton on work which attempted to unify the laws of physics until his death.