1. Carl Friedrich von Weizsäcker and Bartel Leendert van der Waerden, Werner Heisenberg (Munich: Carl Hanser Verlag, 1977), 25–26. However, in 1963 Weizsäcker recalled that they first met in January 1927, in Thomas Kuhn and John Heilbron, “Interview with Carl Weizsäcker,” Carlsberg, July 9, 1963, Niels Bohr Library and Archives, AIP, College Park, MD, online: http://www.aip.org/history/ohilist/4947.html .
2. Weizsäcker and Waerden, Heisenberg (ref. 1), 26; Werner Heisenberg, “Über den anschaulichen Inhalt der Quantentheoretischen Kinematik und Dynamik,” Zeitschrift für Physik 43 (1927), 172–198, reprinted in Werner Heisenberg, Gesammelte Werke/Collected Works, Helmut Rechenberg et al., eds., multi-volume (Berlin: Springer-Verlag, 1985ff), A1:478–504.
3. Heisenberg to his parents, June 4, 1928, in Werner Heisenberg, Liebe Eltern! Briefe aus kritischer Zeit 1918 bis 1945, Anna Maria Hirsch-Heisenberg, ed. (Munich: Langen Müller in der F. A. Herbig Verlagsbuchhandlung, 2003), 134.
4. See Ulrich Völklein, Die Weizsäckers: Macht und Moral—Porträt einer deutschen Familie (Munich: Droemer, 2004). Weizsäcker’s younger siblings were Adelheid, Heinrich, and Richard. Heinrich, an army officer, was killed in Poland on the first day of what became World War II. Richard was later president of West Germany. Their father was convicted at Nuremberg in the Foreign Ministries Case.
5. Heisenberg to his mother, October 27, 1932, in Heisenberg, Liebe Eltern! (ref. 3), 207.