In 1921 I believed-and I shared this belief with most of my contemporary physicists-that science produced an objective knowledge of the world, which is governed by deterministic laws. The scientific method seemed to me superior to other, more subjective ways of forming a picture of the world­ philosophy, poetry, and religion; and I even thought the unambiguous language of science to be a step towards a better understanding between human beings. In 1951 I believed in none of these things. The border between object and subject had been blurred, deterministic laws had been replaced by statistical ones, and although physicists understood one another well enough across all national frontiers they had contributed nothing to a better understanding of nations, but had helped in inventing and applying the most horrible weapons of destruction.