Albert Einstein ( 14 March 1879 – 18 April 1955) was a theoretical physicist. His many contributions to physics include the special and general theories of relativity, the founding of relativistic cosmology, the first post-Newtonian expansion, explaining the perihelion advance of Mercury, prediction of the deflection of light by gravity andgravitational lensing, the first fluctuation dissipation theorem which explained the Brownian movement of molecules, the photon theoryand wave-particle duality, the quantum theory of atomic motion in solids, the zero-point energy concept, the semiclassical version of theSchrödinger equation, and the quantum theory of a monatomic gas which predicted Bose-Einstein condensation.

Einstein is best known for his theories of special relativity and general relativity. 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."

Einstein published more than 300 scientific and over 150 non-scientific works. He is often regarded as the father of modern physics.