Einstein's Theory of Relativity in a nutshell. He received the Nobel Prize in Phisics in 1921 for the photoelectric effect. In 1905, he formulated the Theory of Special Relativity : In a vacuum, the light propagates at constant speed, giving rise to time dilation and contractionoflength. As well as the famous equation of the mass/energy equivalence E = MC² Energy = mass M × speed of light c² . In 1916, he published the Theory of General Relativity . It describes the gravitational interaction as