Albert Einstein was a German-born physicist who became well known after earning his Ph.D. and publishing scientific articles. His theories on relativity and photoelectric effect are his most famous discoveries.
Special Theory of Relativity Many people are familiar with Einstein's general theory of relativity but his first discovery was actually called the special theory of relativity. This theory was an expansion of a relative theory first discussed by Galileo. Einstein's special theory of relativity states that the speed of light is the same everyone regardless of the source of the motion. The theory also covers time dilation and length contraction by stating that a moving person seems to shrink in the direction of his or her motion and the time slows down with both time dilation and length contraction becoming more noticeable as the object gets closer to the speed of light. The special part of this theory refers to the restriction of objects in constant relative motion.
General Theory of Relativity Einstein published his general theory of relativity in 1915 and it became one of the most important theories developed for modern astrophysics. The general theory expanded on his previous special theory. This theory finds that gravity and motion affect time and space. Einstein used his equivalency theory to help form the basis of his relativity theory. The equivalency theory states that gravity's pull on an object in one direction is equivalent to the rate of acceleration in the opposite direction. This helped him discover the theory of relativity by explaining how if light is bent by acceleration than it must also be bent by gravity. In 1919, two separate space expeditions proved that Einstein was correct. These expeditions noted how star light bent due to the force of gravity created by the sun during a solar eclipse. This theory also held to prove that there was an anti-gravity force at work in the universe that prevented everything from collapsing in on itself. Einstein called this the cosmological constant.
Rest Energy E=MC2 is a familiar formula designed by Einstein. The formula stands for energy equals mass times the speed of light in a vacuum squared. It's an equivalency formula that proved that particles have rest energy along with kinetic and potential energies. This finding is what implies that gravity can bend light. This formula also calculates the amount of released or consumed energy during a nuclear reaction. It was this rest energy formula that helped to create the first atomic bomb, and Einstein is given credit for writing a letter to then-President Franklin Roosevelt encouraging him to fund uranium for the making of nuclear warfare during the Second World War.
Nobel Peace Prize Although most people know Einstein for his theory of relativity, he actually won the Nobel Peace Prize in Physics in 1921 for his work on the photoelectric effect. Einstein studied the steps needed for a metallic surface to emit electrons when exposed to electromagnetic radiation, a discovery credited to Heinrich Hertz but expounded upon by Einstein, which led to the discovery of wave-particle duality. Controversy surrounding his theories of relativity prevented his theories from being considered for the Nobel Peace Prize, which is why he was honored for his work on photoelectric magnetism.