Albert Einstein was a German-American physicist who, in 1905, published three papers, each of which had a profound effect on the development of physics. In one paper, he proposed the theory of special relativity, which provides a correct description for particles traveling at high speeds. The two postulates of the special theory of relativity were that the speed of light in a vacuum is constant and that the laws of physics are the same for all inertial reference frames. Using special relativity, Einstein derived the now famous equivalence of mass and energy, E=mc².

In a second paper also published in 1905, Einstein argued that light consisted of discrete bundles of radiation (photons). He used this interpretation to explain the photoelectric effect, by which certain metals emit electrons when illuminated by light with a given frequency. Einstein's theory, and his subsequent elaboration of it, formed the basis for much of quantum mechanics. The third of Einstein's seminal papers of 1905 concerned statistical mechanics, where he extended Boltzmann's work and provided evidence for the physical existence of atom-sized molecules, ideas that were independently proved by subsequent experimental work.

He won the 1921 Nobel Prize in Physics for “his services to theoretical physics, and especially for his discovery of the law of the photoelectric effect.” With the rise of fascism in Germany, Einstein moved to the United States in 1933 and eventually urged President Franklin D. Roosevelt to develop an atomic bomb before Germany did. The letter, composed by Einstein's friend Leo Szilard, was one of many exchanged between the White House and Einstein, and it contributed to Roosevelt's decision to fund what became the Manhattan Project.