Einstein was an intellectual giant of the 20th century whose name has become synonymous with genius. Recognized as one of the greatest physicists of all time, Einstein made countless important contributions to physics, including his theories of relativity, which profoundly revolutionized scientific and philosophical inquiry. In 1921, he received the Nobel Prize for his work on theoretical physics. Though he sought it for decades, Einstein never discovered a unified field theory, which is what? Discuss
Source: The Free Dictionary