Albert Einstein, (1879-1955), theoretical physicist, and his sister Maja as small children, 1880s.

Albert Einstein, (1879-1955), theoretical physicist, and his sister Maja as small children, 1880s. Einstein's main contribution to science was the theory of relativity, regarded by many as the most important theory in the history of physics. His special (1905) and general (1916) theories of relativity, proved the concept that time does not exist at the same rate for everyone and everything. Special Relativity produced the equation which expresses the equivalence between matter and energy: E=mc squared. In 1921, Einstein received the Nobel Prize for Physics. His Jewish faith meant that he had to leave Germany during the Nazi period, emigrating to the USA and taking American citizenship. (Photo by Ann Ronan Pictures/Print Collector/Getty Images)