Albert Einstein (14 March 1879 – 18 April 1955) was a German-born theoretical physicist who developed the theory of relativity, one of the two pillars of modern physics (alongside quantum mechanics). His work is also known for its influence on the philosophy of science. He is best known to the general public for his mass–energy equivalence formula E = mc2, which has been dubbed "the world's most famous equation". He received the 1921 Nobel Prize in Physics "for his services to theoretical physics, and especially for his discovery of the law of the photoelectric effect", a pivotal step in the development of quantum theory.
Near the beginning of his career, Einstein thought that the laws of classical mechanics could no longer be reconciled with those of the electromagnetic field. This led him to develop his special theory of relativity during his time as a patent clerk. In 1905, called his annus mirabilis ('miracle year'), he published four groundbreaking papers which attracted the attention of the academic world; the first paper outlined the theory of the photoelectric effect, the second explained Brownian motion, the third introduced special relativity, and the fourth mass–energy equivalence. That year, at the age of 26, he was awarded a PhD by the University of Zurich.
Although initially treated with skepticism from many in the scientific community, Einstein's works gradually came to be recognised as significant advancements. He continued to deal with problems of statistical mechanics and quantum theory, which led to his explanations of particle theory and the motion of molecules. He also investigated the thermal properties of light and the quantum theory of radiation, the basis of the laser, which laid the foundation of the photon theory of light. In 1917, he applied the general theory of relativity to model the structure of the universe.
In 1933, while Einstein was visiting the United States, Adolf Hitler came to power. Because of his Jewish background, Einstein did not return to Germany. He settled in the United States and became an American citizen in 1940.
Einstein was affiliated with the Institute for Advanced Study in Princeton, New Jersey, until his death in 1955. He published more than 300 scientific papers and more than 150 non-scientific works. His intellectual achievements and originality have made the word "Einstein" synonymous with "genius".