German born Albert Einstein is one of the most well known physicists ever to live. His contributions to the world of science and his theories still have great impact today. His most well known works are based on relativity, light and gravity. These are the Special Theory of Relativity and the General Theory of Relativity.
The Special Theory of Relativity is a description of what occurs to particles when they approach the speed of light. Basically Einstein stated that the speed of light was constant and that that nothing could reach or exceed it because it would take an infinite amount of energy to do so. This theory of particle motion is somewhat different and more accurate than Newton's theory. Isaac Newton described the motion of fairly large, slow moving objects with a fair degree of accuracy, yet his laws basically broke down when speeds close to the speed of light were reached. Einstein also described with his famous equation, E=mc2, the relationship and relativity between mass and energy, where (energy) equals (mass) multiplied by (the speed of light squared).
The General Theory of Relativity was basically a new view on the function and creation of gravity. Einstein stated that gravity was the effect of massive objects on space-time. This would create curvatures in the universe, as would a ball on a trampoline. Proof for this theory was obtained during a solar eclipse. Comparing the positions of stars during the eclipse and their same positions afterwards accomplished this. The General Theory of Relativity again refuted Newton's laws. Newton stated that each object exerts some type of pull on every other object, when in fact, this was found to be false.