Imagination is more important than knowledge, because knowledge is limited. This seems to be the secret of Albert Einstein, because of his intellectual originality he became a genius of natural science. The significance of his theory of relativity still extends to all processes in nature today. But Einstein was more than a physicist. He was admired for his goodness, his courage, his love of truth and his commitment to peace. As the musician Pablo Casals wrote: "After Einstein's death, it is as if the world has lost weight and part of its substance".