Einstein is often regarded as the greatest scientist of the 20th century. In 1905 he published his special theory of relativity and in 1915 he succeeded in incorporating gravitation in his general theory of relativity, which was vindicated when one of its predictions was observed during the solar eclipse of 1919. However, Einstein searched without success for a unified field theory embracing electromagnetism, gravitation, relativity, and quantum mechanics. He influenced the decision to build an atom bomb but after the war he spoke out passionately against nuclear weapons.