(1) Über die in der Theorie der Elementarteilchen auftretende universelle Länge. Offprint from Annalen d. Physik, 5th ser., 32. (2) Die Grenzen der Anwendbarkeit der bisherigen Quantentheorie. Offprint from Zeitschrift für Physik 110

1938. Heisenberg, Werner (1901-76). (1) Über die in der Theorie der Elementarteilchen auftretende universelle Länge. Offprint from Annalen der Physik, 5th series, 32 (1938). 20-33pp. 231 x 156 mm. Without wrappers as issued. Light toning. (2) Die Grenzen der Anwendbarkeit der bisherigen Quantentheorie. Offprint from Zeitschrift für Physik 110 (1938). 251-266pp. 230 x 156 mm. Original printed wrappers, vertically creased, light toning. Together 2 offprints. Very good. First Editions, Offprint Issues. In the mid-1930s, while researching high-energy collisions (truncated) of elementary particles in cosmic rays, Heisenberg came up with the idea of a universal minimum length—about the size of an electron—which remained a permanent feature of his physics going forward. He expressed this idea in the above two papers, “On the universal length entering into the theory of elementary particles” and “On the limitation of the applicability of the present quantum theory.” “The main argument put forward by Heisenberg was the following: In the field theories of nuclear forces (as in quantum field theory in general), a universal length r0 = e2/mc2 = 2.81 x 10-13—the classical electron radius, which agreed closely with the Compton wavelength of the Yukawa or cosmic-ray particle—played a fundamental role” (Mehra & Rechenberg, The Historical Development of Quantum Theory, 6, p. 956). The first paper listed above is one of eleven early QED papers featured in A. I. Miller’s Early Quantum Electrodynamics: A Source Book (1994). Cassidy & Baker, Werner Heisenberg: A Bibliography of his Writings, 1938a, 1938e. . (Inventory #: 50911)