later sent to the Theresienstadt concentration camp where most of them did survive. His friend and for a time fiancee Tina Strobos was not Jewish and thus was freer of restrictions and threat of incarceration. She arranged hiding places for Pais and other Jews in Amsterdam. When the Germans began forcing the Dutch Jews into a ghetto in the old Jewish quarter of Amsterdam, his sister Annie and her husband Hermann complied. Tina found them a place to hide, but despite Pais's urgent pleas for them to take advantage of it, they did not think it necessary. Annie was later killed at the Sobibór extermination camp. Tina had found refuge for Pais's parents on a farm outside Amsterdam where they survived the war. She also acted as a courier between Pais and his parents during the war, though neither knew of the other's specific location. His last hiding place was in an apartment with his university friend Lion Nordheim, his wife Jeanne, and her sister Trusha van Amerongen. In the course of his hiding he kept in touch with the scientific community through visits at his hiding place by Hendrik Anthony Kramers and Lambertus Broer. Jeanne and Trusha had blond hair and blue eyes and ventured out in public as non-Jews, while Lion and Pais hid in the apartment. In March 1945, however, they were betrayed and all four were arrested. The same week the Americans had crossed the Rhine and cut the rail lines, making impossible their transfer to a concentration camp. The women were soon released. After a month of interrogation by the Gestapo, Pais was released several days before the end of the war. Nordheim was executed ten days before the end of the war. Career in particle physics During World War II, Pais's doctoral dissertation had attracted the attention of Niels Bohr, who invited him to come to Denmark as his assistant. Pais was forced into hiding before he could leave the Netherlands. In 1946, following the war, Pais was able to accept that invitation and served as a personal assistant to Bohr at his country home in Tisvilde for a year. In 1947 he accepted a position at the Institute for Advanced Study in the United States and thus became a colleague of Albert Einstein. In 1949 he became corresponding member of the Royal Netherlands Academy of Arts and Sciences. For the next 25 years