Johannes Hans Daniel Jensen was born in Hamburg, Germany, on June 25, 1907. His mother was Helene Ohm Jensen, and his father was Karl Jensen. The youth's outstanding performance in school won him a scholarship to the Oberrealschule in Hamburg. After graduating in 1926, he attended the University of Hamburg, majoring in physical chemistry, mathematics, and philosophy. He received a doctorate in physics in 1932 and remained at the university as a scientific assistant. In 1936 he obtained an additional postgraduate degree and in 1937 became a lecturer at the university. In 1941, Jensen was appointed professor of theoretical physics at the Technical University of Hanover.

Jensen's first research applied quantum mechanics--the mathematical theory of the interaction between matter and radiation--to the study of crystals, whose atoms are arranged in a repetitive pattern. He also observed the properties of crystals under high pressure. Jensen was also interested in constructing a theoretical model of the atomic...