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Born in Germany (1879-1955) Albert Einstein (a theoretical physicist and humanist) was arguably the most influential thinker of the twentieth century. He revolutionized the way we see and think about the world. His unconventional views and theories had a tremendous impact not only in Physics but also in Philosophy, Psychology, even Religion. Every scientific field was influenced by his theories, one way or another.
Einstein introduced two major theories in Physics, the so called "Theories of Relativity". To them we owe the destruction of the concept of "space" and "time" as absolutes. One of them, the General theory of relativity, describes the force of Gravity and its influence on the space-time canvas (or concept). The other major theory, the Special theory of relativity, deals with objects moving near the speed of light and the way that motion affects space-time. This latter theory came to complement and expand Newton's and Galileo's laws of motion. Its highest point is the famous equation E=mc2 , the Energy-Mass equivalence.
Einstein's contributions go beyond these two theories. He explained the photoelectric effect, introducing the concept of "quanta of light", receiving the Nobel prize. His work with the Indian physicist Bose predicted the existence of "Bose-Einstein condensations", a new state of matter, that was recently created in the lab using laser-trapping of atoms. But most importantly, Einstein worked (without success) on a Unified theory of gravity and electromagnetism (the only known forces at the time). This unification effort is still going on in physics but with the addition of two modern forces in the game, the radioactivity (weak force) and the nuclear (or strong) force.
Einstein believed in an ultimate simplicity, in a fundamental and unified reality that is the same across the Universe, and this was his motivation behind his unification work. "The amazing fact is not the laws of the Universe but the fact that it has laws" used to say. Einstein did not believe in randomness, "God does not play dice with the Universe" he used to say. Well, he was proved to be wrong this time. The element of randomness and probability is an inseparable part of Quantum reality.
Einstein dared follow unconventional paths, break established ideas and ways of thinking, introducing concepts and ideas that are so foreign to our way of thinking that even today most of us cannot fully understand.