The German-American physicist Albert Einstein( 1879-1955), born in Ulm, Germany, contributed more than any other scientist to the 20th- century vision of physical reality. He is best known for his theory of relativity which revolutionized scientific thought with new conceptions of time, space, mass, motion and gravitation. He treated matter and energy as interchangeable, not distinct. His famous equation relating energy and mass E = mc² led to the development of nuclear physics.

  He graduate from the Zurich Polytechnic in 1900 and worked as a secondary school teacher of mathematics and physics. He obtained a post at the Swiss patent office in Bern where he completed an astonishing range of publications in theoretical physics.  By 1909, Einstein was recognized throughout German-speaking Europe as a leading scientific thinker. In the first of three seminal papers that were published in 1905, Einstein examined the phenomenon discovered by Max Planck, according to which electromagnetic energy seemed to be emitted from radiating objects in quantities that were ultimately discrete. The energy of these emitted quantities--the so-called light-quanta--was directly proportional to the frequency of the radiation. This circumstance was perplexing because classical electromagnetic theory, based on Maxwell's equations and the laws of

Albert Einstein Credit:AIP

thermodynamics, had assumed that electromagnetic energy consisted of waves. Einstein used Planck's quantum hypothesis to describe visible electromagnetic radiation, or light. According to Einstein's viewpoint, light could be imagined to consist of discrete bundles of radiation. Einstein 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 second of Einstein's 1905 papers proposed what is today called the special theory of relativity. in which Einstein elaborated how, in a certain manner of speaking, mass and energy were equivalent. The third of Einstein's seminal papers of 1905 concerned statistical mechanics. The General Theory of Relativity Einstein's greatest contribution to physics was published late 1915. In it the gravitational field equations were covariant; that is, similar to Maxwell's equations, the field equations took the same form in all equivalent frames of reference. Einstein received Nobel Prize in 1921-- not for relativity but for his 1905 work on the photoelectric effect. With the rise of fascism in Germany, Einstein moved (1933) to the United States where he sent (1939) a letter to President Franklin D. Roosevelt that urged that the United States proceed to develop an atomic bomb before Germany did. Until the end of his life Einstein thought a unified field theory, whereby the phenomena of gravitation and electromagnetism could be derived from one set of equations. Physicists are now striving to combine Einstein's relativity theory with quantum theory in a "theory of everything," by means of such highly advanced mathematical models as superstring theories.