Albert Einstein

Albert Einstein (1879–1955) was a German-born theoretical physicist whose theories of special relativity (1905) and general relativity (1915) revolutionized understanding of space, time, gravity, and the relationship between matter and energy, establishing the conceptual and mathematical framework of modern physics and rendering classical Newtonian mechanics a limiting case applicable at non-relativistic velocities. Born in Ulm, Württemberg, he attended the Polytechnic in Zurich and obtained Swiss citizenship in 1901; after teaching briefly, he secured a position at the Swiss Patent Office in Bern (1902–1909), where he conducted his most revolutionary theoretical work while maintaining relative intellectual independence from institutional pressures. His 1905 papers—his annus mirabilis year—addressed the photoelectric effect (proposing the photon hypothesis and explaining light's particle-like properties through E = hν), Brownian motion (providing kinetic-molecular justification), and special relativity (postulating the constancy of the speed of light and deriving the famous mass-energy equivalence E = mc²). His special theory of relativity (1905) eliminated the luminiferous aether and unified mechanics and electromagnetism while introducing time dilation, length contraction, and the relativity of simultaneity, fundamentally reconceptualizing the structure of spacetime. His general theory of relativity (1915–1916)—a geometric theory of gravitation formulated as curved spacetime geometry—replaced Newtonian gravitational force with geodesic curvature, predicting phenomena including gravitational time dilation, the deflection of light by massive bodies (verified during the 1919 solar eclipse by Eddington), and the existence of black holes. His 1921 Nobel Prize in Physics honored his services to theoretical physics and the discovery of the law of the photoelectric effect, and his later advocacy for nuclear physics research and his 1939 letter to President Franklin D. Roosevelt prompted U.S. mobilization toward atomic weapons development.